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1、智課網(wǎng)TOEFL備考資料托福閱讀練習(xí)材料:Silk(蠶絲)--托福閱讀蠶絲制品是我們平時(shí)非常常見(jiàn)的,但是蠶絲竟然是最強(qiáng)韌的天然纖維這點(diǎn)很多人不知道。下面,就請(qǐng)隨小編進(jìn)入今天的新托福閱讀練習(xí)材料,討論關(guān)于蠶絲的話題。Silkisthestrongestnaturalfiberintheworld,asfarasweknow.Scientistslongtounderstandjusthowexactlythesilkwormmanagestheprocessofsilkweaving,sotheycanreplicatetheprocessinordertomanufactur
2、esuchthingsashigh-strengthandhigh-performancematerialsforsportsandlawenforcement.Thoughourunderstandingofthesilk-makingprocessisnotyetcomplete,scientistsdoknowthatthekeytomakingsilkliesintheanimal’scarefulmanagingofthewatercontentinitssilkglands.Silkgetsitsstrengthfromitsproteins.Partsofthe
3、proteinsarehydrophilic,orwater-loving;andpartsarehydrophobic,orwater-fearing.Forsometimeitwasamysteryhowsilkwormsmanagedtoconverttheseproteinsintosilkthreadswithouttheproteinscrystallizingbeforetheanimalisreadytospinthem.Prematurecrystallizationwouldcloguptheirsilkglands,whichwouldlikelypro
4、vefataltothelittlecreatures.Theanswerliesinthesilkworm’sslowlydecreasingthewatercontentinitssilkglandsandintheproteins’abilitytoretainwater,keepingthesolutionsolubleupuntilitisspun.Asthewaterdecreases,thewater-lovingpartsoftheproteinsfoldtogetherinchains,forcingthewater-fearingpartstogether
5、.Asthewaterlevelcontinuestodrop,thefoldedchainsofsilkpushtogethermoreandmoretoformlargerandlargergel-likestructures.Allthewhilethewater-lovingpartsretainenoughwatersothatthesolutiondoesnotcrystallizeprematurely,beforethereisenoughofthematerialtobeginspinning.蠶絲是史上全世界最強(qiáng)韌的天然纖維。長(zhǎng)久以來(lái),科學(xué)家想知道蠶如何產(chǎn)
6、絲,然后仿效制絲過(guò)程,生產(chǎn)高強(qiáng)高性能的運(yùn)動(dòng)原材及執(zhí)法材料。雖然我們對(duì)制絲的整個(gè)過(guò)程了解的不多,但是科學(xué)家可以肯定關(guān)鍵在于蠶如何細(xì)心掌控絲腺里的水分。蠶絲的高強(qiáng)性是因?yàn)榈鞍踪|(zhì)。蛋白質(zhì)部分是親水的;部分是疏水的。蠶吐絲前,蛋白質(zhì)尚未結(jié)晶,蠶是如何將蛋白質(zhì)轉(zhuǎn)換成蠶線一直是個(gè)未解之謎。而過(guò)早的結(jié)晶會(huì)阻塞絲腺,蠶很可能為此喪命。奧秘在于絲腺里的水分逐步流失,而蛋白質(zhì)可以?xún)?chǔ)存水分,蠶在吐絲前先溶解于水。水分漸漸流失,親水的蛋白質(zhì)絲絲縷縷纏繞在一起,將疏水的部分也裹在一起。水分繼續(xù)流失,包裹在一起的蠶絲像滾雪球般形成凝膠狀。親水的蛋白質(zhì)始終儲(chǔ)存足夠水分避免過(guò)早結(jié)晶。結(jié)晶后,蠶吐出蠶絲。fi
7、ber:纖維convert:轉(zhuǎn)換spin:(蠶)吐絲;過(guò)去式spun或span過(guò)去分詞spun現(xiàn)在分詞spinningfatal:致命的以上就是今天的托福閱讀材料,大家可以在練習(xí)托福閱讀材料的同時(shí),積累一些相關(guān)詞匯及句型,以便考試的時(shí)候更好地把握文意,奪得托福閱讀的高分。