全文获取类型
收费全文 | 24165篇 |
免费 | 1693篇 |
国内免费 | 1093篇 |
专业分类
化学 | 1594篇 |
晶体学 | 33篇 |
力学 | 2613篇 |
综合类 | 310篇 |
数学 | 19658篇 |
物理学 | 2743篇 |
出版年
2024年 | 51篇 |
2023年 | 245篇 |
2022年 | 510篇 |
2021年 | 534篇 |
2020年 | 532篇 |
2019年 | 551篇 |
2018年 | 616篇 |
2017年 | 711篇 |
2016年 | 674篇 |
2015年 | 513篇 |
2014年 | 1043篇 |
2013年 | 1677篇 |
2012年 | 1237篇 |
2011年 | 1218篇 |
2010年 | 1120篇 |
2009年 | 1476篇 |
2008年 | 1520篇 |
2007年 | 1603篇 |
2006年 | 1367篇 |
2005年 | 1133篇 |
2004年 | 944篇 |
2003年 | 986篇 |
2002年 | 864篇 |
2001年 | 691篇 |
2000年 | 706篇 |
1999年 | 584篇 |
1998年 | 572篇 |
1997年 | 521篇 |
1996年 | 390篇 |
1995年 | 366篇 |
1994年 | 273篇 |
1993年 | 228篇 |
1992年 | 226篇 |
1991年 | 185篇 |
1990年 | 154篇 |
1989年 | 102篇 |
1988年 | 90篇 |
1987年 | 81篇 |
1986年 | 81篇 |
1985年 | 110篇 |
1984年 | 102篇 |
1983年 | 40篇 |
1982年 | 53篇 |
1981年 | 45篇 |
1980年 | 36篇 |
1979年 | 52篇 |
1978年 | 34篇 |
1977年 | 43篇 |
1976年 | 26篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
131.
In this paper we deal with nonlinear second-order boundary value problems with impulses. The impulsive functions depend implicitly on the different considered variables and the boundary value conditions are nonlinear. In both cases functional dependence on the solution is allowed. The existence results follow from the existence of a pair of well-ordered lower and upper solutions. 相似文献
132.
Peter Francis Guangming Zhang Karen Smilowitz 《European Journal of Operational Research》2007,180(3):1045-1059
This paper presents modeling and solution method improvements for the Multi-Resource Routing Problem (MRRP) with flexible tasks. The MRRP with flexible tasks is used to model routing and scheduling problems for intermodal drayage operations in which two resources (tractors and trailers) perform tasks to transport loaded and empty equipment. Tasks may be either well defined, in which both the origin and the destination of a movement are given, or flexible, in which the origin or the destination is chosen by the model. This paper proposes methods to effectively manage the number of options considered for flexible tasks (either feasible origins for a known destination or feasible destinations for a known origin). This modeling change generates sufficient options to allow for low-cost solutions while maintaining reasonable computational effort. We also propose a new solution method that uses randomized route generation. Computational results from test cases show that these changes improve the quality of solutions by at least 5% in the test cases as compared to methods from previous studies. 相似文献
133.
B. Ivorra A. M. Ramos B. Mohammadi 《Journal of Optimization Theory and Applications》2007,135(3):549-561
This paper has two objectives. We introduce a new global optimization algorithm reformulating optimization problems in terms
of boundary-value problems. Then, we apply this algorithm to a pointwise control problem of the viscous Burgers equation,
where the control weight coefficient is progressively decreased. The results are compared with those obtained with a genetic
algorithm and an LM-BFGS algorithm in order to check the efficiency of our method and the necessity of using global optimization
techniques. 相似文献
134.
An energy-dependent partitioning scheme is explored for extracting a small number of eigenvalues of a real symmetric matrix with the help of genetic algorithm. The proposed method is tested with matrices of different sizes (30 × 30 to 1000 × 1000). Comparison is made with Löwdin’s strategy for solving the problem. The relative advantages and disadvantages of the GA-based method are analyzed 相似文献
135.
V. S. Klimov 《Mathematical Notes》2007,81(1-2):61-71
We study homology characteristics of critical values and extremals of Lipschitz functionals defined on bounded closed convex subsets of a reflexive space that are invariant under deformations. Sufficient conditions for the existence of a bifurcation point of a multivalued potential operator (the switch principle for the typical number of an extremal) are established. 相似文献
136.
本文研究了由目标函数扰动的集值优化问题的有效点集所定义的集值映射的半连续性.讨论了目标函数扰动的集值优化问题在上半连续意义下的稳定性.特别地,在广义适定性条件下,证明了集值优化问题在上半连续意义下的稳定性. 相似文献
137.
138.
We study a variation of the knapsack problem in which each item has a profit, a weight and a penalty; the sum of profits of the selected items minus the largest penalty associated with the selected items must be maximized. We present an ILP formulation and an exact optimization algorithm. 相似文献
139.
We consider a multiperiod mean-variance model where the model parameters change according to a stochastic market. The mean
vector and covariance matrix of the random returns of risky assets all depend on the state of the market during any period
where the market process is assumed to follow a Markov chain. Dynamic programming is used to solve an auxiliary problem which,
in turn, gives the efficient frontier of the mean-variance formulation. An explicit expression is obtained for the efficient
frontier and an illustrative example is given to demonstrate the application of the procedure. 相似文献
140.
In the present paper, we consider the problem of the optimal reconstruction of the solution of the wave equation from the approximate values of the Fourier coefficients of the function specifying the initial form of the string. For an operator defined on the weight space of vectors from l 2, we present the solution of the more general problem of reconstruction from the approximate values of the coordinates of these vectors. 相似文献