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   79549篇
  免费   353篇
  国内免费   380篇
化学   25243篇
晶体学   816篇
力学   6761篇
数学   32237篇
物理学   15225篇
  2018年   10436篇
  2017年   10265篇
  2016年   6075篇
  2015年   860篇
  2014年   314篇
  2013年   364篇
  2012年   3811篇
  2011年   10555篇
  2010年   5646篇
  2009年   6060篇
  2008年   6645篇
  2007年   8816篇
  2006年   278篇
  2005年   1348篇
  2004年   1577篇
  2003年   2026篇
  2002年   1060篇
  2001年   265篇
  2000年   302篇
  1999年   165篇
  1998年   210篇
  1997年   167篇
  1996年   235篇
  1995年   144篇
  1994年   98篇
  1993年   117篇
  1992年   77篇
  1991年   80篇
  1990年   69篇
  1989年   83篇
  1988年   77篇
  1987年   85篇
  1986年   78篇
  1985年   88篇
  1984年   80篇
  1983年   73篇
  1982年   78篇
  1981年   70篇
  1980年   60篇
  1979年   71篇
  1978年   72篇
  1977年   49篇
  1976年   49篇
  1975年   52篇
  1973年   47篇
  1914年   48篇
  1913年   40篇
  1912年   40篇
  1909年   43篇
  1908年   42篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
In this paper, we construct some continuous but non-differentiable functions defined by quinary decimal, that are Kiesswetter-like functions. We discuss their properties, then investigate the Hausdorff dimensions of graphs of these functions and give a detailed proof.  相似文献   
132.
This article provides a status report on discrete mathematics in America's schools, including an overview of publications and programs that have had major impact. It discusses why discrete mathematics should be introduced in the schools and the authors' efforts to advocate, facilitate, and support the adoption of discrete mathematics topics in the schools. Their perspective is that discrete mathematics should be viewed not only as a collection of new and interesting mathematical topics, but, more importantly, as a vehicle for providing teachers with a new way to think about traditional mathematical topics and new strategies for engaging their students in the study of mathematics.  相似文献   
133.
A New Cohomology Theory of Orbifold   总被引:7,自引:0,他引:7  
Based on the orbifold string theory model in physics, we construct a new cohomology ring for any almost complex orbifold. The key theorem is the associativity of this new ring. Some examples are computed.Both authors partially supported by the National Science Foundation  相似文献   
134.
A general class of analytical solutions of the lattice Boltzmann equation is derived for two-dimensional, steady-state unidirectional flows. A subset of the solutions that verifies the corresponding Navier-Stokes equations is given. It is pointed out that this class includes, e.g., the Couette and the Poiseuille flow but not, e.g., the basic Kolmogorov flow. For steady-state non-unidirectional flows, first and second order solutions of the lattice Boltzmann equation are derived. Practical consequences of the analysis are mentioned. Differences between the technique applied here and those used in some earlier works are emphasized.  相似文献   
135.
A subgroupH of a groupG is said to bepermutable ifHX=XH for every subgroupX ofG. In this paper the structure of groups in which every subgroup either is abelian or permutable is investigated. This work was done while the last author was visiting the University of Napoli Federico II. He thanks the “Dipartimento di Matematica e Applicazioni” for its financial support.  相似文献   
136.
We study the elastic responses of double-(ds) and single-stranded (ss) DNA at external force fields. A double-strand-polymer elastic model is constructed and solved by path integral methods and Monte Carlo simulations to understand the entropic elasticity, cooperative extensibility, and supercoiling property of dsDNA. The good agreement with experiments indicates that short-ranged base-pair stacking interaction is crucial for the stability and the high deformability of dsDNA. Hairpin-coil transition in ssDNA is studied with generating function method. A threshold force is needed to pull the ssDNA hairpin patterns, stabilized by base pairing and base-pair stacking, into random coils. This phase transition is predicted to be of first order for stacking potential higher than some critical level, in accordance with experimental observations.  相似文献   
137.
An improved search for B s 0 oscillations is performed in the ALEPH data sample collected during the first phase of LEP, and reprocessed in 1998. Three analyses based on complementary event selections are presented. First, decays of B s 0 mesons into hadronic flavour eigenstates are fully reconstructed. This selection yields a small sample of candidates with excellent decay length and momentum resolution and hi gh average B s 0 purity. Semileptonic decays with a reconstructed D s - meson provide a second sample with larger statistics, high average B s 0 purity, but a poorer momentum and decay length resolution due to the partial decay reconstruction. Finally, semileptonic b-hadron decays are inclusively selected and yield the data sample with the highest sensitivity to B s 0 oscillations, as the much higher statistics compensate for the low average B s 0 purity and poorer time resolution. A lower limit is set atps-1 at 95% C.L., significantly lower than the expected limit of 15.2 ps-1. Received: 21 February 2003 / Published online: 11 June 2003  相似文献   
138.
139.
140.
In this paper a new definition of a lattice valued intuitionistic fuzzy set (LIFS) is introduced, in an attempt to overcome the disadvantages of earlier definitions. Some properties of this kind of fuzzy sets and their basic operations are given. The theorem of synthesis is proved: For every two families of subsets of a set satisfying certain conditions, there is an lattice valued intuitionistic fuzzy set for which these are families of level sets. The research supported by Serbian Ministry of Science and Technology, Grant No. 1227.  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