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pets4閱讀理解預(yù)測(cè)文章
漸漸進(jìn)入2017年的下半年，有的考生已經(jīng)在進(jìn)行2017年下半年pets4的備考了。小編認(rèn)為考生可以在復(fù)習(xí)時(shí)候，進(jìn)行一些pets4閱讀文章預(yù)測(cè)，更充分地備考。下面是小編為大家整理的一篇pets4閱讀理解預(yù)測(cè)文章，供大家參考。
英語(yǔ)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 rays.The 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(shù)的每一個(gè)進(jìn)步都給科學(xué)家提供了看待生物體的功能和其性質(zhì)的新 觀察方式。16 世紀(jì)晚期可視光顯微鏡的發(fā)明引入了一個(gè)以前一無(wú)所知的單細(xì)胞植物和動(dòng)物的領(lǐng)域。20 世紀(jì)電子顯微鏡提供了對(duì)病毒和極微物體的表面結(jié)構(gòu)的直接觀察。現(xiàn)在一種新的顯微鏡，利用X 光而不是自然可見(jiàn)光或電子，為觀察微小細(xì)節(jié)提供了不同的觀察方式，它將擴(kuò)展人類(lèi)對(duì)自然世界進(jìn)行的更深入的認(rèn)識(shí)。研制 X 光顯微鏡的夢(mèng)想可追溯到1875 年;但它的發(fā)展卻在 20 世紀(jì) 40 年代實(shí)際上停止了，因?yàn)殡娮语@微鏡的發(fā)展進(jìn)行很快。 在 40 年代，電子顯微鏡毫無(wú)例外地比可見(jiàn)光顯微鏡獲得了更好的分辨能力。然而 X 光顯微鏡的表現(xiàn)卻沒(méi)有改進(jìn)。但近年來(lái)，對(duì)它的興趣又復(fù)活了，這很大程度是因?yàn)槔?X 射線在新光源上的發(fā)展的結(jié)果。結(jié)果，今天可得到的亮度是大半個(gè)世紀(jì)以來(lái)唯一可得到的 X 光源-X 光管的幾百萬(wàn)倍。新的X 光顯微鏡相當(dāng)大地提高了電子學(xué)顯微鏡提供的分辨能力。它們也可用來(lái)給某些化學(xué)元素繪制分布圖。某些 X 光顯微鏡可以在極短的時(shí)間里成像。另一些可望具備三維成像的特殊功能。與傳統(tǒng)的電子顯微鏡成像術(shù)不同，X 光顯微鏡成像術(shù)可使分析樣本保留在空氣或水中。這就意味著生物樣品可以在與它們自然環(huán)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(zhǎng)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(wú)缺的生物細(xì)胞并成像。由于使用的 X 射線的波長(zhǎng)使軟性 X 射線顯微鏡永遠(yuǎn)比不上電子顯微鏡可能具有的最高分辨力。不過(guò)他們特殊的功能將可能補(bǔ)充那些用自然光和電子儀器所進(jìn)行的觀察。環(huán)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(zhǎng)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(wú)缺的生物細(xì)胞并成像。
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