首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   118971篇
  免费   1994篇
  国内免费   2692篇
化学   84065篇
晶体学   69篇
力学   1549篇
综合类   88篇
数学   2865篇
物理学   35021篇
  2023年   202篇
  2022年   232篇
  2021年   181篇
  2020年   165篇
  2019年   168篇
  2018年   229篇
  2017年   130篇
  2016年   280篇
  2015年   247篇
  2014年   439篇
  2013年   381篇
  2012年   10186篇
  2011年   14372篇
  2010年   2606篇
  2009年   727篇
  2008年   10894篇
  2007年   11223篇
  2006年   11457篇
  2005年   11110篇
  2004年   8795篇
  2003年   6554篇
  2002年   5809篇
  2001年   4015篇
  2000年   4649篇
  1999年   1385篇
  1998年   582篇
  1997年   450篇
  1996年   1828篇
  1995年   1346篇
  1994年   1639篇
  1993年   2155篇
  1992年   1893篇
  1991年   846篇
  1990年   818篇
  1989年   689篇
  1988年   603篇
  1987年   606篇
  1986年   633篇
  1985年   611篇
  1984年   223篇
  1983年   155篇
  1982年   142篇
  1981年   126篇
  1979年   93篇
  1975年   142篇
  1958年   164篇
  1957年   124篇
  1956年   109篇
  1955年   119篇
  1954年   92篇
排序方式: 共有10000条查询结果,搜索用时 722 毫秒
51.
用闪光蒸镀法在77K制备了NdxFe1-x(x=0.06-0.80)非晶薄膜,原位测定了其电阻随温度的变化。结果表明:在0.192和ρ(T)∝T。晶化不是在一个固定的温度,而是在一个温度区间发生。  相似文献   
52.
In the present study, proteins and glycoproteins of mouse embryos at 2-cell,morula and blastocyst stages were analyzed.The techniques of ~(35)S-Met incorporation,ConA antiserum-precipitating ConA-binding proteins, mini-2D-electrophoresis, fluorography,video densitometer scanning and the computer-lmage system were used for analyses.Results of the investigations indicated that proteins and glycoproteins were synthesized by the embryos in a gradual increase manner from 2-cell to blastocyst. A relatively large amount of glycoproteins was synthesized during the morula and blastocyst stages.Two specific small glycoproteins respectively with molecular weights about 6500 and 9000 and PIs at 5.0 and 6.5 were apparently synthesized in the blastocyst but not in the 2-cell or the morula.  相似文献   
53.
I.IntroductionThepcrformanccsofAcousto-optic(AO)dcviccareoftenlimitcdbythepropertiesofAOmcdiawhenitisusedinAOsigna1processingsystems.Thespectrumanalyzersandcorre1ationreceivers,forinstancc,areexpcctcdtoimprovcthereso1utionanddynamicrangcwhilereducingtheproccssorvolume.Rccent1y,ancwclassofmateria1s,themercurousha1ides,promiscstocontributeimportantsolutionstosuchnccdsandisrefincdtopractica1uti1izations.Themecurousha1ideweconsidcrinthispapcrismecurouschloride(Hg,C1,).Thesing1ecrystalofHg,Cl…  相似文献   
54.
The electrochemical oxidation of 1, 3-benzenedithiol was investigated in a 0. 100 mol/L tetrabutylammonium perchlorate/acetonitrile electrolyte. The electrochemical techniques used were potential sweep, bulk electrolysis, rotating disc and the potential step method. The combination of the techniques yielded the number of electrons transferred per molecule, the reaction order, the transfer coefficient, the diffusion coefficient and concentration of dithiol anions, the standard heterogeneous rate constant as well as the formal potential and equilibrium constant of the preceeding dissociation reaction. This paper also illustrates the methods for studying the electrode kinetics of reactions which (a) involve a chemical reaction preceeding the electron-transfer process, (b) have insoluble polymer products, and (c) are totally irreversible.  相似文献   
55.
Polysubstituted indoles can be prepared directly from functionalized nitroalkanes under very mildly acidic conditions in a simple, one-pot, two-stage procedure.  相似文献   
56.
Introduction Adrenoceptors(ARs),membersofthesuperfami lyofG proteincoupledreceptors,arethemostimpor tantreceptorsinvolvedincardiacregulation[1].ARsin cardiacmuscleincludebothαARsandβARssub types,whileinmostmammalianheart,βARsarethe predominantsubtypes.…  相似文献   
57.
Chrysene and 1.2-benzanthracene are successfully doped in a solid wax film and their vibrational spectra in gooo--400cm^-1 are discussed. The harmonic frequencies and relative intensities of both the molecules observed in the film are compared with theoretical values calculated by the density functional theory (DFT) model as well as with the previous experimental data. The effects on spectra due to change of matrix and some additional bands observed in the wax film are also reported. Excellent agreement in the spectral positions and strengths between the experiments and DFT values are found.  相似文献   
58.
IntroductionOver the past few years, dimethyl carbonate(DMC) has been proven to be an efficientmethylating,methoxylating, and methoxycarbonylating agent inorganic syntheses, in which DMC is used to replace thetoxic methyl halides, dimethyl sulfate or carb  相似文献   
59.
Let T be a bounded linear operator in a Banach space, with σ(T)={1}. In 1983, Esterle-Berkani' s conjecture was proposed for the decay of differences (I - T) T^n as follows: Eitheror lim inf (n→∞(n+1)||(I-T)T^n||≥1/e or T = I. We prove this claim and discuss some of its consequences.  相似文献   
60.
<正> §5.数乘一个数λ与一个函数φ(x)的数乘运算λφ(x)有下列性质1°。如果φ_n(x)是基本列,则λφ_n(x)也是基本列。这个性质能使我们把这种运算推广到任意的广义函数f(x)=[φ_n(x)]上,只要假定  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号