全文获取类型
收费全文 | 2388篇 |
免费 | 106篇 |
国内免费 | 213篇 |
专业分类
化学 | 195篇 |
力学 | 37篇 |
综合类 | 30篇 |
数学 | 2309篇 |
物理学 | 136篇 |
出版年
2024年 | 3篇 |
2023年 | 22篇 |
2022年 | 31篇 |
2021年 | 28篇 |
2020年 | 38篇 |
2019年 | 50篇 |
2018年 | 51篇 |
2017年 | 45篇 |
2016年 | 60篇 |
2015年 | 45篇 |
2014年 | 102篇 |
2013年 | 159篇 |
2012年 | 86篇 |
2011年 | 100篇 |
2010年 | 91篇 |
2009年 | 152篇 |
2008年 | 196篇 |
2007年 | 145篇 |
2006年 | 137篇 |
2005年 | 128篇 |
2004年 | 88篇 |
2003年 | 99篇 |
2002年 | 83篇 |
2001年 | 88篇 |
2000年 | 86篇 |
1999年 | 82篇 |
1998年 | 76篇 |
1997年 | 64篇 |
1996年 | 54篇 |
1995年 | 33篇 |
1994年 | 27篇 |
1993年 | 30篇 |
1992年 | 22篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 25篇 |
1984年 | 17篇 |
1983年 | 5篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1976年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有2707条查询结果,搜索用时 15 毫秒
1.
When an organization solves a portfolio problem with public projects evaluated by multiple criteria, in which the economic dimension is not essential or not well characterized, the classical methods are not useful. We propose a non-linear preference model developed from normative Value Theory and using fuzzy sets to model some sources of imprecision. This model can be considered as a generalization of the classical approaches. However, the optimization problem is very complex in order to be solved with non-linear programming techniques. Therefore, the model is exploited by an evolutionary algorithm, able to achieve a strong improvement of the quality of solution. 相似文献
2.
This paper presents a unified analysis of decomposition algorithms for continuously differentiable optimization problems defined on Cartesian products of convex feasible sets. The decomposition algorithms are analyzed using the framework of cost approx imation algorithms. A convergence analysis is made for three decomposition algorithms: a sequential algorithm which extends the classical Gauss-Seidel scheme, a synchronized parallel algorithm which extends the Jacobi method, and a partially asynchronous parallel algorithm. The analysis validates inexact computations in both the subproblem and line search phases, and includes convergence rate results. The range of feasible step lengths within each algorithm is shown to have a direct correspondence to the increasing degree of parallelism and asynchronism, and the resulting usage of more outdated information in the algorithms. 相似文献
3.
We construct a correspondence between the set of partitions of a finite set M and the set of pairs of walks to the same vertex on a graph giving the Bratteli diagram of the partition algebra on M. This is the precise analogue of the correspondence between the set of permutations of a finite set and the set of pairs of Young tableaux of the same shape, called the Robinson–Schensted correspondence. 相似文献
4.
External difference families (EDFs) are a type of new combinatorial designs originated from cryptography. In this paper, some
earlier ideas of recursive and cyclotomic constructions of combinatorial designs are extended, and a number of classes of
EDFs and disjoint difference families are presented. A link between a subclass of EDFs and a special type of (almost) difference
sets is set up. 相似文献
5.
Silvia Vogel 《Annals of Operations Research》2006,142(1):269-282
The paper considers upper semicontinuous behavior in distribution of sequences of random closed sets. Semiconvergence in distribution
will be described via convergence in distribution of random variables with values in a suitable topological space. Convergence
statements for suitable functions of random sets are proved and the results are employed to derive stability statements for
random optimization problems where the objective function and the constraint set are approximated simultaneously.
The author is grateful to two anonymous referees for helpful suggestions. 相似文献
6.
Jonathan M. Borwein 《Optimization Letters》2007,1(1):21-32
This paper is a companion to a lecture given at the Prague Spring School in Analysis in April 2006. It highlights four distinct variational methods of proving that a finite dimensional Chebyshev set is convex and hopes to inspire renewed work on the open question of whether every Chebyshev set in Hilbert space is convex. 相似文献
7.
An extremum problem is embedded in a parametric scheme which contains, as a particular case, the classic perturbation function. The introduction of the image of the embedded problem allows one to derive a generalized duality and, in particular, Lagrangian and Fenchel duality. 相似文献
8.
We study game formulas the truth of which is determined by a semantical game of uncountable length. The main theme is the study of principles stating reflection of these formulas in various admissible sets. This investigation leads to two weak forms of strict-II11 reflection (or ∑1-compactness). We show that admissible sets such as H(ω2) and Lω2 which fail to have strict-II11 reflection, may or may not, depending on set-theoretic hypotheses satisfy one or both of these weaker forms. Mathematics Subject Classification : 03C70, 03C75. 相似文献
9.
Optimization theory provides a framework for determining the best decisions or actions with respect to some mathematical model of a process. This paper focuses on learning to act in a near-optimal manner through reinforcement learning for problems that either have no model or the model is too complex. One approach to solving this class of problems is via approximate dynamic programming. The application of these methods are established primarily for the case of discrete state and action spaces. In this paper we develop efficient methods of learning which act in complex systems with continuous state and action spaces. Monte-Carlo approaches are employed to estimate function values in an iterative, incremental procedure. Derivative-free line search methods are used to obtain a near-optimal action in the continuous action space for a discrete subset of the state space. This near-optimal control policy is then extended to the entire continuous state space via a fuzzy additive model. To compensate for approximation errors, a modified procedure for perturbing the generated control policy is developed. Convergence results under moderate assumptions and stopping criteria are established. 相似文献
10.
Let G(x,y) and GD(x,y) be the Green functions of rotationally invariant symmetric α-stable process in Rd and in an open set D, respectively, where 0<α<2. The inequality GD(x,y)GD(y,z)/GD(x,z)?c(G(x,y)+G(y,z)) is a very useful tool in studying (local) Schrödinger operators. When the above inequality is true with c=c(D)∈(0,∞), then we say that the 3G theorem holds in D. In this paper, we establish a generalized version of 3G theorem when D is a bounded κ-fat open set, which includes a bounded John domain. The 3G we consider is of the form GD(x,y)GD(z,w)/GD(x,w), where y may be different from z. When y=z, we recover the usual 3G. The 3G form GD(x,y)GD(z,w)/GD(x,w) appears in non-local Schrödinger operator theory. Using our generalized 3G theorem, we give a concrete class of functions belonging to the non-local Kato class, introduced by Chen and Song, on κ-fat open sets. As an application, we discuss relativistic α-stable processes (relativistic Hamiltonian when α=1) in κ-fat open sets. We identify the Martin boundary and the minimal Martin boundary with the Euclidean boundary for relativistic α-stable processes in κ-fat open sets. Furthermore, we show that relative Fatou type theorem is true for relativistic stable processes in κ-fat open sets. The main results of this paper hold for a large class of symmetric Markov processes, as are illustrated in the last section of this paper. We also discuss the generalized 3G theorem for a large class of symmetric stable Lévy processes. 相似文献