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   33654篇
  免费   3245篇
  国内免费   2318篇
化学   2533篇
晶体学   47篇
力学   3242篇
综合类   536篇
数学   26364篇
物理学   6495篇
  2024年   63篇
  2023年   329篇
  2022年   515篇
  2021年   613篇
  2020年   776篇
  2019年   779篇
  2018年   851篇
  2017年   1050篇
  2016年   1086篇
  2015年   758篇
  2014年   1542篇
  2013年   2660篇
  2012年   1663篇
  2011年   1734篇
  2010年   1590篇
  2009年   2005篇
  2008年   2152篇
  2007年   2231篇
  2006年   2034篇
  2005年   1747篇
  2004年   1468篇
  2003年   1464篇
  2002年   1412篇
  2001年   1172篇
  2000年   1110篇
  1999年   1000篇
  1998年   854篇
  1997年   769篇
  1996年   632篇
  1995年   516篇
  1994年   379篇
  1993年   287篇
  1992年   296篇
  1991年   255篇
  1990年   187篇
  1989年   126篇
  1988年   125篇
  1987年   127篇
  1986年   109篇
  1985年   148篇
  1984年   134篇
  1983年   61篇
  1982年   81篇
  1981年   52篇
  1980年   57篇
  1979年   62篇
  1978年   35篇
  1977年   36篇
  1976年   24篇
  1974年   12篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
A Tabu-Search Hyperheuristic for Timetabling and Rostering   总被引:4,自引:0,他引:4  
Hyperheuristics can be defined to be heuristics which choose between heuristics in order to solve a given optimisation problem. The main motivation behind the development of such approaches is the goal of developing automated scheduling methods which are not restricted to one problem. In this paper we report the investigation of a hyperheuristic approach and evaluate it on various instances of two distinct timetabling and rostering problems. In the framework of our hyperheuristic approach, heuristics compete using rules based on the principles of reinforcement learning. A tabu list of heuristics is also maintained which prevents certain heuristics from being chosen at certain times during the search. We demonstrate that this tabu-search hyperheuristic is an easily re-usable method which can produce solutions of at least acceptable quality across a variety of problems and instances. In effect the proposed method is capable of producing solutions that are competitive with those obtained using state-of-the-art problem-specific techniques for the problems studied here, but is fundamentally more general than those techniques.  相似文献   
102.
In this paper, some solvability problems for functional equations of the form
are studied. Here I is a finite closed interval in , F is an unknown continuous function, and are given continuous maps of I into itself, and , and are real-valued continuous functions on I. Such equations are of interest not only by themselves as an object of analysis, but they are also a necessary link in solving various problems in such diverse fields as integral and functional equations, measure theory, and boundary problems for hyperbolic differential equations. The major part of the proofs is based on the new results in the theory of dynamical systems generated by a noncommutative semigroup with two generators.  相似文献   
103.
本文考虑了R^n 1空间中椭圆函数和准椭圆函数的一些性质,然后分别讨论了周期和准周期Riemann边值问题,给出了解的表达式和可解条件。  相似文献   
104.
通过对平面动力问题控制方程的分析,研究了相应的应力函数,得出了关于应力函数的基本方程。  相似文献   
105.
具有非线性扰动的中立型系统的时滞相关稳定性   总被引:1,自引:0,他引:1  
本研究了具有非线性扰动的中立型系统鲁棒稳定的时滞相关准则。基于LMI方法,并利用S—过程获得了依赖于时滞的鲁棒稳定性准则,所得结果优于已有结论。最后给出一个实例说明本方法的有效性。  相似文献   
106.
以美国南弗洛里达州递避飓风袭击为例建立了紧急输送情况下的线性规划模型。其中具体建立了以SCEPD(美国南弗洛里达州紧急情况预防部门)提出的公路反向,地区分块撤离,使用小路等三个最受人们关注的策略的模型。模型的灵敏度分析能很好地解释建立更多的临时避难所、限制车辆等策略对撤离的影响。在相近的环境下,中模型解得的结果很接近官方预测的结果,并且本的模型能对更广泛的情况进行分析.可给SCEPD提供一定参考。  相似文献   
107.
§ 1. Introduction  LetΩ R3beasmoothboundedopenset,f(t,x ,v)bethedistributionfunctionofcar riersattimet >0 ,positionvectorx∈Ωandvelocityvectorv∈R3.Theforcefieldactingonthecarriersisdenotedbythe3 dimensionalvectorfunctionE(t,x) ,thepotentialcorespondingtoE(t,x)isdenotedbyu(t,x) ,then (f,E)satisfythefollowingBoltzmann Poissonsystem tf +v· xf +E· vf =Q(f) ,  (t,x ,v)∈R+ ×Ω×R3,(1 .1 )E =- xu ,-Δxu =ρ ,  (t,x) ∈R+ ×Ω ,(1 .2 )whereρ(t,x) =∫R3 f(t,x ,v)dvisthecarriernum…  相似文献   
108.
In this paper, we present a new relaxation method for mathematical programs with complementarity constraints. Based on the fact that a variational inequality problem defined on a simplex can be represented by a finite number of inequalities, we use an expansive simplex instead of the nonnegative orthant involved in the complementarity constraints. We then remove some inequalities and obtain a standard nonlinear program. We show that the linear independence constraint qualification or the Mangasarian–Fromovitz constraint qualification holds for the relaxed problem under some mild conditions. We consider also a limiting behavior of the relaxed problem. We prove that any accumulation point of stationary points of the relaxed problems is a weakly stationary point of the original problem and that, if the function involved in the complementarity constraints does not vanish at this point, it is C-stationary. We obtain also some sufficient conditions of B-stationarity for a feasible point of the original problem. In particular, some conditions described by the eigenvalues of the Hessian matrices of the Lagrangian functions of the relaxed problems are new and can be verified easily. Our limited numerical experience indicates that the proposed approach is promising.  相似文献   
109.
We consider the problem of analytic continuation of a solution to the system of Maxwell equations in a bounded spatial domain from data on part of the boundary of the domain. We construct an approximate solution to the problem using the Carleman matrix method.  相似文献   
110.
On the Application of the Auxiliary Problem Principle   总被引:6,自引:0,他引:6  
The auxiliary problem principle (APP) derives from a general theory on decomposition-coordination methods establishing a comprehensive framework for both one-level and two-level methods. In this paper, the results of the two-level methods of APP are specialized for an efficient application to some engineering problems.  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