全文获取类型
收费全文 | 29961篇 |
免费 | 3702篇 |
国内免费 | 3404篇 |
专业分类
化学 | 9837篇 |
晶体学 | 106篇 |
力学 | 2153篇 |
综合类 | 225篇 |
数学 | 8065篇 |
物理学 | 11062篇 |
无线电 | 5619篇 |
出版年
2024年 | 105篇 |
2023年 | 398篇 |
2022年 | 642篇 |
2021年 | 843篇 |
2020年 | 1003篇 |
2019年 | 874篇 |
2018年 | 870篇 |
2017年 | 1009篇 |
2016年 | 1186篇 |
2015年 | 1136篇 |
2014年 | 1691篇 |
2013年 | 2471篇 |
2012年 | 1797篇 |
2011年 | 1992篇 |
2010年 | 1535篇 |
2009年 | 1848篇 |
2008年 | 1933篇 |
2007年 | 1955篇 |
2006年 | 1682篇 |
2005年 | 1417篇 |
2004年 | 1144篇 |
2003年 | 1147篇 |
2002年 | 1055篇 |
2001年 | 843篇 |
2000年 | 811篇 |
1999年 | 684篇 |
1998年 | 635篇 |
1997年 | 488篇 |
1996年 | 355篇 |
1995年 | 331篇 |
1994年 | 284篇 |
1993年 | 278篇 |
1992年 | 261篇 |
1991年 | 210篇 |
1990年 | 218篇 |
1989年 | 210篇 |
1988年 | 175篇 |
1987年 | 168篇 |
1986年 | 140篇 |
1985年 | 142篇 |
1984年 | 143篇 |
1983年 | 80篇 |
1982年 | 115篇 |
1981年 | 107篇 |
1980年 | 99篇 |
1979年 | 101篇 |
1978年 | 80篇 |
1977年 | 78篇 |
1976年 | 76篇 |
1973年 | 61篇 |
排序方式: 共有10000条查询结果,搜索用时 274 毫秒
141.
We consider some types of packet discretization for continuous spectra in quantum scattering problems. As we previously showed, this discretization leads to a convenient finite-dimensional (i.e., matrix) approximation for integral operators in the scattering theory and allows reducing the solution of singular integral equations connected with the scattering theory to some suitable purely algebraic equations on an analytic basis. All singularities are explicitly singled out. Our primary emphasis is on realizing the method practically. 相似文献
142.
In this paper, by means of the method of upper and lower solutions and monotone iterative technique, the existence of maximal and minimal solutions of the boundary value problems for first order impulsive delay differential equations is established. 相似文献
143.
This paper develops a theory for the global solution of nonconvex optimization problems with parameter-embedded linear dynamic systems. A quite general problem formulation is introduced and a solution is shown to exists. A convexity theory for integrals is then developed to construct convex relaxations for utilization in a branch-and-bound framework to calculate a global minimum. Interval analysis is employed to generate bounds on the state variables implied by the bounds on the embedded parameters. These bounds, along with basic integration theory, are used to prove convergence of the branch-and-bound algorithm to the global minimum of the optimization problem. The implementation of the algorithm is then considered and several numerical case studies are examined thoroughly 相似文献
144.
Mixed integer programming (MIP) models are extensively usedto aid strategic and tactical decision making in many businesssectors. Solving MIP models is a computationally intensive processand there is a need to develop solution approaches that enablelarger models to be solved within acceptable timeframes. Inthis paper, we describe the implementation of a two-stage parallelbranch and bound (PB & B) algorithm for MIP. In stage 1of the algorithm, a multiple heuristic search is implementedin which a number of alternative search trees are investigatedusing a forest search in the hope of finding a good solutionquickly. In stage 2, the search is reorganized so that the branchesof a chosen tree are investigated in parallel. A new heuristicis introduced, based on a best projection criterion, which evaluatesalternative B & B trees in order to choose one for investigationin stage 2 of the algorithm. The heuristic also serves as away of implementing a quality load balancing scheme for stage2 of the algorithm. The results of experimental investigationsare reported for a range of models taken from the MIPLIB libraryof benchmark problems. 相似文献
145.
146.
We study the elastic responses of double-(ds) and single-stranded (ss) DNA at external force fields. A double-strand-polymer
elastic model is constructed and solved by path integral methods and Monte Carlo simulations to understand the entropic elasticity,
cooperative extensibility, and supercoiling property of dsDNA. The good agreement with experiments indicates that short-ranged
base-pair stacking interaction is crucial for the stability and the high deformability of dsDNA. Hairpin-coil transition in
ssDNA is studied with generating function method. A threshold force is needed to pull the ssDNA hairpin patterns, stabilized
by base pairing and base-pair stacking, into random coils. This phase transition is predicted to be of first order for stacking
potential higher than some critical level, in accordance with experimental observations. 相似文献
147.
Alfonso Carriazo Luis M. Ferná ndez 《Proceedings of the American Mathematical Society》2004,132(11):3327-3336
In this paper we present an interesting relationship between graph theory and differential geometry by defining submanifolds of almost Hermitian manifolds associated with certain kinds of graphs. We show some results about the possibility of a graph being associated with a submanifold and we use them to characterize CR-submanifolds by means of trees. Finally, we characterize submanifolds associated with graphs in a four-dimensional almost Hermitian manifold.
148.
Elena Castellani 《International Journal of Theoretical Physics》2004,43(6):1503-1514
We examine the relevance of Dirac's view on the use of transformation theory and invariants in modern physics to current reflections on the meaning of physical symmetries, especially gauge symmetries. 相似文献
149.
150.
We present a general risk model where the aggregate claims, as well as the premium function, evolve by jumps. This is achieved by incorporating a Lévy process into the model. This seeks to account for the discrete nature of claims and asset prices. We give several explicit examples of Lévy processes that can be used to drive a risk model. This allows us to incorporate aggregate claims and premium fluctuations in the same process. We discuss important features of such processes and their relevance to risk modeling. We also extend classical results on ruin probabilities to this model. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献