全文获取类型
收费全文 | 377篇 |
免费 | 92篇 |
国内免费 | 45篇 |
专业分类
化学 | 504篇 |
晶体学 | 1篇 |
综合类 | 3篇 |
物理学 | 6篇 |
出版年
2024年 | 1篇 |
2023年 | 4篇 |
2022年 | 16篇 |
2021年 | 13篇 |
2020年 | 23篇 |
2019年 | 17篇 |
2018年 | 11篇 |
2017年 | 12篇 |
2016年 | 35篇 |
2015年 | 33篇 |
2014年 | 23篇 |
2013年 | 70篇 |
2012年 | 35篇 |
2011年 | 28篇 |
2010年 | 27篇 |
2009年 | 18篇 |
2008年 | 23篇 |
2007年 | 19篇 |
2006年 | 16篇 |
2005年 | 12篇 |
2004年 | 6篇 |
2003年 | 27篇 |
2002年 | 3篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 3篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 4篇 |
1994年 | 4篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1987年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有514条查询结果,搜索用时 46 毫秒
21.
22.
An Alkene‐Promoted Borane‐Catalyzed Highly Stereoselective Hydrogenation of Alkynes to Give Z‐ and E‐Alkenes
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Yongbing Liu Lianrui Hu Prof. Dr. Hui Chen Prof. Dr. Haifeng Du 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3495-3501
The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ and E‐alkenes by the same catalytic hydrogenation system using molecular H2 has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C6F5)2‐catalyzed metal‐free hydrogenation of alkynes was adopted. Significantly, both Z‐ and E‐alkenes can be furnished by hydrogenation with molecular H2 in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H2 play an essential role in promoting the hydrogenolysis reaction. 相似文献
23.
The insertion of an alkyne into transition metal–hydrogen bonds is a key elementary step in catalytic polymerization and hydrogenation processes. It was found that a (Z)- or (E)-type alkyenyl complex can be formed through trans/cis stereospecific processes. In this work, the reaction mechanism of Cp2M(L)H [Cp = η5-C5H5; M = Nb, V; L = CO, P (OMe)3] with dimethylacetylene dicarboxylate (DMAD), and the factors influencing the stereoselectivity have been investigated based on density functional theory calculations. The calculated results show that all of the reactions are exothermic. For L = CO, the Z-isomer product forms first even at low temperatures because of the low Gibbs free energy barrier (ΔG#). Then the Z-pro converts to E-pro , while for L = P (OMe)3, the exclusive product is the E-isomer. For different metal centers, the reaction mechanisms of the Cp2M(CO)H + DMAD (M = Nb and V) reaction are similar, while their products are different at room temperature. For M = Nb, because the energy barrier of the isomerization from Z-pro to E-pro is low and the relative free energies of Z-pro and E-pro are almost equal, both Z-pro and E-pro can be obtained. While for the Cp2V(CO)H + DMAD reaction, only the Z-pro can be obtained under mild conditions, E-pro can be obtained only at high temperatures. For the Cp2M(CO)H+DMAD(M=V and Nb) reactions, the formation of E-isomer products proceeds via two five-membered ring transition states. The calculated results provide an reasonable explanation for the experimental results and predict a new insertion reaction. 相似文献
24.
Haobing Wang Xia Wu Yang Yang Masayoshi Nishiura Zhaomin Hou 《Angewandte Chemie (International ed. in English)》2020,59(18):7173-7177
The precise control of monomer sequence and stereochemistry in copolymerization is of much interest and importance for the synthesis of functional polymers, but studies toward this goal have met with only limited success to date. Now, the co‐syndiospecific alternating copolymerization of methoxyphenyl‐ and N,N‐dimethylaminophenyl‐functionalized propylenes with styrene by half‐sandwich rare‐earth catalysts is reported. This reaction efficiently afforded the corresponding functionalized propylene‐alt‐styrene copolymers with a perfect alternating sequence and excellent co‐syndiotacticity (rrrr >99 %), thus constituting the first example of co‐stereospecific alternating copolymerization of polar and non‐polar olefins. 相似文献
25.
26.
27.
P. P. Onys'ko T. V. Kim E. I. Kiseleva A. D. Sinytsa 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4):73-76
Abstract Allylic and heteroallylic compounds are classical objects of organic chemistry and can serve as models in the investigation of various theoretical problems. The anions and 1,3-dipoles generated from azaallylic derivatives are widely used in the synthesis of cyclic and acyclic nitrogen-containing compounds. 相似文献
28.
H. D. Durst D. K. Rohrbaugh S. Munavalli 《Phosphorus, sulfur, and silicon and the related elements》2013,188(11):2902-2909
The reaction of dialkylphosphonites with N-(bromomethyl)phthalimide furnishes alkyl phenyl hydrogenphosphinates, dialkyl phenylphosphonates, and N-[(bromomethyl)phthalimido)]-phosphinates. The stereoselectivity of the primary product of the reaction appears to increase with the increasing size of the groups attached to the phosphorus atom. 相似文献
29.
30.
Enantiopure Ferrocene‐Based Planar‐Chiral Iridacycles: Stereospecific Control of Iridium‐Centred Chirality
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Ross A. Arthurs Dr. Muhammad Ismail Christopher C. Prior Dr. Vasily S. Oganesyan Dr. Peter N. Horton Dr. Simon J. Coles Dr. Christopher J. Richards 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(9):3065-3072
Reaction of [IrCp*Cl2]2 with ferrocenylimines (Fc=NAr, Ar=Ph, p‐MeOC6H4) results in ferrocene C?H activation and the diastereoselective synthesis of half‐sandwich iridacycles of relative configuration Sp*,RIr*. Extension to (S)‐2‐ferrocenyl‐4‐(1‐methylethyl)oxazoline gave highly diastereoselective control over the new elements of planar chirality and metal‐based pseudo‐tetrahedral chirality, to give both neutral and cationic half‐sandwich iridacycles of absolute configuration Sc,Sp,RIr. Substitution reactions proceed with retention of configuration, with the planar chirality controlling the metal‐centred chirality through an iron–iridium interaction in the coordinatively unsaturated cationic intermediate. 相似文献