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   304544篇
  免费   2005篇
  国内免费   645篇
化学   156861篇
晶体学   4654篇
力学   14925篇
综合类   10篇
数学   33575篇
物理学   97169篇
  2020年   2805篇
  2019年   3281篇
  2018年   4643篇
  2017年   4772篇
  2016年   6219篇
  2015年   3215篇
  2014年   5510篇
  2013年   12263篇
  2012年   9730篇
  2011年   11657篇
  2010年   8972篇
  2009年   9193篇
  2008年   11187篇
  2007年   10968篇
  2006年   10256篇
  2005年   9218篇
  2004年   8660篇
  2003年   7897篇
  2002年   7938篇
  2001年   9758篇
  2000年   7186篇
  1999年   5501篇
  1998年   4452篇
  1997年   4360篇
  1996年   4057篇
  1995年   3709篇
  1994年   3657篇
  1993年   3516篇
  1992年   4008篇
  1991年   4388篇
  1990年   4149篇
  1989年   4162篇
  1988年   4051篇
  1987年   4071篇
  1986年   3750篇
  1985年   4690篇
  1984年   4728篇
  1983年   3942篇
  1982年   3994篇
  1981年   3760篇
  1980年   3566篇
  1979年   4134篇
  1978年   4318篇
  1977年   4373篇
  1976年   4423篇
  1975年   4114篇
  1974年   4029篇
  1973年   4225篇
  1972年   3152篇
  1971年   2778篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
The results obtained in V. P. Maslov’s article [1] can automatically be carried over to arbitrary semiotic systems if the string of signs is sufficiently long. We shall show in this article, by using arguments based on the ideas of Kolmogorov complexity and by applying the theorem of V. P. Maslov from [2], that one can obtain similar formulas for the distribution of various semiotic objects. In order to do this, we must introduce notions generalizing the occurrence frequency of words in corpora of texts. We also interpret a formula due to Maslov (appearing in [3]) from the point of view of the general semiotic notions introduced here.  相似文献   
74.
The gas phase chemical kinetics of SF4, SF5, and S2F10 are reviewed with particular emphasis on relevance to the general problem of the dielectric breakdown of SF6. Specific reaction systems treated are SF4 + F2, SF5 + SF5, and the pyrolysis of S2F10. Computer modeling calculations were carried out to arrive at the best estimates of rate parameters. Based on the results of these calculations, sets of recommended rate parameters are provided. The major discrepancies and problems in establishing the kinetic data base are described. Thermochemical consequences of different model calculations are given.  相似文献   
75.
76.
Specific features of the initiated oxidation of polyethylene and its low-molecular-weight analogue tridecane, associated with the occurrence of the process in the short-chain mode, were studied.  相似文献   
77.
78.
A theory that predicts the effect of the counterion size on the swelling and collapse of a weakly charged polyelectrolyte gel was developed. In addition to excluded-volume interactions between monomer units of the gel, the theory involves the counterion-monomer unit and counterion-counterion interactions in terms of the virial approximation. The character of interactions between different units in the system varies from repulsion to attraction depending on the type of solvent, counterion, and dielectric permittivity of the solvent. For solvents with a low permittivity, the effect of condensation of counterions resulting in the formation of ion pairs is taken into account.  相似文献   
79.
The behavior of real disperse systems with organic impurities was examined under conditions of destabilization by inorganic coagulants. A number of physicochemical methods of analysis and a simulation method were used to identify the character and type of the complexes formed and to calculate their stability constants.  相似文献   
80.
The known plant growth regulator, Al'den [1-(3,7-dimethyloctyl)-1-allylpiperidinium bromide], and also 1-(3,7-dimethyloctyl)-1-methylpiperidinium iodide were synthesized by treatment with allyl bromide and methyl iodide, respectively, of exhaustively hydrogenated 1-nerylpiperidine which was obtained by anionic telomerization of isoprene with piperidine. Various quaternary ammonium salts having a terpene sub- stituent with unnatural dimethyloctane skeleton, which effectively stimulate florification of Aster Chinensis L., were prepared by the action of alkyl halides on telomerization products derived from isoprene and piperidine or morpholine in the presence of palladium complexes.  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