全文获取类型
收费全文 | 2005篇 |
免费 | 60篇 |
国内免费 | 7篇 |
专业分类
化学 | 1525篇 |
晶体学 | 22篇 |
力学 | 22篇 |
数学 | 84篇 |
物理学 | 419篇 |
出版年
2023年 | 7篇 |
2022年 | 18篇 |
2021年 | 24篇 |
2020年 | 35篇 |
2019年 | 36篇 |
2018年 | 27篇 |
2017年 | 8篇 |
2016年 | 46篇 |
2015年 | 34篇 |
2014年 | 39篇 |
2013年 | 112篇 |
2012年 | 86篇 |
2011年 | 121篇 |
2010年 | 46篇 |
2009年 | 73篇 |
2008年 | 106篇 |
2007年 | 112篇 |
2006年 | 124篇 |
2005年 | 122篇 |
2004年 | 129篇 |
2003年 | 119篇 |
2002年 | 106篇 |
2001年 | 62篇 |
2000年 | 46篇 |
1999年 | 31篇 |
1998年 | 16篇 |
1997年 | 22篇 |
1996年 | 21篇 |
1995年 | 21篇 |
1994年 | 12篇 |
1993年 | 20篇 |
1992年 | 14篇 |
1991年 | 9篇 |
1990年 | 6篇 |
1989年 | 16篇 |
1988年 | 25篇 |
1987年 | 14篇 |
1986年 | 18篇 |
1985年 | 22篇 |
1984年 | 30篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 14篇 |
1977年 | 11篇 |
1975年 | 9篇 |
1974年 | 11篇 |
1973年 | 9篇 |
排序方式: 共有2072条查询结果,搜索用时 31 毫秒
31.
Sadao Arai Masanori Ishikura Kiyoshi Sato Takamichi Yamagishi 《Journal of heterocyclic chemistry》1995,32(3):1081-1083
The 16c-azonia[6]helicene salts, in which a carbon atom at the inner helix skeleton of [6]helicene is replaced by a quaternary nitrogen atom, have been synthesized by photo-induced intramolecular quater-nization of 2-[2-(1-chloronaphthyl)vinyl]benzo[h]quinolines in acetonitrile. 相似文献
32.
Spirodienones bearing the 1-azaspiro[4.5]decane ring system have been synthesized from N-methoxy-(4-halogenophenyl)amides by the intramolecular ipso attack of a nitrenium ion generated with [hydroxy(tosyloxy)iodo]benzene in trifluoroethanol. 相似文献
33.
Masatoshi Sakae Masanori Katsurada Mayumi Watanabe Fumio Yoneda Sadao Nishigaki Toshimasa Ishida 《Journal of heterocyclic chemistry》1997,34(1):157-160
The reaction of 2-bromoethylamine 1 with methylisothiocyanate 2 under mild condition gave 2-methyl-amino-2-thiazoline 3 as the major product together with two kinds of byproducts, 3-(N-methylthiocar-bamoyl)-2-methyliminothiazolidine 4 and N,N′-dimethyl-N-(2-thiazolin-2-yl)thiourea 5. Thermal isomer-ization of 5 to 4 was observed. The structures of the byproducts were confirmed by X-ray crystallography. 相似文献
34.
Novel synthetic procedure of heterocycles was developed using nickel-mediated alkylative carboxylation, and the total synthesis of erythrocarine was achieved using this method and RCM of dienyne as the key steps. [reaction: see text] 相似文献
35.
Shin-ichi Hirano Toshinobu Yogo Wataru Sakamoto Seiji Yamada Tomoyuki Nakamura Tomoe Yamammto Hiroyuki Ukai Kouichi Banno Tomoko Nakafuku Yukari Ando 《Journal of Sol-Gel Science and Technology》2003,26(1-3):35-41
Nano sized crystalline particles/polymer hybrids were synthesized form designed metal-organic precursors. The newly developed method is composed of the synthesis of organic matrix by polymerization and the in situ nucleation and growth of crystalline oxide particles in the organic matrix below 100°C. The design of metal-organic precursor modified with polymerizable ligand and the selection of reaction conditions does influence the size and crystallinity of ceramic particles in organic matrix. The nano-sized magnetic particle/polymer hybrid exhibits the interesting feature of superparamagnetism and quantum size effect. The crystalline particles of BaTiO3/, PbTiO3/, and KNbO3/polymer hybrids behave to be dielectric and show the typical electro-rheological behavior. 相似文献
36.
37.
This review covers newly isolated simple indole alkaloids, structure determinations, total syntheses and biological activities reported in the literature in 2003. 相似文献
38.
Kawasaki T Nonaka Y Watanabe K Ogawa A Higuchi K Terashima R Masuda K Sakamoto M 《The Journal of organic chemistry》2001,66(4):1200-1204
The reverse aromatic Cope rearrangement of 2-allyl-3-alkylideneindolines obtained by Horner-Wadsworth-Emmons olefination of 2-allylindolin-3-ones was performed. When 2-allylindolin-3-ones were treated with phosphonium ylides in refluxing toluene, domino Wittig reaction and reverse aromatic Cope rearrangement took place to give alpha-allyl-3-indole acetate derivatives in good yields. The aromatization as a new driving force in the Cope rearrangement is preferable to the conjugation with the carbonyl and cyano groups and also to the alkyl substitution pattern, which are well-known driving forces. 相似文献
39.
Application of dibutyltin oxide method to regioselective acylation and alkylation of tylosin at C-4' 总被引:1,自引:0,他引:1
K Kiyoshima M Sakamoto T Ishikura Y Fukagawa T Yoshioka H Naganawa T Sawa T Takeuchi 《Chemical & pharmaceutical bulletin》1989,37(4):861-865
4'-O-Acyl-, 4'-O-alkyl- and 4'-deoxy-tylosin derivatives were synthesized using 2'-O-acetyl-3',4'-O-(dibutyl-stannio)tylosin as a synthetic intermediate. The in vitro biological evaluation showed that the new derivatives were active against macrolide-resistant clinical isolates of bacteria and mycoplasmas, and that they were resistant to hepatic esterase. 相似文献
40.
Yutaka Sawada Junji Yamaguchi Osamu Sakurai Keizo Uematsu Nobuyasu Mizutani Masanori Kato 《Thermochimica Acta》1979,34(2):233-237
An exothermic phenomenon and a simultaneous rapid evolution of a small amount of carbon dioxide at ?500°C during thermal decomposition of hydromagnesite 4 MgCO3 · Mg(OH)2 · 4 H2O was studied by isothermal DSCTG in a carbon dioxide atmosphere. It was quantitatively confirmed that the exothermic phenomenon was due to crystallization of MgCO3 from the amorphous phase and that the evolution of carbon dioxide was due to decomposition of the MgCO3 by the heat of crystallization (?3.4 kcal mole?1. 相似文献