The preservation of embryos and juveniles is a rate occurrence in the fossil record. The tiny, delicate skeletons are usually scattered by scavengers or destroyed by weathering before they can be fossilized. Ichthyosaurs had a higher chance of being

发表于:2018-12-04 / 阅读(56) / 评论(0) 分类 考研背诵50篇

In science, a theory is a reasonable explanation of observed events that are related. A theory often involves an imaginary model that helps scientists picture the way an observed event could be produced. A good example of this is found in the kinetic

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Cells cannot remain alive outside certain limits of temperature and much narrower limits mark the boundaries of effective functioning. Enzyme systems of mammals and birds are most efficient only within a narrow range around 37C; a departure of a few

发表于:2018-12-30 / 阅读(60) / 评论(0) 分类 考研背诵50篇

American black bears appear in a variety of colors despite their name. In the eastern part of their range, most of these brown, red, or even yellow coats. To the north, the black bear is actually gray or white in color. Even in the same litter, both

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The invention of the incandescent light bulb by Thomas A. Edison in 1879 created a demand for a cheap, readily available fuel with which to generate large amounts of electric power. Coal seemed to fit the bill, and it fueled the earliest power statio

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Atmospheric pressure can support a column of water up to 10 meters high. But plants can move water much higher; the sequoia tree can pump water to its very top more than 100 meters above the ground. Until the end of the nineteenth century, the moveme

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The theory of plate tectonics describes the motions of the lithosphere, the comparatively rigid outer layer of the Earth that includes all the crust and part of the underlying mantle. The lithosphere(n.[ 地 ] 岩石圈 )is divided into a few dozen p

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The increase in international business and in foreign investment has created a need for executives with knowledge of foreign languages and skills in cross-cultural communication. Americans, however, have not been well trained in either area and, cons

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Accustomed though we are to speaking of the films made before 1927 as silent, the film has never been, in the full sense of the word, silent. From the very beginning, music was regarded as an indispensable accompaniment; when the Lumiere films were s

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The ways of history are so intricate and the motivations of human actions so complex that it is always hazardous to attempt to represent events covering a number of years, a multiplicity of persons, and distant localities as the expression of one int

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people appear to born to compute. The numerical skills of children develop so early and so inexorably that it is easy to imagine an internal clock of mathematical maturity guiding their growth. Not long after learning to walk and talk, they can set t

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