全文获取类型
收费全文 | 37067篇 |
免费 | 5373篇 |
国内免费 | 2629篇 |
专业分类
化学 | 5030篇 |
晶体学 | 121篇 |
力学 | 4974篇 |
综合类 | 494篇 |
数学 | 10689篇 |
物理学 | 12452篇 |
无线电 | 11309篇 |
出版年
2024年 | 102篇 |
2023年 | 405篇 |
2022年 | 945篇 |
2021年 | 1032篇 |
2020年 | 1267篇 |
2019年 | 1006篇 |
2018年 | 980篇 |
2017年 | 1373篇 |
2016年 | 1699篇 |
2015年 | 1448篇 |
2014年 | 2291篇 |
2013年 | 2814篇 |
2012年 | 2374篇 |
2011年 | 2645篇 |
2010年 | 2146篇 |
2009年 | 2468篇 |
2008年 | 2369篇 |
2007年 | 2339篇 |
2006年 | 1978篇 |
2005年 | 1772篇 |
2004年 | 1608篇 |
2003年 | 1367篇 |
2002年 | 1243篇 |
2001年 | 972篇 |
2000年 | 922篇 |
1999年 | 776篇 |
1998年 | 688篇 |
1997年 | 514篇 |
1996年 | 459篇 |
1995年 | 436篇 |
1994年 | 382篇 |
1993年 | 316篇 |
1992年 | 285篇 |
1991年 | 208篇 |
1990年 | 189篇 |
1989年 | 140篇 |
1988年 | 132篇 |
1987年 | 135篇 |
1986年 | 114篇 |
1985年 | 133篇 |
1984年 | 143篇 |
1983年 | 74篇 |
1982年 | 99篇 |
1981年 | 66篇 |
1980年 | 29篇 |
1979年 | 39篇 |
1978年 | 30篇 |
1977年 | 29篇 |
1976年 | 16篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We give an account of the appearance and first developments of the statistical model of atoms proposed by Thomas and Fermi, focusing on the main results achieved by Fermi and his group in Rome. Particular attention is addressed to the unknown contribution to this subject by Majorana, anticipating some important results reached later by leading physicists. 相似文献
42.
Marco Pretti 《Journal of statistical physics》2003,111(3-4):993-1015
In this article we deal with the variational approach to cactus trees (Husimi trees) and the more common recursive approach, that are in principle equivalent for finite systems. We discuss in detail the conditions under which the two methods are equivalent also in the analysis of infinite (self-similar) cactus trees, usually investigated to the purpose of approximating ordinary lattice systems. Such issue is hardly ever considered in the literature. We show (on significant test models) that the phase diagram and the thermodynamic quantities computed by the variational method, when they deviates from the exact bulk properties of the cactus system, generally provide a better approximation to the behavior of a corresponding ordinary system. Generalizing a property proved by Kikuchi, we also show that the numerical algorithm usually employed to perform the free energy minimization in the variational approach is always convergent. 相似文献
43.
Numerical schemes for systems with multiple spatio-temporal scales are investigated. The multiscale schemes use asymptotic results for this type of systems which guarantee the existence of an effective dynamics for some suitably defined modes varying slowly on the largest scales. The multiscale schemes are analyzed in general, then illustrated on a specific example of a moderately large deterministic system displaying chaotic behavior due to Lorenz. Issues like consistency, accuracy, and efficiency are discussed in detail. The role of possible hidden slow variables as well as additional effects arising on the diffusive time-scale are also investigated. As a byproduct we obtain a rather complete characterization of the effective dynamics in Lorenz model. 相似文献
44.
A. M. Povolotsky V. B. Priezzhev Chin-Kun Hu 《Journal of statistical physics》2003,111(5-6):1149-1182
An asymmetric stochastic process describing the avalanche dynamics on a ring is proposed. A general kinetic equation which incorporates the exclusion and avalanche processes is considered. The Bethe ansatz method is used to calculate the generating function for the total distance covered by all particles. It gives the average velocity of particles which exhibits a phase transition from an intermittent to continuous flow. We calculated also higher cumulants and the large deviation function for the particle flow. The latter has the universal form obtained earlier for the asymmetric exclusion process and conjectured to be common for all models of the Kardar–Parisi–Zhang universality class. 相似文献
45.
Nonlinear susceptibility of a quantum dot (QD) embedded in a two-sided cavity, is studied theoretically from a weak-coupling to a strong-coupling regime. In the relevance of a quantum logic gate, the corresponding nonlinear phase shifts (Kerr effect) are estimated for coherent wavepackets including one photon on average. In the weak-coupling regime, the phase shift enhances strongly as a function of a coupling constant between the cavity photon and QD, and eventually saturates in the strong-coupling regime. We also show transmission spectra to evaluate the efficiency of the phase shift. Although the efficiency decreases monotonically in the weak-coupling regime, it rises in the strong-coupling regime. 相似文献
46.
47.
A Novel Segmentation and Feedback Model for Resolving Contention in Optical Burst Switching 总被引:2,自引:0,他引:2
A novel segmentation and feedback model (SFM) applied to resolve contention is proposed. Simulation and performance analyses show that the SFM effectively avoids contentions in optical burst switching (OBS). The long delay time of deflection routing and the immature technology of wavelength converters and optical buffers are not deployed in the SFM. The SFM does not only realize fast switching but also allows preemption by higher priority bursts. 相似文献
48.
移动式数据挖掘平台模型 总被引:1,自引:0,他引:1
本文提出了一种移动式网络海量数据挖掘平台,给出了数据挖掘任务的形式化描述,详细讨论了平台的体系结构、工作原理与流程。该平台克服了传统网络计算模式的缺陷,支持对异质、分散数据源和知识源的挖掘和检索,具有开放性、可伸缩性、灵活性、可扩展性、健壮性。 相似文献
49.
50.
中国3G业务的市场需求有两个方面:一是迅猛增长、规模庞大的用户群对移动语音业务的需求;二是较高收入用户群对移动数据业务的需求。3G运营商的目标市场包括大众用户对移动语音的需求、大众用户对移动数据业务的需求、企业用户对移动数据业务的需求以及批发型用户的需求等。本结合国内外移动运营商的数据业务开展状况,初步探讨了中国3G运营商的移动数据业务模式和3G业务的收入模式。 相似文献