234 résultats pour "végétation"

• Africa - history.

  Africa’s other major mountainous regions occur at the northern and southern fringes of the continent. The Atlas Mountains, a system of high ranges, extend for 2,200 km(1,400 mi) across Morocco, Algeria, and Tunisia, roughly parallel to the northern coast. These ranges enclose a number of broad inland basins and plateaus. In the west, theHigh (or Grand) Atlas contains Toubkal (4,165 m/ 13,665 ft), the highest peak of the system. Toward the east, the Atlas consists of two parallel ranges: the Tell...

• Africa.

  The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...

• Asia - geography.

  the Himalayas, the world’s highest mountain system. The Pacific Ocean plate drifted westward, scraping along the Eurasian plate and slipping under its coastal edge. This created the islands of Japan, Taiwan, the Kurils, theRyūky ūs, and the Philippines. Southeast Asia lies at the intersection of the Eurasian, Pacific Ocean, and Indian Ocean plates. Over time the contact between these platescreated the mountain ranges of mainland Southeast Asia. The continued slow movement of the plates causes fr...

• Asia - history.

  the Himalayas, the world’s highest mountain system. The Pacific Ocean plate drifted westward, scraping along the Eurasian plate and slipping under its coastal edge. This created the islands of Japan, Taiwan, the Kurils, theRyūky ūs, and the Philippines. Southeast Asia lies at the intersection of the Eurasian, Pacific Ocean, and Indian Ocean plates. Over time the contact between these platescreated the mountain ranges of mainland Southeast Asia. The continued slow movement of the plates causes fr...

• vache (faune & Flore).

  5 RELATIONS AVEC L’HOMME ET SYMBOLIQUE 5.1 La vache sacrée Symbole de fertilité et de fécondité, signe de richesse et de renouveau, la vache est également associée à la Lune et au monde céleste. Dans le panthéon égyptien, ladéesse du Ciel Hathor est ainsi souvent représentée sous la forme d’une vache. Des cornes de vache entourent également le disque solaire qui surmonte la tête d’Isis,déesse de la Fertilité et de la Maternité. Dans les mythologies et les cultures occidentales, la vache est l’...

• agronomie - agriculture et agroalimentaire.

  Ce n’est que plus tard que la recherche développa des insecticides chimiques : cependant, leur toxicité sur l’environnement et l’apparition de plantes naturellementrésistantes forcèrent les ingénieurs agronomes à concevoir de nouvelles approches, comme l’utilisation de virus s’attaquant spécifiquement aux parasites végétaux dont onveut se débarrasser ( voir Parasites, lutte contre les). Il faut non seulement protéger les plantes, mais aussi améliorer leur productivité. Puisque l’enrichissement...

• nerveux, système - Anatomie.

  4.2. 1 Système nerveux somatique Le système nerveux somatique comprend l’ensemble des structures qui permettent à l’animal d’appréhender son environnement (neurones sensitifs reliés aux organes dessens), et de réagir en fonction de celui-ci (neurones moteurs responsables des contractions musculaires). Il comprend également les neurones impliqués, de façon nonvolontaire, dans la tonicité musculaire. 4.2. 2 Système nerveux autonome ou végétatif Le système nerveux autonome contrôle et régule l...

• nerveux, système (Biologie et Anatomie).

  4.2. 1 Système nerveux somatique Le système nerveux somatique comprend l’ensemble des structures qui permettent à l’animal d’appréhender son environnement (neurones sensitifs reliés aux organes dessens), et de réagir en fonction de celui-ci (neurones moteurs responsables des contractions musculaires). Il comprend également les neurones impliqués, de façon nonvolontaire, dans la tonicité musculaire. 4.2. 2 Système nerveux autonome ou végétatif Le système nerveux autonome contrôle et régule l...

• ENCYCLOPEDIE: Afrique

  marécageux, le nord-est de l'Afrique est occupé par le désert oriental ponctué d'oasis, qui s'étend du Feuan (confins de la Tunisie et de la libye) à la mer Rouge en passant par le désert libyque. le Nil est le seul grand fleuve de la région. En Égypte, ses crues irriguent une étroite bande de terre cultivable sur 1 500 km de long. la régulation de son cours par le haut barrage d'Assouan et sa retenue, le lac Nasser (60 000 km'), contribue à fertili...

