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   52993篇
  免费   7882篇
  国内免费   11970篇
化学   38183篇
晶体学   1339篇
力学   3252篇
综合类   1150篇
数学   7762篇
物理学   21159篇
  2024年   89篇
  2023年   572篇
  2022年   1190篇
  2021年   1358篇
  2020年   1470篇
  2019年   1449篇
  2018年   1298篇
  2017年   1516篇
  2016年   1680篇
  2015年   2061篇
  2014年   2349篇
  2013年   3387篇
  2012年   3718篇
  2011年   5150篇
  2010年   3866篇
  2009年   3999篇
  2008年   3960篇
  2007年   3553篇
  2006年   3377篇
  2005年   3142篇
  2004年   3386篇
  2003年   2415篇
  2002年   2252篇
  2001年   2075篇
  2000年   1757篇
  1999年   1364篇
  1998年   1056篇
  1997年   860篇
  1996年   851篇
  1995年   743篇
  1994年   690篇
  1993年   984篇
  1992年   976篇
  1991年   710篇
  1990年   681篇
  1989年   636篇
  1988年   358篇
  1987年   244篇
  1986年   246篇
  1985年   224篇
  1984年   194篇
  1983年   146篇
  1982年   141篇
  1981年   101篇
  1980年   88篇
  1979年   88篇
  1978年   55篇
  1976年   45篇
  1974年   42篇
  1973年   49篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
141.
Electrochemiluminescence (ECL), like other chemiluminescence technique, offers high signal-to-noise ratio. Furthermore, it has the advantage over other chemiluminescence techniques of being initiated by a voltage potential. Thus, it provides a better-controlled luminescence. This technique has been used in measuring many kinds of organic and inorganic matters, and analyzing many kinds of antigen, antibody and hapten, such as carcinoembryonic antigen and alpha-fetoprotein, etc1-6. The ele…  相似文献   
142.
Metabolites of A Novel Antibiotic Bitespiramycin in Rat Urine and Bile   总被引:3,自引:0,他引:3  
A sensitive analytical method to identify active metabolites of bitespiramycin in rat urine and bile was developed by liquid chromatography-electrospray ionization tandem mass spectrometry(LC/ESI-MS^n).Bitespiramycin and its major active metabolites in rat urine and bile were isolated and identified as M1 serial(spiramycin Ⅰ,Ⅱ,Ⅲ),M2 serial(platenomycin A1,josamycin and leucomycin A1) and M3 serial(deisovalerylplatenomycin A1,deisovaleryljosamycin,deisovalerylleucomycin A1).  相似文献   
143.
As photosensitizer for solar cell, a new ruthenium (Ⅱ) complex with four ester groups had been synthesized, in which a phenol substituted by {[(2-hydroxy-5-tert-butylbenzyl)(pyridyl-2-methyl)amino]methyl} is covalently linked to ruthenium (Ⅱ) tris-bipyridine. The structures of the new compounds were confirmed by NMR and ESI-MS spectra. The electrochemical and photochemical properties were also studied.  相似文献   
144.
The titled inorganic fullerene-like molecule (hereafter abbreviated as IFM) was recently synthe-sized by Bai et al.[1], which attracts a lot of interests from inorganic and organometallic chemists, and questions are raised for this smart molecule: (ⅰ) Why CuCl can react with Cp*FeP5 in solvent CH3CN to form IFM? (ⅱ) What is the nature of chemical bond-ing? (ⅲ) What is the covalence of Cu in this mole-cule? In this paper we intend to answer these questions in terms of the soft-hard …  相似文献   
145.
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported.  相似文献   
146.
The first hyperpolarizabilities of a series of novel azulenic-barbituric acid chromophores have been studied by using 12 excitation wavelengths, ranging from 900 to 1907 nm. The dispersion relation of the first hyperpolarizabilities of chromophores holds the same tendency as the experimental results. In addition, the static first hyperpolarizability β0 of molecules was calculated by means of the Sum-Over-States (SOS) expression and the two-level formula respectively. The results show that these molecules possess large static first hyperpolarizabilities and the, β0 value increases as the donor or acceptor strength enhances; the distorted degree of molecules has also an important influence on the β0 value.  相似文献   
147.
Baker‘s yeast mediated reduction of optically active diketone is described. The two keto groups are efficiently differentiated and the ee value of the recovered material is considerably raised. It affords highly optically active key intermediates efficiently for the synthesis of natural polyhydroxylated agarofuran products.  相似文献   
148.
程志林  万惠霖刘赞 《中国化学》2004,22(12):1454-1455
Zeolite A rods by self-assembly of zeolite A microcrystal were successfully synthesized by microwave-assisted hydrotherrnal synthesis. The average size of zeolite crystals consisting of self-assembling materials was about 300 nm and the length of zeolite rods was in the range of 15--30μm.  相似文献   
149.
The relation of the isoelectric point (IEP) and the point of zero net charge (PZNC) of the hydrotalcite-like compounds was discussed. It was found that the IEP does not equal to the PZNC and the IEP is higher than the PZNC. The structural positive charges existing in the HTlc,which cause the difference between the IEP and the PZNC. The effects of the structural positive charges of the HTlc on its IEP and PZNC are the same as the specific adsorption of metal cations.  相似文献   
150.
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