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   13183篇
  免费   1150篇
  国内免费   578篇
化学   1796篇
晶体学   31篇
力学   1333篇
综合类   286篇
数学   8719篇
物理学   2746篇
  2024年   23篇
  2023年   131篇
  2022年   328篇
  2021年   428篇
  2020年   261篇
  2019年   308篇
  2018年   315篇
  2017年   439篇
  2016年   471篇
  2015年   338篇
  2014年   671篇
  2013年   783篇
  2012年   809篇
  2011年   693篇
  2010年   595篇
  2009年   784篇
  2008年   809篇
  2007年   837篇
  2006年   730篇
  2005年   615篇
  2004年   480篇
  2003年   452篇
  2002年   432篇
  2001年   385篇
  2000年   380篇
  1999年   275篇
  1998年   293篇
  1997年   263篇
  1996年   192篇
  1995年   191篇
  1994年   171篇
  1993年   131篇
  1992年   123篇
  1991年   100篇
  1990年   84篇
  1989年   81篇
  1988年   55篇
  1987年   47篇
  1986年   48篇
  1985年   70篇
  1984年   59篇
  1983年   16篇
  1982年   28篇
  1981年   27篇
  1980年   25篇
  1979年   32篇
  1978年   22篇
  1977年   32篇
  1976年   23篇
  1974年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
We consider a class of non-linear mixed integer programs with n integer variables and k continuous variables. Solving instances from this class to optimality is an NP-hard problem. We show that for the cases with k=1 and k=2, every optimal solution is integral. In contrast to this, for every k≥3 there exist instances where every optimal solution takes non-integral values. Received: August 2001 / Accepted: January 2002?Published online March 27, 2002  相似文献   
212.
Scalarization for pointwise well-posed vectorial problems   总被引:1,自引:1,他引:0  
The aim of this paper is to develop a method of study of Tykhonov well-posedness notions for vector valued problems using a class of scalar problems. Having a vectorial problem, the scalarization technique we use allows us to construct a class of scalar problems whose well-posedness properties are equivalent with the most known well-posedness properties of the original problem. Then a well-posedness property of a quasiconvex level-closed problem is derived.   相似文献   
213.
The improper handling and disposal of hazardous wastes cause threats to human health and the environment. One reason for the improper handling and disposal of these wastes is that not much consideration is usually given to the logistical aspects of hazardous waste systems. In this paper an integer goal programming model is developed that takes into consideration the multiple goals and needs of many groups involved in managing and planning hazardous waste systems. The model can easily be implemented and can be used to address many of the issues related to facility location, recycling, treatment, and disposal of hazardous wastes.  相似文献   
214.
<正> In this paper we'll prove a fundameutal property of the vector space by means of the ex-tension field,i.e.the numbers of the elements of a basis of the vector space V over the field Fequal to the d imensions(V:F).  相似文献   
215.
Contingent epiderivatives and set-valued optimization   总被引:24,自引:0,他引:24  
In this paper we introduce the concept of the contingent epiderivative for a set-valued map which modifies a notion introduced by Aubin [2] as upper contingent derivative. It is shown that this kind of a derivative has important properties and is one possible generalization of directional derivatives in the single-valued convex case. For optimization problems with a set-valued objective function optimality conditions based on the concept of the contingent epiderivative are proved which are necessary and sufficient under suitable assumptions.  相似文献   
216.
针对重力输水管道设计中存在的问题,文章以管道造价最小为目标,应用动态规划,提出了一种新的重力输水管道优化设计方法,对输水管的当量管径、流量分配、连接管设置与可靠性校核计算等问题作了探讨。该方法可用于沿线有节点流量流出的并联输水管道优化设计,能明显节省投资,有良好的实用性  相似文献   
217.
Linear propagation of two pulses through methanol solution of aluminum phthalocyanine chloride is investigated using a modified white-light Michelson interferometer. The observed coherence time of the white light is 6 fs, and the separation between the two-excitation pulses is set to about 10 fs. The excitation is dependent on the phase-relation between the two pulses. We have observed an enhancement of the excitation when the two pulses are in-phase and strong suppression of the excitation when the two pulses are out of phase by π.  相似文献   
218.
The theory of p-regularity is applied to optimization problems and to singular ordinary differential equations (ODE). The special variant of the method of the modified Lagrangian function proposed by Yu.G. Evtushenko for constrained optimization problems with inequality constraints is justified on the basis of the 2-factor transformation. An implicit function theorem is given for the singular case. This theorem is used to show the existence of solutions to a boundary value problem for a nonlinear differential equation in the resonance case. New numerical methods are proposed including the p-factor method for solving ODEs with a small parameter.  相似文献   
219.
It is proved that the center of an automorphism group Aut(FVL2) of a free vector lattice FVL2 on a set of two free generators is isomorphic to a multiplicative group of positive reals. It is shown that the free vector lattice FVL2 has an isomorphic representation by continuous piecewise linear functions of the real line; as a consequence, the ideal lattice and the root system for rectifying ideals in FVL2 are amply described. Similar results are obtained for a free vector lattice FVL2 Q 2 generated by two elements over a field of rational numbers.  相似文献   
220.
In this paper, a procedure is presented which allows the optimal reconstruction of images from blurred noisy data. The procedure relies on a general Bayesian approach, which makes proper use of all the available information. Special attention is devoted to the informative content of the edges; thus, a preprocessing phase is included, with the aim of estimating the jump sizes in the gray level. The optimization phase follows; existence and uniqueness of the solution is secured. The procedure is tested against simple simulated data and real data.  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