全文获取类型
收费全文 | 42808篇 |
免费 | 6401篇 |
国内免费 | 4878篇 |
专业分类
化学 | 12757篇 |
晶体学 | 153篇 |
力学 | 4666篇 |
综合类 | 733篇 |
数学 | 17075篇 |
物理学 | 18703篇 |
出版年
2024年 | 83篇 |
2023年 | 450篇 |
2022年 | 701篇 |
2021年 | 1021篇 |
2020年 | 1263篇 |
2019年 | 1149篇 |
2018年 | 1165篇 |
2017年 | 1506篇 |
2016年 | 1759篇 |
2015年 | 1492篇 |
2014年 | 2323篇 |
2013年 | 3411篇 |
2012年 | 2425篇 |
2011年 | 2830篇 |
2010年 | 2357篇 |
2009年 | 2857篇 |
2008年 | 3080篇 |
2007年 | 3179篇 |
2006年 | 2632篇 |
2005年 | 2298篇 |
2004年 | 2048篇 |
2003年 | 1881篇 |
2002年 | 1691篇 |
2001年 | 1329篇 |
2000年 | 1217篇 |
1999年 | 1102篇 |
1998年 | 979篇 |
1997年 | 797篇 |
1996年 | 632篇 |
1995年 | 630篇 |
1994年 | 442篇 |
1993年 | 414篇 |
1992年 | 341篇 |
1991年 | 354篇 |
1990年 | 284篇 |
1989年 | 234篇 |
1988年 | 236篇 |
1987年 | 198篇 |
1986年 | 157篇 |
1985年 | 168篇 |
1984年 | 143篇 |
1983年 | 66篇 |
1982年 | 107篇 |
1981年 | 106篇 |
1980年 | 83篇 |
1979年 | 91篇 |
1978年 | 70篇 |
1977年 | 74篇 |
1976年 | 65篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
1.
Dynamical analysis,circuit realization,and application in pseudorandom number generators of a fractional-order laser chaotic system 下载免费PDF全文
Chenguang Ma 《中国物理 B》2021,30(12):120504-120504
A new five-dimensional fractional-order laser chaotic system (FOLCS) is constructed by incorporating complex variables and fractional calculus into a Lorentz-Haken-type laser system. Dynamical behavior of the system, circuit realization and application in pseudorandom number generators are studied. Many types of multi-stable states are discovered in the system. Interestingly, there are two types of state transition phenomena in the system, one is the chaotic state degenerates to a periodical state, and the other is the intermittent chaotic oscillation. In addition, the complexity of the system when two parameters change simultaneously is measured by the spectral entropy algorithm. Moreover, a digital circuit is design and the chaotic oscillation behaviors of the system are verified on this circuit. Finally, a pseudo-random sequence generator is designed using the FOLCS, and the statistical characteristics of the generated pseudo-random sequence are tested with the NIST-800-22. This study enriches the research on the dynamics and applications of FOLCS. 相似文献
2.
3.
We generalize the P(N)-graded Lie superalgebras of Martinez-Zelmanov. This generalization is not so restrictive but suffcient enough so that we are able to have a classification for this generalized P(N)-graded Lie superalgebras. Our result is that the generalized P(N)-graded Lie super-algebra L is centrally isogenous to a matrix Lie superalgebra coordinated by an associative superalgebra with a super-involution. Moreover, L is P(N)-graded if and only if the coordinate algebra R is commutative and the super-involution is trivial. This recovers Martinez-Zelmanov's theorem for type P(N). We also obtain a generalization of Kac's coordinatization via Tits-Kantor-Koecher construction. Actually, the motivation of this generalization comes from the Fermionic-Bosonic module construction. 相似文献
4.
5.
The aim of this paper is to study the asymptotic behavior of solutions for some reaction–diffusion systems in biology. First, we establish a Liouville type theorem for entire solutions of these reaction–diffusion systems. Based on this theorem, we derive the stabilization of the solutions of the reaction–diffusion system to the unique positive constant state, under the condition that this positive constant state is globally stable in the corresponding kinetic systems. Two specific examples about spreading phenomena from ecology and epidemiology are given to illustrate the application of this theory. 相似文献
6.
7.
《Mendeleev Communications》2022,32(4):467-470
Isomeric forms of indoline spiropyrans show unusual behavior compared with similar compounds, according to experimental data. DFT modeling for gas phase was made to consider the simplest case without environmental effects, which revealed the intramolecular reasons for occurrence of ring opening reaction depending on the particular structure of the compound. The questions of charge redistributions, the changes of geometry and chemical bonds in the structures are also discussed. 相似文献
8.
本文提出了一种新的能够计及尺度效应的微纳米蜂窝等效模量的计算方法。将一种单参数应变梯度理论引入到本构方程当中,并基于能量等效原理推导了蜂窝面内等效模量地计算公式。算例分析表明,本文方法能够有效地计及尺度效应对蜂窝等效模量的影响。尺度效应与胞壁厚度和长度的值都有关,当胞壁厚度较小时,尺度效应显著,本文方法预测的模量会明显高于传统方法;而当胞壁厚度较大时,尺度效应变得微弱乃至可以忽略不计。但如果胞壁的长度/厚度比很大,则面内等效模量会趋近于0,此时是否考虑尺度效应意义不大。 相似文献
9.
10.