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   533576篇
  免费   5719篇
  国内免费   1530篇
化学   269439篇
晶体学   8042篇
力学   24735篇
综合类   10篇
数学   75138篇
物理学   163461篇
  2020年   3180篇
  2019年   3333篇
  2018年   11761篇
  2017年   12600篇
  2016年   10231篇
  2015年   5613篇
  2014年   7157篇
  2013年   20332篇
  2012年   18928篇
  2011年   29443篇
  2010年   18703篇
  2009年   18560篇
  2008年   26459篇
  2007年   29521篇
  2006年   16906篇
  2005年   21352篇
  2004年   16924篇
  2003年   15261篇
  2002年   13298篇
  2001年   13843篇
  2000年   10767篇
  1999年   8312篇
  1998年   6818篇
  1997年   6533篇
  1996年   6596篇
  1995年   6033篇
  1994年   5777篇
  1993年   5555篇
  1992年   6236篇
  1991年   6036篇
  1990年   5763篇
  1989年   5567篇
  1988年   5799篇
  1987年   5516篇
  1986年   5269篇
  1985年   7439篇
  1984年   7596篇
  1983年   6333篇
  1982年   6747篇
  1981年   6614篇
  1980年   6399篇
  1979年   6627篇
  1978年   6727篇
  1977年   6552篇
  1976年   6542篇
  1975年   6385篇
  1974年   6227篇
  1973年   6566篇
  1972年   3992篇
  1971年   3044篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The spectral projected gradient method SPG is an algorithm for large-scale bound-constrained optimization introduced recently by Birgin, Martínez, and Raydan. It is based on the Raydan unconstrained generalization of the Barzilai-Borwein method for quadratics. The SPG algorithm turned out to be surprisingly effective for solving many large-scale minimization problems with box constraints. Therefore, it is natural to test its perfomance for solving the sub-problems that appear in nonlinear programming methods based on augmented Lagrangians. In this work, augmented Lagrangian methods which use SPG as the underlying convex-constraint solver are introduced (ALSPG) and the methods are tested in two sets of problems. First, a meaningful subset of large-scale nonlinearly constrained problems of the CUTE collection is solved and compared with the perfomance of LANCELOT. Second, a family of location problems in the minimax formulation is solved against the package FFSQP.  相似文献   
992.
In this paper, a model of a linear multilevel programming problem with dominated objective functions (LMPPD(l)) is proposed, where multiple reactions of the lower levels do not lead to any uncertainty in the upper-level decision making. Under the assumption that the constrained set is nonempty and bounded, a necessary optimality condition is obtained. Two types of geometric properties of the solution sets are studied. It is demonstrated that the feasible set of LMPPD(l) is neither necessarily composed of faces of the constrained set nor necessarily connected. These properties are different from the existing theoretical results for linear multilevel programming problems.  相似文献   
993.
For vector quasivariational inequalities involving multifunctions in topological vector spaces, an existence result is obtained without a monotonicity assumption and with a convergence assumption weaker than semicontinuity. A new type of quasivariational inequality is proposed. Applications to quasicomplementarity problems and traffic network equilibria are considered. In particular, definitions of weak and strong Wardrop equilibria are introduced for the case of multivalued cost functions.  相似文献   
994.
Defining speed of diffusion as the amount of time it takes to get from one penetration level to a higher one, we introduce a dynamic model in which we study the link between pricing policy, speed of diffusion, and number of competitors in the market. Our analysis shows that, in the case of strategic (oligopolistic) competition, the speed of diffusion has an important influence on the optimal pricing policy. In particular, we find that higher speeds of diffusion create an incentive to strategically interacting firms to lower their prices.  相似文献   
995.
996.
997.
We shall answer several questions concerning additive or multiplicative commutators in a division ring which are algebraic of bounded degree over its center.  相似文献   
998.
There is growing evidence that temporal lobe seizures are preceded by a preictal transition, characterized by a gradual dynamical change from asymptomatic interictal state to seizure. We herein report the first prospective analysis of the online automated algorithm for detecting the preictal transition in ongoing EEG signals. Such, the algorithm constitutes a seizure warning system. The algorithm estimates STLmax, a measure of the order or disorder of the signal, of EEG signals recorded from individual electrode sites. The optimization techniques were employed to select critical brain electrode sites that exhibit the preictal transition for the warning of epileptic seizures. Specifically, a quadratically constrained quadratic 0-1 programming problem is formulated to identify critical electrode sites. The automated seizure warning algorithm was tested in continuous, long-term EEG recordings obtained from 5 patients with temporal lobe epilepsy. For individual patient, we use the first half of seizures to train the parameter settings, which is evaluated by ROC (Receiver Operating Characteristic) curve analysis. With the best parameter setting, the algorithm applied to all cases predicted an average of 91.7% of seizures with an average false prediction rate of 0.196 per hour. These results indicate that it may be possible to develop automated seizure warning devices for diagnostic and therapeutic purposes.Mathematics Subject Classification (1991):20E28, 20G40, 20C20  相似文献   
999.
1000.
This paper concerns the existence of nontrivial solutions of the Riemann‐Hilbert problem with a continuous coefficient whose values belong to two rays in the complex plane. Our results extend those recently obtained by E. Shargorodsky and J. F. Toland [6]. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  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