全文获取类型
收费全文 | 1589篇 |
免费 | 52篇 |
国内免费 | 4篇 |
专业分类
化学 | 1358篇 |
晶体学 | 15篇 |
力学 | 15篇 |
数学 | 40篇 |
物理学 | 217篇 |
出版年
2022年 | 10篇 |
2021年 | 13篇 |
2020年 | 13篇 |
2019年 | 18篇 |
2018年 | 19篇 |
2017年 | 10篇 |
2016年 | 24篇 |
2015年 | 40篇 |
2014年 | 40篇 |
2013年 | 92篇 |
2012年 | 72篇 |
2011年 | 76篇 |
2010年 | 46篇 |
2009年 | 46篇 |
2008年 | 79篇 |
2007年 | 107篇 |
2006年 | 103篇 |
2005年 | 77篇 |
2004年 | 82篇 |
2003年 | 69篇 |
2002年 | 78篇 |
2001年 | 39篇 |
2000年 | 32篇 |
1999年 | 31篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 17篇 |
1995年 | 16篇 |
1994年 | 21篇 |
1993年 | 14篇 |
1992年 | 22篇 |
1991年 | 18篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 29篇 |
1984年 | 28篇 |
1983年 | 11篇 |
1982年 | 18篇 |
1981年 | 21篇 |
1980年 | 16篇 |
1979年 | 14篇 |
1978年 | 8篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 14篇 |
1974年 | 6篇 |
1967年 | 8篇 |
排序方式: 共有1645条查询结果,搜索用时 31 毫秒
221.
F. Higashide K. Omata Y. Nozawa H. Yoshioka 《Journal of polymer science. Part A, Polymer chemistry》1977,15(8):2019-2028
Permeability to oxygen of poly(methyl methacrylate) (PMMA) films containing glass flakes (GF) was investigated. The glass flakes were treated with five kinds of silanes and K2Cr2O7-H2SO4 solution to improve the affinity with PMMA. The permeability curves were classified into five representative types, which depend on the pretreatment of the glass flakes and the type of silane used as a coupling agent. The factors which influence permeability were studied from the point of view of permeative retardation with the aid of several methods, such as determination of the apparent density of the glass flakes treated with the silanes, the shearing and tensile strength of the PMMA films containing the glass flakes, ESR spectra of films irradiated by γ-rays, and x-ray diffraction patterns of the films. It was found that the three very effective methods to retard the permeability are (a) pretreatment of the glass flakes with NaOH, (b) treatment with γ-methacryloxypropyltrimethoxysilane or ditrimethylsiloxymethylsilane, and (c) heat pressing of the films. The lowest permeability constant which was attained in this study was about one-eighth that with PMMA alone. 相似文献
222.
223.
A nitro group in nitroolefins is displaced by hydrogen giving the corresponding olefins in good yields by the reaction of nitroolefins with sodium sulfide in the presence of benzenethiol. It proceeds rapidly at room temperature. 相似文献
224.
Kazuhiko Orito Harumi Kaga Mitsuomi Itoh S. Osmund De Silva Richard H. Manske Russel Rodrigo 《Journal of heterocyclic chemistry》1980,17(3):417-423
Aromatic methoxy and/or methylenedioxy substituted 7-methyltetrahydrobenz[d]indeno[1,2-b]-azepines 7 and their 12-oxo derivatives 8 were efficiently synthesized by the general method consisting of two types of intramolecular dehydrative cyclizations, as follows. N-Methyl-N-β-phenethylacetamides 1 were cyanomethylated in the two-step process of chloromethylation and treatment of the resultant benzyl chlorides with sodium cyanide. The condensation of the benzyl cyanides 2 with the appropriate benzaldehydes, followed by reduction of the benzylidene function, gave α,β-diphenylpropionitriles 3 . Successively, hydrolysis to the amino acids 4 and the thermal cyclization converted 3 to the benzylbenzazepinones 5 , which were also prepared by benzylation of the benzazepinones 6 smoothly by heating of 5 with phosphoryl chloride to afford the title azepines 7 . Further, these tetracyclic enamines 7 underwent autoxidation to the corresponding 12-oxo derivatives 8 , on exposure to oxygen in the presence of Triton B. 相似文献
225.
Kazuhiko Saigo Masataka Kubo Ru-Jang Lin Akira Youda Masaki Hasegawa 《Tetrahedron letters》1985,26(10):1325-1328
A novel cyclophane, 17, 17, 40, 40-tetramethyl-7, 30-dinitro-1, 10, 24, 33-tetraoxa[2.2.1.2.2.1] metaparaparametaparaparacyclophane, was synthesized by 2:2 cyclization of 3,5-bis(bromomethyl)nitrobenzene, derived from 3,5-dimethylnitrobenzene, and bisphenol A. The cyclophane was found to form 1:1 complex with benzene. 相似文献
226.
Shinichi Ueji Kazumi Nakatsu Hiroshi Yoshioka Kenji Kinoshita 《Tetrahedron letters》1982,23(11):1173-1176
The crystals of the title compound contain both intra- and inter-molecular OH?π hydrogen bonds (the first example of bifurcated OH?π bonds), the stereochemistry of which has been elucidated by an X-ray structure analysis; this bifurcated bond is also supported by the observation based on the IR spectrum of the crystals. 相似文献
227.
Teruji Tsuji Takahiro Kataoka Mitsuru Yoshioka Yuji Sendo Yasuhiro Nishitani Shoichi Hirai Takashi Maeda Wataru Nagata 《Tetrahedron letters》1979,20(30):2793-2796
The benzyl ester protecting group in β-lactam derivatives can be cleanly removed by treatment with aluminum trichloride under mild conditions, preferably in the presence of anisole, to give the corresponding free acids in high yields. 相似文献
228.
229.
Yuji Oikawa Tatsuyoshi Tanaka Kiyoshi Horita Tadao Yoshioka Osamu Yonemitsu 《Tetrahedron letters》1984,25(47):5393-5396
The DMPM (3,4-dimethoxybenzyl) protection for hydroxy function was deprotected more readily than the MPM (p-methoxybenzyl) protection by DDQ oxidation under neutral conditions, and applied to the synthesis of some synthons to macrolide and polyether antibiotics. 相似文献
230.