pets4閲讀理解預測文章

漸漸進入2017年的下半年，有的考生已經在進行2017年下半年pets4的備考了。小編認為考生可以在複習時候，進行一些pets4閲讀文章預測，更充分地備考。下面是小編為大家整理的一篇pets4閲讀理解預測文章，供大家參考。

　英語短文

Each advance in microscopic technique has provided scientists with new perspectives on the function of living organisms and the nature of matter itself. The invention of the visible light microscope late in the sixteenth century introduced a previously unknown realm of single celled plants and animals. In the twentieth century, electron microscopes have provided direct views of viruses and minuscule surface structures. Now another type of microscope, one that utilizes x rays rather than light or electrons, offers a different way of examining tiny details; it should extend human perception still farther into the natural world. The dream of building an x ray microscope dates to back 1895; its development, however was virtually halted in the 1940's because the development of the electron microscope was progressing rapidly. During the 1940's, electron microscopes routinely achieved resolution better than that poss ible with a visible light microscope, while the performance of x ray microscopes resisted improvement. In recent years, however, interest in x ray microscopes has revived, largely because of advances such as the developmen t of new sources of x ray illumination. As a result, the brightness available today is millions of times tha t of x ray tubes, which, for most of the century, were the only available sources of soft x new x ray microscopes considerably improve on the resolution provided by optical microscopes. They can also be used to map the distribution of certain chemical elements. Some can form pictures in extremely short times; others hold the promise of special capabilities such as three dimensional imaging. Unlike conventional electron microscope, x ray microscope enables specimens to be kept in air and in water, which means that biological samples can be studied under conditions similar to their natural state. The illumination used, so called soft x rays in the wavelength range of twenty to forty angstroms (an angstrom is one ten billionth of a meter), is also sufficiently penetrating to image intact biological cells in ma ny cases. Because of the wavelength of the x rays used, soft x ray microscopes will never match the highest resolution possible with electron microscopes. Rather, their special properties will make possible investigations that will complement those performed with light and electron based instruments.

　中文譯文

顯微鏡技術的每一個進步都給科學家提供了看待生物體的功能和其性質的新 觀察方式。16 世紀晚期可視光顯微鏡的發明引入了一個以前一無所知的單細胞植物和動物的領域。20 世紀電子顯微鏡提供了對病毒和極微物體的表面結構的直接觀察。現在一種新的顯微鏡，利用X 光而不是自然可見光或電子，為觀察微小細節提供了不同的觀察方式，它將擴展人類對自然世界進行的更深入的認識。研製 X 光顯微鏡的夢想可追溯到1875 年;但它的發展卻在 20 世紀 40 年代實際上停止了，因為電子顯微鏡的發展進行很快。 在 40 年代，電子顯微鏡毫無例外地比可見光顯微鏡獲得了更好的分辨能力。然而 X 光顯微鏡的表現卻沒有改進。但近年來，對它的興趣又復活了，這很大程度是因為例如 X 射線在新光源上的發展的結果。結果，今天可得到的`亮度是大半個世紀以來唯一可得到的 X 光源-X 光管的幾百萬倍。新的X 光顯微鏡相當大地提高了電子學顯微鏡提供的分辨能力。它們也可用來給某些化學元素繪製分佈圖。某些 X 光顯微鏡可以在極短的時間裏成像。另一些可望具備三維成像的特殊功能。與傳統的電子顯微鏡成像術不同，X 光顯微鏡成像術可使分析樣本保留在空氣或水中。這就意味着生物樣品可以在與它們自然環境相近的條件下被 觀察研究。其使用的照明度，即所謂的軟性 X 射線，其波長在 20 到 40 埃之間(1 米的 100 億分之一為 1 埃)。 在許多情況下也能夠穿透完整無缺的生物細胞併成像。由於使用的 X 射線的波長使軟性 X 射線顯微鏡永遠比不上電子顯微鏡可能具有的最高分辨力。不過他們特殊的功能將可能補充那些用自然光和電子儀器所進行的觀察。環境相近的條件下被觀察研究。其使用的照明度，即所謂的軟性X 射線，其波長在 20 到 40 埃之間(1 米的 100 億分之一為 1 埃)。 在許多情況下也能夠穿透完整無缺的生物細胞併成像。