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   296380篇
  免费   3175篇
  国内免费   1039篇
化学   165129篇
晶体学   4892篇
力学   12015篇
综合类   9篇
数学   29939篇
物理学   88610篇
  2016年   3406篇
  2015年   2565篇
  2014年   3580篇
  2013年   11934篇
  2012年   8089篇
  2011年   10210篇
  2010年   6643篇
  2009年   6443篇
  2008年   9289篇
  2007年   9414篇
  2006年   9185篇
  2005年   8631篇
  2004年   7786篇
  2003年   6998篇
  2002年   6849篇
  2001年   8421篇
  2000年   6486篇
  1999年   5245篇
  1998年   4264篇
  1997年   4295篇
  1996年   4187篇
  1995年   4042篇
  1994年   3711篇
  1993年   3523篇
  1992年   4241篇
  1991年   4059篇
  1990年   3916篇
  1989年   3962篇
  1988年   3953篇
  1987年   3937篇
  1986年   3681篇
  1985年   5009篇
  1984年   5089篇
  1983年   4260篇
  1982年   4690篇
  1981年   4473篇
  1980年   4433篇
  1979年   4570篇
  1978年   4876篇
  1977年   4630篇
  1976年   4617篇
  1975年   4368篇
  1974年   4249篇
  1973年   4446篇
  1972年   2818篇
  1971年   2309篇
  1969年   2183篇
  1968年   2789篇
  1967年   3036篇
  1966年   2616篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
In this paper a new state called odd-excited binomial state (OEBS) is introduced. It interpolates between the odd number state and the odd-excited coherent state. We discuss some statistical properties, such as the Glauber second-order correlation function and squeezing phenomenon (normal and amplitude-squared squeezing) for this state. The quasiprobability distribution functions (Husimi Q-function and Wigner W-function) are also examined.  相似文献   
22.
23.
5‐Amino‐4‐methyl‐2‐phenyl‐6‐substitutedfuro[2,3‐d]pyrimidines ( 2a‐c ) were reacted with 2,5‐dimethoxytetrahydrfuran to afford the pyrrolyl derivatives 3a‐c . Compound 3a was chosen as intermediate for the synthesis of poly fused heterocycles incorporated furopyrimidines moiety 4–11 . Some of the synthesized compounds were screened for their antibacterial and antifungal activities.  相似文献   
24.
This paper gives a comprehensive treatment of EVPI-based sequential importance sampling algorithms for dynamic (multistage) stochastic programming problems. Both theory and computational algorithms are discussed. Under general assumptions it is shown that both an expected value of perfect information (EVPI) process and the corresponding marginal EVPI process (the supremum norm of the conditional expectation of its generalized derivative) are nonanticipative nonnegative supermartingales. These processes are used as importance criteria in the class of sampling algorithms treated in the paper. When their values are negligible at a node of the current sample problem scenario tree, scenarios descending from the node are replaced by a single scenario at the next iteration. On the other hand, high values lead to increasing the number of scenarios descending from the node. Both the small sample and asymptotic properties of the sample problem estimates arising from the algorithms are established, and the former are evaluated numerically in the context of a financial planning problem. Finally, current and future research is described. Bibliography: 49 titles. __________ Published in Zapiski Nauchnykh Seminarov POMI, Vol. 312, 2004, pp. 94–129.  相似文献   
25.
26.
A method using third order moments for estimating the regression coefficients as well as the latent state scores of the reduced-rank regression model when the latent variable(s) are non-normally distributed is presented in this paper. It is shown that the factor analysis type indeterminacy of the regression coefficient matrices is eliminated. A real life example of the proposed method is presented. Differences of this solution with the reduced-rank regression eigen solution are discussed.  相似文献   
27.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow.  相似文献   
28.
Although coupled liquid chromatographygas chromatography (LC-GC) was first demonstrated ten years ago, only in the last few years has there been a sudden surge of interest in the technique. Approximately 70% of the total number of LC-GC applications have been published in the last two years (1987–88) alone. This review categorizes LC-GC publications into four main application areas: fossil fuels, foods, environmental samples, biologiical/pharmaceutical samples, and miscellaneous samples. Multidimensional separations carried out using other coupled-column chromatographic techniques (such as supercritical fluid chromatography (SFC) with GC, and on-line trace enrichment-GC) have also been included in this review.  相似文献   
29.
The concepts of quasi-Chebyshev and weakly-Chebyshev and σ-Chebyshev were defined [3 - 7], andas a counterpart to best approximation in normed linear spaces, best coapprozimation was introduced by Franchetti and Furi^[1]. In this research, we shall define τ-Chebyshev subspaces and τ-cochebyshev subspaces of a Banach space, in which the property τ is compact or weakly-compact, respectively. A set of necessary and sufficient theorems under which a subspace is τ-Chebyshev is defined.  相似文献   
30.
J. H. Eberly 《Laser Physics》2006,16(6):921-926
We examine the application of Schmidt mode analysis to pure-state entanglement. Several examples permitting exact analytic calculation of Schmidt eigenvalues and eigenfunctions are included, as well as evaluation of the associated degree of entanglement.  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