全文获取类型
收费全文 | 47022篇 |
免费 | 3365篇 |
国内免费 | 1943篇 |
专业分类
化学 | 23285篇 |
晶体学 | 435篇 |
力学 | 2387篇 |
综合类 | 79篇 |
数学 | 10917篇 |
物理学 | 15227篇 |
出版年
2023年 | 395篇 |
2022年 | 643篇 |
2021年 | 763篇 |
2020年 | 765篇 |
2019年 | 752篇 |
2018年 | 1890篇 |
2017年 | 1994篇 |
2016年 | 1655篇 |
2015年 | 1359篇 |
2014年 | 1500篇 |
2013年 | 2015篇 |
2012年 | 4766篇 |
2011年 | 4007篇 |
2010年 | 2919篇 |
2009年 | 2575篇 |
2008年 | 1728篇 |
2007年 | 1621篇 |
2006年 | 1558篇 |
2005年 | 5175篇 |
2004年 | 4455篇 |
2003年 | 2694篇 |
2002年 | 910篇 |
2001年 | 617篇 |
2000年 | 365篇 |
1999年 | 559篇 |
1998年 | 387篇 |
1997年 | 360篇 |
1996年 | 332篇 |
1995年 | 289篇 |
1994年 | 253篇 |
1993年 | 237篇 |
1992年 | 313篇 |
1991年 | 313篇 |
1990年 | 266篇 |
1989年 | 208篇 |
1988年 | 188篇 |
1987年 | 130篇 |
1986年 | 109篇 |
1985年 | 91篇 |
1984年 | 86篇 |
1983年 | 58篇 |
1982年 | 51篇 |
1980年 | 42篇 |
1976年 | 95篇 |
1975年 | 53篇 |
1974年 | 53篇 |
1973年 | 63篇 |
1972年 | 44篇 |
1969年 | 45篇 |
1968年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
31.
给出了线和n-2的n阶(0,1)-矩阵的最大积和式的积分表达式,并证明了该积分表达式与[1]得到的组合表达式等价。 相似文献
32.
According to an induced-matter approach, Liu and Wesson obtained the rest mass of a typical particle from the reduction of a 5D Klein–Gordon equation to a 4D one. Introducing an extra-dimension momentum operator identified with the rest mass eigenvalue operator, we consider a way to generalize the 4D Dirac equation to 5D. An analogous normal Dirac equation is gained when the generalization reduces to 4D. We find the rest mass of a particle in curved space varies with spacetime coordinates and check this for the case of exact solitonic and cosmological solution of the 5D vacuum gravitational field equations. 相似文献
33.
34.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献
35.
36.
Hongbo Zhang Rui Wang Kaixin Chen Han Yang Daming Zhang Maobin Yi Guoquan Wang Zhenchang Ma 《Optics & Laser Technology》2002,34(4):283-286
A new method, based on zero point of longitudinal electric field, was used to determine the spatial resolution of external electro-optic (EO) probing equipment. Considering the diffraction of Gauss beam, the result of external EO probing was simulated which was in accordance with the experiment. A spatial resolution <1 μm was demonstrated initially in our equipment using 650 nm laser diode as probe beam and semi-insulating GaP as probe tip. 相似文献
37.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献
38.
39.
Could simple intraannular-arm macrocyclic systems exist in enantiopure stable forms? The effective synthesis of two representative compounds of such a class, their resolution into enantiomers, and experiments justifying their stability toward racemization are presented. 相似文献
40.