全文获取类型
收费全文 | 1785篇 |
免费 | 23篇 |
国内免费 | 3篇 |
专业分类
化学 | 1059篇 |
晶体学 | 17篇 |
力学 | 24篇 |
综合类 | 1篇 |
数学 | 57篇 |
物理学 | 653篇 |
出版年
2023年 | 6篇 |
2021年 | 5篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 8篇 |
2017年 | 8篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 73篇 |
2012年 | 47篇 |
2011年 | 75篇 |
2010年 | 40篇 |
2009年 | 46篇 |
2008年 | 89篇 |
2007年 | 112篇 |
2006年 | 97篇 |
2005年 | 114篇 |
2004年 | 101篇 |
2003年 | 87篇 |
2002年 | 82篇 |
2001年 | 51篇 |
2000年 | 52篇 |
1999年 | 34篇 |
1998年 | 28篇 |
1997年 | 31篇 |
1996年 | 35篇 |
1995年 | 34篇 |
1994年 | 29篇 |
1993年 | 36篇 |
1992年 | 48篇 |
1991年 | 23篇 |
1990年 | 20篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 30篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 27篇 |
1983年 | 12篇 |
1982年 | 20篇 |
1981年 | 20篇 |
1980年 | 18篇 |
1979年 | 22篇 |
1978年 | 17篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 12篇 |
1974年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有1811条查询结果,搜索用时 15 毫秒
61.
Fujita M Nakao Y Matsunaga S Seiki M Itoh Y Yamashita J Van Soest RW Fusetani N 《Journal of the American Chemical Society》2003,125(51):15700-15701
A novel MMP inhibitor, ageladine A (1) with antiangiogenic activity was isolated from a marine sponge Agelas nakamurai. Structure 1 was determined by a combination of spectroscopic and chemical methods to be an unprecedented structure of 4-(4,5-dibromo-1H-pyrrol-2-yl)]-1H-imidazo[4,5-c]pyridin-2-amine. 相似文献
62.
Akihito Sakakibara Maki Itoh Itaru Mita 《Journal of polymer science. Part A, Polymer chemistry》1995,33(8):1293-1303
Aromatic polybenzobisoxazoles, having polydimethylsiloxane side chains (SCPBOs), were prepared using terephthaloyl chloride-terminated polydimethylsiloxane macromonomers and 3,3′-bis(trimethylsiloxy)-4,4′-bis(trimethylsilylamino)biphenyl for the purpose of dispersing rigid-rod molecules in silicone matrices for molecular reinforcement. The degree of polymerization of the side chain was varied from 7.8 to 45.4, and a small amount of (3-butenyloxy)terephthaloyl chloride was copolymerized to give the polymers a functionality that can be linked to the matrices. For all the SCPBOs, the WAXD pattern showed only diffuse reflections, suggesting limited structural regularity, although the polymers were optically anisotropic. No melting transition was observed below the side chain decomposition temperature, 350°C. A polydimethylsiloxane/polybenzobisoxazole composite elastomer was obtained first curing the polysiloxane matrix containing the prepolymer of the SCPBO, followed by in situ thermal ring closure of the prepolymer. Some reinforcement was observed, but the presence of plasticizing effect by the unbound SCPBO was suggested at the same time. © 1995 John Wiley & Sons, Inc. 相似文献
63.
64.
65.
66.
67.
Y. Yamada M. Itoh K. Egawa N. Kiriyama K. Komura K. Ueno 《Journal of Radioanalytical and Nuclear Chemistry》1992,164(1):47-57
Various f-elements are separated as anionic complexes from both acidic and alkaline solutions by precipitation with alkylpyridinium salts. The precipitates are also cationic surfactants where the simple counter-ion (e.g. nitrate or chloride) is replaced by the negatively charged complex anion of an actinide or lanthanide. The low solubility of these precipitates is explained by a strong affinity of divalent complex counter-ions of f-elements to the quaternary nitrogen. Precipitations in solutions of nitric acid allow to separate tetravalent f-elements from other metals, in alkaline carbonate solutions tetravalent and hexavalent actinides are precipitated simultaneously. The last procedure yields precipitates, which are very intimate mixtures of hexavalent and tetravalent actinides. This allows to prepare mixed oxides in a simple way. 相似文献
68.
Five Ci-Se...O...Se-Ci atoms in anthraquinone and 9-(methoxy)anthracene bearing phenylselanyl groups at 1,8-positions align linearly, the origin of which is shown to be a nonbonded 5c-6e interaction of the five atoms. 相似文献
69.
Miyuki Narita Junya Itoh Tohru Kikuchi Fumio Hamada 《Journal of inclusion phenomena and macrocyclic chemistry》2002,42(1-2):107-114
-Cyclodextrin dimer linked with ethylenediamine at the upper rim of the cyclodextrin has been synthesized and then modified with two dansyl moieties inthe presence of N,N'-dicyclohexylcarbodiimide. The sensing ability and bindingproperty of the title compound were investigated for steroids and terpenoids. Thefluorescence intensity of this dimer was decreased when a host–guest complex was formed. The value I/I0, where I0 and I are fluorescence intensitiesin the absence and presence of a guest and I is I0- I, was used as a parameter of sensitivity. This host exhibited a much higher sensitivity and selective molecular recognition ability for bile acids such as ursodeoxycholic acid andchenodeoxycholic acid and terpenoids such as (-)-borneol than the dansyl-modifiedcyclodextrins reported previously including -cyclodextrin dimer. The behaviors of the appended moieties of the host during the formation of host–guest complexes were studied using induced circular dichroism (ICD) and fluorescence spectra. The ICD intensityof this dimer was decreased on accommodation of a guest and this spectral pattern of the title dimer was opposite to that of bis dansyl-modified -cyclodextrin monomer. Theguest-induced variations in the fluorescence and ICD intensities suggest that this dimer formed a 1 : 1 host–guest complex and the appended moieties act as a hydrophobic cap. 相似文献
70.
[reaction: see text] Highly basic lithium enolates are shown to be applicable to radical trifluoromethylation. The reaction is extremely fast, and the minimum reaction time is approximately 1 s. 相似文献