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   221864篇
  免费   5812篇
  国内免费   3757篇
化学   127983篇
晶体学   3621篇
力学   9138篇
综合类   238篇
数学   21818篇
物理学   68635篇
  2020年   1949篇
  2019年   2020篇
  2018年   2032篇
  2017年   1935篇
  2016年   3355篇
  2015年   2798篇
  2014年   3705篇
  2013年   9683篇
  2012年   7428篇
  2011年   9016篇
  2010年   6115篇
  2009年   6020篇
  2008年   7839篇
  2007年   7840篇
  2006年   7394篇
  2005年   6726篇
  2004年   6005篇
  2003年   5286篇
  2002年   5156篇
  2001年   6436篇
  2000年   4945篇
  1999年   4057篇
  1998年   3218篇
  1997年   3203篇
  1996年   3179篇
  1995年   2888篇
  1994年   2747篇
  1993年   2619篇
  1992年   3090篇
  1991年   2926篇
  1990年   2833篇
  1989年   2811篇
  1988年   2732篇
  1987年   2707篇
  1986年   2534篇
  1985年   3399篇
  1984年   3370篇
  1983年   2768篇
  1982年   2967篇
  1981年   2884篇
  1980年   2798篇
  1979年   2944篇
  1978年   3173篇
  1977年   2983篇
  1976年   2922篇
  1975年   2779篇
  1974年   2734篇
  1973年   2753篇
  1967年   2137篇
  1966年   1931篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
131.
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   
132.
李建林  魏广生 《数学学报》2002,45(5):847-850
设函数f(w)为凸区域D内的单叶解析函数,对于2≤n≤8和所有w∈D,本文得到估计式|f(n)(w)/f'(w)|的精确上界.这个结果推广了一些已知的结论.  相似文献   
133.
It is shown that in gravitational theories with torsion one is led to commutation rules corresponding to Landau-Peierls type uncertainty relations.  相似文献   
134.
135.
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   
136.
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   
137.
成功地在六路高功率Nd玻璃激光装置上建立了2660紫外激光探针和适合紫外波段的Normaski干涉仪,首次将可见波长的连续激光应用于紫外干涉仪中靶成像调整和光路准直。利用该紫外光干涉仪,在铜柱状靶(φ500μm)上测量了厚等离子体中高达0.6n。的电子密度。  相似文献   
138.
The excitation function of the fission probability P E E x) for238U has been measured in the reaction238U(α, α′ f) at 480 MeV bombarding energy. The reaction mechanism of this reaction is discussed for excitation energies belowB nf , the threshold for second chance fission, and aboveB nf up toE x =37 MeV. In comparing with results from fission induced by photons and by particle transfer reactions the (α, α′f) reaction gives too low values for the fission probabilityP f at excitation energies well aboveB nE . The role of the quasi-elastic knock-out process in this reaction is discussed.  相似文献   
139.
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   
140.
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