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   1891篇
  国内免费   26篇
  完全免费   12篇
  数学   1929篇
  2019年   12篇
  2018年   18篇
  2017年   4篇
  2016年   3篇
  2015年   66篇
  2014年   99篇
  2013年   76篇
  2012年   62篇
  2011年   91篇
  2010年   135篇
  2009年   200篇
  2008年   173篇
  2007年   177篇
  2006年   132篇
  2005年   96篇
  2004年   67篇
  2003年   72篇
  2002年   70篇
  2001年   44篇
  2000年   44篇
  1999年   41篇
  1998年   43篇
  1997年   28篇
  1996年   37篇
  1995年   20篇
  1994年   19篇
  1993年   15篇
  1992年   12篇
  1991年   11篇
  1990年   8篇
  1989年   6篇
  1988年   9篇
  1987年   4篇
  1986年   8篇
  1985年   3篇
  1984年   2篇
  1983年   3篇
  1981年   4篇
  1978年   2篇
  1977年   2篇
  1976年   6篇
  1974年   1篇
  1973年   1篇
  1971年   1篇
  1970年   1篇
  1967年   1篇
排序方式: 共有1929条查询结果,搜索用时 140 毫秒
1.
Convergence properties of the Fletcher-Reeves method   总被引:29,自引:0,他引:29  
This paper investigates the global convergence properties ofthe Fletcher-Reeves (FR) method for unconstrained optimization.In a simple way, we prove that a kind of inexact line searchcondition can ensure the convergence of the FR method. Severalexamples are constructed to show that, if the search conditionsare relaxed, the FR method may produce an ascent search direction,which implies that our result cannot be improved.  相似文献
2.
Credit risk optimization with Conditional Value-at-Risk criterion   总被引:27,自引:0,他引:27  
This paper examines a new approach for credit risk optimization. The model is based on the Conditional Value-at-Risk (CVaR) risk measure, the expected loss exceeding Value-at-Risk. CVaR is also known as Mean Excess, Mean Shortfall, or Tail VaR. This model can simultaneously adjust all positions in a portfolio of financial instruments in order to minimize CVaR subject to trading and return constraints. The credit risk distribution is generated by Monte Carlo simulations and the optimization problem is solved effectively by linear programming. The algorithm is very efficient; it can handle hundreds of instruments and thousands of scenarios in reasonable computer time. The approach is demonstrated with a portfolio of emerging market bonds. Received: November 1, 1999 / Accepted: October 1, 2000?Published online December 15, 2000  相似文献
3.
Wiener Index of Hexagonal Systems   总被引:18,自引:0,他引:18  
The Wiener index W is the sum of distances between all pairs of vertices of a (connected) graph. Hexagonal systems (HS's) are a special type of plane graphs in which all faces are bounded by hexagons. These provide a graph representation of benzenoid hydrocarbons and thus find applications in chemistry. The paper outlines the results known for W of the HS: method for computation of W, expressions relating W with the structure of the respective HS, results on HS's extremal w.r.t. W, and on integers that cannot be the W-values of HS's. A few open problems are mentioned. The chemical applications of the results presented are explained in detail.  相似文献
4.
A Unified Monotonic Approach to Generalized Linear Fractional Programming   总被引:14,自引:0,他引:14  
We present an efficient unified method for solving a wide class of generalized linear fractional programming problems. This class includes such problems as: optimizing (minimizing or maximizing) a pointwise maximum or pointwise minimum of a finite number of ratios of linear functions, optimizing a sum or product of such ratios, etc. – over a polytope. Our approach is based on the recently developed theory of monotonic optimization.  相似文献
5.
