全文获取类型
收费全文 | 527034篇 |
免费 | 5904篇 |
国内免费 | 1615篇 |
专业分类
化学 | 268759篇 |
晶体学 | 7292篇 |
力学 | 25421篇 |
综合类 | 13篇 |
数学 | 82733篇 |
物理学 | 150335篇 |
出版年
2021年 | 4059篇 |
2020年 | 4571篇 |
2019年 | 4871篇 |
2018年 | 15912篇 |
2017年 | 15611篇 |
2016年 | 15282篇 |
2015年 | 6959篇 |
2014年 | 9473篇 |
2013年 | 21861篇 |
2012年 | 20467篇 |
2011年 | 30252篇 |
2010年 | 19462篇 |
2009年 | 19535篇 |
2008年 | 24915篇 |
2007年 | 26605篇 |
2006年 | 17587篇 |
2005年 | 16743篇 |
2004年 | 15700篇 |
2003年 | 14315篇 |
2002年 | 13131篇 |
2001年 | 13936篇 |
2000年 | 10609篇 |
1999年 | 8275篇 |
1998年 | 6894篇 |
1997年 | 6558篇 |
1996年 | 6487篇 |
1995年 | 5716篇 |
1994年 | 5616篇 |
1993年 | 5482篇 |
1992年 | 6045篇 |
1991年 | 6081篇 |
1990年 | 5804篇 |
1989年 | 5610篇 |
1988年 | 5623篇 |
1987年 | 5504篇 |
1986年 | 5213篇 |
1985年 | 6727篇 |
1984年 | 6830篇 |
1983年 | 5415篇 |
1982年 | 5491篇 |
1981年 | 5470篇 |
1980年 | 5054篇 |
1979年 | 5448篇 |
1978年 | 5580篇 |
1977年 | 5455篇 |
1976年 | 5396篇 |
1975年 | 4976篇 |
1974年 | 4934篇 |
1973年 | 4962篇 |
1972年 | 3504篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Aziridines react with trifluoromethyl hypofluorite at ? 40°C to produce mixtures of 1-(aziridine)carbonyl fluoride and 1-fluoroaziridine , the proportions of which depend on steric effects. Several compounds react with starting materials to give 1, 1′-(carbonyl)bisaziridines . Most compounds and all compounds are isolated. Chemical properties and ir and nmr data of , , are described; the formation of an isocyanate and a substituted urea from a compound is observed. A mechanism for this reaction is suggested. 相似文献
992.
Complete determination of all proton hyperfine splitting constants in magnitude and sign, and their specific assignment in two stable rigid nitroxides are presented. Long range γ-splitting has been calculated by an MO method (INDO approximation) and by a modification of a valence bond calculation. The results are consistent with a non-planar and rapidly inverting NO group. 相似文献
993.
994.
Dissociation rates of N2 in N2-H2 mixtures and of H2 in Ar-H2 mixtures have been calculated for conditions typical of gas discharges. The results have been obtained by solving a system of master equations including V-V (vibration-vibration), V-T (vibration-translation) and e-V (electron-vibration) energy exchanges. The results show that these rates are much smaller than the corresponding ones for pure gases, as a consequence of the increased importance of V-T processes. A simplified model, which takes into account the main features of the distribution of vibrational levels in an electrical discharge, has been built up to rationalize the present results as well as those derived in our previous work. 相似文献
995.
A. B. Trofimov B. A. Trofimov N. M. Vitkovskaya M. V. Sigalov 《Chemistry of Heterocyclic Compounds》1991,27(6):583-590
The electron and conformational structures, as well as the internal rotation, of 2-(2-furyl)pyrrole and its -protonated forms were studied by the MNDO method with complete optimization of the geometry. In conformity with the experiments (PMR), the two delocalized cations with a cis orientation of the heteroatoms that are formed as a result of protonation of the pyrrole or furan ring have the greatest and virtually equal stabilities (H=738.7 and 740.6 kJ/mole).Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 746–753, June, 1991. 相似文献
996.
V. M. Rogovik N. I. Delyagina E. I. Mysov V. F. Cherstkov S. R. Sterlin L. S. German 《Russian Chemical Bulletin》1990,39(9):1879-1882
-Fluorosulfatoperfluoroethyl isopropyl ketone I and fluorosulfatopentafluoroacetone II react with alkali metal chlorides and bromides to form the corresponding -haloperfluoro ketones as a result of direct nucleophilic substitution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2066–2069, September, 1990. 相似文献
997.
998.
999.
1000.