全文获取类型
收费全文 | 55913篇 |
免费 | 4526篇 |
国内免费 | 5699篇 |
专业分类
化学 | 36711篇 |
晶体学 | 717篇 |
力学 | 3162篇 |
综合类 | 315篇 |
数学 | 14208篇 |
物理学 | 11025篇 |
出版年
2024年 | 77篇 |
2023年 | 728篇 |
2022年 | 1117篇 |
2021年 | 1265篇 |
2020年 | 1646篇 |
2019年 | 1707篇 |
2018年 | 1504篇 |
2017年 | 1684篇 |
2016年 | 1863篇 |
2015年 | 1792篇 |
2014年 | 2359篇 |
2013年 | 3858篇 |
2012年 | 2770篇 |
2011年 | 3639篇 |
2010年 | 2848篇 |
2009年 | 3610篇 |
2008年 | 3667篇 |
2007年 | 3511篇 |
2006年 | 3023篇 |
2005年 | 2693篇 |
2004年 | 2607篇 |
2003年 | 2134篇 |
2002年 | 2622篇 |
2001年 | 1567篇 |
2000年 | 1351篇 |
1999年 | 1235篇 |
1998年 | 1006篇 |
1997年 | 878篇 |
1996年 | 979篇 |
1995年 | 901篇 |
1994年 | 832篇 |
1993年 | 607篇 |
1992年 | 572篇 |
1991年 | 397篇 |
1990年 | 318篇 |
1989年 | 326篇 |
1988年 | 277篇 |
1987年 | 249篇 |
1986年 | 202篇 |
1985年 | 211篇 |
1984年 | 193篇 |
1983年 | 91篇 |
1982年 | 175篇 |
1981年 | 202篇 |
1980年 | 163篇 |
1979年 | 156篇 |
1978年 | 126篇 |
1977年 | 115篇 |
1976年 | 96篇 |
1973年 | 39篇 |
排序方式: 共有10000条查询结果,搜索用时 920 毫秒
101.
The structural possibilities of decreasing the compliance of a composite saddle-shaped cable roof having a compliant support contour are investigated. The use of a supporting contour consisting of cables joined together with tie-bars is considered as a structural method enabling one to decrease the compliance of the roof. Each cable of the support has its own initial flexure. The method is most efficient from the viewpoint of material consumption per unit of covered area relative to the increasing rigidity and prestress level of the cable net.The efficiency of the method was evaluated by a numerical experiment, which was carried out for a composite saddle-shaped cable roof 50 × 50 m in the plan. The roof was formed by two orthogonal cable groups joined with a compliant supporting contour. A hybrid composite cable based on a carbon-fiber-reinforced plastic, a glass-fiber-reinforced plastic, and steel was considered as a material for the cable net in combination with steel. The material consumption and the maximum vertical displacement of the cable net in relation to the initial geometrical characteristics of the supporting contour were obtained. A possibility of decreasing the maximum vertical displacements of the roof by 8% was established. 相似文献
102.
103.
104.
Franz-Viktor Kuhlmann 《Advances in Mathematics》2004,188(2):399-424
We consider the Zariski space of all places of an algebraic function field F|K of arbitrary characteristic and investigate its structure by means of its patch topology. We show that certain sets of places with nice properties (e.g., prime divisors, places of maximal rank, zero-dimensional discrete places) lie dense in this topology. Further, we give several equivalent characterizations of fields that are large, in the sense of F. Pop's Annals paper Embedding problems over large fields. We also study the question whether a field K is existentially closed in an extension field L if L admits a K-rational place. In the appendix, we prove the fact that the Zariski space with the Zariski topology is quasi-compact and that it is a spectral space. 相似文献
105.
MATLAB/SIMULINK在电力系统仿真中的应用 总被引:2,自引:0,他引:2
介绍了Matlab/Simulink仿真工具在电力系统仿真中的应用方法. 相似文献
106.
We investigate heteroclinic orbits between equilibria and rotating waves for scalar semilinear parabolic reaction-advection-diffusion equations with periodic boundary conditions. Using zero number properties of the solutions and the phase shift equivariance of the equation, we establish a necessary and sufficient condition for the existence of a heteroclinic connection between any pair of hyperbolic equilibria or rotating waves. 相似文献
107.
108.
109.
E. L. Kristallovich A. G. Eshimbetov N. D. Chuvylkin L. I. Belen'kii Kh. M. Shakhidoyatov 《Chemistry of Natural Compounds》2003,39(5):495-500
The principal types of electronic transitions in absorption spectra of deoxyvasicinone and its 6-amino- and 6-nitro-derivatives were determined by analyzing the electron-density distributions in excited states calculated using ZINDO/S. 相似文献