全文获取类型
收费全文 | 358199篇 |
免费 | 2653篇 |
国内免费 | 739篇 |
专业分类
化学 | 187764篇 |
晶体学 | 5872篇 |
力学 | 16612篇 |
综合类 | 18篇 |
数学 | 38993篇 |
物理学 | 112332篇 |
出版年
2020年 | 3305篇 |
2019年 | 3893篇 |
2018年 | 5163篇 |
2017年 | 5366篇 |
2016年 | 7103篇 |
2015年 | 3798篇 |
2014年 | 6697篇 |
2013年 | 15267篇 |
2012年 | 11318篇 |
2011年 | 13665篇 |
2010年 | 10479篇 |
2009年 | 10598篇 |
2008年 | 12683篇 |
2007年 | 12545篇 |
2006年 | 11482篇 |
2005年 | 10288篇 |
2004年 | 9608篇 |
2003年 | 8808篇 |
2002年 | 8740篇 |
2001年 | 10368篇 |
2000年 | 7744篇 |
1999年 | 5976篇 |
1998年 | 5046篇 |
1997年 | 4876篇 |
1996年 | 4574篇 |
1995年 | 4245篇 |
1994年 | 4119篇 |
1993年 | 3954篇 |
1992年 | 4631篇 |
1991年 | 4840篇 |
1990年 | 4685篇 |
1989年 | 4758篇 |
1988年 | 4671篇 |
1987年 | 4708篇 |
1986年 | 4409篇 |
1985年 | 5631篇 |
1984年 | 5654篇 |
1983年 | 4631篇 |
1982年 | 4776篇 |
1981年 | 4751篇 |
1980年 | 4367篇 |
1979年 | 4964篇 |
1978年 | 5100篇 |
1977年 | 5247篇 |
1976年 | 5167篇 |
1975年 | 4781篇 |
1974年 | 4668篇 |
1973年 | 4793篇 |
1972年 | 3622篇 |
1968年 | 3187篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
M. Zh. Ovakimyan S. K. Barsegyan A. S. Pogosyan N. M. Kikoyan M. G. Indzhikyan 《Russian Journal of General Chemistry》2006,76(11):1757-1759
Dehydrogenation of 1-(diphenylphosphinoyl)-2-hydrazino-substituted ethanes and N-butyl-N′-phenylhydrazine to the corresponding hydrazone derivatives is performed. Both reactions were established to involve predominantly, if not exclusively, an azo intermediate. 相似文献
992.
Devyatkina T. I. Gun'ko Yu. L. Mikhalenko M. G. 《Russian Journal of Applied Chemistry》2001,74(7):1122-1125
The influence exerted by addition of -hydroxynaphthoic acid and combined additive Hg + Pb + -hydroxynaphthoic acid on the corrosion and self-discharge of a porous zinc electrode in alkali solution was studied. 相似文献
993.
Veliev M. G. Chalabieva A. Z. Shatirova M. I. Akperova E. G. 《Russian Journal of Organic Chemistry》2003,39(6):825-830
Diene condensation of cyclopentadiene with 2-substituted allylacetylenes occurs nonselectively at a double and triple bonds; therewith the dienophile activity grows in parallel with the electron-withdrawing properties of the substituent. Depending on electronic character of functional groups the reaction proceeds as neutral diene synthesis. The relative activity of cyclopentadiene and 1,3-cyclohexadiene in reactions with allylacetylenes is essentially governed by the different distance between the 1,4-reactive sites in these systems. 相似文献
994.
S. L. Bogza K. I. Kobrakov M. Yu. Zubritskii S. Yu. Suikov V. I. Dulenko 《Chemistry of Heterocyclic Compounds》1997,33(1):74-77
Treatment of N-phenyl-2-(1-R-indol-3-yl)succinimides with acetyl perchlorate leads to acylation of the benzene ring of the indole substituent.L. M. Litvinenko Institute of Physico-Organic and Carbon Chemistry, Ukrainian Academy of Sciences, Donetsk 340114. A. N. Kosygin State Textile Academy, Moscow 117918, GSP-1. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 85–88, January, 1997. 相似文献
995.
996.
The catalytic action of acid solutions involves an equilibrium step in the formation of a reactive complex of reactant molecules with catalyst entities. The relative concentrations of these complexes are determined by using thermodynamic parameters (acidity functions and activities of catalyst components). Data on the structure of complexes with strong H-bonds can be obtained from the vibrational spectra of these species. These data are required for establishing the mechanisms of catalytic reactions and for predicting the catalytic properties of acid solutions containing these complexes. 相似文献
997.
I. K. Buchina O. Kh. Kholbekov A. A. Abduvakhabov 《Chemistry of Natural Compounds》1994,30(1):121-123
The synergisic properties of docosa-5Z, 17Z-diene — one of the by-products of the synthesis of the synthetic cotton bollworm pheromone — have been revealed.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax 627071. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 130–132, January–February, 1994. 相似文献
998.
Amorphous precursors for PbZrO3 and PbTiO3 ceramics were prepared from lead acetate and the transition metaln-propoxide inn-propanol orn-butoxide inn-butanol and hydrolysed with an excess of water.
According to GLC and TGA/EGA analyses, the type of alkoxide group influences distinctly the structure of heterometallic precursors,
i.e., oxo or acetate bridging, and the amounts of hydroxyl and organic groups bound to the metal network.
The local environments of metal atoms in the amorphous precursors were also studied by EXAFS. The analysis reveals that in
Pb−Zr precursors alkoxide groups modify the coordination spheres of the zirconium atoms. Conversely, local environments of
both lead and titanium atoms within the analysed range of 3.4 A depend weakly on the type of alkoxide used. 相似文献
999.
1000.
A carborane-containing stable simple enol — 1-2-isopropyl-o-carboran-I-yl)-1-phenyl2-mesityl-2-lrydroxyctlrylcne — has been synthesized. This enol does not isomerize to the starting ketone or keto-enol mixture even after prolonged heating in benzene in the presence of CF3COOH.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1561–1563, June, 1996. 相似文献