全文获取类型
收费全文 | 19539篇 |
免费 | 4632篇 |
国内免费 | 2728篇 |
专业分类
化学 | 8440篇 |
晶体学 | 294篇 |
力学 | 2518篇 |
综合类 | 201篇 |
数学 | 1363篇 |
物理学 | 14083篇 |
出版年
2024年 | 36篇 |
2023年 | 175篇 |
2022年 | 575篇 |
2021年 | 565篇 |
2020年 | 695篇 |
2019年 | 585篇 |
2018年 | 565篇 |
2017年 | 747篇 |
2016年 | 856篇 |
2015年 | 678篇 |
2014年 | 1190篇 |
2013年 | 1598篇 |
2012年 | 1264篇 |
2011年 | 1490篇 |
2010年 | 1236篇 |
2009年 | 1399篇 |
2008年 | 1456篇 |
2007年 | 1325篇 |
2006年 | 1352篇 |
2005年 | 1079篇 |
2004年 | 1054篇 |
2003年 | 886篇 |
2002年 | 782篇 |
2001年 | 759篇 |
2000年 | 662篇 |
1999年 | 489篇 |
1998年 | 518篇 |
1997年 | 427篇 |
1996年 | 372篇 |
1995年 | 321篇 |
1994年 | 284篇 |
1993年 | 254篇 |
1992年 | 232篇 |
1991年 | 170篇 |
1990年 | 146篇 |
1989年 | 123篇 |
1988年 | 123篇 |
1987年 | 88篇 |
1986年 | 58篇 |
1985年 | 48篇 |
1984年 | 53篇 |
1983年 | 22篇 |
1982年 | 36篇 |
1981年 | 25篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 19篇 |
1977年 | 9篇 |
1976年 | 8篇 |
1973年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
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
122.
聚芳香杂环甲烯的三阶非线性光学效应与时间分辨光克尔效应 总被引:6,自引:4,他引:2
合成了一系列聚芳香杂环甲烯,包括聚吡咯甲烯和聚噻吩甲烯.采用四波混频法研究材料的共振三阶非线性光学效应(λ=532nm),其共振二阶超分子极化率γ三阶非线性光学系数分别达到10-30esu和10-8esu.选择具有良好溶解性、成膜性的聚吡咯对二甲氨基苯甲烯(PPDMAB),采用飞秒时间分辨光克尔效应方法研究材料的非共振三阶非线性光学效应(λ=790nm).实验表明,翠绿亚胺碱溶液的光克尔信号仅表现一超快响应的成分,归功于π电子云扭转产生的非共振激发.PPDMAB的非共振二阶超分子极化率γ三阶非线性光学系数分别达到γ=5.78×10-32esu和χ(3)=1.26×10-10esu. 相似文献
123.
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
124.
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
125.
126.
127.
128.
E. Kajari R. Walser W. P. Schleich A. Delgado 《General Relativity and Gravitation》2004,36(10):2289-2316
We present exact expressions for the Sagnac effect of Gödel's Universe. For this purpose we first derive a formula for the Sagnac time delay along a circular path in the presence of an arbitrary stationary metric in cylindrical coordinates. We then apply this result to Gödel's metric for two different experimental situations: First, the light source and the detector are at rest relative to the matter generating the gravitational field. In this case we find an expression that is formally equivalent to the familiar nonrelativistic Sagnac time delay. Second, the light source and the detector are rotating relative to the matter. Here we show that for a special rotation rate of the detector the Sagnac time delay vanishes. Finally we propose a formulation of the Sagnac time delay in terms of invariant physical quantities. We show that this result is very close to the analogous formula of the Sagnac time delay of a rotating coordinate system in Minkowski spacetime. 相似文献
129.
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
130.