• Arctique.

  voisine et pendant la même période, la température moyenne est en général de - 7 °C, en raison de courants océaniques relativement chauds. Le pôle Nord n’est pas lepoint le plus froid de l’Arctique, car le climat est tempéré par l’océan. Les régions les plus froides sont situées dans le nord-est de la Sibérie ; c’est Oymyakon qui détient lerecord de la température la plus basse, avec - 68 °C. En Amérique du Nord, la température la plus froide a été enregistrée à Snag, dans le territoire du Yukon...

• À la charnière entre l'Europe occidentale et centrale, entre l'Europe du Nord et la Méditerranée, ce petit pays montagnard est maître des voies de passage internationales à travers le Jura et les Alpes.

  à l'accumulation des matériaux morainiques. Les cours d'eau s'écoulent vers le sillon qui longe le Jura ; barrés par des moraines, ils forment de grands lacs (lacs Léman, de Neuchâtel, de Bienne, de Zurich, de Constance). Cette région est la plus riche et la plus peuplée du pays. Au sud, les Alpes occupent les trois cinquièmes du territoire et renferment le cœur historique du pays, qualifié de « réduit alpin ». Le sillon tracé par le Rhône (Valais) et le Rhin sépare deux séries de massifs cris...

• environnement (faune & Flore).

  sont celles dont le pH est inférieur à 5,6. Dans le nord-ouest de l’Europe, le pH moyen des pluies est aujourd’hui de 4,3 et on a enregistré aux États-Unis un pH record de2,3, égal à celui du vinaigre. Les pluies acides sont un exemple de pollution sans frontières. Celles qui dégradent les eaux douces du sud de la Norvège et font disparaîtreles poissons ont leur origine dans les zones industrielles d’Allemagne et d’Angleterre et celles qui provoquent le dépérissement des forêts d’érables à sucre...

• Africa.

  The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...

• Africa - Geography.

  The highest elevations in Africa are found in the various ranges of East Africa. After Kilimanjaro, the next highest peaks are Mount Kenya (5,199 m/17,057 ft), north ofKilimanjaro in central Kenya; Margherita Peak (5,109 m/ 16,762 ft) in the Ruwenzori Range on the border between Uganda and the Democratic Republic of the Congo(DRC); Ras Dashen (4,620 m/ 15,157 ft) in the Ethiopian Highlands of northern Ethiopia; Mount Meru (4,565 m/ 14,977 ft), close to Kilimanjaro in Tanzania; and MountElgon (4,...

• Barbados - country.

  Barbados is served by a public library system centered in Bridgetown. B Culture The culture of Barbados combines English institutions, which evolved through more than three centuries of English rule, with a folk culture of African origin. Because ofits English traditions, Barbados is sometimes called “Little England.” Cricket has traditionally been the national game, and the island has produced some of the sport’sgreatest players. Water sports including surfing, swimming, snorkeling, and sailin...

• Florida - USA History.

  accidentally introduced into the region in the 1880s, and it spread with alarming rapidity throughout the upper reaches of the river. The plant is very difficult toeradicate, and it has also clogged the channels of other Florida rivers. To increase drainage of the Everglades, which drain naturally to Florida Bay and the Gulf ofMexico, a number of drainage channels and canals have been built across southern Florida. Among the rivers flowing from the peninsula to the Gulf of Mexico are the Suwanne...

• California - geography.

  The Basin and Range province is an arid area of mountain ranges, basins, and deserts. In California it is represented primarily by parts of the Great Basin and SonoranDesert sections. Within the Great Basin lies Death Valley, whose lowest elevation, 86 m (282 ft) below sea level, is the lowest point in the Western Hemisphere. TheSonoran Desert section is characterized by numerous flat plains separated by low but rugged ranges. It includes the extensive Mojave, or Mohave, Desert. Also in thisprov...

