全文获取类型
收费全文 | 193篇 |
免费 | 18篇 |
国内免费 | 94篇 |
专业分类
化学 | 143篇 |
力学 | 9篇 |
数学 | 39篇 |
物理学 | 114篇 |
出版年
2015年 | 1篇 |
2013年 | 2篇 |
2011年 | 34篇 |
2010年 | 24篇 |
2009年 | 25篇 |
2007年 | 7篇 |
2006年 | 8篇 |
2005年 | 14篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 11篇 |
2001年 | 12篇 |
2000年 | 5篇 |
1999年 | 13篇 |
1998年 | 21篇 |
1997年 | 23篇 |
1996年 | 7篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1993年 | 15篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 4篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1984年 | 1篇 |
排序方式: 共有305条查询结果,搜索用时 15 毫秒
91.
92.
93.
用密度泛函理论(DFT)的Bexke3lyp方法,对铀原子采用相对论有效原子实势及(6s5p2d4f)/[3s3p2d2f]收缩价基集合,碳、氧原子采用6-311G价基集合,应用Gaussian98程序对一氧化碳气体与铀表面相互作用的可能分子结构U-C-O、U-O-C、C-U-O(角形Cs和线形C∞v)等,进行abinitio优化计算.得到了十二种三重态或五重态的相对稳定结构的电子状态、几何构形、能量、谐振频率、力学性质和电性质等,并给出了角形和线形结构的正则振动分析图.结果表明,Cs构型的能量都比较低,尤其以U-C-O角形结构(3A″)为最低;通过对各成键原子间重叠布居数及键能分析知,U与CO的结合力较弱,O原子比C原子与U原子的结合力稍强. 相似文献
94.
Epoxidation of allyl chloride with H_2O_2 on Ti-ZSM-5 prepared by the isomorphous substitution 总被引:1,自引:0,他引:1
The epoxidation of allyl chloride with H2O2 on Ti-ZSM-5 prepared by isomorphous substitution of HZSM-5 with TiCl4 gas was studied. The results show that Ti-ZSM-5 has a high catalytic efficiency for the epoxidation of allyl chloride. The H2O2 utilization reaches 99.50% when the allyl chloride/H2O2 molar ratio is > 1. The effect of solvent species, catalyst concentration, H2O2 and allyl chloride concentration and reaction temperature on the epoxidation was investigated simultaneously. It is found that methanol is the best solvent for the reaction. The reaction rate equation with v = k[Cat. ] [H2O2]1/2-[C3H5Cl] and the apparent activation energy with Ea = 63.462 kJ/mol are obtained according to the kinetics study. 相似文献
95.
HUANG Chong ZHANG WenHan &LIU Bo Key Laboratory of Green Chemistry&Technology Ministry of Education College of Chemistry Sichuan University Chengdu China Key Laboratory of Synthetic Chemistry of Natural Substances 《中国科学B辑(英文版)》2011,(1)
An account of the total synthesis of(±)-,(+)-heliespirone A and(±)-,(-)-heliespirone C is presented.In the first-generation total synthesis,we found rac-24a could be easily transformed to rac-heliespirones A&C in a biomimic way.Taking the disappointing diastereoselectivity of prenylation from 3 to 4,the nonselective dihydroxylation from 4 to 5 and the lenthy route in strategy A into account,we designed a different synthetic plan targeting a highly enantioselective,concise and protective-group free synthesis... 相似文献
96.
LIN Feng ZHAO NanRong & LUO JiuLi Institute of Chemical Physics College of Chemistry Sichuan University Chengdu China 《中国科学B辑(英文版)》2011,(5)
A stochastic model of chemical reaction-heat conduction-diffusion for a one-dimensional gaseous system under Dirichlet or zero-fluxes boundary conditions is proposed in this paper. Based on this model,we extend the theory of the broadening exponent of critical fluctuations to cover the chemical reaction-heat conduction coupling systems as an asymptotic property of the corresponding Markovian master equation (ME),and establish a valid stochastic thermodynamics for such systems. As an illustration,the non-iso... 相似文献
97.
98.
99.
100.