全文获取类型
收费全文 | 9088篇 |
免费 | 1717篇 |
国内免费 | 684篇 |
专业分类
化学 | 901篇 |
晶体学 | 24篇 |
力学 | 526篇 |
综合类 | 89篇 |
数学 | 796篇 |
物理学 | 3205篇 |
无线电 | 5948篇 |
出版年
2024年 | 56篇 |
2023年 | 160篇 |
2022年 | 224篇 |
2021年 | 305篇 |
2020年 | 335篇 |
2019年 | 263篇 |
2018年 | 267篇 |
2017年 | 310篇 |
2016年 | 409篇 |
2015年 | 431篇 |
2014年 | 635篇 |
2013年 | 643篇 |
2012年 | 643篇 |
2011年 | 718篇 |
2010年 | 518篇 |
2009年 | 599篇 |
2008年 | 612篇 |
2007年 | 598篇 |
2006年 | 607篇 |
2005年 | 455篇 |
2004年 | 391篇 |
2003年 | 402篇 |
2002年 | 317篇 |
2001年 | 271篇 |
2000年 | 277篇 |
1999年 | 189篇 |
1998年 | 146篇 |
1997年 | 128篇 |
1996年 | 95篇 |
1995年 | 88篇 |
1994年 | 48篇 |
1993年 | 69篇 |
1992年 | 46篇 |
1991年 | 28篇 |
1990年 | 25篇 |
1989年 | 43篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 27篇 |
1983年 | 3篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1976年 | 3篇 |
1973年 | 2篇 |
1959年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 679 毫秒
71.
C. Fabre U. Andersen H. Bachor B. Buchler S. Gigan P. K. Lam A. Maître N. Treps 《Superlattices and Microstructures》2002,32(4-6)
Optical images can be used to transport, store and process information in a parallel way. We discuss different results obtained in the domain of ‘quantum imaging’, aiming at exploiting at the same time the quantum properties of optical images and their intrinsic parallelism. We define the notion of standard quantum limit (SQL) in optical resolution, set by the quantum noise of usual coherent light, and show that it can be much lower than the diffraction limit. We also prove that this limit can be circumvented by especially designed nonclassical and multimode light. We present an experiment showing that OPOs oscillating inside an exactly confocal cavity actually produce such transverse multimode nonclassical light. We finally describe another experiment which has surpassed the SQL in the case of beam positioning, both in the 1D and 2D cases. 相似文献
72.
一类广义维里拉普拉斯,把在白噪声分析构架中通常定义的维里拉普拉斯作为特殊情形而包含。 相似文献
73.
The cross-spectral estimation methods are efficient in estimating the parameters of sinusoidal signals embedded in colored noise. But up to now, only FPT and cross-periodogram methods are used in this field, the modern auto-spectral estimation method is introduced into cross-spectral estimation in this paper, meanwhile the cross-correlation based Yule-Walker equation is proposed theoretically and the moment and singular-value decomposition (SVD)) algorithms for cross-spectral estimation have been developed. Finally, a numerical example is given for comparing the presented methods with the well-known Cadzow's SVD method. 相似文献
74.
75.
76.
基于邻域统计特性的概率神经网络及其在自动目标识别中的应用 总被引:5,自引:0,他引:5
在概率神经的一种改进模型-FDO网络的基础上,提出在设计网络收敛域时进一步考虑每一像素点周围8邻域的影响,对网络的作用函数加以修,使改进后的网络具有稳定性好且收敛速度快的优点。通过实验对改进前后网络的识别性能加以比较,证明改进后的网络特别适用于噪声图像的识别。 相似文献
77.
Gabor Schmera Adi Bulsara David Pierson Frank Moss Enrico Di Cera 《Journal of statistical physics》1993,71(5-6):1179-1190
We consider the class of experiments which can be characterized by a Fokker-PIanck dynamics corresponding to the overdamped motion of a state point in a suitable stochastic potential. We assume that the general form of the potential is known (or can be guessed with reasonable accuracy), but that its parameters are to be determined experimentally by measurements made with a noisy instrument. This possible method for determining the potential parameters, which exploits the system's own internal stochastic motion in order to explore rapidly its available parameter space, is substantially more efficient than traditional methods involving time averages of single point measurements, and yet does not appear to have been previously considered. The method could be important when, for example, the experiment must be completed in a limited time owing either to the expense of the experimental materials or to the temporary stationarity of the preparation, situations which are commonly encountered in experimental biochemistry and biology. 相似文献
78.
Hans C. Fogedby 《Journal of statistical physics》1992,69(1-2):411-425
We elaborate in some detail on a new phase space approach to complexity, due to Y.-C. Zhang. We show in particular that the connection between maximal complexity and power law noise or correlations can be derived from a simple variational principle. For a 1D signal we find 1/f noise, in accordance with Zhang. 相似文献
79.
Solomon Fekade Mulugeta Bekele 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):369-374
We analyze the relaxation behavior of a bistable system when the background temperature profile is inhomogeneous due to the
presence of a localized hot region (blowtorch) on one side of the potential barrier. Since the diffusion equation for inhomogeneous
medium is model-dependent, we consider two physical models to study the kinetics of such system. Using a conventional stochastic
method, we obtain the escape and equilibration rates of the system for the two physical models. For both models, we find that
the hot region enhances the escape rate from the well where it is placed while it retards the escape rate from the other well. However, the value of the escape rate from the well where the hot region is placed differs
for the two models while that of the escape rate from the other well is identical for both. This work, for the first time,
gives a detailed report of the similarities and differences of the escape rates and, hence, exposes the common and distinct
features of the two known physical models in determining the way the bistable system relaxes.
Received 25 September 2001 相似文献
80.