Dissipativity of Runge-Kutta methods for dynamical systems with delays   总被引:12,自引:0,他引:12  
This paper is concerned with the numerical solution of dissipativeinitial value problems with delays by Runge-Kutta methods. Asufficient condition for the dissipativity of the systems isgiven. The concepts of D(l)-dissipativity and GD(l)-dissipativityare introduced. We investigate the dissipativity propertiesof (k,l)-algebraically stable Runge-Kutta methods with piecewiseconstant or linear interpolation procedures for finite-dimensionaland infinite-dimensional dynamical systems with delays.  相似文献
6.
Let be a smooth bounded domain in RN. We prove general uniquenessresults for equations of the form – u = aub(x)f(u) in , subject to u = on . Our uniqueness theorem is establishedin a setting involving Karamata's theory on regularly varyingfunctions, which is used to relate the blow-up behavior of u(x)with f(u) and b(x), where b 0 on and a certain ratio involvingb is bounded near . A key step in our proof of uniqueness usesa modification of an iteration technique due to Safonov. 2000Mathematics Subject Classification 35J25 (primary), 35B40, 35J60(secondary).  相似文献
7.
This paper presents a simple evolutionary procedure based on finite element analysis to minimize the weight of structures while satisfying stiffness requirements. At the end of each finite element analysis, a sensitivity number, indicating the change in the stiffness due to removal of each element, is calculated and elements which make the least change in the stiffness; of a structure are subsequently removed from the structure. The final design of a structure may have its weight significantly reduced while the displacements at prescribed locations are kept within the given limits. The proposed method is capable of performing simultaneous shape and topology optimization. A wide range of problems including those with multiple displacement constraints, multiple load cases and moving loads are considered. It is shown that existing solutions of structural optimization with stiffness constraints can easily be reproduced by this proposed simple method. In addition some original shape and layout optimization results are presented.  相似文献
8.
Summary. This paper studies projected Barzilai-Borwein (PBB) methods for large-scale box-constrained quadratic programming. Recent work on this method has modified the PBB method by incorporating the Grippo-Lampariello-Lucidi (GLL) nonmonotone line search, so as to enable global convergence to be proved. We show by many numerical experiments that the performance of the PBB method deteriorates if the GLL line search is used. We have therefore considered the question of whether the unmodified method is globally convergent, which we show not to be the case, by exhibiting a counter example in which the method cycles. A new projected gradient method (PABB) is then considered that alternately uses the two Barzilai-Borwein steplengths. We also give an example in which this method may cycle, although its practical performance is seen to be superior to the PBB method. With the aim of both ensuring global convergence and preserving the good numerical performance of the unmodified methods, we examine other recent work on nonmonotone line searches, and propose a new adaptive variant with some attractive features. Further numerical experiments show that the PABB method with the adaptive line search is the best BB-like method in the positive definite case, and it compares reasonably well against the GPCG algorithm of Moré and Toraldo. In the indefinite case, the PBB method with the adaptive line search is shown on some examples to find local minima with better solution values, and hence may be preferred for this reason.This work was supported by the EPRSC in UK (no. GR/R87208/01) and the Chinese NSF grant (no. 10171104).Acknowledgement The authors would like to thank the two anonymous referees for their useful suggestions and comments.  相似文献
9.
It is well-known that on uniform meshes the piecewise linearconforming finite element solution of the Poisson equation approximatesthe interpolant to a higher order than the solution itself.In this paper, this type of superclose property is studied forthe canonical interpolant defined by the nodal functionals ofseveral non-conforming finite elements of lowest order. By givingexplicit examples we show that some non-conforming finite elementsdo not admit the superclose property. In particular, we discusstwo non-conforming finite elements which satisfy the supercloseproperty. Moreover, applying a postprocessing technique, wecan also state a superconvergence property for the discretizationerror of the postprocessed discrete solution to the solutionitself. Finally, we show that an extrapolation technique leadsto a further improvement of the accuracy of the finite elementsolution.  相似文献
10.
Using the fixed point method we prove an existence result for positive solutions of nonlinear second order ordinary differential equations. An application to semilinear Schrödinger equations in exterior domains is also presented. Mathematics Subject Classification (2000) 34C10  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