全文获取类型
收费全文 | 3316篇 |
免费 | 677篇 |
国内免费 | 280篇 |
专业分类
化学 | 3029篇 |
晶体学 | 35篇 |
力学 | 104篇 |
综合类 | 27篇 |
数学 | 774篇 |
物理学 | 304篇 |
出版年
2024年 | 1篇 |
2023年 | 34篇 |
2022年 | 31篇 |
2021年 | 59篇 |
2020年 | 148篇 |
2019年 | 102篇 |
2018年 | 92篇 |
2017年 | 75篇 |
2016年 | 203篇 |
2015年 | 201篇 |
2014年 | 202篇 |
2013年 | 305篇 |
2012年 | 254篇 |
2011年 | 285篇 |
2010年 | 231篇 |
2009年 | 261篇 |
2008年 | 257篇 |
2007年 | 198篇 |
2006年 | 202篇 |
2005年 | 177篇 |
2004年 | 167篇 |
2003年 | 171篇 |
2002年 | 118篇 |
2001年 | 62篇 |
2000年 | 66篇 |
1999年 | 61篇 |
1998年 | 45篇 |
1997年 | 85篇 |
1996年 | 33篇 |
1995年 | 22篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 3篇 |
1987年 | 7篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1977年 | 3篇 |
1969年 | 1篇 |
排序方式: 共有4273条查询结果,搜索用时 31 毫秒
101.
A series of imidazolium chlorides for the formation of tridentate CNO‐donor palladium(II) complexes featuring N‐heterocyclic carbene moieties have been developed from cheap and readily available starting materials with high yields. Their palladium complexes were prepared by reactions between the ligand precursors and PdCl2 using K2CO3 as base in pyridine with reasonable yields. These air‐stable metal complexes were characterized using 1H NMR and 13C{1H} NMR spectroscopy and elemental analyses. Heteronuclear multiple bond correlation experiments were performed to identify key NMR signals of these compounds. The structures of two of the complexes were also established by single‐crystal X‐ray diffraction analysis. One of these complexes was successfully applied in the direct C―H functionalization reactions between heterocyclic compounds and aryl bromides, producing excellent yields of coupled products. The coupling reactions were scalable, allowing grams of coupled products to be obtained with a mere 2 mol% of Pd loading. The catalyst system developed allowed the large‐scale preparation of several push–pull chromophores straightforwardly. Photophysical properties based on UV–visible and fluorescence spectroscopy for these chromophores were investigated. Deep blue photoluminescence with moderate quantum efficiency and twisted intramolecular charge transfer excited state were observed for these chromophores. Density functional theory (DFT) and time‐dependent DFT calculations were performed to support the experimental results. 相似文献
102.
103.
104.
Back Cover: Rhodium‐Catalyzed Ketone Methylation Using Methanol Under Mild Conditions: Formation of α‐Branched Products (Angew. Chem. Int. Ed. 3/2014) 下载免费PDF全文
105.
106.
107.
Xiaoqiang Hu Dr. Yixin Zhang Baixiang Li Prof. Dr. Zhongbao Jian 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(46):11935-11942
Fluorine substituents in transition metal catalysts are of great importance in olefin polymerization catalysis; however, the comprehensive effect of fluorine substituents is elusive in seminal late transition metal α-diimine catalytic system. In this contribution, fluorine substituents at various positions (ortho-, meta-, and para-F) and with different numbers (Fn; n=0, 1, 2, 3, 5) were installed into the well-defined N-terphenyl amine and thus were studied for the first time in the nickel α-diimine promoted ethylene polymerization and copolymerization with polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity, polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given. As a notable result, the ortho-F substituted α-diimine nickel catalyst produced highly linear polyethylenes with an extremely high molecular weight (Mw=8703 kDa) and a significantly low degree of branching of 1.4/1000 C; however, the meta-F and/or para-F substituted α-diimine nickel catalysts generated highly branched (up to 80.2/1000 C) polyethylenes with significantly low molecular weights (Mw=20-50 kDa). 相似文献
108.
109.
Dr. Michael L. Lejkowski Dr. Ronald Lindner Dr. Takeharu Kageyama Dr. Gabriella É. Bódizs Dipl.‐Chem. Philipp N. Plessow Dr. Imke B. Müller Dr. Ansgar Schäfer Dr. Frank Rominger Prof. Dr. Peter Hofmann Dr. Cornelia Futter Dr. Stephan A. Schunk Dr. Michael Limbach 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(44):14017-14025
For more than three decades the catalytic synthesis of acrylates from the cheap and abundantly available C1 building block carbon dioxide and alkenes has been an unsolved problem in catalysis research, both in academia and industry. Herein, we describe a homogeneous catalyst based on nickel that permits the catalytic synthesis of the industrially highly relevant acrylate sodium acrylate from CO2, ethylene, and a base, as demonstrated, at this stage, by a turnover number of greater than 10 with respect to the metal. 相似文献
110.