大学英语六级考试拓展阅读-背诵美文73
<p> <span word="Each">Each</span> <span word="advance">advance</span> <span word="in">in</span> <span word="microscopic">microscopic</span> <span word="technique">technique</span> <span word="has">has</span> <span word="provided">provided</span> <span word="scientists">scientists</span> <span word="with">with</span> <span word="new">new</span> <span word="perspectives">perspectives</span> <span word="on">on</span> <span word="the">the</span> <span word="function">function</span> <span word="of">of</span> <span word="living">living</span> <span word="organisms">organisms</span> <span word="and">and</span> <span word="the">the</span> <span word="nature">nature</span> <span word="of">of</span> <span word="matter">matter</span> <span word="itself">itself</span>. <span word="The">The</span> <span word="invention">invention</span> <span word="of">of</span> <span word="the">the</span> <span word="visible">visible</span> <span word="light">light</span> <span word="microscope">microscope</span> <span word="late">late</span> <span word="in">in</span> <span word="the">the</span> <span word="sixteenth">sixteenth</span> <span word="century">century</span> <span word="introduced">introduced</span> <span word="a">a</span> <span word="previously">previously</span> <span word="unknown">unknown</span> <span word="realm">realm</span> <span word="of">of</span> <span word="single">single</span> <span word="celled">celled</span> <span word="plants">plants</span> <span word="and">and</span> <span word="animals">animals</span>. <span word="In">In</span> <span word="the">the</span> <span word="twentieth">twentieth</span> <span word="century">century</span>, <span word="electron">electron</span> <span word="microscopes">microscopes</span> <span word="have">have</span> <span word="provided">provided</span> <span word="direct">direct</span> <span word="views">views</span> <span word="of">of</span> <span word="viruses">viruses</span> <span word="and">and</span> <span word="minuscule">minuscule</span> <span word="surface">surface</span> <span word="structures">structures</span>. <span word="Now">Now</span> <span word="another">another</span> <span word="type">type</span> <span word="of">of</span> <span word="microscope">microscope</span>, <span word="one">one</span> <span word="that">that</span> <span word="utilizes">utilizes</span> <span word="x">x</span> <span word="rays">rays</span> <span word="rather">rather</span> <span word="than">than</span> <span word="light">light</span> <span word="or">or</span> <span word="electrons">electrons</span>, <span word="offers">offers</span> <span word="a">a</span> <span word="different">different</span> <span word="way">way</span> <span word="of">of</span> <span word="examining">examining</span> <span word="tiny">tiny</span> <span word="details">details</span>; <span word="it">it</span> <span word="should">should</span> <span word="extend">extend</span> <span word="human">human</span> <span word="perception">perception</span> <span word="still">still</span> <span word="farther">farther</span> <span word="into">into</span> <span word="the">the</span> <span word="natural">natural</span> <span word="world">world</span>. <span word="The">The</span> <span word="dream">dream</span> <span word="of">of</span> <span word="building">building</span> <span word="an">an</span> <span word="x">x</span> <span word="ray">ray</span> <span word="microscope">microscope</span> <span word="dates">dates</span> <span word="to">to</span> <span word="back">back</span> 1895; <span word="its">its</span> <span word="development">development</span>, <span word="however">however</span> <span word="was">was</span> <span word="virtually">virtually</span> <span word="halted">halted</span> <span word="in">in</span> <span word="the">the</span> 1940<span word="s">s</span> <span word="because">because</span> <span word="the">the</span> <span word="development">development</span> <span word="of">of</span> <span word="the">the</span> <span word="electron">electron</span> <span word="microscope">microscope</span> <span word="was">was</span> <span word="progressing">progressing</span> <span word="rapidly">rapidly</span>. <span word="During">During</span> <span word="the">the</span> 1940<span word="s">s</span>, <span word="electron">electron</span> <span word="microscopes">microscopes</span> <span word="routinely">routinely</span> <span word="achieved">achieved</span> <span word="resolution">resolution</span> <span word="better">better</span> <span word="than">than</span> <span word="that">that</span> <span word="poss">poss</span> <span word="ible">ible</span> <span word="with">with</span> <span word="a">a</span> <span word="visible">visible</span> <span word="light">light</span> <span word="microscope">microscope</span>, <span word="while">while</span> <span word="the">the</span> <span word="performance">performance</span> <span word="of">of</span> <span word="x">x</span> <span word="ray">ray</span> <span word="microscopes">microscopes</span> <span word="resisted">resisted</span> <span word="improvement">improvement</span>. <span word="In">In</span> <span word="recent">recent</span> <span word="years">years</span>, <span word="however">however</span>, <span word="interest">interest</span> <span word="in">in</span> <span word="x">x</span> <span word="ray">ray</span> <span word="microscopes">microscopes</span> <span word="has">has</span> <span word="revived">revived</span>, <span word="largely">largely</span> <span word="because">because</span> <span word="of">of</span> <span word="advances">advances</span> <span word="such">such</span> <span word="as">as</span> <span word="the">the</span> <span word="developmen">developmen</span> <span word="t">t</span> <span word="of">of</span> <span word="new">new</span> <span word="sources">sources</span> <span word="of">of</span> <span word="x">x</span> <span word="ray">ray</span> <span word="illumination">illumination</span>. <span word="As">As</span> <span