全文获取类型
收费全文 | 2367篇 |
免费 | 42篇 |
国内免费 | 1篇 |
专业分类
化学 | 1310篇 |
晶体学 | 10篇 |
力学 | 32篇 |
数学 | 151篇 |
物理学 | 907篇 |
出版年
2020年 | 26篇 |
2019年 | 20篇 |
2016年 | 37篇 |
2015年 | 24篇 |
2014年 | 33篇 |
2013年 | 92篇 |
2012年 | 82篇 |
2011年 | 75篇 |
2010年 | 56篇 |
2009年 | 50篇 |
2008年 | 107篇 |
2007年 | 91篇 |
2006年 | 103篇 |
2005年 | 94篇 |
2004年 | 81篇 |
2003年 | 51篇 |
2002年 | 46篇 |
2001年 | 51篇 |
2000年 | 41篇 |
1999年 | 23篇 |
1998年 | 29篇 |
1997年 | 34篇 |
1996年 | 40篇 |
1995年 | 34篇 |
1994年 | 43篇 |
1993年 | 56篇 |
1992年 | 49篇 |
1991年 | 25篇 |
1990年 | 37篇 |
1989年 | 26篇 |
1988年 | 25篇 |
1987年 | 40篇 |
1986年 | 34篇 |
1985年 | 36篇 |
1984年 | 39篇 |
1983年 | 22篇 |
1981年 | 20篇 |
1980年 | 24篇 |
1979年 | 17篇 |
1978年 | 29篇 |
1977年 | 39篇 |
1976年 | 33篇 |
1975年 | 27篇 |
1974年 | 20篇 |
1973年 | 35篇 |
1970年 | 20篇 |
1957年 | 30篇 |
1956年 | 16篇 |
1955年 | 29篇 |
1954年 | 21篇 |
排序方式: 共有2410条查询结果,搜索用时 15 毫秒
41.
The restricted rotation about the partial C,N double bond in 2-chloro-6-NR2-pyran-4-ones is discussed in the light of NMR spectroscopic data and theoretical calculations.Ab initio calculations at the HF/6-31G* level were carried out using a continuum model to take solvent effects into account. The delocalization of-electron density [described by natural bond orbital analysis (NBO)] was applied to determine the degree of conjugation in the ground state (GS) and in the transition state (TS) for the restricted rotation of the compounds studied. The reason for the different barriers to rotation of the NR2 substituents (pyrrolidino > dimethylamino > morpholidino > piperidino) at the 2-chloro-pyran-4-one ring appears to be the different steric hindrance of the NR2 substituents in the GS for the restricted rotation. 相似文献
42.
D. Grunenberg D. Sommer K. H. Koch 《Fresenius' Journal of Analytical Chemistry》1995,353(5-8):514-520
For the analysis of surfaces with poor conductivity the use of the direct current sputter process, usual in SNMS, produces unreproducible depth profiles with often widened transition widths. An efficient method for eliminating static charging in the case of non-coducting samples is the use of a high-frequency discharge. By comparison of the direct current mode with high frequency mode it is shown, that the use of SNMS with HF sputtering is the universal analysis method for most matrices, technical surfaces as well as oxidic materials. For non-conducting or poorly conducting samples, however, matrix-adjusted factors are to be used. 相似文献
43.
44.
45.
46.
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
47.
48.
49.
50.