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   180152篇
  免费   787篇
  国内免费   262篇
化学   90039篇
晶体学   2647篇
力学   9382篇
综合类   7篇
数学   20927篇
物理学   58199篇
  2020年   1848篇
  2019年   2298篇
  2018年   3398篇
  2017年   3528篇
  2016年   4163篇
  2015年   1859篇
  2014年   3593篇
  2013年   7073篇
  2012年   5549篇
  2011年   6622篇
  2010年   5527篇
  2009年   5651篇
  2008年   6397篇
  2007年   6359篇
  2006年   5652篇
  2005年   5012篇
  2004年   4842篇
  2003年   4388篇
  2002年   4537篇
  2001年   5012篇
  2000年   3697篇
  1999年   2825篇
  1998年   2607篇
  1997年   2464篇
  1996年   2260篇
  1995年   2048篇
  1994年   2007篇
  1993年   2044篇
  1992年   2081篇
  1991年   2383篇
  1990年   2319篇
  1989年   2389篇
  1988年   2269篇
  1987年   2300篇
  1986年   2128篇
  1985年   2661篇
  1984年   2676篇
  1983年   2322篇
  1982年   2375篇
  1981年   2277篇
  1980年   2078篇
  1979年   2399篇
  1978年   2554篇
  1977年   2642篇
  1976年   2737篇
  1975年   2538篇
  1974年   2469篇
  1973年   2636篇
  1972年   2152篇
  1971年   1973篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
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   
52.
53.
54.
The study deals with estimating the reliability of classification algorithms. The present article (the first of three) examines the statistical methods used for point estimation of the reliability of classifiers in the frequency approach. The estimation results are applicable to the small-sample case, which is of considerable importance in practice.  相似文献   
55.
A new quasi-hydrodynamic algorithm is proposed for numerical analysis of convective flows in the presence of a homogeneous external magnetic field. The Marangoni convection problem in a square cross-section cavity is solved.  相似文献   
56.
Some isomorphism criteria for Lubin–Tate formal groups over the ring of integers of a multidimensional local field are given. Bibliography: 4 titles.  相似文献   
57.
The nonprimary subgroups of the symmetric group S 9 are investigated. Embedding properties of these subgroups are listed in a table. Properties such as abnormality, pronormality, paranormality, weak normality, etc. were checked with the help of a computer. Algorithms and codes of the first author were used for this purpose. The research leans upon the technique of Burnside marks, as well as upon pertinent information on the table of marks of S 9 from the computer algebra package GAP. The subgroups were investigated up to conjugacy; the total number of conjugacy classes of nonprimary subgroups of S 9 is 432. Some subgroups were additionally checked by other programs based on the double coset method. Bibliography: 24 titles.  相似文献   
58.
The thermal expansion coefficients and the thermal conductivity of Bridgman-grown crystals of CuGa1−x InxTe2 solid solutions are investigated. It is found that the thermal expansion coefficient varies with x linearly, while the thermal conductivity is minimal when x=0.5. The Debye temperature and the rms dynamic atomic displacements are calculated from experimental data. It is shown that the Debye temperature decreases and the rms displacements in the crystal lattice sharply increase as the In content in the solid solutions grows.  相似文献   
59.
The kinetics of decay of a phase hologram in a semiconductor CdF2 crystal with bistable In centers is studied. Kinetic constants of the hologram decay are found, and the potential relief of the bistable center is plotted. The resolving power of the crystal is evaluated and recording of a transparency is demonstrated.  相似文献   
60.
We investigate Banach spaces possessing (or not possessing) the approximation properties AP s, 0 < s ≤ 1, in connection with the following known question in the geometric theory of operators: under which conditions on Banach spaces X and Y and on positive numbers r and p does the p-nuclearity of the second adjoint of a continuous operator T from X to Y imply the p-nuclearity of T? Actually, we give necessary and sufficient conditions under which this question is answered affirmatively. In addition, the corresponding counterexamples are obtained in the maximally strong form. For instance, it is shown (and this statement is a significant strengthening of the previous results of that sort) that there exists a pair of separable Banach spaces Z and W such that the spaces Z ** and W have Schauder bases, while for every p, 1 ≤ p < 2, there is a non-p-nuclear operator from W to Z with a p-nuclear second adjoint. Earlier, in similar examples, the corresponding spaces did not possess even the Grothendieck approximation property. The technique developed in this paper does not allow us to treat the case p > 2. That case will be studied in a forthcoming paper of the author. Bibliography: 11 titles.  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