全文获取类型
收费全文 | 211篇 |
免费 | 3篇 |
专业分类
化学 | 157篇 |
力学 | 13篇 |
数学 | 23篇 |
物理学 | 21篇 |
出版年
2022年 | 2篇 |
2021年 | 6篇 |
2020年 | 4篇 |
2019年 | 8篇 |
2018年 | 5篇 |
2017年 | 2篇 |
2016年 | 7篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 7篇 |
2012年 | 15篇 |
2011年 | 9篇 |
2010年 | 6篇 |
2009年 | 9篇 |
2008年 | 13篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 7篇 |
2004年 | 10篇 |
2003年 | 10篇 |
2002年 | 5篇 |
2001年 | 5篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 2篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 2篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1974年 | 4篇 |
1973年 | 1篇 |
1970年 | 1篇 |
1963年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有214条查询结果,搜索用时 0 毫秒
211.
212.
Ivan I. Zakharov Vladimir A. Zakharov Alexandr G. Potapov Georgii M. Zhidomirov 《Macromolecular theory and simulations》1999,8(3):272-278
The electronic structure and geometry of polymethylaluminoxane (MAO) [—Al(CH3)O—]n with different size (n = 4–12) have been studied using quantum‐chemical DFT (density functional theory) calculations. It has been found: 1) Starting from n = 6, the three‐dimensional oxo‐bridged (cage) structure of MAO is more stable than the cyclic structure. 2) Both for cage structure and for cyclic structure the Lewis acidity of Al atoms characterized by their net positive charge amplifies with increasing size of MAO (n). 3) Trimethylaluminium (AlMe3) reacts with the cage structure of MAO with cleavage of an Al‐O dative bond and formation of acidic tri‐coordinated Alv and basic di‐coordinated Ov atoms in the MAO molecule. Two molecules AlMe3 are associated with acidic Alv and basic Ov centers. As the MAO increases in size, the acidity of Alv centers amplifies and the distance Alv‐(AlMe3) shortens; on the contrary, interaction of AlMe3 with Ov centers weakens and the distance Ov‐(AlMe3) increases with increasing n value. The total heat of Al2Me6 interaction with MAO (sum interaction of Alv‐(AlMe3) and Ov‐(AlMe3)) noticeably decreases as the size of MAO increases (from 50.9 kcal/mol for n = 4 to 20.2 kcal/mol for n = 12). It is proposed that acidic Alv and basic Ov centers formed in the cage structure of MAO interact with zirconocene yielding ‘cation‐like’ zirconium active centers. 相似文献
213.
Ivan I. Zakharov Vladimir A. Zakharov Georgii M. Zhidomirov 《Macromolecular theory and simulations》1996,5(5):837-843
Using the ab initio method of SCF MO LCAO 1 SCF MO LCAO: Self-consistent field molecular orbital linear combination of atomic orbitals. in a valency-splitted basis of the Gaussian functions we have studied the addition of various monomers (C3H8, C2H4, C2H2) and dihydrogen to the titanium-alkyl bond in the complex H2TiCH3. The structure of transition states in the insertion reaction, heats of π-complex formation and activation energies for the insertion of the coordinated monomers have been calculated. The calculation results show that the reactivity decreases in the order C2H2 > C2H4 > C3H8 > H2. According to the results obtained, the energy of the π*-antibonding orbital of monomers can serve as an index of relative reactivity in the insertion reaction into the metal-alkyl bond. 相似文献
214.
Triethylgermylpentafluorobenzene C6F5GeEt3 reacts with CF3SO3H, HSO3Cl, Me3SiOSO2Cl, chlorine, bromine, Cl2/AlCl3, or Br2/AlBr3 with cleavage of the Caryl Ge bond. Cesium fluoride promotes electrophilic degermylation of C6F5GeEt3, possibly via the intermediate formation of a tetraorganylfluorogermanate. 相似文献