全文获取类型
收费全文 | 3132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 | 2926篇 |
出版年
2024年 | 23篇 |
2023年 | 31篇 |
2022年 | 85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4043条查询结果,搜索用时 156 毫秒
821.
The prediction of road traffic noise levels in areas not directly exposed, such as areas behind buildings and courtyards, is difficult using standardised methods. This is mainly due to the fact that traditionally only one or a few sources are included. Here a simple model that assumes a flat city on rigid ground is used to demonstrate that sources from a large area are important. Calculations are compared to measurements for four cases, and the proposed method predicts levels 6-10 dB too high for the equivalent level at all measurement positions. If a correction is applied for this over-estimation, the results agree well. 相似文献
822.
Claas Becker 《Journal of Geometry and Physics》1993,11(1-4):529-543
Wilson loops exp (i A (x) dx) are investigated in two-dimensional Euclidean space-time. The electromagnetic vector potential A is regarded as a generalized random field given by the stochastic partial differential equation A = F where is a first-order differential operator and F is white noise. We give a rigorous definition of Wilson loops and examine the properties of the N-loop Schwinger functions. 相似文献
823.
介绍了12电极ECT成像系统测量的原理及设计.研制了一种高频抗杂散电容的充电转换差分放大探测电路,并设计出与12电极相配合、数据稳定、高分辨的一套控制时序,较好的实现了低漂移、高灵敏度及低噪声的测量.该测量电路可应用于最大成像率为100帧/s的系统 相似文献
824.
A self-weighted quantile procedure is proposed to study the inference for a spatial unilateral autoregressive model with independent and identically distributed innovations belonging to the domain of attraction of a stable law with index of stability α, α ∈ (0, 2]. It is shown that when the model is stationary, the self-weighted quantile estimate of the parameter has a closed form and converges to a normal limiting distribution, which avoids the difficulty of Roknossadati and Zarepour (2010) in deriving their limiting distribution for an M-estimate. On the contrary, we show that when the model is not stationary, the proposed estimates have the same limiting distributions as those of Roknossadati and Zarepour. Furthermore, a Wald test statistic is proposed to consider the test for a linear restriction on the parameter, and it is shown that under a local alternative, the Wald statistic has a non-central chisquared distribution. Simulations and a real data example are also reported to assess the performance of the proposed method. 相似文献
825.
Tamás Tél 《Journal of statistical physics》1988,50(5-6):897-912
A double expansion in powers of the damping coefficient and noise intensity is shown to be a powerful method for obtaining the stationary distribution of systems that after rescaling become weakly damped conservative ones. Systems undergoing Hopf bifurcations belong to this class. As an illustrative example, the generalized van der Pol oscillator is considered around its bifurcation point. A calculation is carried out up to third order in both the noise intensity and the bifurcation parameter (damping coefficient). 相似文献
826.
It is shown that a certain class of nonlinear systems possesses a unique and stable stationary state when subjected to periodic dichotomous modulations of an external parameter. This result enables us to define a probability density for the system and to characterize its shape and support. We compare this probability density with the one obtained in the case that the external parameter fluctuates randomly like a Markovian dichotomous noise and discuss various fluctuation-induced transition phenomena. The effects of these two types of fluctuations are quite dissimilar: the random fluctuations give rise to a richer behavior. The results are applied to the Freedericksz transition in nematic liquid crystals.Fellow of the University of Texas at Austin. 相似文献
827.
A. D. Sukhanov 《Theoretical and Mathematical Physics》2006,148(2):1123-1134
We introduce the Schrödinger correlator as the holistic characteristic of two types of fluctuation correlations in quantum dynamics and in statistical thermodynamics. We are the first to derive it using methods of thermofield dynamics for the coordinate-momentum variables of a quantum oscillator in a thermostat. We show that the obtained value ensures that the Schrödinger uncertainty relation becomes an equality at all temperatures. We find that the thermal equilibrium for the quantum oscillator has the sense of the thermal correlated coherent state and can be adequately described by a wave function with temperature-dependent amplitude and phase. 相似文献
828.
一种改进的SAR图像边缘检测方法 总被引:6,自引:0,他引:6
针对Ration边缘提取算法对弱边缘检测效果差,边缘定位精度低的缺点,提出了一种改进算法用于检测微弱边缘,并给出具有FCAR特性的阀值选取办法,实际应用中,将两种方法结合为一种综合处理方法,对真实SAR图像的处理结果表明,该综合处理方法具有较高检测正确率及较好的边缘定位精度。 相似文献
829.
830.
John J. Benedetto Rodney Kerby 《Journal of Mathematical Analysis and Applications》2003,279(2):740-755
Wiener's generalized harmonic analysis (GHA) provides a theory of harmonic analysis for subspaces of tempered functions not accessible to the L1,L2, and Fourier series theories; and it does it in a way that is usually more quantitative than that provided by the theory of distributions. On the other hand, GHA does not yield an adequate spectral analysis of large classes of functions, including nonstationary processes and, in particular, 1/f noise. In this paper we adapt GHA to deal with 1/f noise by extending the Wiener-Wintner theorem to the case of 1/f power spectra. 相似文献