全文获取类型
收费全文 | 585734篇 |
免费 | 9440篇 |
国内免费 | 5890篇 |
专业分类
化学 | 303987篇 |
晶体学 | 8336篇 |
力学 | 29831篇 |
综合类 | 339篇 |
数学 | 76050篇 |
物理学 | 182521篇 |
出版年
2021年 | 6552篇 |
2020年 | 7130篇 |
2019年 | 7899篇 |
2018年 | 10066篇 |
2017年 | 10031篇 |
2016年 | 13693篇 |
2015年 | 7999篇 |
2014年 | 12805篇 |
2013年 | 26794篇 |
2012年 | 21938篇 |
2011年 | 25425篇 |
2010年 | 19132篇 |
2009年 | 18986篇 |
2008年 | 23540篇 |
2007年 | 23069篇 |
2006年 | 21046篇 |
2005年 | 18778篇 |
2004年 | 17346篇 |
2003年 | 15558篇 |
2002年 | 15570篇 |
2001年 | 16270篇 |
2000年 | 12581篇 |
1999年 | 9825篇 |
1998年 | 8596篇 |
1997年 | 8280篇 |
1996年 | 7763篇 |
1995年 | 6973篇 |
1994年 | 7018篇 |
1993年 | 6706篇 |
1992年 | 6990篇 |
1991年 | 7453篇 |
1990年 | 7172篇 |
1989年 | 7003篇 |
1988年 | 6749篇 |
1987年 | 6522篇 |
1986年 | 6256篇 |
1985年 | 7837篇 |
1984年 | 8160篇 |
1983年 | 6893篇 |
1982年 | 7156篇 |
1981年 | 6629篇 |
1980年 | 6293篇 |
1979年 | 6844篇 |
1978年 | 7088篇 |
1977年 | 6972篇 |
1976年 | 7003篇 |
1975年 | 6681篇 |
1974年 | 6511篇 |
1973年 | 6834篇 |
1972年 | 5060篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
971.
972.
The corresponding 2,3-diphenyl[3,2-a]pyrimidinium salts were obtained by the condensation of 4,5-diphenyl-2-aminothiazole perchlorate with -diketones, -chlorovinyl ketones, -chlorovinyl aldehydes, and 1,1,3,3-tetraethoxypropane. The PMR spectra were used to prove the structures of the compounds obtained, particularly to select the structures of the isomeric salts obtained in the condensation with unsymmetrical -diketones, -chlorovinyl ketones, and -chlorovinyl aldehydes. As a rule, the latter give one isomer — the -unsubstituted (relative to the bridge nitrogen atom) derivative.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 629–631, May, 1972. 相似文献
973.
G. A. Gailyunas G. V. Nurtdinova V. P. Yur'ev G. A. Tolstikov S. R. Rafikov 《Russian Chemical Bulletin》1982,31(4):806-812
Conclusions The high catalytic activity of (CH2=CHSiR3)·Fe(CO)4 complexes was demonstrated in the reaction of vinylsilanes with polyhalomethanes and hydrosilanes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 914–920, April, 1982. 相似文献
974.
William W. Paudler Richard A. Vandahm Young N. Park 《Journal of heterocyclic chemistry》1972,9(1):81-85
The diazaanalog of “cycl[3,2,2]azine”, “1,4-diazacycl[3,2,2]azine” (1,4,7b-triazacyclopent-[cd]indene) and its 2-methyl derivative were prepared. These compounds are subject to facile acid-catalyzed hydrolysis affording substituted imidazo[1,2-a]pyridines. 相似文献
975.
-(2-Carboxy-5-chlorophenylamino)propionic acid cyclizes in acetic anhydride to form 4-chloro-2-(2,4-dioxopiperidino)benzoic acid, which subsequently undergoes conversion into its lactone. Under the same conditions, -[acetyl(2-carboxy-5-chlorophenyl)amino]-propionitrile forms 7-chloro-1--cyanoethyl-1,2,3,4-tetrahydroquinoline-2,4-dione. The structures of the compounds obtained were confirmed by their IR, UV, and PMR spectra. An evaluation of the stability of the ketonic and enolic forms of the compounds obtained on the basis of calculations by Hückel's method has been made.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 7, pp. 879–884, July, 1970. 相似文献
976.
977.
978.
The use of pH gradients in borate buffer with a polyhydroxy compound for separation of proteins in a free-flow electrophoretic apparatus is outlined. The composition of the pH gradients, the free-flow apparatus design and its operation, and the main causes of failures in the protein separation are considered. 相似文献
979.
980.
Conclusions Charge separation in solutions of liposomes sensitized by MP at low temperatures and apparently also at 20°C takes place according to a mechanism of two-quantum photoionization of dimeric molecules of the metalloporphyrins.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 2, pp. 277–282, February, 1985. 相似文献