全文获取类型
收费全文 | 1814篇 |
免费 | 86篇 |
国内免费 | 8篇 |
专业分类
化学 | 1488篇 |
晶体学 | 22篇 |
力学 | 20篇 |
数学 | 119篇 |
物理学 | 259篇 |
出版年
2023年 | 16篇 |
2022年 | 18篇 |
2021年 | 24篇 |
2020年 | 18篇 |
2019年 | 46篇 |
2018年 | 30篇 |
2017年 | 20篇 |
2016年 | 56篇 |
2015年 | 48篇 |
2014年 | 48篇 |
2013年 | 100篇 |
2012年 | 126篇 |
2011年 | 135篇 |
2010年 | 62篇 |
2009年 | 59篇 |
2008年 | 126篇 |
2007年 | 111篇 |
2006年 | 127篇 |
2005年 | 125篇 |
2004年 | 95篇 |
2003年 | 105篇 |
2002年 | 68篇 |
2001年 | 20篇 |
2000年 | 32篇 |
1999年 | 17篇 |
1998年 | 9篇 |
1997年 | 24篇 |
1996年 | 25篇 |
1995年 | 4篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 16篇 |
1991年 | 6篇 |
1990年 | 9篇 |
1989年 | 8篇 |
1987年 | 5篇 |
1985年 | 19篇 |
1984年 | 15篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 8篇 |
1978年 | 15篇 |
1977年 | 10篇 |
1976年 | 16篇 |
1975年 | 12篇 |
1974年 | 3篇 |
1971年 | 2篇 |
1968年 | 2篇 |
排序方式: 共有1908条查询结果,搜索用时 578 毫秒
81.
Naoki Taka Hiroshi Koga Haruhiko Sato Takenori Ishizawa Tadakatsu Takahashi 《合成通讯》2013,43(23):4263-4269
The novel potassium channel openers benzopyran-4-amides have been synthesized via palladium-catalyzed amidation of 4-bromobenzopyrans under an atmoshere in the presence of an equivalent of potassium iodide. 相似文献
82.
83.
84.
Masaaki Yoshifuji Katsuhiro Shibayama Ichiro Shima Naoki Inamoto 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-3):11-14
Abstract Some reactions of diphosphenes and the related species involving oxidation, reduction, alkylation, sulfurization, and 6η-coordination are described. 相似文献
85.
Highly active polymeric organocatalyst: Chiral ionic polymers prepared from 10,11‐didehydrogenated cinchonidinium salt
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Md. Mehadi Hassan Naoki Haraguchi Shinichi Itsuno 《Journal of polymer science. Part A, Polymer chemistry》2016,54(5):621-627
Since few examples of 10,11‐didehydrogenated (3‐ethynyl) cinchona alkaloids have been utilized as organocatalysts in asymmetric reaction, we synthesized 10,11‐didehydrogenated cinchonidine. The 3‐vinyl group of cinchonidine was transformed into a 3‐ethynyl functionality. Based on the resulting 10,11‐didehydrogenated cinchonidine, the corresponding quaternary ammonium salt and its dimers were prepared. The ion‐exchange reaction between the quaternary ammonium salt and sodium sulfonate produced the quaternary ammonium sulfonate as a stable ionic compound. Chiral ionic polymers were then synthesized by the ion‐exchange polymerization of the 10,11‐didehydrogenated cinchonidinium salt dimer and a disulfonate. The chiral ionic polymers were found to be capable of efficiently catalyzing the asymmetric alkylation of N‐(diphenylmethylene)glycine tert‐butyl ester. The enantioselectivities obtained with the polymeric catalysts were higher than those obtained with the corresponding monomeric catalyst. Dimers of 10,11‐didehydrogenated cinchonidinium salts were prepared. Treatment of the dimer with disodium disulfonate gave the chiral ionic polymers, which showed high catalytic activity in asymmetric benzylation of N‐(diphenylmethylen)glycine tert‐butyl ester. The polymeric catalysts were reused several times without the loss of catalytic activity. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 621–627 相似文献
86.
Pd‐initiated polymerization of diazo compounds bearing dialkoxyphosphinyl group and hydrolysis of the resulting polymers and oligomers to afford phosphonic acid‐containing products
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hiroaki Shimomoto Akira Oda Motoki Kanayama Tomoya Sako Tomomichi Itoh Eiji Ihara Naohiro Hoshikawa Akihiko Koiwai Naoki Hasegawa 《Journal of polymer science. Part A, Polymer chemistry》2016,54(12):1742-1751
Pd‐initiated polymerization and oligomerization of diazo compounds containing a dialkoxyphosphinyl group are described. Polymerization of 2‐dialkoxyphosphinylethyl diazoacetates with π‐allylPdCl‐based initiating systems afforded C? C main chain polymers bearing phosphonate on each main chain carbon atom. The quantitative transformation of the side chain phosphonate to phosphonic acid resulted in the formation of water soluble polymers having the acid groups accumulated around their main chains, although the carbonyl ester linkage in the side chain was cleaved via intramolecular acid‐assisted hydrolysis in water at 80 °C. Pd‐initiated oligomerization of diethyl diazomethylphosphonate yielded an oligomeric product bearing diethoxyphosphiny groups directly attached to its main chain carbons, with unexpected incorporation of azo group in the main chain framework. Hydrolysis of the phosphonate of the oligomer afforded a water‐soluble product, which was revealed to show higher proton conductivity than poly(vinylphosphonic acid) under certain conditions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1742–1751 相似文献
87.
Hiroyuki Nishide Naoki Yoshioka Yukoh Saitoh Ritsuko Gotoh Takeshi Miyakawa Eishun Tsuchida 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(9):775-786
Abstract m- and p Bis(diphenylene)propenylphenylacetylene (m-, p-8) were synthesized and polymerized with WCI6, MoCl5, and Rh catalyst, yielding solvent-soluble poly(phenylacetylene)s bearing a π-conjugated bis(di-phenylene)propenyl groups (m-, p-7a). The polymers gave their polyanion derivatives, which were electrolytically and chemically oxidized to yield the corresponding polyradicals (m-, p-7b). The polyradicals were chemically very stable due to the resonance stabilization of an unpaired electron whose spin concentration could be increased up to ca. 2 × 1023 spins per molar monomer unit. ESR spectroscopy suggested an antiferro-magnetic interaction between unpaired electrons. 相似文献
88.
89.
In this paper, we report the preparation and red-light-emitting behavior of benzothiadiazole–tris(alkyloxy)phenylethene dyes. In solution, we observed an efficient red light emission with high fluorescence quantum yields (up to 0.78). With increase in solvent polarity, the emission bands shifted to longer wavelengths accompanied by a large Stokes shift of up to 152 nm. A moderate fluorescence quantum yield of 0.52 could be achieved even in the polar solvent dimethylformamide. Red light emission with good fluorescence quantum yields (up to 0.50) was also observed in the bulk solid, liquid, and film state. 相似文献
90.
The reaction of 1-bromo-2-(1-isothiocyanatoalkyl)benzenes, which are easily derived from 2-bromophenyl ketones or (2-bromophenyl)methanamine, with butyllithium generates 1-(1-isothiocyanatoalkyl)-2-lithiobenzenes, which immediately underwent intramolecular cyclization to give rise to the corresponding 3-substituted and 3,3-disubstituted 2,3-dihydro-1H-isoindole-1-thiones in good yields. 相似文献