全文获取类型
收费全文 | 3953篇 |
免费 | 445篇 |
国内免费 | 311篇 |
专业分类
化学 | 2587篇 |
晶体学 | 27篇 |
力学 | 197篇 |
综合类 | 20篇 |
数学 | 488篇 |
物理学 | 1390篇 |
出版年
2023年 | 50篇 |
2022年 | 119篇 |
2021年 | 98篇 |
2020年 | 133篇 |
2019年 | 98篇 |
2018年 | 101篇 |
2017年 | 94篇 |
2016年 | 130篇 |
2015年 | 138篇 |
2014年 | 165篇 |
2013年 | 236篇 |
2012年 | 322篇 |
2011年 | 290篇 |
2010年 | 216篇 |
2009年 | 193篇 |
2008年 | 255篇 |
2007年 | 211篇 |
2006年 | 193篇 |
2005年 | 161篇 |
2004年 | 128篇 |
2003年 | 113篇 |
2002年 | 104篇 |
2001年 | 90篇 |
2000年 | 102篇 |
1999年 | 74篇 |
1998年 | 66篇 |
1997年 | 55篇 |
1996年 | 75篇 |
1995年 | 56篇 |
1994年 | 60篇 |
1993年 | 52篇 |
1992年 | 54篇 |
1991年 | 36篇 |
1990年 | 28篇 |
1989年 | 41篇 |
1988年 | 37篇 |
1987年 | 31篇 |
1986年 | 41篇 |
1985年 | 30篇 |
1984年 | 35篇 |
1983年 | 26篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 22篇 |
1979年 | 12篇 |
1978年 | 11篇 |
1977年 | 15篇 |
1976年 | 17篇 |
1975年 | 17篇 |
1973年 | 9篇 |
排序方式: 共有4709条查询结果,搜索用时 15 毫秒
91.
92.
We have observed a fixed wavelength emission at 178.7 nm in sodium vapour under 578.7 nm two-photon resonance excitation. The proposed non-linear wave mixing scheme is described by 178.7 nm = 2L + 465.7 nm; where 178.7 is the 178.7 nm photon frequency, L is the laser-photon frequency, and 465.7 is the 465.7 nm photon frequency. This 465.7 nm emission comes from another six-wave mixing process involving two hyper-electronic Raman scattering photons. The excitation spectrum of the 178.7 nm emission has a typical multiwave mixing pattern with a competing effect appearing at higher temperatures under two-photon resonance excitation. Numerical analysis indicates that this vacuum ultraviolet emission has a poor phase-match condition that will depress the emission intensity to a certain extent. This makes the observation more difficult compared with other reported four-wave mixing generated emissions. Fortunately, on the one hand, it is enhanced by quasi-auto-ionization resonance when the 3s–5s transition is coupled to the sodium continuum by a 330.2 nm photon. On the other hand, its wavelength sits so close to the sodium Cooper minimum that weak absorption will not suppress this vacuum ultraviolet emission further. 相似文献
93.
94.
95.
96.
97.
The loss of three CO groups from derivatives of π-C6H5COC5H4Mn(CO)3 is a two-step mechanism in which the loss of two CO groups is followed by a third. Subsequent fragmentations generally involve rearrangement processes which often result in ring closure within the organic substrate. The central metal atoms plays an important part in such rearrangement processes and the positive charge can reside either on the metal or the ligand depending on the nature of the ligand. Fragmentation patterns are proposed for these systems. 相似文献
98.
99.
A linear response time-dependent density functional theory is described and used to calculate the dynamic polarizabilities and van der Waals C(6) coefficients of complex atom pairs. We present values of C(6) for dimers of main group atoms and the first row of transition metal atoms. 相似文献
100.