李克

新东方在线推荐：2018年考研一次顺利提分课程！！一科不过，全科免费Theintensiveworkofmaterialsscientistsandsolid-statephysicistshasgivenrisetoaclassofsolidsknownasamorphousmetallicalloysorglassymetals.Thereisagrowinginterestamongtheoreticalandappliedresearchersalikeinthestructuralpropertiesofthesematerials.Whenamoltenmetalormetallicalloyiscooledtoasolid,acrystallinestructureisformedthatdependsontheparticularalloycomposition.Incontrast,moltennonmetallicglass-formingmaterialswhencooleddonotassumeacrystallinestructure,butinsteadretainastructuresomewhatlikethatoftheliquid—anamorphousstructure.Atroomtemperaturethenaturallong-termtendencyforbothtypesofmaterialsistoassumethecrystallinestructure.Thedifferencebetweenthetwoisinthekineticsorrateofformationofthecrystallinestructurewhichiscontrolledbyfactorssuchasthenatureofthechemicalbondingandtheeasewithwhichatomsmoverelativetoeachother.Thus,inmetals,thekineticsfavorsrapidformationofacrystallinesstructurewhereasinnonmetallicglassestherateofformationissoslowthatalmostanycoolingrateissufficienttoresultinanamorphousstructure.Forglassymetalstobeformed,themoltenmetalmustbecooledextremelyrapidlysothatcrystallizationissuppressed.Thestructureofglassymetalsisthoughttobesimilartothatofliquidmetals.OneofthefirstattemptstomodelthestructureofaliquidwasthatbythelateJ.D.BernaloftheUniversityofLondon,whopackedhardspheresintoarubbervesselinsuchawayastoobtainthemaximumpossibledensity.Theresultingdense,random-packedstructurewasthebasisformanyattemptstomodelthestructureofglassymetals.CalculationsofthedensityofalloysbasedonBernal-typemodelsofthealloysmetalcomponentagreefairlywellwiththeexperimentallydeterminedvaluesfrommeasurementsonalloysconsistingofanoblemetaltogetherwithametalloidsuchasalloysofpalladiumandsiliconoralloysconsistingofironphosphors,andcarbon,althoughsmalldiscrepanciesremained.OnedifferencebetweenrealalloysandthehardspheresareainBernalmodelsisthatthecomponentsofanalloyhavedifferentsize,sothatmodelsbasedontwosizesofspheresaremoreappropriateforabinaryalloyforexample.Thesmallermetalloidatomsofthealloysmightfitintoholesinthedenserandom-packedstructureofthelargermetalatoms.Oneofthemostpromisingpropertiesofglassymetalsistheirhighstrengthcombinedwithhighmalleability.Inusualmaterials,onefindsaninverserelationbetweenthetwoproperties,whereasformanypracticalapplicationssimultaneouspresenceofbothpropertiesisdesirable.Oneresialobstacletopracticalapplicationsthatislikelytobeovercomeisthefactthatglassymetalswillcrystallizeatrelativelylowtemperatureswhenheatedslightly.1.Theauthorisprimarilyconcernedwithdiscussing[A]crystallinesolidsandtheirbehavioratdifferenttemperatures.[B]moltenmaterialsandthekineticsoftheformationoftheircrystallinestructure.[C]glassymetalsandtheirstructuralcharacteristics.[D]metallicalloysandproblemsindeterminingtheirdensity.2.Theauthor’sattitudetowardtheprospectsfortheeconomicutilizationofglassymetalsisoneof[A]disinterest.[B]impatience.[C]optimism.[D]apprehension.3.Accordingtothetext,whichofthefollowingdeterminesthecrystallinestructureofametallicalloy?[A]Atwhatratethemoltenalloyiscooled.[B]Howrapidtherateofformationofthecrystallinephaseis.[C]Howthedifferent-sizedatomsfitintoadenserandom-packedstructure.[D]Whatthealloyconsistsofandinwhatratios.4.Whichofthefollowingbestdescribestherelationshipbetweenthestructureofliquidmetalsandthestructureofglassymetals,asitispresentedinthetext?[A]Thelatterisanillustrativeexampleoftheformer.[B]Thelatterisalarge-scaleversionoftheformer.[C]Theformerisastructuralelaborationofthelatter.[D]Theformerisafairapproximationofthelatter.5.Itcanbeinferredfromthetextthat,theoretically,moltennonmetallicglassesassumeacrystallinestructureratherthananamorphousstructureonlyiftheyarecooled[A]veryevenly,regardlessoftherate.[B]rapidly,followedbygentleheating.[C]veryslowly.[D]toroomtemperature. 更多

随着社会的快速发展，经济学考研的热度也有所增加，对于初次备考的同学，考研经济学部分，具体的考试题型，也是大家要重点积累的。下面小编为考生整理了2022考研经济学之学科组织框架简介，供大家参考!。教育部将高等院校里的学科分类目录里面，经济学学科门类的硕士专业分为理论经济学与应用经济学两个一级学科。其中，理论经济学包括6个二级学科，有部分学校还新增了网络经济学、企业经济学、可持续发展经济学等新型专业。应用经济学包括10个二级学科。理论经济学，顾名思义比较侧重于经济理论问题的研究，其中西方经济学和政治经济学值得推荐，其他几个二级学科实际上属于冷门，报考人数很少。如世界经济，经济思想史，人口、资源与环境经济学等，这些专业中，除世界经济外，大多属于冷门专业，报考人数少，一些院校基本只招收个别研究生，有时还需经过调剂完成招生名额。由于录取名额太少，一些重点学校会由于报考人数较多而录取线异常高。应用经济学，是比较侧重于实际应用的学科，其中金融学和国际贸易学是极其热门的学科，财政学、产业经济学、数量经济学、统计学也广受关注。2011年研究生的报考人数比2010年有所增加，共151万人。结合最新北京教育考试院公布数据分析，近三年，北京地区报考应用经济学类专业增幅连续三年超过12.8%。 更多

考研网快讯，据广西大学研究生院消息，2014年广西大学农业机械化工程考研报录比还未公布。为方便网友及时了解广西大学农业机械化工程的报录比信息，故开启了关于广西大学农业机械化工程考研报录比的帖子，网友可以进入原帖参与讨论。        同时也可以收藏2014年各院校考研报录比统计，考研网会第一时间及时发布关于广西大学报录比的信息。      更多