• California - USA History.

  The Basin and Range province is an arid area of mountain ranges, basins, and deserts. In California it is represented primarily by parts of the Great Basin and SonoranDesert sections. Within the Great Basin lies Death Valley, whose lowest elevation, 86 m (282 ft) below sea level, is the lowest point in the Western Hemisphere. TheSonoran Desert section is characterized by numerous flat plains separated by low but rugged ranges. It includes the extensive Mojave, or Mohave, Desert. Also in thisprov...

• Asia - Geography.

  Borneo, the world’s third largest island after Greenland and New Guinea. To the southeast is the Timor Sea separating the Asian island of Timor from the Australiancontinent. The Indian subcontinent is flanked by the Bay of Bengal on the east and the Arabian Sea on the west. The island of Sri Lanka and the much smaller Maldives andNicobar Islands trail away to the south. The Arabian Sea’s Gulf of Aden, the Red Sea, the Mediterranean Sea, and the Black Sea form an arc along the western rim of Asia...

• Asia - History.

  Borneo, the world’s third largest island after Greenland and New Guinea. To the southeast is the Timor Sea separating the Asian island of Timor from the Australiancontinent. The Indian subcontinent is flanked by the Bay of Bengal on the east and the Arabian Sea on the west. The island of Sri Lanka and the much smaller Maldives andNicobar Islands trail away to the south. The Arabian Sea’s Gulf of Aden, the Red Sea, the Mediterranean Sea, and the Black Sea form an arc along the western rim of Asia...

• Tunisia - country.

  mixture of Berber and Arab stock, and they regard themselves as Arabs. Nearly everyone speaks Arabic. The population of Tunisia is concentrated in the coastal plain. It is fairly dense in the hilly north, but the arid plateau, basin, and south are thinly settled. About two-thirds of the country’s people live in urban areas. A Principal Cities The capital and largest city of Tunisia is the seaport of Tunis. Other important cities include Sfax, a port and center of trade on the eastern coast; Sūs...

• Iceland - country.

  III PEOPLE Icelanders are one of the most homogenous peoples in the world. They are predominantly of Nordic origin, descendants of the hardy people who emigrated fromNorway to Iceland in the Middle Ages. There are also some Celtic influences from Irish and Scottish immigrants who arrived from the British Isles ( see Celts). The population of Iceland (2008 estimate) is 304,367. Numerous times in its history, Iceland has suffered major population losses due to epidemics, volcanic eruptions, and...

• Pollution.

  One of the greatest challenges caused by air pollution is global warming, an increase in Earth’s temperature due to the buildup of certain atmospheric gases such ascarbon dioxide. With the heavy use of fossil fuels in the 20th century, atmospheric concentrations of carbon dioxide have risen dramatically. Carbon dioxide and othergases, known as greenhouse gases, reduce the escape of heat from the planet without blocking radiation coming from the Sun. Because of this greenhouse effect,average glob...

• Arctic - Geography.

  The Arctic is not a frozen desert devoid of life on land or sea, even during the cold, dark winter months. Spring brings a phenomenal resurgence of plant and animal life.Low temperatures are not always the critical element—moisture, the type of soil, and available solar energy are also extremely important. Some animals adapt well toArctic conditions; for instance, a number of species of mammals and birds carry additional insulation, such as fat, in cold months. Arctic summers with extended dayli...

• Tiger - biology.

  have a simple digestive system designed to process meat so that the nutrients can be readily absorbed into the bloodstream. With the exception of white tigers, which have blue eyes, all tigers have yellow eyes. Tigers mainly use vision to find prey. Although tigers see about as well as humansduring the day, their large eye openings gather more light than do human eyes, making tiger night vision far superior to that of humans. In addition, a special structurein the tiger’s eye, called the tapetu...

• Asien - geographie.

