全文获取类型
收费全文 | 3211篇 |
免费 | 367篇 |
国内免费 | 93篇 |
专业分类
化学 | 321篇 |
晶体学 | 4篇 |
力学 | 79篇 |
综合类 | 25篇 |
数学 | 1840篇 |
物理学 | 1402篇 |
出版年
2023年 | 19篇 |
2022年 | 57篇 |
2021年 | 55篇 |
2020年 | 50篇 |
2019年 | 79篇 |
2018年 | 78篇 |
2017年 | 81篇 |
2016年 | 81篇 |
2015年 | 76篇 |
2014年 | 165篇 |
2013年 | 237篇 |
2012年 | 160篇 |
2011年 | 243篇 |
2010年 | 182篇 |
2009年 | 207篇 |
2008年 | 236篇 |
2007年 | 228篇 |
2006年 | 179篇 |
2005年 | 136篇 |
2004年 | 123篇 |
2003年 | 114篇 |
2002年 | 107篇 |
2001年 | 83篇 |
2000年 | 81篇 |
1999年 | 89篇 |
1998年 | 80篇 |
1997年 | 58篇 |
1996年 | 51篇 |
1995年 | 42篇 |
1994年 | 33篇 |
1993年 | 23篇 |
1992年 | 23篇 |
1991年 | 17篇 |
1990年 | 12篇 |
1989年 | 14篇 |
1988年 | 16篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1980年 | 10篇 |
1979年 | 14篇 |
1978年 | 13篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 5篇 |
1974年 | 7篇 |
1973年 | 8篇 |
排序方式: 共有3671条查询结果,搜索用时 17 毫秒
11.
12.
Yoshikazu Takada 《Annals of the Institute of Statistical Mathematics》1998,50(2):325-335
This paper gives a condition which implies the nonexistence of parametric statistical procedures with bounded risk or error performance characteristics. Many examples for which such a condition is satisfied are considered. 相似文献
13.
I. Ogawa Y. Miyake T. Idehara S. Sabchevski 《International Journal of Infrared and Millimeter Waves》2002,23(1):1-19
A novel focusing mirror based on the shifting of the beam phase according to the Gaussian beam optics enabled us to realize a focusing elements with different focal lengths in different directions and to convert the gyrotron output into a Gaussian-like beam. In this paper, we compare the quality of beams produced by the new system (which includes novel mirrors) and a conventional system consisting of a quasi-optical antenna, an ellipsoidal mirror and two parabolic cylinder mirrors. 相似文献
14.
15.
We have presented an investigation of the induced focusing in Kerr media of two laser beams, the pump beam and the probe beam,
which could be either Gaussian or elliptic Gaussian or a combination of the two. We have used variational formalism to derive
relevant beam-width equations. Among several important findings, the finding that a very week probe beam can be guided and
focused when power of both beams are well below their individual threshold for self-focusing, is a noteworthy one. It has
been found that induced focusing is not possible for laser beams of any wavelength and beam radius. In case both beams are
elliptic Gaussian, we have shown that when power of both beams is above a certain threshold value then the effective radius
of both beams collapses and collapse distance depends on power. Moreover, it has been found that induced focusing can be employed
to convert a circular Gaussian beam into an elliptic Gaussian beam. 相似文献
16.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart. 相似文献
17.
Pham Huu Anh Ngoc 《Journal of Differential Equations》2007,243(1):101-122
We study stability radii of linear Volterra-Stieltjes equations under multi-perturbations and affine perturbations. A lower and upper bound for the complex stability radius with respect to multi-perturbations are given. Furthermore, in some special cases concerning the structure matrices, the complex stability radius can precisely be computed via the associated transfer functions. Then, the class of positive linear Volterra-Stieltjes equations is studied in detail. It is shown that for this class, complex, real and positive stability radius under multi-perturbations or multi-affine perturbations coincide and can be computed by simple formulae expressed in terms of the system matrices. As direct consequences of the obtained results, we get some results on robust stability of positive linear integro-differential equations and of positive linear functional differential equations. To the best of our knowledge, most of the results of this paper are new. 相似文献
18.
19.
Changes in the spectrum of Gaussian Schell-model beams propagating through turbulent atmosphere 总被引:1,自引:0,他引:1
Based on the extended Huygens-Fresnel principle, the spectrum of Gaussian Schell-model (GSM) beams propagating through turbulent atmosphere is derived analytically. It is shown that, if the scaling law is valid, the normalized spectrum S(ω) of GSM beams propagating through turbulent atmosphere is the same as the normalized source spectrum S(0)(ω), whether GSM source is quasi-homogenous or not. On the other hand, if the scaling law fails, S(ω) of GSM is different from S(0)(ω). The structure constant of the refractive index, transverse coordinate of observation point and spatial correlation length of the source affect the spectrum, which is illustrated numerically. 相似文献
20.
用波导本征模展开方法对用于高功率微波发射系统的方角锥高斯馈源口面场进行分析,提出结合馈源远场辐射特性和避免高功率击穿折衷选定相应的高斯模注腰半径,进而确定多个波导模幅值,从而为运用模匹配或耦合波理论设计高斯馈源提供依据。 相似文献