全文获取类型
收费全文 | 272篇 |
免费 | 21篇 |
国内免费 | 2篇 |
专业分类
化学 | 252篇 |
力学 | 4篇 |
数学 | 9篇 |
物理学 | 30篇 |
出版年
2023年 | 3篇 |
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 10篇 |
2019年 | 9篇 |
2018年 | 12篇 |
2017年 | 1篇 |
2016年 | 15篇 |
2015年 | 4篇 |
2014年 | 7篇 |
2013年 | 11篇 |
2012年 | 10篇 |
2011年 | 27篇 |
2010年 | 9篇 |
2009年 | 5篇 |
2008年 | 16篇 |
2007年 | 13篇 |
2006年 | 20篇 |
2005年 | 12篇 |
2004年 | 14篇 |
2003年 | 7篇 |
2002年 | 15篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 4篇 |
1998年 | 2篇 |
1997年 | 4篇 |
1996年 | 9篇 |
1995年 | 2篇 |
1994年 | 3篇 |
1993年 | 2篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1980年 | 1篇 |
1976年 | 2篇 |
1975年 | 1篇 |
1968年 | 3篇 |
1967年 | 1篇 |
1965年 | 1篇 |
1930年 | 1篇 |
1902年 | 1篇 |
排序方式: 共有295条查询结果,搜索用时 62 毫秒
61.
Cover Picture: Dipole Effects on Electron Transfer are Enormous (Angew. Chem. Int. Ed. 38/2018) 下载免费PDF全文
62.
Dr. Maciej Krzeszewski Eli M. Espinoza Dr. Ctirad Červinka James B. Derr John A. Clark Dr. Dan Borchardt Prof. Gregory J. O. Beran Prof. Daniel T. Gryko Prof. Valentine I. Vullev 《Angewandte Chemie (International ed. in English)》2018,57(38):12365-12369
Molecular dipoles present important, but underutilized, methods for guiding electron transfer (ET) processes. While dipoles generate fields of Gigavolts per meter in their vicinity, reported differences between rates of ET along versus against dipoles are often small or undetectable. Herein we show unprecedentedly large dipole effects on ET. Depending on their orientation, dipoles either ensure picosecond ET, or turn ET completely off. Furthermore, favorable dipole orientation makes ET possible even in lipophilic medium, which appears counterintuitive for non‐charged donor–acceptor systems. Our analysis reveals that dipoles can substantially alter the ET driving force for low solvent polarity, which accounts for these unique trends. This discovery opens doors for guiding forward ET processes while suppressing undesired backward electron transduction, which is one of the holy grails of photophysics and energy science. 相似文献
63.
64.
Valentine P Ananikov Denis A Malyshev Grigory G Aleksandrov 《Journal of organometallic chemistry》2003,679(2):162-172
A mechanistic study of the hydroselenation of alkynes catalyzed by Pd(PPh3)4 and Pt(PPh3)4 has shown that the palladium complex gives products of both SeH and SeSe bond addition to the triple bond of alkynes, while the platinum complex selectively catalyzes SeH bond addition. The key intermediate of PhSeH addition to the metal center, namely Pt(H)(SePh)(PPh3)2, was detected by 1H-NMR spectroscopy. The analogous palladium complex rapidly decomposes with evolution of molecular hydrogen. A convenient method was developed for the preparation of Markovnikov hydroselenation products H2CC(SePh)R, and the scope of this reaction was investigated. The first X-ray structure of the Markovnikov product H2CC(SePh)CH2N+HMe2·HOOCCOO− is reported. 相似文献
65.
Valentine G. Nenajdenko Georgy N. Varseev Alexey V. Shastin 《Journal of fluorine chemistry》2004,125(9):1339-1345
An olefination of hydrazones of aromatic aldehydes by CBrF2-CBrF2 under copper catalysis was investigated. In situ prepared aldehydes hydrazones were converted to (3-bromo-2,2,3,3-tetrafluoropropyl)arenes by reaction with CBrF2-CBrF2 in the presence of CuCl. Subsequent elimination of HF by sodium hydroxide resulted in stereospecific formation of fluorocontaining alkenes. Elimination proceeds stereoselectively, only Z-isomers of alkenes are formed. Elimination of two molecules of HF from (3-bromo-2,2,3,3-tetrafluoropropyl)arenes by treatment with potassium tert-butoxide leads to formation of (bromodifluoromethyl)alkynes. As a result a simple and efficient transformation of aromatic aldehydes to range of various fluorinated alkanes, alkenes and alkynes was elaborated. 相似文献
66.
Abstract— Biologically active f2-RNA, Obtained from bacteriophage f2, was inactivated by ultraviolet (u.v) light (2537 Å) with a quantum yield of 3.3 ± 0.3 times 10-3 when assayed in the dark with protoplasts of an F- strain of E. coli k12. Assay under “black light” gave a quantum yield of 2.7 ± 0.5 times 10-3 which was just enough lower to suggest that 17 per cent photorecovery of the u.v. lesions has taken place. Intact phage f2 was inactivated by u.v. radiation with a quantum yield of 0.7 ± 0.12 times 10-3, Thus the whole phage is much less sensitive than the free RNA. No evidence of photorecovery was found in u.v.-irradiated RNA phage 7S assayed in its host Pseudomonas aeruginosa. 相似文献
67.
68.
69.
Kourouli T Kefalas P Ragoussis N Ragoussis V 《The Journal of organic chemistry》2002,67(13):4615-4618
A general and convenient synthesis of beta-ketols and alpha,beta-alkenones has been achieved by a Knoevenagel condensation of a beta-ketoacid with an aldehyde in aqueous medium. Saponification of a beta-ketoester by an aqueous KOH 10% solution gives the potassium salt of the beta-ketoacid, which is condensed in situ with an aldehyde at pH 7.8-8.0, at 60 degrees C for 5-6 h. The intermediate beta-ketocarboxylate is smoothly decarboxylated in the reaction medium, giving the beta-ketol in high yield (75-90%). Acidification of the reaction mixture at pH 1 and heating at 70 degrees C under vigorous stirring for 6 h, leads directly to the corresponding alpha,beta-unsaturated ketone in good yield (65-75%). 相似文献
70.