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   1319694篇
  免费   25739篇
  国内免费   7754篇
化学   656337篇
晶体学   20005篇
力学   74073篇
综合类   104篇
数学   239460篇
物理学   363208篇
  2021年   13483篇
  2020年   15897篇
  2019年   16039篇
  2016年   27278篇
  2015年   20555篇
  2014年   30370篇
  2013年   74216篇
  2012年   36953篇
  2011年   32590篇
  2010年   35760篇
  2009年   38302篇
  2008年   32384篇
  2007年   27495篇
  2006年   35447篇
  2005年   26834篇
  2004年   28839篇
  2003年   27386篇
  2002年   28793篇
  2001年   27820篇
  2000年   24433篇
  1999年   22324篇
  1998年   20931篇
  1997年   20935篇
  1996年   21048篇
  1995年   19128篇
  1994年   18549篇
  1993年   18096篇
  1992年   17977篇
  1991年   18274篇
  1990年   17451篇
  1989年   17559篇
  1988年   17065篇
  1987年   17080篇
  1986年   16021篇
  1985年   22435篇
  1984年   23713篇
  1983年   19918篇
  1982年   21608篇
  1981年   20863篇
  1980年   20183篇
  1979年   20297篇
  1978年   21684篇
  1977年   21246篇
  1976年   20950篇
  1975年   19661篇
  1974年   19291篇
  1973年   19810篇
  1972年   14277篇
  1968年   12097篇
  1967年   12482篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
52.
53.
The Weierstrass nowhere differentiable function, and functions constructed from similar infinite series, have been studied often as examples of functions whose graph is a fractal. Though there is a simple formula for the Hausdorff dimension of the graph which is widely accepted, it has not been rigorously proved to hold. We prove that if arbitrary phases are included in each term of the summation for the Weierstrass function, the Hausdorff dimension of the graph of the function has the conjectured value for almost every sequence of phases. The argument extends to a much wider class of Weierstrass-like functions.

  相似文献   

54.
NaY zeolite samples loaded with sodium metal by vapor phase deposition have been investigated using129Xe NMR spectroscopy. At low sodium concentration, the129Xe NMR spectrum showed three resonance lines which clearly indicate the existence of distinct domains in the zeolite sample. Such an observation suggests that the diffusion of the xenon atoms into each domain only occurs with respect to the NMR time scale (2.9 ms). As the sodium concentration increases, observation of a single broad line indicate a macroscopic homogenization of the system. The shift of this line is explained in part due to a paramagnetic interaction between the xenon atoms and the unpaired electrons of particles containing an odd number of sodium atoms. The linewidth is due to the distribution of the local magnetic fields partially averaged by the rapid motion of the xenon atoms and to the statistical distribution of the sodium particles in the supercage cavities. The paramagnetic interaction vanishes with the oxidation of the sample leading to a narrowing and a shift of the line to higher magnetic fields.  相似文献   
55.
The Thoms effect observed with water-soluble cationic copolymer of acrylamide was studied in relation to the concentration, molecular weight, and molecular weight polydispersity of the polymeric additive, with its composition and composition polydispersity being constant.  相似文献   
56.
    
  相似文献   
57.
We prove a character formula for any finite-dimensional irreducible representationV of the “queer” Lie superalgebra g=q(n). It expresses chV in terms of the multiplicities of the irreducible g-subquotients of the cohomology groups of certain dominant g-bundles on the Π-symmetric projective spaces (i.e., on the homogeneous superspacesG/P whose reduced space is a projective space, whereG=Q(n)). We also establish recurrent relations for the above multiplicities, and this enables us to compute explicitly chV for any givenV. This provides a complete solution to the Kac character problem for the Lie superalgebraq(n). Finally, we consider the particular cases ofq(2), q(3), andq(4) in which we compare the new character formula with the generic character formula of [12]. Translated from Itogi Nauki i Tekhniki, Seriya Sovremennaya Matematika i Ee Prilozheniya. Tematicheskie Obzory. Vol. 41, Algebraic Geometry-7, 1997.  相似文献   
58.
An explicit way for producing invariants for 6-valent graphs with rigid vertices within the framework of Kauffman's approach to graph invariants is presented. These invariants can be used to detect the chirality of a 6-valent graph with rigid vertices. A relevant example is considered. Bibliography: 19 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 223, 1995, pp. 251–262. Translated by A. M. Nikitin  相似文献   
59.
60.
We consider the method of normal forms, the Bogolyubov averaging method, and the method of asymptotic decomposition proposed by Yu. A. Mitropol’skii and the author of this paper. Under certain assumptions about group-theoretic properties of a system of zero approximation, the results obtained by the method of asymptotic decomposition coincide with the results obtained by the method of normal forms or the Bogolyubov averaging method. We develop a new algorithm of asymptotic decomposition by a part of the variables and its partial case — the algorithm of averaging on a compact Lie group. For the first time, it became possible to consider asymptotic expansions of solutions of differential equations on noncommutative compact groups.  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