2007-03-26 所屬欄目:新東方背誦文選

Sleet is part of a person's daily activity cycle. There are several different stages of sleep, and they too occur in cycles. If you are an average sleeper, your sleep cycle is as

2007-03-26 所屬欄目:新東方背誦文選

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

2007-03-26 所屬欄目:新東方背誦文選

A folk culture is a small isolated, cohesive, conservative, nearly self-sufficient group that is homogeneous in custom and race with a strong family or clan structure and highly de

2007-03-26 所屬欄目:新東方背誦文選

Bacteria are extremely small living things. While we measure our own sizes in inches or centimeters, bacterial size is measured in microns. One micron is a thousandth of a millimet

2007-03-26 所屬欄目:新東方背誦文選

A summary of the physical and chemical nature of life must begin, not on the Earth, but in the Sun; in fact, at the Sun's very center. It is here that is to be found the source of

2007-03-26 所屬欄目:新東方背誦文選

Human vision like that of other primates has evolved in an arboreal environment. In the dense complex world of a tropical forest, it is more important to see well that to develop a

2007-03-26 所屬欄目:新東方背誦文選

There were two widely divergent influences on the early development of statistical methods. Statistics had a mother who was dedicated to keeping orderly records of government units

2007-03-26 所屬欄目:新東方背誦文選

The concept of obtaining fresh water from icebergs that are towed to populated areas and arid regions of the world was once treated as a joke more appropriate to cartoons than real

2007-03-26 所屬欄目:新東方背誦文選

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 b

2007-03-26 所屬欄目:新東方背誦文選

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

2007-03-26 所屬欄目:新東方背誦文選

If the salinity of ocean waters is analyzed, it is found to vary only slightly from place to place. Nevertheless, some of these small changes are important. There are three basic p

2007-03-26 所屬欄目:新東方背誦文選

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

2007-03-26 所屬欄目:新東方背誦文選

Icebergs are among nature's most spectacular creations, and yet most people have never seen one. A vague air of mystery envelops them. They come into being ----- somewhere ------i

2007-03-26 所屬欄目:新東方背誦文選

Topaz is a hard, transparent mineral. It is a compound of aluminum, silica, and fluorine. Gem topaz is valuable. Jewelers call this variety of the stone "precious topaz". The best-

2007-03-26 所屬欄目:新東方背誦文選

An important new industry, oil refining, grew after the Civil war. Crude oil, or petroleum - a dark, thick ooze from the earth - had been known for hundreds of years, but little us

2007-03-26 所屬欄目:新東方背誦文選

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 mant

2007-03-26 所屬欄目:新東方背誦文選

Scattered through the seas of the world are billions of tons of small plants and animals called plankton. Most of these plants and animals are too small for the human eye to see. T

2007-03-26 所屬欄目:新東方背誦文選

In the oysters were raised in much the same way as dirt farmers raised tomatoes- by transplanting them. First, farmers selected the oyster bed, cleared the bottom of old shells and

2007-03-26 所屬欄目:新東方背誦文選

British Columbia is the third largest Canadian provinces, both in area and population. It is nearly 1.5 times as large as Texas, and extends 800 miles(1,280km) north from the Unite

2007-03-26 所屬欄目:新東方背誦文選

Botany, the study of plants, occupies a peculiar position in the history of human knowledge. For many thousands of years it was the one field of awareness about which humans had an

2007-03-26 所屬欄目:新東方背誦文選

Telecommuting-- substituting the computer for the trip to the job ---- has been hailed as a solution to all kinds of problems related to office work.
For workers it promises free

2007-03-26 所屬欄目:新東方背誦文選

By the mid-nineteenth century, the term "icebox" had entered the American language, but ice was still only beginning to affect the diet of ordinary citizens in the United States. T

2007-03-26 所屬欄目:新東方背誦文選

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 e

2007-03-26 所屬欄目:新東方背誦文選

One of the most important social developments that helped to make possible a shift in thinking about the role of public education was the effect of the baby boom of the 1950's and

2007-03-26 所屬欄目:新東方背誦文選

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 r