全文获取类型
收费全文 | 5512篇 |
免费 | 104篇 |
国内免费 | 14篇 |
专业分类
化学 | 3632篇 |
晶体学 | 46篇 |
力学 | 79篇 |
数学 | 917篇 |
物理学 | 956篇 |
出版年
2019年 | 41篇 |
2016年 | 81篇 |
2015年 | 61篇 |
2014年 | 81篇 |
2013年 | 162篇 |
2012年 | 163篇 |
2011年 | 190篇 |
2010年 | 116篇 |
2009年 | 107篇 |
2008年 | 180篇 |
2007年 | 173篇 |
2006年 | 178篇 |
2005年 | 166篇 |
2004年 | 174篇 |
2003年 | 151篇 |
2002年 | 144篇 |
2001年 | 96篇 |
2000年 | 122篇 |
1999年 | 85篇 |
1998年 | 83篇 |
1997年 | 76篇 |
1996年 | 96篇 |
1995年 | 124篇 |
1994年 | 105篇 |
1993年 | 76篇 |
1992年 | 88篇 |
1991年 | 84篇 |
1990年 | 76篇 |
1989年 | 90篇 |
1988年 | 93篇 |
1987年 | 75篇 |
1986年 | 76篇 |
1985年 | 110篇 |
1984年 | 82篇 |
1983年 | 98篇 |
1982年 | 111篇 |
1981年 | 98篇 |
1980年 | 88篇 |
1979年 | 99篇 |
1978年 | 76篇 |
1977年 | 77篇 |
1976年 | 67篇 |
1975年 | 61篇 |
1974年 | 72篇 |
1973年 | 72篇 |
1972年 | 44篇 |
1971年 | 56篇 |
1970年 | 41篇 |
1968年 | 39篇 |
1966年 | 39篇 |
排序方式: 共有5630条查询结果,搜索用时 15 毫秒
21.
Werner Fudickar 《Tetrahedron》2006,62(46):10639-10646
The photooxygenation of homochiral cyclohexene ketals, which are easily available from 2-cyclohexenone and l-tartrates, affords hydroperoxides and after reduction the corresponding allylic alcohols in good yields and high regioselectivities. This can be rationalized by electronic repulsions in a perepoxide intermediate and provides evidence for unfavorable 1,3 diaxial interactions with a dioxolane oxygen atom. Only low stereoselectivities were observed, due to the flexibility of the cyclohexene ring. However, the diastereomers could be separated and after cleavage of the auxiliary, 4-hydroxy-2-cyclohexen-1-one was isolated in enantiomerically pure form, which can serve as a building block for natural product synthesis. 相似文献
22.
23.
24.
25.
26.
Vincenzo Piazza Vittorio PellegriniFabio Beltram Werner Wegscheider 《Solid State Communications》2003,127(2):163-168
Time-dependent capacitance measurements reveal an unstable phase of electrons in gallium arsenide quantum well that occurs when two Landau levels with opposite-spin are brought close to degeneracy by applying a gate voltage. This phase emerges below a critical temperature and displays a peculiar non-equilibrium dynamical evolution. The relaxation dynamics is found to follow a stretched-exponential behaviour and correlates with hysteresis loops observed by sweeping the magnetic field. These experiments indicate that metastable randomly distributed magnetic domains with peculiar excitations are involved in the relaxation process in a way that is equivalently tunable by a change in gate voltage or temperature. 相似文献
27.
The surface body is a generalization of the floating body. Its relation to p-affine surface area is studied. 相似文献
28.
29.
An experimental investigation to assess the effect of tumbling by hard-steel, blunt-faced cylindrical projectiles on the impact response of thin 4130 steel and polycarbonate target plates was performed. Deformation and failure phenomena were observed and discussed; comparisons of the results with analytical models and numerical stimulation, described in a previous paper, were also performed for the steel targets. The final velocity of the projectile and the crater length in the target were correlated with the striker impact angle (or yaw angle with a zero oblique angle); reasonable agreement was attained among the experimental, analytical and numerical results. It was found that an increase of the impact angle can increase the velocity drop and the crater length markedly. The increase tends to be stabilized after the impact angle exceeds 50° and the consequences in such a case are almost the same as in side-on impact. 相似文献
30.