全文获取类型
收费全文 | 11219篇 |
免费 | 771篇 |
国内免费 | 445篇 |
专业分类
化学 | 2157篇 |
晶体学 | 59篇 |
力学 | 1251篇 |
综合类 | 146篇 |
数学 | 6852篇 |
物理学 | 1970篇 |
出版年
2024年 | 16篇 |
2023年 | 155篇 |
2022年 | 245篇 |
2021年 | 378篇 |
2020年 | 260篇 |
2019年 | 262篇 |
2018年 | 288篇 |
2017年 | 374篇 |
2016年 | 360篇 |
2015年 | 269篇 |
2014年 | 542篇 |
2013年 | 653篇 |
2012年 | 708篇 |
2011年 | 628篇 |
2010年 | 522篇 |
2009年 | 655篇 |
2008年 | 655篇 |
2007年 | 697篇 |
2006年 | 565篇 |
2005年 | 470篇 |
2004年 | 379篇 |
2003年 | 345篇 |
2002年 | 318篇 |
2001年 | 291篇 |
2000年 | 288篇 |
1999年 | 224篇 |
1998年 | 248篇 |
1997年 | 223篇 |
1996年 | 157篇 |
1995年 | 179篇 |
1994年 | 143篇 |
1993年 | 134篇 |
1992年 | 114篇 |
1991年 | 87篇 |
1990年 | 81篇 |
1989年 | 67篇 |
1988年 | 54篇 |
1987年 | 43篇 |
1986年 | 44篇 |
1985年 | 56篇 |
1984年 | 51篇 |
1983年 | 15篇 |
1982年 | 24篇 |
1981年 | 22篇 |
1980年 | 19篇 |
1979年 | 38篇 |
1978年 | 20篇 |
1977年 | 31篇 |
1976年 | 18篇 |
1974年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 328 毫秒
991.
Philip E. Gill Walter Murray Michael A. Saunders John A. Tomlin Margaret H. Wright 《Discrete Optimization》2008,5(2):151-158
We pay homage to George B. Dantzig by describing a less well-known part of his legacy–his early and dedicated championship of the importance of systems optimization in solving complex real-world problems. 相似文献
992.
Many formalisms have been proposed over the years to capture combinatorial optimization algorithms such as dynamic programming, branch and bound, and greedy. In 1989 Helman [9] presented a common formalism that captures dynamic programming and branch and bound type algorithms. The formalism was later extended to include greedy algorithms. In this paper, we describe the application of automated reasoning techniques to the domain of our model, in particular considering some representational issues and demonstrating that proofs about the model can be obtained by an automated reasoning program. The long-term objective of this research is to develop a methodology for using automated reasoning to establish new results within the theory, including the derivation of new lower bounds and the discovery (and verification) of new combinatorial search strategies. 相似文献
993.
Conjugate Gradient Methods with Armijo-type Line Searches 总被引:14,自引:0,他引:14
Yu-Hong DAIState Key Laboratory of Scientific Engineering Computing Institute of Computational Mathematics Academy of Mathematics System Sciences Chinese Academy of Sciences Beijing China 《应用数学学报(英文版)》2002,18(1):123-130
Abstract Two Armijo-type line searches are proposed in this paper for nonlinear conjugate gradient methods.Under these line searches, global convergence results are established for several famous conjugate gradientmethods, including the Fletcher-Reeves method, the Polak-Ribiere-Polyak method, and the conjugate descentmethod. 相似文献
994.
Luiz Augusto N. Barroso Márcia H.C. Fampa Rafael Kelman Mario V.F. Pereira Priscila Lino 《Annals of Operations Research》2002,117(1-4):247-270
The objective of this work is to investigate market power issues in bid-based hydrothermal scheduling. Initially, market power was simulated with a single stage Cournot–Nash equilibrium model. In this static model the equilibrium was calculated analytically. It was shown that the total production of N strategic agents is smaller than the least-cost solution by a factor of (N/(N+1)). Market power analysis for multiple stages was then carried through a stochastic dynamic programming scheme, where the decision in each stage and state is the Cournot–Nash equilibrium of a multi-agent game. Case studies with data taken from the Brazilian system are presented. 相似文献
995.