  2.4 Klima Aufgrund seiner großen Ausdehnung und der starken Gliederung des Geländes hat Asien Anteil an mehreren Klimazonen. Die riesige Landmasse bedingt in weiten Teilen desKontinents ein ausgeprägtes Kontinentalklima mit starken Temperaturgegensätzen im Jahresverlauf. Die heißen Sommer und kalten Winter werden von häufig nur kurzeZeit andauernden Übergangsjahreszeiten getrennt. Extrem sind auch die räumlichen Temperaturgegensätze. Der nordöstliche Teil Sibiriens ist das kälteste Gebiet. Hier...

• Global Warming.

  some of the warming influence of increasing greenhouse gases. A1 Carbon Dioxide Carbon dioxide is the second most abundant greenhouse gas, after water vapor. Carbon dioxide constantly circulates in the environment through a variety of naturalprocesses known as the carbon cycle. It is released into the atmosphere from natural processes such as eruptions of volcanoes; the respiration of animals, whichbreathe in oxygen and exhale carbon dioxide; and the burning or decay of plants and other organic...

• Archaeology.

  Prehistoric archaeology is practiced by archaeologists known as prehistorians and deals with ancient cultures that did not have writing of any kind. Prehistory, a term coined by 19th-century French scholars, covers past human life from its origins up to the advent of written records. History—that is, the human past documented insome form of writing—began 5000 years ago in parts of southwestern Asia and as recently as the late 19th century AD in central Africa and parts of the Americas. Becaus...

• Illinois - geography.

  the state before joining the Mississippi River at Grafton. The Illinois has been deepened and straightened and forms part of the Illinois Waterway. The watershed between rivers that flow into the Mississippi river system and rivers that flow into the Great Lakes is low and in many places is not easily discernible. Inwhat is now the Chicago area, explorers had little difficulty portaging, or carrying, their canoes over the low watershed between the Des Plaines River, which flows intothe Illinois,...

• Illinois - USA History.

  the state before joining the Mississippi River at Grafton. The Illinois has been deepened and straightened and forms part of the Illinois Waterway. The watershed between rivers that flow into the Mississippi river system and rivers that flow into the Great Lakes is low and in many places is not easily discernible. Inwhat is now the Chicago area, explorers had little difficulty portaging, or carrying, their canoes over the low watershed between the Des Plaines River, which flows intothe Illinois,...

• Cuba - country.

  Only two land mammals, the hutia, or cane rat, and the solenodon, a rare insectivore that resembles a rat, are known to be indigenous. The island has numerous batsand nearly 300 kinds of birds, including vultures, wild turkeys, quail, finches, gulls, macaws, parakeets, and hummingbirds. The bee hummingbird of Cuba is thesmallest bird in the world. Among the few reptiles are tortoises, caimans, the Cuban crocodile, and a species of boa that can attain a length of 3.7 m (12 ft). More than700 speci...

• Japan - country.

  island’s fertile soils support agriculture and provide the vast majority of Japan’s pasturelands. In addition, Hokkaidō contains coal deposits, and the cold currents off itsshores supply cold-water fish. Winters are long and harsh, so most of Hokkaid ō is lightly settled, housing about 5 percent of Japan’s population on approximately 20 percent of its land area. However,its snowy winters and unspoiled natural beauty attract many skiers and tourists. Hokkaid ō is thought of as Japan’s northern fr...

• Alaska - geography.

  depression surrounded by highlands and have the coldest winter and hottest summer temperatures in Alaska. Once the Kuskokwim River passes through theKuskokwim Mountains, it forms the southern edge of a vast lake-studded alluvial plain bounded on the north by the Yukon River. This water-logged lowland is a majorsummer nesting area for birds. Fairbanks is the major city in this region, while Fort Yukon is the major community in the Yukon Flats and Bethel the largest settlementon the Lower Kuskokwi...

• Alaska - USA History.

  depression surrounded by highlands and have the coldest winter and hottest summer temperatures in Alaska. Once the Kuskokwim River passes through theKuskokwim Mountains, it forms the southern edge of a vast lake-studded alluvial plain bounded on the north by the Yukon River. This water-logged lowland is a majorsummer nesting area for birds. Fairbanks is the major city in this region, while Fort Yukon is the major community in the Yukon Flats and Bethel the largest settlementon the Lower Kuskokwi...