全文获取类型
收费全文 | 4656篇 |
免费 | 466篇 |
国内免费 | 318篇 |
专业分类
化学 | 2865篇 |
晶体学 | 31篇 |
力学 | 215篇 |
综合类 | 20篇 |
数学 | 796篇 |
物理学 | 1513篇 |
出版年
2023年 | 56篇 |
2022年 | 137篇 |
2021年 | 124篇 |
2020年 | 161篇 |
2019年 | 118篇 |
2018年 | 124篇 |
2017年 | 111篇 |
2016年 | 157篇 |
2015年 | 163篇 |
2014年 | 200篇 |
2013年 | 288篇 |
2012年 | 373篇 |
2011年 | 324篇 |
2010年 | 241篇 |
2009年 | 211篇 |
2008年 | 285篇 |
2007年 | 235篇 |
2006年 | 215篇 |
2005年 | 188篇 |
2004年 | 149篇 |
2003年 | 128篇 |
2002年 | 119篇 |
2001年 | 96篇 |
2000年 | 118篇 |
1999年 | 77篇 |
1998年 | 70篇 |
1997年 | 65篇 |
1996年 | 89篇 |
1995年 | 64篇 |
1994年 | 69篇 |
1993年 | 56篇 |
1992年 | 60篇 |
1991年 | 43篇 |
1990年 | 33篇 |
1989年 | 46篇 |
1988年 | 42篇 |
1987年 | 34篇 |
1986年 | 44篇 |
1985年 | 41篇 |
1984年 | 39篇 |
1983年 | 28篇 |
1982年 | 21篇 |
1981年 | 19篇 |
1980年 | 24篇 |
1979年 | 19篇 |
1978年 | 17篇 |
1977年 | 22篇 |
1976年 | 23篇 |
1975年 | 19篇 |
1973年 | 12篇 |
排序方式: 共有5440条查询结果,搜索用时 15 毫秒
111.
112.
113.
The loss of three CO groups from derivatives of π-C6H5COC5H4Mn(CO)3 is a two-step mechanism in which the loss of two CO groups is followed by a third. Subsequent fragmentations generally involve rearrangement processes which often result in ring closure within the organic substrate. The central metal atoms plays an important part in such rearrangement processes and the positive charge can reside either on the metal or the ligand depending on the nature of the ligand. Fragmentation patterns are proposed for these systems. 相似文献
114.
115.
Tuulmets A Nguyen BT Panov D Sassian M Järv J 《The Journal of organic chemistry》2003,68(26):9933-9937
Kinetics of the reactions of butylmagnesium chloride and phenylmagnesium bromide with tetraethoxysilane and methyltrichlorosilane was investigated in diethyl ether and diethyl ether-toluene mixtures. Replacement of ether by toluene significantly accelerates the reaction with alkoxysilanes, while no effect was found for the reaction with chlorosilanes. We established that the reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium center by the silane followed by subsequent rearrangement of the complex to products through a four-center transition state. Chlorosilanes react differently without solvent molecule replacement but also via a four-center transition state. Large negative activation entropies are consistent with formation of cyclic transition states. Small activation enthalpy values together with remarkable exothermicity point to early transition states of the reactions. 相似文献
116.
[reaction: see text] Two different routes to the tricyclic core of Garcinia-derived natural products are described. The first approach is based on a tandem Claisen/Diels-Alder rearrangement and delivers the desired lactone 14. The second approach, employing a Wessely oxidation/Diels-Alder protocol, leads to the same caged heterocycle, albeit with modified constitution. 相似文献
117.
A linear response time-dependent density functional theory is described and used to calculate the dynamic polarizabilities and van der Waals C(6) coefficients of complex atom pairs. We present values of C(6) for dimers of main group atoms and the first row of transition metal atoms. 相似文献
118.
Reactions of (eta5-C5H(5-x)Brx)M(CO)3(M = Re, Mn; x= 1, 3, 4, 5) and IZn(CH2)2R(f8) in the presence of Cl2PdL2 catalysts give the title complexes (eta5)-C5H(5-x)(CH2)2R(f8)x)M(CO3), accompanied in the case of x= 5 by hydride-transfer byproducts. Extremely high fluorophilicities are realized, and the cyclopentadienyl ligands are readily detached (hnu) from the manganese complexes. 相似文献
119.
120.
A comparison between the construction of symmetry-correlation diagrams and the perturbation method for studying chemical reactions is carried out. The perturbation method consists of decomposing the system Hamiltonian H into a sum, H = H0 + H′. Various symmetry correlation schemes appearing in the literature may be explained by the nonuniqueness of the decomposition scheme. All symmetry selection rules may be viewed as the varieties. By examining the symmetry-correlation diagrams, processes under investigation may be called “forbidden” or “allowed,” depending on the topological feature. Of particular importance is the topology associated with the “avoided crossing.” By making the comparison, we can establish the correspondence of the two methods and conclude that the perturbation order furnishes the origin of the “forbiddenness” of a process. 相似文献