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271.
Jernvall J  Fortelius M 《Nature》2002,417(6888):538-540
During the past 20 million years, herbivorous mammals of numerous lineages have evolved hypsodont, or high-crowned, cheek teeth. Hypsodonty is informative ecologically because it is well developed in mammals eating fibrous and abrasive foods that are most abundant in open and generally or seasonally dry environments. Here we report that in the Neogene of Europe mammals with the greatest locality coverages showed an increase in hypsodonty. We used a data set of 209 localities to measure whether large mammals occurring in many fossil localities show a similar increase in hypsodonty to mammals occurring in single or few localities. Taxonomic and morphological groupings show a low average hypsodonty in the early Miocene epoch. From the middle Miocene onwards, only the hypsodonty of commonly found mammals shows a marked increase. Therefore, in the drying Europe of the late Miocene, only increasingly hypsodont mammals may have been able to expand their share of habitats and food resources. These results suggest that the relatively small number of species known from multiple localities are palaeoecologically informative by themselves, irrespective of the rest of the known species.  相似文献   
272.
0 IntroductionHemoglobin(Hb)isthemajorhemeproteinofredbloodcells(RBCs)andisresponsibleforthetransportofoxygentothetissues.ThefunctionofHbdependsupontheabilityoffer rousironinthehemegrouptobindandreleaseoxygen .Despiteitsprincipalroleasanoxygen carrier,theHbmoleculepossessesdifferentenzymaticactivities[1 ] andamethodwasdevelopedforthedeterminationofHbbasedonitsenzymaticactivityfortheox idationofo phenylenediamine (OPDA)withH2 O2 asanoxi dant[2 ] .Hbasamimeticenzymeofperoxidase ,cancataly…  相似文献   
273.
0 IntroductionAblockcipherwithoutdataextensionorexpressionisaper mutation .Thesecurityofablockcipherschemeiscorrela tivewiththe permutations.Quicktrickle permutation[1 ] canmakethedatadisorderedwhenactingatthedataandmakeallprobabledistancebetweentwoelementsappear,soithasgoodcryptographicpropertiesandcanbeusedintheblockcipherwhichrequireshighsecurity.Aprivatekeyblockcipherisapermutationinn dimensionvectorspaceoverF2 atthecontrolofakey[2 ,3] .Moreover,manyblockciphersusepermutationstoexecuteso…  相似文献   
274.
0 IntroductionTheWorldWideWebisconsideredasalargedistributedin formationsystemthatprovidesaccesstoshareddataob jects.AsoneofthemostpopularapplicationscurrentlyrunningontheInternet,theWorldWideWebisofanexponentialgrowthinsize,whichresultsinnetworkcongestionandserveroverloading .Inthefieldsofspatialinformationsystems,therehavethesameproblems.Recently ,attentionhasbeenpaidtoefficientintegra tionoftheWebandGIS(GeographicInformationSystem)appli cation .ThisisbecausetheWebhasmanyadvantages,i…  相似文献   
275.
Research on data combination for Phased-array Ground Penetrating Radar   总被引:1,自引:0,他引:1  
0 IntroductionGroundPenetratingRadar (GPR)isanewandefficientex ploringmeanstodetecttheobjectinshallowsubsurface.Comparedwithotherdetectingmethods,GPRhasmanyadvan tages,suchasquickness,highresolution ,convenientoperationetc.SoGPRisappliedtonationaldefenseandnationaleconomy .IndevelopmentofGPRtechnology ,therecomeforthcontinuous waveradar,FMcontinuous waveradar,andshockpulseradar.Amongoftheseradars,shockpulseradarsendsgreatamplitudeimpulsewithperiodinns,receivingequivalentsamplingtoreali…  相似文献   
276.
0 IntroductionNeuralnetworks,inrecentyears,havebeensuccessfullyusedformodelingfinancialtimeseries.Researchesrevealneuralnetworkshavebetterresultsindescribingdynamiccharac teristicscomparingwithclassicalstatisticalmethods[1 3] .Back propagation (BP)neuralnetworkisamostpopularlyusedneuralnetworkmodelintheareaoffinancialforecasting .AlthoughBP’sstructureissimple ,ithaspowerfulabilityinsolvingvariousproblems.TherearealsoshortcomingswithBP :needsformanycontrolparameters,difficultyingettingsta…  相似文献   
277.
0 IntroductionThegreatattentionhasbeenpaidtorareearthorradioactiverareearthmetalcomplexesfortheirvariousbiologicactivi ties[1 3] .Forexamples,theradioactiverareearthmetal1 53SmⅢ com plexeswerewidelyusedfortumourtherapyofbrain ,liver,lung ,heartandbonetissues[4 5] ;forrareearthmetalEuⅢandTbⅢemitinguniquefluorescence ,theircompoundswereappliedfordiagnosesofvariousdiseases[6 ,7] ;forrareearthmetalGdⅢcontainingthemosthigh spinsingleelectrons,itscomplexeswereusuallyusedforcontrastagentsofmag…  相似文献   
278.
0 IntroductionTheneedforintegrationofdifferentdatabasemanagementsystems (DBMSs) ,makingdifferencesbetweenthesesystemsinvisibleandprovidinguserswithauniformaccesstoallthedatabaseshasgrownrapidlyduringthelastdecade .However,databaseautonomyandheterogeneity…  相似文献   
279.
Inclusion complex of Orange II with β-Cyclodextrin (β-CD) and the anti-photolysis effect under UV-light were investigated. The molar ratio of inclusion complex of β-Cyclodextrin and Orange II is 1∶1. The formation constantK = 1.236×103 L/mol was determined by the UV and Fluorescence spectra respectively, which was quite in accordance with the calculation with a modified Benesi-Hildbrand equation. The inclusion complex was characterized by the IR spectra and the molar ratio of inclusion complex is 1∶1 too. The formation constantK = 1.266×103 L/mol was determined by1H NMR analysis and was nearly the same by UV and fluorescence spectra. The photocatalytic decolorization rate of Orange II solutions containing β-CD and TiO2 was smaller by 51.9% than that of the Orange II solutions only containing TiO2, while in the case of direct photolysis of Orange II solutions, β-CD can lower the photolysis rate by 48.1% under UV-light. This result indicates β-CD can inhibit the photolysis and photocatalytic decolorization of Orange II under UV-light. The β-CD inclusion complex was found to be persistent to UV-light photolysis. Foundation item: Supported by the National Natural Science Foundation of China (20177017) Biography: Lu Ping (1958), male. Associate professor, research direction: environmental photochemistry.  相似文献   
280.
0 IntroductionArtificialarthrosiseshavebeenwidelyusedintheoperatorsclinicalsurgeriesforthepatientswhosearthrosiseswerese riouslyseverelydamaged.Butmostofartificialarthrosisescanon lybeusedforabouttenyearslongduetotheseriousabrasion .Forthisreason ,theimprovementofthelongevityofartificialarthrosisbecomesanimportantsubjectofstudy .TheartificialarthrosisesbeingmadeupofTialloyTC4(Ti 6Al 4V)andthepolythenewithultrahighmolecularweighthavegreatpotentialitiesonim provinglongevitybecauseTC4canreac…  相似文献   
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