全文获取类型
收费全文 | 3676篇 |
免费 | 465篇 |
国内免费 | 819篇 |
专业分类
化学 | 2133篇 |
晶体学 | 35篇 |
力学 | 586篇 |
综合类 | 76篇 |
数学 | 413篇 |
物理学 | 1717篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2017年 | 3篇 |
2016年 | 4篇 |
2015年 | 2篇 |
2014年 | 85篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 2篇 |
2010年 | 2篇 |
2009年 | 2篇 |
2008年 | 1篇 |
2007年 | 3篇 |
2006年 | 1篇 |
2005年 | 1篇 |
2003年 | 325篇 |
2002年 | 1404篇 |
2001年 | 1190篇 |
2000年 | 367篇 |
1999年 | 291篇 |
1998年 | 228篇 |
1997年 | 62篇 |
1996年 | 116篇 |
1995年 | 171篇 |
1994年 | 112篇 |
1993年 | 151篇 |
1992年 | 107篇 |
1991年 | 92篇 |
1990年 | 125篇 |
1989年 | 104篇 |
1985年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有4960条查询结果,搜索用时 15 毫秒
111.
Two new xanthone glycosides, securixanside B and C, were isolated fron the stems of Securidaca inappendiculate. Their structures were determined as 3-O-β-D-glucopyranosyl-1,7-dihydroxyl-2-methoxyxanthone and 6-O-β-D-glucopyranosyl-1-hydroxy-4,7-dimethoxyxanthone by spectroscopic methods. 相似文献
112.
快速响应的温敏性聚(N—异丙基丙烯酰胺)水凝胶——Ⅰ.以CaCO3为成孔剂制备方法、表征及动力学研究 总被引:4,自引:5,他引:4
以不同粒径的CaCO3粒子为成孔剂,合成了快速响应的温敏性聚(N-异丙基丙烯酰胺)(PNIPA)水凝胶,利用扫描电镜观察到水凝胶具有特殊的孔状结构,得到水凝胶的孔径大小为几十微米左右,动力学研究表明,该水凝胶在温敏膨胀或收缩时,具有快速的响应速率,在10min内的失水率可达90%,比较了干凝胶和40℃下失水后的凝胶两种不同状态下水凝胶的膨胀曲线,发现两者的溶胀动力学曲线明显不同,前者的曲线有拐点,同时发现与失水收缩速率相比,水凝胶具有较慢的吸水膨胀速率。 相似文献
113.
The stereoselective synthesis of (2R,4R)-2-N-tert-butyloxycarbonyl amino-4,5-epoxido-valeric acid methyl ester 8,which is the key intermediate for the synthesis of (2′S,2R)-3-trans-nitrocyclopropyl-alanine,was first accomplished. 相似文献
114.
A new method for the synthesis of 3-N-phthaloyl homophenylalanine lactone has been developed and its mechanism was proposed. 相似文献
115.
In continuation of our studies on Aconitum hemsleyanum Pritz.var. pengzhouense, two new norditerpenoid alkaloids, pengshenines A(1) and B(2),have isolated from the roots of the plants and their strucures were elucidated by 1D-and 2D-NMR. 相似文献
116.
The uniform NeFe2O4 powders with different particle size and morphologies (octahedral, cubic and spherical) have been prepared from different precursors via hydrothermal process. The nanocrystallines derived from precursor B in the weak alkali solution (pH≥10) are superparamagnetic. 相似文献
117.
Synthesis of the third-order nonlinear materials:bis (1,4-dihydroxynaphthalene) tetrathiafulvalene and bis (1,4-dialkoxylnaphthalene) tetrathiafulvalene has been achieved in four steps, starting from 2,3-dichloro-1,4-naphthaquinone. The materials exhibit larger third-order nonlinear optical susceptibilities χ. 相似文献
118.
A new diterpenoid was isolated from the ethanolic extract of the dried root bark of Tripterygium wilfordii Hook.f. It is the first example of abietane diterpenoid glycoside isolated from Tripterygium wilfordii Hook.f.Its structure was identified to be 11-0-β-D-glucopyranosyl-neotriptophenolide based on spectral methods. 相似文献
119.
Two Novel Myrinsol Diterpenes from Euphorbia prolifera 总被引:1,自引:1,他引:1
Two novel diterpenes,Euphorprolitherin A(1) and Euphorprolitherin B(2), were isolated from the roots of Euphorbia prolifera. Their structures were elucidated on the basis of spectroscopic methods. 相似文献
120.
Enantiomeric Sesquiterpene Lactones from Senecio tsoongianus 总被引:2,自引:0,他引:2
From Senecio tsoongianus,two pairs of enantiomeric isomers,tsoongianolides A(1) and B(2),tsoongianolides C (3) and D(4) were isolated. Their structures were elucidated by 1D and 2D-NMR techniques and X-ray diffractions. The cytotoxicity to KB cell of 1 and 2 is also reported. 相似文献