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   203669篇
  免费   1322篇
  国内免费   431篇
化学   105145篇
晶体学   3396篇
力学   10305篇
综合类   10篇
数学   21890篇
物理学   64676篇
  2021年   2001篇
  2020年   2030篇
  2019年   2580篇
  2018年   3682篇
  2017年   3688篇
  2016年   4842篇
  2015年   2381篇
  2014年   4327篇
  2013年   8632篇
  2012年   6876篇
  2011年   8088篇
  2010年   6487篇
  2009年   6669篇
  2008年   7658篇
  2007年   7615篇
  2006年   6706篇
  2005年   5929篇
  2004年   5650篇
  2003年   5180篇
  2002年   5161篇
  2001年   5616篇
  2000年   4148篇
  1999年   3132篇
  1998年   2705篇
  1997年   2758篇
  1996年   2544篇
  1995年   2216篇
  1994年   2330篇
  1993年   2235篇
  1992年   2527篇
  1991年   2651篇
  1990年   2561篇
  1989年   2627篇
  1988年   2534篇
  1987年   2553篇
  1986年   2413篇
  1985年   3037篇
  1984年   3102篇
  1983年   2599篇
  1982年   2565篇
  1981年   2528篇
  1980年   2336篇
  1979年   2712篇
  1978年   2672篇
  1977年   2873篇
  1976年   2876篇
  1975年   2667篇
  1974年   2604篇
  1973年   2714篇
  1972年   2085篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
The chlorination of benzene, toluene, and o-xylene with molecular chlorine in the presence of the phthalocyanine complexes of different structures was studied. The transformations of the catalysts during the reaction were investigated. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1644–1647, August, 2008.  相似文献   
92.
93.
Thermodynamic parameters of reactions of methyl and phenyl isocyanates with a series of compounds were determined by quantum-chemical calculations. The products of these reactions model for various functional groups present in commercial polyurethanes. The thermodynamic stability series for compounds formed from aliphatic and aromatic isocyanates were constructed.  相似文献   
94.
Possibilities of utilization of by-products formed in manufacture of epichlorohydrin are considered. A promising way to utilize wastes from production of epichlorohydrin by synthesis of 2,3-dichloropropene from 1,2,3-trichloropropane is suggested.  相似文献   
95.
The alternative: equivalence-singularity on the conic sigma-field is established for a pair of centered Gaussian distributions and a corresponding criterion is given. The behavior of the logarithmic variation is established for the Radon–Nikodym derivative on the conic sigma-subfield. Bibliography: 6 titles.  相似文献   
96.
The luminescence characteristics of hydrated Ln3+ ions and their complexes with some acidic ligands have been investigated. The possibility of determining the stability of the complexes of lanthanides in solutions from the intensity of luminescence bands is shown. The influence of the characteristic features of the f-electron shell of Ln3+ on the formation of the spectrochemical series is discussed.  相似文献   
97.
Local and nonlocal coercive estimates in Lebesgue, Hölder, and Morrey–Campanato spaces are proved for solutions of linear stationary systems of hydrodynamic type. For this purpose, the technique proposed by Italian mathematicians for the study of solutions to equations and systems of elliptic and parabolic types is developed. Bibliography: 14 titles.  相似文献   
98.
Electrohydrodynamic instability in homeotropically oriented nematic samples of 4'-n-octyl-4-cyano-biphenyl and 4'n-alkyloxy-4-cyanobiphenyl, (n = 8.9) have been studied in an a.c. electric field. The domain patterns during the instability in these compounds in a very low frequency a.c. field are very similar to those in a d.c. field. The domain patterns observed at higher frequencies have been identified as 'maltese crosses' or 'crossed isogyres'. The electro-convective 'isotropic' flows near the electrode play an important role in the observed instability.  相似文献   
99.
100.
The effect of rare-earth oxides on the properties of anisotropic barium ferrites has been studied by x-ray structural and Mössbauer methods. Additions of SrCO3, as well as SrCO3 and La2O3, SrCO3 and Pr6O11, SrCO3 and Nd2O3, SrCO3 and Sm2O3 in amounts of 7.5 mole % Sr and 10 mole % rare-earth element to grade-A barium powder results in the substitution of barium ions by Sr and rare-earth ions; consequently, the energy of magnetic anisotropy changes and the technically important parameters Br and (BH)max increase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 34–39, January, 1989.  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