全文获取类型
收费全文 | 5977篇 |
免费 | 198篇 |
国内免费 | 31篇 |
专业分类
化学 | 4722篇 |
晶体学 | 54篇 |
力学 | 81篇 |
数学 | 363篇 |
物理学 | 986篇 |
出版年
2023年 | 23篇 |
2022年 | 39篇 |
2021年 | 59篇 |
2020年 | 69篇 |
2019年 | 101篇 |
2018年 | 54篇 |
2017年 | 48篇 |
2016年 | 116篇 |
2015年 | 104篇 |
2014年 | 137篇 |
2013年 | 299篇 |
2012年 | 331篇 |
2011年 | 409篇 |
2010年 | 224篇 |
2009年 | 252篇 |
2008年 | 397篇 |
2007年 | 394篇 |
2006年 | 435篇 |
2005年 | 392篇 |
2004年 | 355篇 |
2003年 | 291篇 |
2002年 | 288篇 |
2001年 | 104篇 |
2000年 | 83篇 |
1999年 | 68篇 |
1998年 | 75篇 |
1997年 | 68篇 |
1996年 | 69篇 |
1995年 | 59篇 |
1994年 | 37篇 |
1993年 | 48篇 |
1992年 | 38篇 |
1991年 | 41篇 |
1990年 | 22篇 |
1989年 | 23篇 |
1988年 | 29篇 |
1987年 | 38篇 |
1986年 | 51篇 |
1985年 | 67篇 |
1984年 | 51篇 |
1983年 | 29篇 |
1982年 | 55篇 |
1981年 | 55篇 |
1980年 | 47篇 |
1979年 | 40篇 |
1978年 | 37篇 |
1977年 | 39篇 |
1976年 | 27篇 |
1975年 | 19篇 |
1973年 | 24篇 |
排序方式: 共有6206条查询结果,搜索用时 93 毫秒
991.
Direct arylation of aryl(azaaryl)methanes with aryl halides takes place at the benzylic position in the presence of a hydroxide base under palladium catalysis to yield triarylmethanes. 相似文献
992.
993.
994.
995.
Solid-phase synthesis of epigallocatechin gallate derivatives 总被引:1,自引:0,他引:1
Tanaka H Miyoshi H Chuang YC Ando Y Takahashi T 《Angewandte Chemie (International ed. in English)》2007,46(31):5934-5937
996.
997.
998.
Ikeda S Kobayashi H Ikoma Y Harada T Torimoto T Ohtani B Matsumura M 《Physical chemistry chemical physics : PCCP》2007,9(48):6319-6326
A novel core-shell composite photocatalyst, commercially available titanium(IV) oxide (TiO(2)) particles directly incorporated into a hollow amorphous silica shell, was fabricated by successive coating of TiO(2) with a carbon layer and a silica layer followed by heat treatment to remove the carbon layer. The composite induced efficient photocatalytic reactions when relatively small substrates were used, such as methanol dehydration and decomposition of acetic acid, without any reduction in the intrinsic activity of original TiO(2), but did not exhibit efficient photocatalytic activity for decomposition of large substrates, methylene blue and polyvinyl alcohol. The unique size-selective properties of the composites are due to their structural characteristics, i.e., the presence of a pore system and a void space in the silica shell and between the shell and medial TiO(2) particles, respectively. The loading of alkylsilyl groups on the surface of the composite led to highly photostable floatability: the floated sample also induced efficient photocatalytic reaction for decomposition of acetic acid while retaining floatation at the gas/water interface. 相似文献
999.
The first enantioselective total synthesis of isishippuric acid B bearing a novel 4,5-seco-6-norquadrane skeleton was accomplished from (R)-citronellal with use of a Diels-Alder cycloaddition and an intramolecular Michael addition as the ring-forming steps. Comparison of the optical rotation of the synthetic material with that of the natural product confirmed the absolute configuration of isishippuric acid B to be 1R, 2R, 8R, and 11R. 相似文献
1000.
Natural enantiomers of unique tricyclic sesquiterpenoids, valeriananoids A-C 1-3, have been synthesized starting from bicyclo[2.2.2]octane-2,5-dione derivative 11, which was obtained by diastereoselective catalytic domino Michael reaction of oxophorone 5 with 8-phenylmenthyl acrylate 10 by LDA or silica-gel-base (NMAP-Li). The tricyclic ring was closed selectively by intramolecular 6-endo-trig mode cyclization of the ketyl radical, which was generated from keto-allylether 25 by either lithium or sodium naphthalenide. 相似文献