全文获取类型
收费全文 | 4310篇 |
免费 | 200篇 |
国内免费 | 37篇 |
专业分类
化学 | 2947篇 |
晶体学 | 23篇 |
力学 | 102篇 |
综合类 | 1篇 |
数学 | 759篇 |
物理学 | 715篇 |
出版年
2023年 | 24篇 |
2022年 | 37篇 |
2021年 | 111篇 |
2020年 | 98篇 |
2019年 | 85篇 |
2018年 | 80篇 |
2017年 | 64篇 |
2016年 | 154篇 |
2015年 | 147篇 |
2014年 | 154篇 |
2013年 | 276篇 |
2012年 | 321篇 |
2011年 | 346篇 |
2010年 | 230篇 |
2009年 | 226篇 |
2008年 | 325篇 |
2007年 | 290篇 |
2006年 | 277篇 |
2005年 | 219篇 |
2004年 | 172篇 |
2003年 | 150篇 |
2002年 | 139篇 |
2001年 | 65篇 |
2000年 | 66篇 |
1999年 | 47篇 |
1998年 | 33篇 |
1997年 | 28篇 |
1996年 | 34篇 |
1995年 | 34篇 |
1994年 | 28篇 |
1993年 | 25篇 |
1992年 | 25篇 |
1991年 | 18篇 |
1990年 | 24篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 15篇 |
1985年 | 23篇 |
1984年 | 20篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 15篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 5篇 |
1974年 | 8篇 |
1971年 | 5篇 |
排序方式: 共有4547条查询结果,搜索用时 125 毫秒
71.
72.
73.
J. C. Moreno J. Nilsen J. A. Koch B. J. MacGowan J. H. Scofield L. B. Da Silva 《Applied physics. B, Lasers and optics》1994,58(1):3-5
Neon-like niobium X-ray lasers have been studied using both slab and thin-foil target geometries. Niobium foils of various lengths were irradiated from both sides with two beams of the frequency-doubled Nova laser system using a line focus. We looked for gain by measuring spectrally integrated line intensities at different plasma lengths. Gain was observed in four neon-like niobium lines corresponding to 3s–3p transitions. The line profile of theJ = 0–1 line ( = 145.9 ) shows splitting due to the hyperfine effect. Improved contrast in the hyperfine structure is observed as the plasma length is increased. Hyperfine splitting may be relevant to other 3s–3p transitions in neon-like niobium as well as other neon-like X-ray laser systems. 相似文献
74.
75.
76.
77.
J. Nilsen J. C. Moreno B. J. MacGowan J. A. Koch 《Applied physics. B, Lasers and optics》1993,57(5):309-311
We report lasing for the first time in nickel on the neon-like J=01, 3p3s transition at 231 Å as well as several weaker transitions including the J=2»1 lines at 298 Å and 304 Å. Amplification is seen only when the prepulse technique of using a low intensity prepulse before the main optical drive pulse is used to illuminate the nickel target. The prepulse technique is also shown to produce lasing in copper and dramatically improve the output of the germanium laser. 相似文献
78.
79.
New Hg2+ and Cu2+ selective chromo- and fluoroionophore based on a bichromophoric azine 总被引:1,自引:0,他引:1
[graph: see text] A new probe, 1,4-bis(1-pyrenyl)-2,3-diaza-1,3-butadiene, selectively senses Hg2+ and Cu2+ through two different channels: the yellow-deep-pink color change and the enhancement of the fluorescence with the red shift of the excimer emission, which can visually be discernible by a green fluorescence in the presence of Hg2+ and an orange fluorescence in the presence of Cu2+. 相似文献
80.
Alcaide B Almendros P Alonso JM Aly MF 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(14):3415-3426
Imines derived from 4-oxoazetidine-2-carbaldehydes have been found to be versatile Diels-Alder reagents in that they exhibit two reactivity patterns. 2-Azetidinone-tethered imines undergo diastereoselective reaction with Danishefsky's diene in the presence of different Lewis acids. The effect of the amount of catalyst on the conversion rate as well as on the product ratio has been studied. Under standard reaction conditions, indium(III) chloride and zinc(II) iodide provided the best yields, and indium(III) triflate the highest diastereoselectivity in the Lewis acid promoted aza-Diels-Alder cycloaddition. Treatment of the aforementioned imines with cyclopentadiene, 2,3-dimethyl-1,3-butadiene or 3,4-dihydro-2 H-pyran led to cycloadducts arising from inverse electron-demand condensation involving the beta-lactam-tethered aryl imine as the heterodiene component. In addition, the first methodology for preparing indolizidines from beta-lactams has been developed. This process involves amide bond cleavage of the beta-lactam ring in the aza-Diels-Alder cycloadducts with concomitant cyclization. Full chirality transfer occurs when the reaction is performed with an enantiomerically pure substrate. 相似文献