全文获取类型
收费全文 | 135894篇 |
免费 | 4144篇 |
国内免费 | 2332篇 |
专业分类
化学 | 76961篇 |
晶体学 | 1558篇 |
力学 | 5705篇 |
综合类 | 135篇 |
数学 | 13577篇 |
物理学 | 44434篇 |
出版年
2020年 | 1221篇 |
2019年 | 1237篇 |
2018年 | 1129篇 |
2017年 | 1052篇 |
2016年 | 1958篇 |
2015年 | 1675篇 |
2014年 | 2197篇 |
2013年 | 5959篇 |
2012年 | 4753篇 |
2011年 | 5878篇 |
2010年 | 3741篇 |
2009年 | 3504篇 |
2008年 | 4900篇 |
2007年 | 4939篇 |
2006年 | 4810篇 |
2005年 | 4618篇 |
2004年 | 3993篇 |
2003年 | 3483篇 |
2002年 | 3127篇 |
2001年 | 3701篇 |
2000年 | 2729篇 |
1999年 | 2146篇 |
1998年 | 1791篇 |
1997年 | 1865篇 |
1996年 | 1813篇 |
1995年 | 1850篇 |
1994年 | 1642篇 |
1993年 | 1572篇 |
1992年 | 1794篇 |
1991年 | 1749篇 |
1990年 | 1686篇 |
1989年 | 1689篇 |
1988年 | 1658篇 |
1987年 | 1654篇 |
1986年 | 1564篇 |
1985年 | 2124篇 |
1984年 | 2249篇 |
1983年 | 1856篇 |
1982年 | 2164篇 |
1981年 | 1996篇 |
1980年 | 2028篇 |
1979年 | 2040篇 |
1978年 | 2152篇 |
1977年 | 2049篇 |
1976年 | 2081篇 |
1975年 | 2030篇 |
1974年 | 1861篇 |
1973年 | 2085篇 |
1972年 | 1265篇 |
1967年 | 1102篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
91.
92.
Domino Radical Addition/Oxidation Sequence with Photocatalysis: One‐Pot Synthesis of Polysubstituted Furans from α‐Chloro‐Alkyl Ketones and Styrenes 下载免费PDF全文
Shuang Wang Wen‐Liang Jia Lin Wang Prof. Dr. Qiang Liu Prof. Dr. Li‐Zhu Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(39):13794-13798
A new domino reaction has been developed that allows the combination of styrenes and α‐alkyl ketone radicals to afford a wide array of polysubstituted furans in good to excellent yields under mild and simple reaction conditions. The key to success of this novel protocol is the use of photocatalyst fac‐Ir(ppy)3 and oxidant K2S2O8. Mechanistic studies by a radical scavenger and photoluminescence quenching suggest that a radical addition/oxidation pathway is operable. 相似文献
93.
Baeyer–Villiger oxidation of cyclohexanone by molecular oxygen with Fe–Sn–O mixed oxides as catalysts 下载免费PDF全文
Fe–Sn–O mixed oxides were synthesized and used as catalysts for Baeyer–Villiger oxidation of cyclohexanone, which showed both high catalytic activity and selectivity. X‐ray powder diffraction and scanning electron microscopy suggested that the Fe–Sn–O catalysts had a tetragonal structure with a grain size of 29.3 nm. An ε‐caprolactone yield as high as 98.8% was obtained in a small‐scale experiment (5 mmol of cyclohexanone). In a scale‐up test (20 mmol of cyclohexanone), the cyclohexanone conversion and ε‐caprolactone yield were 96.7 and 96.5%, respectively. In addition, the catalysts can be reused five times without any major decline in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
94.
Square‐Planar Ruthenium(II) Complexes: Control of Spin State by Pincer Ligand Functionalization 下载免费PDF全文
Dr. Bjorn Askevold Dr. Marat M. Khusniyarov Dr. Wolfgang Kroener Dr. Klaus Gieb Prof. Paul Müller Dr. Eberhardt Herdtweck Dr. Frank W. Heinemann Dr. Martin Diefenbach Prof. Max C. Holthausen Veacheslav Vieru Prof. Liviu F. Chibotaru Prof. Sven Schneider 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(2):579-589
Functionalization of the PNP pincer ligand backbone allows for a comparison of the dialkyl amido, vinyl alkyl amido, and divinyl amido ruthenium(II) pincer complex series [RuCl{N(CH2CH2PtBu2)2}], [RuCl{N(CHCHPtBu2)(CH2CH2PtBu2)}], and [RuCl{N(CHCHPtBu2)2}], in which the ruthenium(II) ions are in the extremely rare square‐planar coordination geometry. Whereas the dialkylamido complex adopts an electronic singlet (S=0) ground state and energetically low‐lying triplet (S=1) state, the vinyl alkyl amido and the divinyl amido complexes exhibit unusual triplet (S=1) ground states as confirmed by experimental and computational examination. However, essentially non‐magnetic ground states arise for the two intermediate‐spin complexes owing to unusually large zero‐field splitting (D>+200 cm?1). The change in ground state electronic configuration is attributed to tailored pincer ligand‐to‐metal π‐donation within the PNP ligand series. 相似文献
95.
96.
97.
98.
99.
Cover Picture: Coordination Chemistry of N‐Heterocyclic Nitrenium‐Based Ligands (Chem. Eur. J. 19/2015) 下载免费PDF全文
100.