首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
考研
Each advance in microscopic technique has provided scientists with new perspectives on the function of living organisms and the
Each advance in microscopic technique has provided scientists with new perspectives on the function of living organisms and the
admin
2010-02-22
111
问题
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 microscope 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 de tails; it should extend human perception still farther into the natural world.
The dream of building an X-ray microscope dates to 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 possible 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 development of new sources of X-ray illumination. As a result, the brightness available today is millions, of times that of X-ray tubes, which, for most of the century, were the only avail able 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 microscopy, X-ray microscopy 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 many 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.
选项
A、The detail seen through a microscope.
B、Sources of illumination for microscopes.
C、A new kind of microscope.
D、Outdated microscopic techniques.
答案
C
解析
本题考查通读文章,概括大意的能力。文章第一段介绍了显微镜的发展,即从光学显微镜到电子显微镜再到x射线显微镜。第二、三段则着重介绍了新型的x射线显微镜。因此,这篇文章主要讨论了一种新型的显微镜。
转载请注明原文地址:https://kaotiyun.com/show/gh44777K
0
考研英语一
相关试题推荐
【C1】________thewayitfeels,lonelinessoftenhasnothingtodowithbeingalone.Forsomepeople,feelingsof【C2】________ares
Scientistshavediscoveredapowerfulantibioticinthebloodstreamofgiantpandasthatcandestroybacteria.TheChineserese
Scientistshavediscoveredapowerfulantibioticinthebloodstreamofgiantpandasthatcandestroybacteria.TheChineserese
MasstransportationrevisedthesocialandeconomicfabricoftheAmericancityinthreefundamentalways.Itspeededupphysica
Sugarposesenoughhealthrisksthatitshouldbeconsideredacontrolledsubstancejustlikealcoholandtobacco,argueateam
Sugarposesenoughhealthrisksthatitshouldbeconsideredacontrolledsubstancejustlikealcoholandtobacco,argueateam
Substanceabuse(Line5,Paragraph1)ispreferableto"drugabuse"inthat______.physicaldependenceoncertainsubstancesr
Technically,anysubstanceotherthanfoodthataltersourbodilyormentalfunctioningisadrug.Manypeoplemistakenlybeliev
KarlVonLinne(orLinnaeus,asheiswidelyknown)wasaSwedishbiologistwhodevisedthesystemofLatinisedscientificnames
随机试题
A.水成像B.功能性MRI成像C.脂肪抑制D.MRI对比增强检查E.MR血管造影静脉注入顺磁性物质
不能引起特异性感染的是
下列哪项不是毒理学试验中溶剂的选择原则
具有一定毒性,不宜持续和过量服用的药物是
甲公司申请强制执行乙公司的财产,法院将乙公司的一处房产列为执行标的。执行中,丙银行向法院主张,乙公司已将该房产抵押贷款,并以自己享有抵押权为由提出异议。乙公司否认将房产抵押给丙银行。经审查,法院驳回丙银行的异议。丙银行拟向法院起诉,关于本案被告的确定,下列
可以直接使用现金结算的最高限额是( )元。
上市公司应将年度报告备置于()。
任何公司都是“________人”,如果不用严格守法就会轻松获利,那么其就没有任何守法的自觉性和主动性。从这个意义上讲,守法的典范不是“自动生成”的,而是环境________的结果。在不同的制度环境中,天使和魔鬼的角色是很容易转变的。填入画横线部分最恰当
从所给的四个选项中,选择最合适的一个填入问号处,使之呈现一定的规律性:
Atatimewheneveryone’smindistheexplosionsofthemoment,itmightseemobtuseofmetodiscussthefourteenthcentury.Bu
最新回复
(
0
)