全文获取类型
收费全文 | 5986篇 |
免费 | 275篇 |
国内免费 | 28篇 |
专业分类
化学 | 4751篇 |
晶体学 | 20篇 |
力学 | 114篇 |
数学 | 575篇 |
物理学 | 829篇 |
出版年
2024年 | 6篇 |
2023年 | 62篇 |
2022年 | 94篇 |
2021年 | 110篇 |
2020年 | 135篇 |
2019年 | 155篇 |
2018年 | 124篇 |
2017年 | 106篇 |
2016年 | 242篇 |
2015年 | 186篇 |
2014年 | 196篇 |
2013年 | 306篇 |
2012年 | 524篇 |
2011年 | 596篇 |
2010年 | 269篇 |
2009年 | 204篇 |
2008年 | 444篇 |
2007年 | 440篇 |
2006年 | 447篇 |
2005年 | 412篇 |
2004年 | 291篇 |
2003年 | 253篇 |
2002年 | 209篇 |
2001年 | 61篇 |
2000年 | 33篇 |
1999年 | 27篇 |
1998年 | 31篇 |
1997年 | 32篇 |
1996年 | 29篇 |
1995年 | 23篇 |
1994年 | 16篇 |
1993年 | 22篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 11篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 8篇 |
1985年 | 18篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 10篇 |
1977年 | 12篇 |
1976年 | 7篇 |
1971年 | 4篇 |
1967年 | 5篇 |
排序方式: 共有6289条查询结果,搜索用时 0 毫秒
991.
992.
993.
Ionkin AS Marshall WJ Fish BM Schiffhauer MF Davidson F 《Journal of the American Chemical Society》2007,129(29):9210-9215
A beta-oxaphosphoniumbetaine stabilized by two tert-butyl groups at the phosphonium part of the betaine and two trifluoromethyl groups at the carbon adjoined to the oxa part of the betaine was isolated and structurally characterized. Additional stabilization results from the solvation of the betaine by a parent phosphonium salt, as in 4, or by protonation with methanol, as in 10. According to X-ray analysis, the betaine exhibits a sterically strained "gauche" conformeric form, with torsion angles in the P-C-C-O moiety of 32.2 degrees for 4 and 28.1 degrees for 10. The P...O separations of 3.121 A for 4 and 3.086 A for 10 are just under the sum of the O and P van der Waals radii (3.32 A). The fast H/D exchange of alpha hydrogen atoms to the phosphonium center was observed in the solution of 10 in deuterium oxide and MeOH-d4. The beta-oxaphosphoniumbetaine has long been suspected as an intermediate in the Wittig reaction, but this is the first time a stabilized derivative has been isolated. 相似文献
994.
995.
996.
997.
Rational design and synthesis of catalytically driven nanorotors 总被引:1,自引:0,他引:1
Qin L Banholzer MJ Xu X Huang L Mirkin CA 《Journal of the American Chemical Society》2007,129(48):14870-14871
We report the design and synthesis of nanorotors based upon on-wire lithography. Because of their asymmetric structure, the nanorotors exhibit rotation in a H2O2 bath instead of linear motion. By observing the leading edge of rotation and comparing this result to the nanorotor design, we have concluded that the driving force for motion is dynamic catalytic decomposition of H2O2 which propels, rather than pulls, the nanorotor. 相似文献
998.
999.
We have developed and applied an approach to reaction discovery that takes advantage of DNA encoding, DNA-programmed assembly of substrate pairs, in vitro selection, and PCR amplification, yet does not require reaction conditions that support DNA hybridization. This system allows the simultaneous evaluation of >200 potential bond-forming combinations of substrates in a single experiment and can be applied in a range of solvent and temperature conditions. In an initial application, we applied this system to explore Au(III)-mediated chemistry and uncovered a simple, mild method for the selective Markovnikov-type hydroarylation of vinyl arenes and trisubstituted olefins with indoles. 相似文献
1000.