全文获取类型
收费全文 | 3127篇 |
免费 | 799篇 |
国内免费 | 112篇 |
专业分类
化学 | 182篇 |
晶体学 | 11篇 |
力学 | 283篇 |
综合类 | 51篇 |
数学 | 590篇 |
物理学 | 2921篇 |
出版年
2024年 | 23篇 |
2023年 | 31篇 |
2022年 | 80篇 |
2021年 | 62篇 |
2020年 | 95篇 |
2019年 | 83篇 |
2018年 | 87篇 |
2017年 | 120篇 |
2016年 | 166篇 |
2015年 | 113篇 |
2014年 | 241篇 |
2013年 | 236篇 |
2012年 | 166篇 |
2011年 | 252篇 |
2010年 | 168篇 |
2009年 | 222篇 |
2008年 | 224篇 |
2007年 | 206篇 |
2006年 | 183篇 |
2005年 | 145篇 |
2004年 | 110篇 |
2003年 | 143篇 |
2002年 | 135篇 |
2001年 | 118篇 |
2000年 | 132篇 |
1999年 | 86篇 |
1998年 | 74篇 |
1997年 | 56篇 |
1996年 | 37篇 |
1995年 | 33篇 |
1994年 | 21篇 |
1993年 | 28篇 |
1992年 | 21篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 29篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 10篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1973年 | 2篇 |
排序方式: 共有4038条查询结果,搜索用时 15 毫秒
141.
142.
The understanding of mesoscopic transport has now attained an ultimate simplicity. Indeed, orthodox quantum kinetics would seem to say little about mesoscopics that has not been revealed — nearly effortlessly — by more popular means. Such is far from the case, however. The fact that kinetic theory remains very much in charge is best appreciated through the physics of a quantum point contact. While discretization of its conductance is viewed as the exclusive result of coherent, single-electron-wave transmission, this does not begin to address the paramount feature of all metallic conduction: dissipation. A perfect quantum point contact still has finite resistance, so its ballistic carriers must dissipate the energy gained from the applied field. How do they manage that? The key is in standard many-body quantum theory, and its conservation principles. 相似文献
143.
We discuss how the effective parameters characterising averaged motion in nonlinear systems are affected by noise (random fluctuations). In this approach to stochastic dynamics, the stochastic system is replaced by its deterministic equivalent but with noise-dependent parameters. We show that it can help to resolve certain paradoxes and that it has a utility extending far beyond its usual application in passing from the microscopic equations of motion to the macroscopic ones. As illustrative examples, we consider the diode-capacitor circuit, a Brownian ratchet, and a generic stochastic resonance system. In the latter two cases we calculate for the first time their effective parameters of averaged motion as functions of noise intensity. We speculate that many other stochastic problems can be treated in a similar way.
PACS: 05.10.Gg, 05.40.-a, 05.40.Jc 相似文献
144.
The recent expansion of French tram networks and the related local residential complaints mean that a better knowledge of the situations leading to negative reactions from the local inhabitants is required. Hence a research project has been conducted to evaluate and describe noise and vibration emission of trams as well as the perception by the local residents. This paper investigates tram noise emission on common straight track sections, involving two vehicle scales. First the acoustic power and the mean vertical directivity of the total tramset is assessed using an arc of microphones. Then the localisation and the analysis of the main noise sources are performed by means of a cross array during the tram pass-by. Two tram types representing two generations of French rolling stock, both running on two sites with distinct track characteristics, have been investigated considering the effect of speed, tram type, and track type on the noise source contributions and spectral features. Most sources are located in the lower part of the trams, mainly related to rolling noise, with a strong dependence on speed and track type. The tram type dependency, although globally of second importance, influences greatly the noise spectral distribution and behaviour. The HVAC was the only roof-mounted source which could be detected; its contribution towards building storeys becomes significant in configurations of low rolling noise. A tram noise emission model based on the various noise sources has been developed. 相似文献
145.
高架桥声屏障高度对列车气动特性影响的数值模拟 总被引:2,自引:0,他引:2
采用计算流体力学方法对高架桥声屏障高度影响高速列车空气动力特性进行数值研究.通过网格划分、湍流模型选取、边界条件设置等来提高数值计算精度.结果表明,当高速列车运行在下风向时,头车、中间车上的侧向力随着声屏障高度增加而逐渐下降.头车所受的侧翻力矩在整车中最大,且随着声屏障高度的增加而逐渐减小.随着声屏障高度的增加,上风向工况下中间车受到的侧翻力矩要大于下风向工况.上、下风向工况下高速列车气动特性差异主要是由于流动空腔中列车所处的相对位置不同,改变了车体表面的压力分布,从而改变了车体所受到的气动力、力矩. 相似文献
146.
147.
148.
Wei Chen 《Optics & Laser Technology》2011,43(7):1270-1273
Four-wave mixing (FWM) is a significant nonlinear effect in wavelength division multiplexing (WDM) fiber-optic systems. For two-wave transmission, it is easily found that the FWM noise power decreases with frequency spacing and increases with signal power. However, the variation of relative intensity noise (RIN) with frequency spacing and signal power is only 2 dB at most. The intensity fluctuations induced by the energy exchange between the FWM generated new waves and the original ones are trivial and the influence of FWM on RIN can be neglected. It is also found that the increase of RIN with signal power is mainly attributed to stimulated Brillouin scattering (SBS) rather than FWM. 相似文献
149.
150.