全文获取类型
收费全文 | 124793篇 |
免费 | 9592篇 |
国内免费 | 7725篇 |
专业分类
化学 | 42197篇 |
晶体学 | 1940篇 |
力学 | 5733篇 |
综合类 | 1215篇 |
数学 | 39792篇 |
物理学 | 51233篇 |
出版年
2023年 | 527篇 |
2022年 | 852篇 |
2021年 | 1978篇 |
2020年 | 1607篇 |
2019年 | 1941篇 |
2018年 | 1811篇 |
2017年 | 1608篇 |
2016年 | 1662篇 |
2015年 | 1581篇 |
2014年 | 2903篇 |
2013年 | 5016篇 |
2012年 | 3174篇 |
2011年 | 4011篇 |
2010年 | 4441篇 |
2009年 | 9463篇 |
2008年 | 10580篇 |
2007年 | 9086篇 |
2006年 | 7989篇 |
2005年 | 5619篇 |
2004年 | 5347篇 |
2003年 | 5408篇 |
2002年 | 8437篇 |
2001年 | 4982篇 |
2000年 | 4578篇 |
1999年 | 4202篇 |
1998年 | 3611篇 |
1997年 | 2674篇 |
1996年 | 2476篇 |
1995年 | 2793篇 |
1994年 | 2677篇 |
1993年 | 2197篇 |
1992年 | 1707篇 |
1991年 | 1233篇 |
1990年 | 1027篇 |
1989年 | 844篇 |
1988年 | 818篇 |
1987年 | 618篇 |
1986年 | 427篇 |
1985年 | 1292篇 |
1984年 | 880篇 |
1983年 | 637篇 |
1982年 | 915篇 |
1981年 | 1071篇 |
1980年 | 967篇 |
1979年 | 847篇 |
1978年 | 758篇 |
1977年 | 655篇 |
1976年 | 630篇 |
1974年 | 382篇 |
1973年 | 517篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
992.
993.
994.
A BRANCH BOUND METHOD FOR SUBSET SUM PROBLEM 总被引:1,自引:0,他引:1
吴士泉 《应用数学学报(英文版)》1994,10(3):302-314
ABRANCHBOUNDMETHODFORSUBSETSUMPROBLEMWUSHIQUAN(吴士泉)(InstituteofAppliedMathematics,theChineseAcademyofSciences,Beijing100080,C... 相似文献
995.
Derived Brackets 总被引:3,自引:1,他引:2
Yvette Kosmann-Schwarzbach 《Letters in Mathematical Physics》2004,69(1-3):61-87
We survey the many instances of derived bracket construction in differential geometry, Lie algebroid and Courant algebroid theories, and their properties. We recall and compare the constructions of Buttin and of Vinogradov, and we prove that the Vinogradov bracket is the skew-symmetrization of a derived bracket. Odd (resp., even) Poisson brackets on supermanifolds are derived brackets of canonical even (resp., odd) Poisson brackets on their cotangent bundle (resp., parity-reversed cotangent bundle). Lie algebras have analogous properties, and the theory of Lie algebroids unifies the results valid for manifolds on the one hand, and for Lie algebras on the other. We outline the role of derived brackets in the theory of Poisson structures with background'. 相似文献
996.
The paper describes the possibility of designing matched interacting semiconductor quantum wells. It is shown that for a given eigenstate of a quantum well (QW), it is always possible to find another QW in such a way that the coupling leaves the original eigenstate of the host QW unperturbed irrespective of the strength of interaction. For rectangular QWs, the condition is met with whenever the second QW has appropriate width and depth so that phase travelled by an electron wave through it is an integral multiple of π. 相似文献
997.
W. Brüggemann K. Fischer H. Jahnke 《Journal of Mathematical Modelling and Algorithms》2003,2(2):153-169
In Part I of this study, we suggest to identify an operations research (OR) problem with the equivalence class of models describing the problem and enhance the standard computer-science theory of computational complexity to be applicable to this situation of an often model-based OR context. The Discrete Lot-sizing and Scheduling Problem (DLSP) is analysed here in detail to demonstrate the difficulties which can arise if these aspects are neglected and to illustrate the new theoretical concept. In addition, a new minimal model is introduced for the DLSP which makes this problem eventually amenable to a rigorous analysis of its computational complexity. 相似文献
998.
Peptidic aminopeptidase inhibitors, bestatin, phebestin and probestin have been prepared by stereo- and regiocontrolled reactions from a common α,β-epoxy ester precursor. 相似文献
999.
Godfrey Gumbs 《Solid State Communications》2003,128(12):443-448
A model calculation is reported for the tunneling probability of one as well as two interacting electrons from a quantum well within a narrow channel. We discuss the cases when the two electrons are spin polarized or unpolarized by transforming the system to a noninteracting one with the use of quantal density functional theory to obtain an effective single-particle confining potential. A semiclassical approach is used to obtain the tunneling probability from this effective potential. The calculation is motivated by recent measurements of the conductance of an electron gas in a narrow channel but is not meant to explain the anomalous behavior that has been reported since, for example, we deal with a simplified two-level system. Numerical results for the tunneling probability are presented. 相似文献
1000.
We develop a lattice-dynamical model based on the screw symmetry of single-walled carbon nanotubes that allows for reducing the size of the dynamical matrix to six, for all tube chiralities. The model uses force constants derived from fitting to the phonon dispersion of 2D graphite. We present the calculation procedure in a clear and transparent way, making the model easier to follow. We calculate the phonon dispersions of a number of nanotubes of different chiralities. The splitting of two highest Raman active modes and the radial breathing mode frequency are studied by changing the tube diameter and chirality. 相似文献