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   26033篇
  免费   2917篇
  国内免费   3288篇
化学   9911篇
晶体学   107篇
力学   2262篇
综合类   205篇
数学   8868篇
物理学   10885篇
  2024年   78篇
  2023年   260篇
  2022年   504篇
  2021年   623篇
  2020年   801篇
  2019年   736篇
  2018年   728篇
  2017年   849篇
  2016年   988篇
  2015年   860篇
  2014年   1259篇
  2013年   2173篇
  2012年   1368篇
  2011年   1613篇
  2010年   1265篇
  2009年   1661篇
  2008年   1684篇
  2007年   1761篇
  2006年   1455篇
  2005年   1273篇
  2004年   1040篇
  2003年   1055篇
  2002年   986篇
  2001年   778篇
  2000年   781篇
  1999年   671篇
  1998年   602篇
  1997年   458篇
  1996年   322篇
  1995年   319篇
  1994年   262篇
  1993年   263篇
  1992年   242篇
  1991年   191篇
  1990年   205篇
  1989年   199篇
  1988年   177篇
  1987年   171篇
  1986年   149篇
  1985年   195篇
  1984年   192篇
  1983年   126篇
  1982年   144篇
  1981年   108篇
  1980年   94篇
  1979年   104篇
  1978年   83篇
  1977年   85篇
  1976年   75篇
  1973年   61篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
221.
矩孔金属光栅矢量模式理论的数值计算   总被引:1,自引:0,他引:1  
朱文勇  林维德 《光学学报》1997,17(9):251-1255
根据矩孔金属光栅的矢量模式理论,计算了不同入射方向,波长及偏振态情况下衍射场的分布,研究了不同光栅结构对衍射效率,偏振态变化的影响;同时,根据实际需要,加工制作了一批不同深度的矩孔光栅样品,进行了实验测量,并将计算值与实验值进行了比较,两者基本相符。  相似文献   
222.
Let G=(V,E) be a (directed) graph with vertex set V and edge (arc) set E. Given a set P of source-sink pairs of vertices of G, an important problem that arises in the computation of network reliability is the enumeration of minimal subsets of edges (arcs) that connect/disconnect all/at least one of the given source-sink pairs of P. For undirected graphs, we show that the enumeration problems for conjunctions of paths and disjunctions of cuts can be solved in incremental polynomial time. Furthermore, under the assumption that P consists of all pairs within a given vertex set, we also give incremental polynomial time algorithm for enumerating all minimal path disjunctions and cut conjunctions. For directed graphs, the enumeration problem for cut disjunction is known to be NP-complete. We extend this result to path conjunctions and path disjunctions, leaving open the complexity of the enumeration of cut conjunctions. Finally, we give a polynomial delay algorithm for enumerating all minimal sets of arcs connecting two given nodes s1 and s2 to, respectively, a given vertex t1, and each vertex of a given subset of vertices T2.  相似文献   
223.
This paper is concerned with the spectral analysis of a one-velocity transport operator with Maxwell boundary condition in L 1-space. After a detailed spectral analysis it is shown that the associated Cauchy problem is governed by a C 0-semigroup. Next, we discuss the irreducibility of the transport semigroup. In particular, we show that the transport semigroup is irreducible. Finally, a spectral decomposition of the solutions into an asymptotic term and a transient one which will be estimated for smooth initial data is given.  相似文献   
224.
Here we study the behaviour of the spin 0 sector of the DKP field in spaces with torsion. First we show that in a Riemann-Cartan manifold the DKP field presents an interaction with torsion when minimal coupling is performed, contrary to the behaviour of the KG field, a result that breaks the usual equivalence between the DKP and the KG fields.Next we analyse the case of the Teleparallel Equivalent of General Relativity (Weitzenböck manifold), showing that in this case there is a perfect agreement between KG and DKP fields. The origins of both results are also discussed.On leave from  相似文献   
225.
In contrast to stochastic differential equation models used for the calculation of the term structure of interest rates, we develop an approach based on linear dynamical systems under non-stochastic uncertainty with perturbations. The uncertainty is described in terms of known feasible sets of varying parameters. Observations are used in order to estimate these parameters by minimizing the maximum of the absolute value of measurement errors, which leads to a linear or nonlinear semi-infinite programming problem. A regularized logarithmic barrier method for solving (ill-posed) convex semi-infinite programming problems is suggested. In this method a multi-step proximal regularization is coupled with an adaptive discretization strategy in the framework of an interior point approach. A special deleting rule permits one to use only a part of the constraints of the discretized problems. Convergence of the method and its stability with respect to data perturbations in the cone of convexC 1-functions are studied. On the basis of the solutions of the semi-infinite programming problems a technical trading system for future contracts of the German DAX is suggested and developed. Supported by the Stiftung Rheinland/Pfalz für Innovation, No. 8312-386261/307.  相似文献   
226.
Proton induced X-ray emission has been used to measureL-subshell and total ionization cross-sections of Au, Pb and Bi in the energy range of 200–350 keV. The ionization cross-sections have been extracted using the X-ray spectra and other quantities like fluorescence yields, transition probabilities, relative widths and Coster-Krönig fraction etc. involved in the process. The results have been compared with the cross-sections measured before and discussed in the light of known theories regarding the ion-atom collisions.  相似文献   
227.
228.
The projector formalism of Zwanzig-Mori type is extended to obtain generalized Fokker-Planck and generalized nonlinear Langevin equations for coarse-grained variables when the underlying microscopic dynamics is dissipative and noisy (stochastic).  相似文献   
229.
230.
利用三角函数幂公式、L′Hospital法则、分部积分公式,得到含有三角函数的第一类广义积分integral from n=0 to ∞(((sin(θ_x))/x)~ndx)的计算公式,其中n≥1且θ≠0.  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