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   60035篇
  免费   10501篇
  国内免费   30511篇
化学   59555篇
晶体学   2247篇
力学   2866篇
综合类   1933篇
数学   10503篇
物理学   23943篇
  2024年   512篇
  2023年   1837篇
  2022年   2326篇
  2021年   2747篇
  2020年   2076篇
  2019年   2445篇
  2018年   1754篇
  2017年   2476篇
  2016年   2765篇
  2015年   2993篇
  2014年   4308篇
  2013年   4807篇
  2012年   5002篇
  2011年   4787篇
  2010年   4424篇
  2009年   4948篇
  2008年   5437篇
  2007年   5130篇
  2006年   5411篇
  2005年   4902篇
  2004年   4822篇
  2003年   3823篇
  2002年   2853篇
  2001年   2662篇
  2000年   2117篇
  1999年   2140篇
  1998年   1550篇
  1997年   1278篇
  1996年   1140篇
  1995年   1132篇
  1994年   1056篇
  1993年   879篇
  1992年   992篇
  1991年   973篇
  1990年   820篇
  1989年   787篇
  1988年   371篇
  1987年   192篇
  1986年   124篇
  1985年   106篇
  1984年   58篇
  1983年   44篇
  1982年   25篇
  1981年   3篇
  1980年   1篇
  1979年   1篇
  1959年   10篇
  1936年   1篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
191.
The polyacrylic acid functionalized polystyrene nanospheres were synthesized and self-assembled into irregular, densely packed monolayers in non-aqueous media. The polymer nanoparticles were chemically adhered to substrates. The morphologies of the resulting films were investigated. The impact of the volume fraction of alcohol in the mixed solvents on the particle adsorption and fabrication of nanosphere assembled films was examined.  相似文献   
192.
A concise and efficient synthesis of the new compounds tetrahydroisoquino [2,1-c] [1,3]benzodiazepine 5 and 7 is reported.  相似文献   
193.
A new cobalt(Ⅱ) complex with tridentate ligand 2, 6-bis (benzimidazol-2-yl)pyridine has been synthesized by microwave irradiation method and characterized by elemental analysis,electrochemical and spectral methods. The binding of the complex with calf thymus DNA has also been investigated by absorption and fluorescence spectra.  相似文献   
194.
A mild, regioselective 1, 3-dipolar cycloaddition protocol for the preparation ofphenylselenomethyl isoxazolines through substituted allyl phenyl selenides and nitrile oxides wasreported.  相似文献   
195.
2,5-Disubstituted oxazoles were prepared conveniently by treatment of aromatic α-methyl ketones and nitriles with poly[styrene(iodosodiacetate)] in one-pot process.  相似文献   
196.
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   
197.
The first intramolecular charge transfer transition based on 2-ureido-4[1H]-pyrimidinone binding module was reported.  相似文献   
198.
A facile solid phase synthesis of 2-substituted 1,3-oxazin-6-ones using polymer-supported Meldrum‘s acid has been reported. Reaction of the resin-bound cyclic malonic acid ester with triethyl orthoformate and subsequent double substitution with amide, afforded the corresponding polymer-supported acylaminomethylene cyclic malonic acid ester, which upon thermal treatment led to 1, 3-oxazin-6-ones in good yields and with high purity.  相似文献   
199.
Optically active aziridino alcohols containing ferrocenyl groups were prepared from commercially available L-threonine in excellent yields and used as catalysts to promote the asymmetric addition of diethylzinc to aryaldehydes to afford 1-arylpropanol in up to 84% enantiomeric excesses with moderate to good yields.  相似文献   
200.
The adsorption of asymmetrical triblock copolymers from a non-selective solvent on solid surface has been studied by using Scheutjens-Fleer mean-field theory and Monte Carlo simulation method on lattice model. The main aim of this paper is to provide detailed computer simulation data, taking A8-kB20Ak as a key example, to study the influence of the structure of copolymer on adsorption behavior and make a comparison between MC and SF results. The simulated results show that the size distribution of various configurations and density-profile are dependent on molecular structure and adsorption energy. The molecular structure will lead to diversity of adsorption behavior. This discrepancy between different structures would be enlarged for the surface coverage and adsorption amount with increasing of the adsorption energy. The surface coverage and the adsorption amount as well as the bound fraction will become larger as symmetry of the molecular structure becomes gradually worse. The adsorption layer becomes thicker with increasing of symmetry of the molecule when adsorption energy is smaller but it becomes thinner when adsorption energy is higher. It is shown that SF theory can reproduce the adsorption behavior of asymmetrical triblock copolymers. However, systematic discrepancy between the theory and simulation still exists.The approximations inherited in the mean-filed theory such as random mixing and the allowance of direct back folding may be responsible for those deviations.  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