全文获取类型
收费全文 | 2496篇 |
免费 | 57篇 |
国内免费 | 10篇 |
专业分类
化学 | 1968篇 |
晶体学 | 28篇 |
力学 | 45篇 |
数学 | 104篇 |
物理学 | 418篇 |
出版年
2022年 | 12篇 |
2021年 | 21篇 |
2020年 | 28篇 |
2019年 | 25篇 |
2018年 | 15篇 |
2016年 | 44篇 |
2015年 | 34篇 |
2014年 | 43篇 |
2013年 | 116篇 |
2012年 | 81篇 |
2011年 | 123篇 |
2010年 | 71篇 |
2009年 | 71篇 |
2008年 | 124篇 |
2007年 | 138篇 |
2006年 | 114篇 |
2005年 | 129篇 |
2004年 | 119篇 |
2003年 | 116篇 |
2002年 | 149篇 |
2001年 | 61篇 |
2000年 | 51篇 |
1999年 | 39篇 |
1998年 | 29篇 |
1997年 | 26篇 |
1996年 | 31篇 |
1995年 | 19篇 |
1994年 | 30篇 |
1993年 | 38篇 |
1992年 | 47篇 |
1991年 | 35篇 |
1990年 | 29篇 |
1989年 | 26篇 |
1988年 | 31篇 |
1987年 | 22篇 |
1986年 | 12篇 |
1985年 | 47篇 |
1984年 | 45篇 |
1983年 | 27篇 |
1982年 | 38篇 |
1981年 | 44篇 |
1980年 | 32篇 |
1979年 | 28篇 |
1978年 | 23篇 |
1977年 | 24篇 |
1976年 | 18篇 |
1975年 | 17篇 |
1974年 | 19篇 |
1973年 | 24篇 |
1970年 | 12篇 |
排序方式: 共有2563条查询结果,搜索用时 15 毫秒
91.
SERS from crystal violet (CV) on a Ag electrode was investigated under preresonance and resonance conditions. The excitation profile of the chemisorbed species is like that of dissolved molecules but intensities are ≈ 1000 times larger. The Raman enhancement is ≈ 108 and exhibits a specific potential dependence even in the absence of adsorption-desorption process. At potentials where reduction of CV occurs leuco crystal violet was detected. 相似文献
92.
Isolation of lignan glucosides and neolignan sulfate from the leaves of Glochidion zeylanicum (Gaertn) A. Juss 总被引:2,自引:0,他引:2
Six lignan and neolignan derivatives (1-6) were isolated from the n-BuOH-soluble fraction of a MeOH extract of the leaves of Glochidion zeylanicum. On the basis of spectral data, their structures were elucidated to be (+)-isolarisiresinol 3a-O-beta-glucopyranoside (1), dihydrodehydrodiconiferyl alcohol 4-, 9- and 9'-O-beta-D-glucopyranosides (2-4, respectively), (+)-isolarisiresinol 2a-O-beta-D-glucopyranoside (5), and dihydrodehydrodiconiferyl alcohol 9-O-sulfate (6), and 5 and 6 were new compounds. 相似文献
93.
94.
95.
96.
Takeda Y Isai N Masuda T Honda G Takaishi Y Ito M Otsuka H Ashurmetov OA Khodzhimatov OK 《Chemical & pharmaceutical bulletin》2001,49(8):1039-1041
From the aerial parts of Phlomis spinidens, two new flavonol bisglycosides, phlomisflavosides A (1) and B (2), were isolated together with the known compounds, astragalin, isoquercitrin, lamiridoside, phlomoside A, shanzhiside methyl ester, 8-O-acetylshanzhiside methyl ester, phlorigidoside C, rodioloside (=salidroside), forsythoside B, citroside A and lariciresinol-4'-O-beta-D-glucoside. The structures of the new compounds were elucidated based on spectral and chemical evidence. 相似文献
97.
Mikio Hori Tadashi Kataoka Hiroshi Shimizu Eiji Imai Yukiharu Matsumoto Iwao Miura 《Tetrahedron letters》1981,22(13):1259-1262
The novel ring transformation reactions were found in the reactions of 1,3,7,9-tetra-alkyl-8,9-dihydroxanthines and acetylenic compounds. The reaction of the dihydroxanthine with DMAD gave a propellane type compound and with methyl propiolate afforded the similar type compound and a pyrimido[4,5-b]diazepine derivative. The mechanism of these reactions was also discussed. 相似文献
98.
Tadashi Okuyama 《Tetrahedron letters》1982,23(26):2665-2666
1,2-Ethanedithiol and 1,3-propanedithiol were treated with perchloric acid in acetic anhydride to give 2-methyl-1,3-dithiolan-2-yl and 2-methyl-1,3-dithian-2-yl perchlorates, respectively, which were converted to ketene dithioacetals by deprotonation with tertiary amines. 相似文献
99.
100.
Eigoro Murayama Masahiro Uematsu Hiroyuki Nishio Tadashi Sato 《Tetrahedron letters》1984,25(3):313-316
Internal reaction of secondary alkyltin(IV) compounds having thionium ion gave internal trans olefins with high yield and regio- and stereoselectivity via 1,5- or 1,6-transfer of a hydride β to the trialkylstannyl group. 相似文献