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   77565篇
  免费   558篇
  国内免费   111篇
化学   41188篇
晶体学   1260篇
力学   3277篇
综合类   1篇
数学   7827篇
物理学   24681篇
  2022年   569篇
  2021年   869篇
  2020年   965篇
  2019年   1103篇
  2018年   1596篇
  2017年   1685篇
  2016年   2148篇
  2015年   1022篇
  2014年   1718篇
  2013年   3268篇
  2012年   2897篇
  2011年   3274篇
  2010年   2636篇
  2009年   2634篇
  2008年   2996篇
  2007年   2872篇
  2006年   2767篇
  2005年   2432篇
  2004年   2237篇
  2003年   2071篇
  2002年   2133篇
  2001年   2233篇
  2000年   1623篇
  1999年   1252篇
  1998年   1125篇
  1997年   1036篇
  1996年   891篇
  1995年   831篇
  1994年   811篇
  1993年   811篇
  1992年   864篇
  1991年   933篇
  1990年   877篇
  1989年   905篇
  1988年   816篇
  1987年   767篇
  1986年   739篇
  1985年   864篇
  1984年   961篇
  1983年   818篇
  1982年   834篇
  1981年   746篇
  1980年   701篇
  1979年   768篇
  1978年   890篇
  1977年   913篇
  1976年   808篇
  1975年   774篇
  1974年   790篇
  1973年   760篇
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
841.
842.
Copper(II) coordination compounds with p-chlorphenylbiguanide of the type: [Cu(Cl-PhBig)2]X2 and [Cu(Cl–PhBig)X2] with X =Cl?, Br? NO3, OH?, NCS?, NCO?, N3, have been studied by EPR spectroscopy using polycrytalline powders and solutions in DMF. The parameters of the EPR spectra have been used to estimate molecular orbital coefficient, in these compounds and to discuss details of the chemical bonding.  相似文献   
843.
844.
845.
846.
Conclusions 1-Pentanol, 1-dimethylaminopentane or 4-penten-1-o1, 1-pentanol, and 1,5-pentanediol are the major products of the hydroamination of tetrahydrofurfuryl alcohol by dimethylamine and the hydrogenation of this alcohol on a promoted, fused reduced iron catalyst.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2847–2849, December, 1987.The authors express their gratitude to V. G. Zaikin and A. I. Mikaya for assistance in interpreting the mass spectral data.  相似文献   
847.
Reaction of phenyl-ß-naphthylamines with formaldehyde and acetone in the presence of HCl and nitrobenzene in butanol solution leads to cyclization involving the naphthalene and phenyl rings, and formation of N-aryllepidine salts. 15 lepidine and 5, 6-benzoepidine salts are synthesized and characterized by their UV absorption spectra, as well as by their picrates.For Part LIII see [3].  相似文献   
848.
Conclusions 1-(N,N-Dimethylhydrazino)-4-methyl-2,2,3,3-tetracyanocyclopentane is isomerized reverslbly in solution, with inversion of the configuration of the tetrahedral carbon atom in position 1.For previous communication, see [1].Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1075–1079, May, 1989.  相似文献   
849.
A planar structure for molecules of 2-(2-methylaminophenyl)-4H-3,1-benzoxazine-4-one was found by x-ray structural analysis. Shortening of the N-Ph bond and lengthening of the distance between amino- and azine-N atoms in comparison to the tosyl analog was demonstrated to lead to a bathochromic shift of the absorption spectrum and a hypsochromic displacement of the luminescence spectrum. As a result, the Stokes shift of 2-(2-methylaminophenyl)-4H-3,1-benzoxazine-4-one is smaller than that of 2-(2-tosylaminophenyl)-4H-3,1-benzoxazine-4-one. In the crystal, molecules of 2-(2-methylaminophenyl)-4H-3,1-benzoxazine-4-one are stacked with intermolecular interaction energy between molecules in the stack of –12.5 and –14.2 kcal/mole. The stacks are joined into layers parallel to (010).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1781–1785, August, 1989.  相似文献   
850.
A novel heterocyclic compound, 4-acetoxy-5,6-dihydro-5,5-dinitro-2H-1,3-oxazineN-oxide, has been synthesized by the reaction of the dipotassium salt of 1,1,5,5-tetranitro-3-oxapentane with aqueous acetic acid. The synthesized compound has been studied by X-ray diffraction analysis.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2207–2210, December, 1994.We would like to thank G. V. Lagodzinskaya (Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences) for recording and interpreting1H NMR spectra, A. M. Korolev (Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences) for helpful discussion, and V. I. Fetisov (Institute of Physiologically Active Compounds, Russian Academy of Sciences) for performing quantum-chemical calculations by the AM1 SCF MO LCAO method.  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