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   411982篇
  免费   3049篇
  国内免费   1374篇
化学   207061篇
晶体学   5997篇
力学   20378篇
综合类   9篇
数学   66392篇
物理学   116568篇
  2021年   2600篇
  2020年   2924篇
  2019年   3294篇
  2018年   14484篇
  2017年   14293篇
  2016年   12126篇
  2015年   4482篇
  2014年   6018篇
  2013年   14658篇
  2012年   14460篇
  2011年   23317篇
  2010年   14865篇
  2009年   15188篇
  2008年   19033篇
  2007年   21012篇
  2006年   12248篇
  2005年   12160篇
  2004年   11238篇
  2003年   10860篇
  2002年   9682篇
  2001年   10787篇
  2000年   8260篇
  1999年   6214篇
  1998年   4976篇
  1997年   5045篇
  1996年   4757篇
  1995年   4074篇
  1994年   4122篇
  1993年   3966篇
  1992年   4543篇
  1991年   4658篇
  1990年   4457篇
  1989年   4362篇
  1988年   4280篇
  1987年   4293篇
  1986年   4023篇
  1985年   5135篇
  1984年   5293篇
  1983年   4241篇
  1982年   4478篇
  1981年   4207篇
  1980年   4004篇
  1979年   4452篇
  1978年   4653篇
  1977年   4588篇
  1976年   4543篇
  1975年   4286篇
  1974年   4259篇
  1973年   4406篇
  1972年   2963篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
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   
82.
Off-the-shell anomalous factors of the two-body Coulomb transition matrices appear in the integral form of the Faddeev second-order nuclear-electronic amplitude, for proton-hydrogen charge transfer scattering in a typical nlmnlm′ transition. A symmetric-impulse approximation (SIA) is applied to eliminate these factors and an induction method is proposed to analytically calculate the remaining integrals. The nuclear-electronic amplitude is derived for the general case, and for totally symmetric collisions, in terms of generalized hypergeometric functions of two variables, F 4, and of one variable, 3 F 2, respectively. The angular distribution of the second-order nuclear-electronic charge transfer amplitude shows the Thomas mechanism as a peak or a hump for symmetric and asymmetric collisions. There also exists a peak in the forward angular distribution of the second-order nuclear-electronic amplitude, which partly cancels the kinematic peak in the angular distribution of the charge transfer differential cross sections.  相似文献   
83.
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   
84.
Phase synchronization in a system of three virtual-cathode microwave oscillators (vircators) simulated by coupled van der Pol oscillators is studied. The phasing dynamics of the vircators is visualized with the phase portraits of the system in the triangular coordinates. Different phasing conditions are found.  相似文献   
85.
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   
86.
The class of previously found stationary axisymmetric perfect fluid solutions of Einstein's equations is written inh-orthogonal coordinates,h being a space-like coordinate. Matching of a big number of solutions of the class with each other seems to be possible for a proper choice of some parameters. The exterior solutions of the class are matched explicitly with interior solutions. Also, interior solutions are matched explicitly with each other.  相似文献   
87.
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   
88.
89.
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   
90.
Ascidia malaca gametes before fertilization incubated in 10?5 or 10?7 M solutions of tributyltin(IV) chloride, TBTCl, for 3 h appear highly damaged under transmission electron microscopy observation. Also, the fertilization process is affected by the compound: the damaged spermatozoa are present in the vitelline coat and the egg does not cleave. An increase of microbodies, structurally similar to peroxisomes, have been detected in the egg peripheral cytoplasm, probably in relation to their role in alleviating damage to some cellular components. The results have shown that the reproduction of ascidians under unfavourable environmental conditions is prevented. Copyright © 2003 John Wiley & Sons, Ltd.  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