全文获取类型
收费全文 | 502475篇 |
免费 | 3872篇 |
国内免费 | 1490篇 |
专业分类
化学 | 245973篇 |
晶体学 | 7403篇 |
力学 | 26229篇 |
综合类 | 13篇 |
数学 | 80062篇 |
物理学 | 148157篇 |
出版年
2020年 | 3513篇 |
2019年 | 3889篇 |
2018年 | 15150篇 |
2017年 | 14861篇 |
2016年 | 13248篇 |
2015年 | 5331篇 |
2014年 | 7496篇 |
2013年 | 18331篇 |
2012年 | 17412篇 |
2011年 | 26553篇 |
2010年 | 17185篇 |
2009年 | 17296篇 |
2008年 | 21721篇 |
2007年 | 23938篇 |
2006年 | 15162篇 |
2005年 | 14652篇 |
2004年 | 13877篇 |
2003年 | 13041篇 |
2002年 | 11906篇 |
2001年 | 12455篇 |
2000年 | 9730篇 |
1999年 | 7448篇 |
1998年 | 6429篇 |
1997年 | 6333篇 |
1996年 | 5988篇 |
1995年 | 5527篇 |
1994年 | 5508篇 |
1993年 | 5172篇 |
1992年 | 5803篇 |
1991年 | 5886篇 |
1990年 | 5688篇 |
1989年 | 5380篇 |
1988年 | 5514篇 |
1987年 | 5453篇 |
1986年 | 5140篇 |
1985年 | 6806篇 |
1984年 | 7193篇 |
1983年 | 5981篇 |
1982年 | 6287篇 |
1981年 | 6177篇 |
1980年 | 6046篇 |
1979年 | 6101篇 |
1978年 | 6437篇 |
1977年 | 6366篇 |
1976年 | 6449篇 |
1975年 | 5954篇 |
1974年 | 6017篇 |
1973年 | 6277篇 |
1972年 | 4297篇 |
1971年 | 3509篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
Yu. P. Andreichikov M. I. Knyazhanskii Ya. R. Tymyanskii G. E. Trukhan G. N. Dorofeenko 《Chemistry of Heterocyclic Compounds》1974,10(6):696-698
The electronic spectra of a number of benzylidene derivatives of N-aminoarylpyridinium perchlorates are associated with absorption localized on the individual pyridinium and azomethine fragments and with intramolecular charge transfer (ICT) from the azomethine fragment to the pyridinium ring. The luminescence is associated with the latter process. The photochromism is due to proton transfer in the excited state of the azomethine fragment, which competes with ICT, and is also due to structural factors. 相似文献
953.
954.
955.
956.
Alan D. Potoff Bertrand L. Chamberland Lewis Katz 《Journal of solid state chemistry》1973,8(3):234-237
A single crystal study of hydrothermally prepared eight-layer BaMnO3 has been carried out which confirms the (Zhdanov notation) 121121 layer stacking scheme for the BaO3 layers. The MnO6 octahedra share faces in strings of four, and these strings are connected to each other by corner sharing. The compound has an hexagonal unit cell of dimensions a = 5.667 ± 0.003 and c = 18.738 ± 0.009 Å, probable space group . Its structure has been determined from 352 independent reflections, of which 242 were considered observed, collected manually by a counter technique and refined to a conventional R value of 0.079. 相似文献
957.
G. Innorta S. Torroni S. Pignataro V. Mancini 《Journal of mass spectrometry : JMS》1973,7(12):1399-1406
The mass spectra of a series of substituted diphenylmethanes were obtained. The mass spectral features were compared with those of the corresponding 1,2 diphenylethanes and discussed in terms of the factors which influence the electron-impact fragmentation. In the series examined, it is shown that the activation energy is the most important factor in determining cracking patterns. The meaning of the averaged rate constants is criticised. 相似文献
958.
Electrical resistivity (4.2–800°K) and magnetic susceptibility (4.2–500°K) measurements are carried out on Cu3–xAs, Cu5–xAs2 and the recently obtained, tetragonal Cu2As. All three compounds appear to be metallic conductors, but have high residual resistances because of the large defect concentrations (resulting from non-stoichiometry and preparation method). Cu3–xAs is diamagnetic; Cu5–xAs2 is Pauli-paramagnetic; Cu2As has a very small, constant, positive susceptibility above room temperature and a more pronounced Curie-Weiss behaviour at lower temperatures. The Pauli-paramagnetic contributions have been estimated. A slight anomaly in the electric and magnetic behaviour of Cu3–xAs is observed at 220°K. To clarify the high-temperature phenomena, a series of D.T.A. and X-ray experiments has also been carried out. 相似文献
959.
960.