Walter J. Gutjahr 《Methodology and Computing in Applied Probability》2006,8(1):105-133
An analytical framework for investigating the finite-time dynamics of ant colony optimization (ACO) under a fitness-proportional
pheromone update rule on arbitrary construction graphs is developed. A limit theorem on the approximation of the stochastic
ACO process by a deterministic process is demonstrated, and a system of ordinary differential equations governing the process
dynamics is identified. As an example for the application of the presented theory, the behavior of ACO on three different
construction graphs for subset selection problems is analyzed and compared for some basic test functions. The theory enables
first rough theoretical predictions of the convergence speed of ACO.
AMS 2000 Subject classification 68W20, 68W40 相似文献
996.
The paper introduces an intelligent decision-making model which is based on the application of artificial neural networks (ANN) and swarm intelligence technologies. The proposed model is used to generate one-step forward investment decisions for stock markets. The ANN are used to make the analysis of daily stock returns and to calculate one day forward decision for purchase of the stocks. Subsequently the Particle Swarm Optimization (PSO) algorithm is applied in order to select the “the best” ANN for the future investment decisions and to adapt the weights of other networks towards the weights of the best network. The experimental investigations were made considering different forms of decision-making model: different number of ANN, ANN inputs, sliding windows, and commission fees. The paper introduces the decision-making model, its evaluation results and discusses its application possibilities. 相似文献
997.
In convex optimization the significance of constraint qualifications is evidenced by the simple duality theory, and the elegant subgradient optimality conditions which completely characterize a minimizer. However, the constraint qualifications do not always hold even for finite dimensional optimization problems and frequently fail for infinite dimensional problems. In the present work we take a broader view of the subgradient optimality conditions by allowing them to depend on a sequence of ε-subgradients at a minimizer and then by letting them to hold in the limit. Liberating the optimality conditions in this way permits us to obtain a complete characterization of optimality without a constraint qualification. As an easy consequence of these results we obtain optimality conditions for conic convex optimization problems without a constraint qualification. We derive these conditions by applying a powerful combination of conjugate analysis and ε-subdifferential calculus. Numerical examples are discussed to illustrate the significance of the sequential conditions. 相似文献
998.
We develop new algorithms for global optimization by combining well known branch and bound methods with multilevel subdivision
techniques for the computation of invariant sets of dynamical systems. The basic idea is to view iteration schemes for local
optimization problems – e.g. Newton’s method or conjugate gradient methods – as dynamical systems and to compute set coverings
of their fixed points. The combination with bounding techniques allow for the computation of coverings of the global optima
only. We show convergence of the new algorithms and present a particular implementation.
Michael Dellnitz - Research of the authors is partially supported by the Deutsche Forschungsgemeinschaft within the Sonderforschungsbereich
376 相似文献
999.
On Finite Element Approximations to a Shape Gradient Flow in Shape Optimization of Elliptic Problems
Chunxiao Liu & Shengfeng Zhu 《计算数学(英文版)》2023,41(5):957-980
Shape gradient flows are widely used in numerical shape optimization algorithms. We investigate the accuracy and effectiveness of approximate shape gradients flows for shape optimization of elliptic problems. We present convergence analysis with a priori error estimates for finite element approximations of shape gradient flows associated with a distributed or boundary expression of Eulerian derivative. Numerical examples are presented to verify theory and show that using the volume expression is effective for shape optimization with Dirichlet and Neumann boundary conditions. 相似文献
1000.
Jiajie Li Shengfeng Zhu Xiaoqin Shen 《Numerical Methods for Partial Differential Equations》2023,39(2):1604-1634
For shape optimization of fluid flows governed by the Navier–Stokes equation, we investigate effectiveness of shape gradient algorithms by analyzing convergence and accuracy of mixed finite element approximations to both the distributed and boundary types of shape gradients. We present convergence analysis with a priori error estimates for the two approximate shape gradients. The theoretical analysis shows that the distributed formulation has superconvergence property. Numerical results with comparisons are presented to verify theory and show that the shape gradient algorithm based on the distributed formulation is highly effective and robust for shape optimization. 相似文献