全文获取类型
收费全文 | 12244篇 |
免费 | 1423篇 |
国内免费 | 676篇 |
专业分类
化学 | 1096篇 |
晶体学 | 11篇 |
力学 | 714篇 |
综合类 | 131篇 |
数学 | 2930篇 |
物理学 | 3093篇 |
无线电 | 6368篇 |
出版年
2024年 | 20篇 |
2023年 | 68篇 |
2022年 | 153篇 |
2021年 | 167篇 |
2020年 | 249篇 |
2019年 | 232篇 |
2018年 | 234篇 |
2017年 | 370篇 |
2016年 | 431篇 |
2015年 | 410篇 |
2014年 | 736篇 |
2013年 | 760篇 |
2012年 | 773篇 |
2011年 | 845篇 |
2010年 | 633篇 |
2009年 | 833篇 |
2008年 | 994篇 |
2007年 | 1019篇 |
2006年 | 878篇 |
2005年 | 736篇 |
2004年 | 661篇 |
2003年 | 560篇 |
2002年 | 457篇 |
2001年 | 379篇 |
2000年 | 360篇 |
1999年 | 283篇 |
1998年 | 245篇 |
1997年 | 208篇 |
1996年 | 132篇 |
1995年 | 108篇 |
1994年 | 81篇 |
1993年 | 53篇 |
1992年 | 42篇 |
1991年 | 32篇 |
1990年 | 29篇 |
1989年 | 28篇 |
1988年 | 38篇 |
1987年 | 23篇 |
1986年 | 7篇 |
1985年 | 9篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 2篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 114 毫秒
61.
The paper deals with the stress, displacement, pore and fissure pressures fields induced by the drilling and/or the pressurization of a vertical borehole in a formation of water-saturated porous media with double porosity. The solution includes the boundary condition of non-hydrostatic in situ state of stress. The solid skeleton is assumed to behave as a linearly poroelastic material with compressible constituents. The analytical solution is derived in Laplace’s space and transformed to the time domain using a numerical inversion technique. The histories of pore and fissure pressures are illustrated to show the influence of permeabilities of the pore and fissure systems. 相似文献
62.
Improved holographic particle sizing by using absolute values of the wavelet transform 总被引:3,自引:0,他引:3
A new method for sizing particle from in-line particle holograms by using absolute values of the wavelet transform is proposed in order to improve accuracy in measurements. The proposed method provides direct calculation of the particle size by using spatial frequency information of a chirp signal at minima position of an envelope function. Simulation and experimental results are presented. 相似文献
63.
A new type of optoelectronic cellular neural network has been developed by providing the capability of coefficients adjusment of cellular neural network (CNN) using Widrow based perceptron learning algorithm. The new supervised cellular neural network is called Widrow-CNN. Despite the unsupervised CNN, the proposed learning algorithm allows to use the Widrow-CNN for various image processing applications easily. Also, the capability of CNN for image processing and feature extraction has been improved using basic joint transform correlation architecture. This hardware application presents high speed processing capability compared to digital applications. The optoelectronic Widrow-CNN has been tested for classic CNN feature extraction problems. It yields the best results even in case of hard feature extraction problems such as diagonal line detection and vertical line determination. 相似文献
64.
Based on the newly constructed two mutually conjugate 3-mode entangled states of continuum variablesin three-mode Fock space we introduce entangled fractional Fourier transform (EFFT) for the tripartite entangled staterepresentations, which are not a direct product of three 1-dimensional FFTs. The eigenmodes of EFFT are obtained,which is different from the usual Hermite polynomials. The EFFT of the three-mode squeezed state is derived. 相似文献
65.
本文主要讨论了当非负位势 V(x)属于某逆Holder类时,由一致椭圆算子L=-div(A(x))+V(x)所定义的 Riesz变换在 Lp空间的有界性。 相似文献
66.
Jin Cheng Ching-Lung Lin Gen Nakamura 《Proceedings of the American Mathematical Society》2005,133(8):2359-2367
In this paper we prove the following kind of unique continuation property. That is, the zero on each geodesic of the solution in a real analytic hypersurface for second order anisotropic hyperbolic systems with real analytic coefficients can be continued along this curve.
67.
68.
分数阶傅立叶变换是经典傅立叶变换的广义形式,它同时从时间域和频率域(或空间域)揭示信号特征。本文系统地分析了分数阶傅立叶变换三种定义形式及其所对应的光学实现系统的组成和原理,说明了光学信息处理系统实现分数阶傅立叶变换的有效性. 相似文献
69.
一种空间自适应小波门限去噪算法 总被引:3,自引:0,他引:3
提出了一种空间自适应小波门限去噪算法,该算法在小波域对含噪小波系数做两次自适应去噪,两次自适应门限分别基于最大似然(ML)方差估计和最大后验概率(MAP)方差估计.仿真结果表明,该算法与其它自适应门限去噪算法相比,去噪后的图象具有更高的峰值信噪比(PSNR). 相似文献
70.
Durand William A.Pham Ngoc Dinh 《Journal of Mathematical Analysis and Applications》2003,282(1):95-106
An electromagnetic diffraction problem in a wedge shaped region is reduced to a system of coupled functional difference equations by means of Sommerfeld integrals and Malyuzhinets theorem. By introducing an integral operator it is shown that the solutions of this system of functional equations can be defined in terms of integral representations whose kernels are solutions of a singular integral equation of Cauchy-Carleman type for which an explicit solution is given. 相似文献