word="a">a</span> <span word="result">result</span>, <span word="the">the</span> <span word="brightness">brightness</span> <span word="available">available</span> <span word="today">today</span> <span word="is">is</span> <span word="millions">millions</span> <span word="of">of</span> <span word="times">times</span> <span word="tha">tha</span> <span word="t">t</span> <span word="of">of</span> <span word="x">x</span> <span word="ray">ray</span> <span word="tubes">tubes</span>, <span word="which">which</span>, <span word="for">for</span> <span word="most">most</span> <span word="of">of</span> <span word="the">the</span> <span word="century">century</span>, <span word="were">were</span> <span word="the">the</span> <span word="only">only</span> <span word="available">available</span> <span word="sources">sources</span> <span word="of">of</span> <span word="soft">soft</span> <span word="x">x</span> <span word="rays">rays</span>.<span word="The">The</span> <span word="new">new</span> <span word="x">x</span> <span word="ray">ray</span> <span word="microscopes">microscopes</span> <span word="considerably">considerably</span> <span word="improve">improve</span> <span word="on">on</span> <span word="the">the</span> <span word="resolution">resolution</span> <span word="provided">provided</span> <span word="by">by</span> <span word="optical">optical</span> <span word="microscopes">microscopes</span>. <span word="They">They</span> <span word="can">can</span> <span word="also">also</span> <span word="be">be</span> <span word="used">used</span> <span word="to">to</span> <span word="map">map</span> <span word="the">the</span> <span word="distribution">distribution</span> <span word="of">of</span> <span word="certain">certain</span> <span word="chemical">chemical</span> <span word="elements">elements</span>. <span word="Some">Some</span> <span word="can">can</span> <span word="form">form</span> <span word="pictures">pictures</span> <span word="in">in</span> <span word="extremely">extremely</span> <span word="short">short</span> <span word="times">times</span>; <span word="others">others</span> <span word="hold">hold</span> <span word="the">the</span> <span word="promise">promise</span> <span word="of">of</span> <span word="special">special</span> <span word="capabilities">capabilities</span> <span word="such">such</span> <span word="as">as</span> <span word="three">three</span> <span word="dimensional">dimensional</span> <span word="imaging">imaging</span>. <span word="Unlike">Unlike</span> <span word="conventional">conventional</span> <span word="electron">electron</span> <span word="microscope">microscope</span>, <span word="x">x</span> <span word="ray">ray</span> <span word="microscope">microscope</span> <span word="enables">enables</span> <span word="specimens">specimens</span> <span word="to">to</span> <span word="be">be</span> <span word="kept">kept</span> <span word="in">in</span> <span word="air">air</span> <span word="and">and</span> <span word="in">in</span> <span word="water">water</span>, <span word="which">which</span> <span word="means">means</span> <span word="that">that</span> <span word="biological">biological</span> <span word="samples">samples</span> <span word="can">can</span> <span word="be">be</span> <span word="studied">studied</span> <span word="under">under</span> <span word="conditions">conditions</span> <span word="similar">similar</span> <span word="to">to</span> <span word="their">their</span> <span word="natural">natural</span> <span word="state">state</span>. <span word="The">The</span> <span word="illumination">illumination</span> <span word="used">used</span>, <span word="so">so</span> <span word="called">called</span> <span word="soft">soft</span> <span word="x">x</span> <span word="rays">rays</span> <span word="in">in</span> <span word="the">the</span> <span word="wavelength">wavelength</span> <span word="range">range</span> <span word="of">of</span> <span word="twenty">twenty</span> <span word="to">to</span> <span word="forty">forty</span> <span word="angstroms">angstroms</span> , <span word="is">is</span> <span word="also">also</span> <span word="sufficiently">sufficiently</span> <span word="penetrating">penetrating</span> <span word="to">to</span> <span word="image">image</span> <span word="intact">intact</span> <span word="biological">biological</span> <span word="cells">cells</span> <span word="in">in</span> <span word="ma">ma</span> <span word="ny">ny</span> <span word="cases">cases</span>. <span word="Because">Because</span> <span word="of">of</span> <span word="the">the</span> <span word="wavelength">wavelength</span> <span word="of">of</span> <span word="the">the</span> <span word="x">x</span> <span word="rays">rays</span> <span word="used">used</span>, <span word="soft">soft</span> <span word="x">x</span> <span word="ray">ray</span> <span word="microscopes">microscopes</span> <span word="will">will</span> <span word="never">never</span> <span word="match">match</span> <span word="the">the</span> <span word="highest">highest</span> <span word="resolution">resolution</span> <span word="possible">possible</span> <span word="with">with</span> <span word="electron">electron</span> <span word="microscopes">microscopes</span>. <span word="Rather">Rather</span>, <span word="their">their</span> <span word="special">special</span> <span word="properties">properties</span> <span word="will">will</span> <span word="make">make</span> <span word="possible">possible</span> <span word="investigations">investigations</span> <span word="that">that</span> <span word="will">will</span> <span word="complement">complement</span> <span word="those">those</span> <span word="performed">performed</span> <span word="with">with</span> <span word="light">light</span> <span word="and">and</span> <span word="electron">electron</span> <span word="based">based</span> <span word="instruments">instruments</span>.</p>
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