全文获取类型
收费全文 | 206篇 |
免费 | 33篇 |
国内免费 | 65篇 |
专业分类
化学 | 302篇 |
晶体学 | 1篇 |
物理学 | 1篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 3篇 |
2020年 | 6篇 |
2019年 | 7篇 |
2018年 | 4篇 |
2017年 | 2篇 |
2016年 | 9篇 |
2015年 | 9篇 |
2014年 | 13篇 |
2013年 | 18篇 |
2012年 | 18篇 |
2011年 | 13篇 |
2010年 | 19篇 |
2009年 | 10篇 |
2008年 | 23篇 |
2007年 | 12篇 |
2006年 | 14篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 14篇 |
2002年 | 3篇 |
2001年 | 7篇 |
2000年 | 2篇 |
1999年 | 8篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 8篇 |
1995年 | 13篇 |
1994年 | 5篇 |
1993年 | 5篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1984年 | 1篇 |
1983年 | 2篇 |
排序方式: 共有304条查询结果,搜索用时 15 毫秒
1.
Pim R. Linnebank Stephan Falcão Ferreira Alexander M. Kluwer Prof. Dr. Joost N. H. Reek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(37):8214-8219
Regioselective catalytic transformations using supramolecular directing groups are increasingly popular as it allows for control over challenging reactions that may otherwise be impossible. In most examples the reactive group and the directing group are close to each other and/or the linker between the directing group is very rigid. Achieving control over the regioselectivity using a remote directing group with a flexible linker is significantly more challenging due to the large conformational freedom of such substrates. Herein, we report the redesign of a supramolecular Rh–bisphosphite hydroformylation catalyst containing a neutral carboxylate receptor (DIM pocket) with a larger distance between the phosphite metal binding moieties and the DIM pocket. For the first time regioselective conversion of internal and terminal alkenes containing a remote carboxylate directing group is demonstrated. For carboxylate substrates that possess an internal double bond at the Δ-9 position regioselectivity is observed. As such, the catalyst was used to hydroformylate natural monounsaturated fatty acids (MUFAs) in a regioselective fashion, forming of an excess of the 10-formyl product (10-formyl/9-formyl product ratio of 2.51), which is the first report of a regioselective hydroformylation reaction of such substrates. 相似文献
2.
考察了双亚磷酸酯配体Bisphosphite 1、Bisphosphite 2及双膦配体DPPE、DPPP、DPPB、BISBI在丁烯氢甲酰化反应中的反应活性和选择性,并对双亚磷酸酯配体和双膦配体进行混合,应用到丁烯氢甲酰化反应当中,对混合配体进行筛选发现Bisphosphite 1与DPPB混合配体的反应效果最佳,明显提高了1-丁烯氢甲酰化产物醛的正异构比,并通过31P NMR等方法推测了混合配体与铑配位的关键配合物中间体.通过正交实验优选了铑催化剂浓度、Bisphosphite 1浓度与DPPB浓度,其优化的催化剂配方对1-丁烯氢甲酰化的正异构比达到76.3,平均TOF 1821 h-1. 相似文献
3.
Rhodium‐Catalyzed Hydroformylation of 1,1‐Disubstituted Allenes Employing the Self‐Assembling 6‐DPPon System 下载免费PDF全文
Alexander Köpfer Prof. Dr. Bernhard Breit 《Angewandte Chemie (International ed. in English)》2015,54(23):6913-6917
A rhodium‐catalyzed hydroformylation of 1,1‐disubstituted allenes is reported. Using a RhI/6‐DPPon catalyst system, one can obtain β,γ‐unsaturated aldehydes in high regio‐ and chemoselectivity. The Z‐configured product is formed with up to >95 % selectivity when unsymmetrically 1,1‐disubstituted allenes are submitted to the reaction conditions. This is the first time that these interesting building blocks are accessible by hydroformylation of allenes. The utility of this methodology is demonstrated by further transformations of one of the obtained products. 相似文献
4.
DFT and CCSD(T) methods were used to examine 61 different rhodium catalysts for the hydroformylation of ethylene. The carbon monoxide (CO) stretching frequency was a key electronic parameter to understand the π-accepting nature of the ligand. Normally, π-accepting ligands lead to increased CO stretching frequencies and a reduction in CO dissociation energy. There was no relationship between CO dissociation energy and CO stretching frequency. However, a clear relationship exists between the ethylene insertion barrier (from the rhodium dicarbonyl hydride resting state) and the CO stretching frequency as stronger π-accepting ligands systematically led to a reduction in the barrier. Due to the multistep nature of the rate-limiting step, the overall barrier can be divided into the CO/ethylene equilibrium and an intrinsic ethylene insertion barrier and both are systematically reduced as the π-accepting nature of the ligand is increased. A comparison of the carbonylation transition state (TS) to the ethylene insertion TS allowed us to understand reversibility of olefin insertion. While the ethylene insertion TS systematically decreases with increasing CO stretching frequency, the carbonylation TS is relatively flat. The lines cross at 2156 cm−1 implying a change in the rate-limiting step in this region given a standard set of process conditions. © 2018 Wiley Periodicals, Inc. 相似文献
5.
6.
Tianbo Li Fang Chen Rui Lang Hua Wang Yang Su Botao Qiao Aiqin Wang Tao Zhang 《Angewandte Chemie (International ed. in English)》2020,59(19):7430-7434
The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water–gas shift reaction on a Rh single‐atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water–gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes. 相似文献
7.
Supramolecular capsules can be used to change the activity and selectivity of a catalyst through the influence of the second coordination sphere, reminiscent of how enzymes control the selectivity of their processes. In enzymes, this approach is used to also control the enantioselectivity of reactions in which the active catalytic site is often not chiral but the second coordination sphere is. We are interested in the possibility to generate a chiral second coordination sphere around an otherwise achiral transition metal complex for asymmetric catalysis. In this paper we show that the ligand template approach can be used to generate a chiral second coordination sphere around a rhodium complex, which is used in asymmetric hydroformylation. 相似文献
8.
Sequential Hydroformylation/Diels–Alder Processes: One‐Pot Synthesis of Polysubstituted Cyclohexenes,Cyclohexadienes, and Phthalates from Alkynes 下载免费PDF全文
Xianjie Fang Dr. Ralf Jackstell Prof. Dr. Matthias Beller 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(26):7939-7942
A novel, one‐pot hydroformylation/Diels–Alder sequence for the synthesis of multisubstituted cyclohexenes, cyclohexadienes, and phthalates has been developed. Various alkynes were efficiently converted into the corresponding products in good yields and with excellent diastereoselectivity through palladium‐catalyzed hydroformylation followed by an AAD‐type reaction (AAD: Amides–Aldehydes–Dienophiles). In view of the availability of the substrates, the atom‐efficiency of the overall process, and the convenient introduction of substituents in the cyclohexene ring, this method complements current methods for the preparation of polysubstituted cyclohexane derivatives. 相似文献
9.
10.