全文获取类型
收费全文 | 37篇 |
免费 | 22篇 |
国内免费 | 32篇 |
专业分类
化学 | 57篇 |
数学 | 10篇 |
物理学 | 24篇 |
出版年
2023年 | 1篇 |
2022年 | 1篇 |
2020年 | 4篇 |
2018年 | 2篇 |
2015年 | 1篇 |
2014年 | 6篇 |
2013年 | 3篇 |
2012年 | 7篇 |
2011年 | 7篇 |
2010年 | 7篇 |
2009年 | 6篇 |
2008年 | 9篇 |
2007年 | 8篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 4篇 |
2003年 | 3篇 |
2002年 | 1篇 |
2001年 | 2篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1997年 | 3篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1988年 | 1篇 |
1982年 | 1篇 |
排序方式: 共有91条查询结果,搜索用时 31 毫秒
1.
2H-1,2,3-Diazaphospholes 3a-3h were prepared from various ketone acylhydrazones and phosphorus trichloride in the presence of triethylamine. Compounds 3 underwent feasible hetero-Diels-Alder reactions with cyclopentadiene to afford the respective anellated [1,2,3]diazaphospholes 4a--4d as well as 4a‘--4d‘ in moderate yields. The endo rule in the reaction was observed under kinetic control conditions. 相似文献
2.
Ling-Tian Tang Yu Wei Yi Wang Shao-Wen Hu Xin-Qi Liu Tai-Wei Chu Xiang-Yun Wang 《Journal of Molecular Structure》2004,686(1-3):25-30
The formation of charge-transfer (CT) complexes between N-methyl-6,7-methylenedioxy-tetrahydro-4-isoquinolone (MMDTIQ, the model molecule of alkaloids) and iodine monochloride has been studied with the density functional B3LYP method. The competition for ICl between n-donor(s) and π-donor in the same molecule has been compared for the first time. The results indicate that the electron-donating ability of various donor sites decreases in the following order: amino nitrogen>carbonyl oxygen>etheric oxygen≈aromatic ring. Complexes with a stoichiometry of 1:1 to 1:5 (MMDTIQ–ICl) might form. Among complexes with a given stoichiometry, the one in which the phenyl ring is involved in the binding is always the least stable. According to these results, in order to ensure an alkaloid iodinated, the amount of ICl should be far beyond that of alkaloids and a low polar solvent should be used, which is quite in agreement with our recent experimental results. 相似文献
3.
4.
5.
6.
Ferroelectric behaviour of 30nm BaTiO3 ceramics prepared by high pressure assisted sintering 下载免费PDF全文
Dense nanocrystalline BaTiO3 ceramics with a homogeneous grain size of 30 nm was obtained by pressure assisted sintering. The ferroelectric behaviour of the ceramics was characterized by the dielectric peak at around 120 ℃, the P-E hysteresis loop and some ferroelectric domains. These experimental results indicate that the critical grain size for the disappearance of ferroelectricity in nanocrystalline BaTiO3 ceramics fabricated by pressure assisted sintering is below 30 nm. The ferroelectric property decreasing with decreasing grain size can be explained by the lowered tetragonality and the 'dilution' effect of grain boundaries. 相似文献
7.
利用密度泛函理论(DFT)计算的方法,对O_2,H_2O单独吸附和共吸附在Au_(38)团簇上的吸附性质进行了结构,能量和电子分析.计算结果表明,O_2倾向于吸附在edge位,H_2O则倾向于吸附在top位.Au(100)表面较之Au(111)表面更有利于O_2,H_2O的吸附,这与实验结果相符合.H_2O和O_2共吸附研究表明,H_2O的存在促进了O_2的吸附.Mulliken和分态密度(PDOS)分析得出:在共吸附中,H_2O将部分电子转移给了O_2,促进了O_2的活化与解离,并生成了类似H_2O_2的中间态,从而为催化氧化反应提供了O活性物种. 相似文献
8.
Xu Xiang-Yun Gao Yu-Tong Wang Ying-Ying Zhou You-Shuang Xiong Bi-Jin Zhu Jin-Tao 《高分子科学》2023,41(6):897-904
Chinese Journal of Polymer Science - Miscible disordered block copolymers (BCPs) are rarely studied due to the limits in self-assembly into ordered microstructures. Herein, we proposed a facile... 相似文献
9.
The mechanism of the gas-phase reaction UF 6 + H 2O --> UOF 4 + 2HF is explored using relativistic density functional theory calculations. Initially, H 2O coordinates with UF 6 to form a 1:1 complex UF 6.H 2O. Over an activation energy barrier of about 19 kcal/mol, H 2O transfers a H atom to a nearby ligand F, resulting in UF 5OH + HF. The eliminated HF or another H 2O molecule may form a hydrogen bond with UF 5OH. Starting from UF 5OH, the second HF elimination results in UOF 4. If UF 5OH is in the isolated form, UF 5OH --> UOF 4 + HF takes place over a barrier of 24 kcal/mol. If UF 5OH is hydrogen-bonded with H 2O or HF, the conversion barrier is less than 10 kcal/mol. Once formed, the unstable UOF 4 tends to associate with additional ligands and hydrogen-bonding donors. The calculated binding energies indicate the significance of such interactions, which may have profound impact on further HF eliminating reactions. The IR spectra features can be used to indicate the formation and interaction type of the intermediates and products. 相似文献
10.
A method for rapid separation and sensitive determination of three water-soluble vitamins, pyridoxine, ascorbic acid (VC), and p-aminobenzoic acid (PABA) has been developed by PDMS microchannel electrophoresis integrated with amperometric detection. After treatment of the microchip with oxygen plasma, the peak shapes of the three analytes were essentially improved. Pyridoxine, VC, and PABA were well separated within only 80 s in a running buffer of 20 mM borate solution (pH 8.5). Good linearity was obtained within the concentration range of 2-200 microM for the three water-soluble vitamins. The detection limits were 1.0 microM for pyridoxine and VC, and 1.5 microM for PABA. The proposed method has been successfully applied to real human urine sample, without solid phase extraction, with recoveries of 80-122% for the three water-soluble vitamins. 相似文献