全文获取类型
收费全文 | 9276篇 |
免费 | 2340篇 |
国内免费 | 1186篇 |
专业分类
化学 | 2417篇 |
晶体学 | 147篇 |
力学 | 1927篇 |
综合类 | 110篇 |
数学 | 710篇 |
物理学 | 7491篇 |
出版年
2024年 | 15篇 |
2023年 | 83篇 |
2022年 | 186篇 |
2021年 | 183篇 |
2020年 | 245篇 |
2019年 | 219篇 |
2018年 | 244篇 |
2017年 | 302篇 |
2016年 | 367篇 |
2015年 | 326篇 |
2014年 | 624篇 |
2013年 | 721篇 |
2012年 | 567篇 |
2011年 | 751篇 |
2010年 | 617篇 |
2009年 | 704篇 |
2008年 | 726篇 |
2007年 | 702篇 |
2006年 | 692篇 |
2005年 | 586篇 |
2004年 | 554篇 |
2003年 | 444篇 |
2002年 | 428篇 |
2001年 | 392篇 |
2000年 | 337篇 |
1999年 | 285篇 |
1998年 | 258篇 |
1997年 | 213篇 |
1996年 | 162篇 |
1995年 | 163篇 |
1994年 | 137篇 |
1993年 | 105篇 |
1992年 | 86篇 |
1991年 | 77篇 |
1990年 | 51篇 |
1989年 | 54篇 |
1988年 | 37篇 |
1987年 | 31篇 |
1986年 | 16篇 |
1985年 | 20篇 |
1984年 | 16篇 |
1983年 | 6篇 |
1982年 | 19篇 |
1981年 | 12篇 |
1980年 | 6篇 |
1979年 | 12篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1974年 | 2篇 |
1973年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
71.
A detailed study of the generalized M2 factor of hard-edged diffracted beams based on the truncated second-order moments method, asymptotic analysis and self-convergent beam width approach is performed. The dependence of the generalized M2 factor on the parameters characterizing the spatial profile, and beam truncation, etc. is analyzed. 相似文献
72.
A mathematical model of laser beam treatment of double layer alloys (Ni/Fe, Al/Fe and Cr/Fe systems) describing the effect of laser beam on different physical and geometrical parameters of coated layer system has been adapted. The numerical solutions of the non-homogeneous heat-transport differential equation could estimate the temperature of the treated region.The suggested model allows investigation of the temperature distribution as a function of treated surface and laser parameters. The physical parameters of the treated materials were taken as functions of temperature due to the change in the temperature of the treated double layer materials. 相似文献
73.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献
74.
Under the nonresonant case where the carrier frequency of a Gaussian beam deviates from the resonant frequency of a Fabry–Perot etalon, the transmission of a Gaussian beam after incidenting nonnormally on a Fabry–Perot etalon has been investigated. The results show that under the nonresonant case, variations of the peak intensity, the position of the peak intensity and the spot size of the transmitted beam with the input angle behave differently and even with a reversed tendency compared with those obtained under the resonant case. 相似文献
75.
C. M. Zhang 《General Relativity and Gravitation》2003,35(8):1467-1472
In the framework of spacetime with torsion and without curvature, the Dirac particle spin precession in the rotational system is studied. We write out the equivalent tetrad of the rotating frame, in the polar coordinate system, through considering the relativistic factor, and the resultant equivalent metric is a flat Minkowski one. The obtained rotation-spin coupling formula can be applied to the high speed rotating case, which is consistent with the expectation. 相似文献
76.
Andrzej Dabrowski Erich Robens Peter Klobes Klaus Meyer Przemyslaw Podkocielny 《Particle & Particle Systems Characterization》2003,20(5):311-322
Since a comprehensive survey published in 1999 [1] much work was done in standardizing measuring methods to characterize the surface geometry of dispersed and/or porous solids and to certify reference materials. The present paper is an extension of a short communication [2]. It gives a survey on existing standards and reports on new drafts and proposals. 相似文献
77.
78.
79.
It has been observed that a quantum theory need not be Hermitian to have a real spectrum. We study the non-Hermitian relativistic quantum theories for many complex potentials, and obtain the real relativistic energy eigenvalues and corresponding eigenfunctions of a Dirac-charged particle in complex statically and spherically symmetric potentials. Complex Dirac–Eckart, complex Dirac–Rosen–Morse II, complex Dirac–Scarf and complex Dirac–Poschl–Teller potential are investigated. 相似文献
80.
N. S. Kazak E. G. Katranji I. A. Utkin A. A. Ryzhevich A. N. Khilo 《Journal of Applied Spectroscopy》2004,71(5):697-701
The phenomenon of self-diffraction of Bessel light beams (BLB) in a nonlinear liquid medium has been studied experimentally and theoretically for the first time. Diffraction maxima which do not correspond to integer orders for an induced periodic structure have been registered. It has been shown that the appearance of these maxima is due to the initial BLB modulation, which can be caused by the departure of the axicon refracting surface from the ideal conical surface, as well as by the imperfection of the form of the Gaussian beam incident on the axicon. 相似文献