全文获取类型
收费全文 | 306篇 |
免费 | 4篇 |
国内免费 | 25篇 |
专业分类
化学 | 330篇 |
物理学 | 5篇 |
出版年
2023年 | 9篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 3篇 |
2019年 | 4篇 |
2018年 | 15篇 |
2017年 | 11篇 |
2016年 | 7篇 |
2015年 | 8篇 |
2014年 | 18篇 |
2013年 | 32篇 |
2012年 | 6篇 |
2011年 | 28篇 |
2010年 | 13篇 |
2009年 | 14篇 |
2008年 | 23篇 |
2007年 | 16篇 |
2006年 | 27篇 |
2005年 | 25篇 |
2004年 | 38篇 |
2003年 | 6篇 |
2002年 | 5篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 2篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
排序方式: 共有335条查询结果,搜索用时 15 毫秒
331.
332.
Efficient synthesis of polyester polyols with tunable molecular weight and microstructures from cyclic anhydride/epoxide mixtures by taking advantage of chain transfer reaction remains a great challenge, because most of the catalysts exhibit poor tolerance to chain transfer agent (CTA). In this contribution, we demonstrated that potassium acetate (KOAc) and 18-crown-6 (18-C-6) combination has great potential in the synthesis of diverse polyester polyols with controllable molecular weight and high-end group fidelity. Compared with KOAc, KOAc/18-C-6 pair could induce a much faster chain transfer between the active and dormant chains, and thus produce polyester polyols with narrow and monomodal distribution. In addition, polyester polyols could be efficiently prepared in laboratory by using commercially available cyclic anhydride without further purification (containing about 2% diacid residual as CTA) with an extremely low catalyst loading ([catalyst pair] : [anhydride] : [epoxide] = 1 : 50000 : 250000, [catalyst pair] = 0.0004 mol%). KOAc/18-C-6 could also promote the self-switchable copolymerization of cyclic anhydride/epoxide/cyclic ester mixtures. Ring- opening copolymerization of cyclic ester was initiated automatically after the full conversion of cyclic anhydride, finally producing polyester polyols with ABA-type block structure. 相似文献
333.
One-Carbon Homologation of α,β-Unsaturated Aldehydes: Access to α-Tertiary β,γ-Unsaturated Aldehydes
Dr. Arnaud Delbrassinne Boris Junior Takam Mba Laurent Collard Prof. Raphaël Robiette 《European journal of organic chemistry》2023,26(40):e202300765
An efficient protocol for the synthesis of enolizable α-substituted β,γ-unsaturated aldehydes is reported. The developed strategy involves two steps, epoxidation and Meinwald rearrangement, to result in a one-carbon homologation of α,β-unsaturated aldehydes enabling the insertion of a CHR unit. 相似文献
334.
Shengxiao Li Dr. Hui Zhu Longfei Li Wanjiao Chen Prof. Dr. Jie Jiang Dr. Zheng-Wang Qu Prof. Stefan Grimme Prof. Dr. Yong-Qiang Zhang 《Angewandte Chemie (International ed. in English)》2023,62(37):e202309525
A nuclearity-dependent enantiodivergent epoxide opening reaction has been developed, in which both antipodes of chiral alcohol products are selectively accessed by mononuclear (salen)TiIII complex and its self-assembled oxygen-bridged dinuclear counterparts within the same stereogenic ligand scaffold. Kinetic studies based on the Eyring equation revealed an enthalpy-controlled enantio-differentiation mode in mononuclear catalysis, whereas an entropy-controlled one in dinuclear catalysis. DFT calculations outline the origin of the enantiocontrol of the mononuclear catalysis and indicate the actual catalyst species in the dinuclear catalytic system. The mechanistic insights may shed a light on a strategy for stereoswichable asymmetric catalysis utilizing nuclearity-distinct transition-metal complexes. 相似文献
335.
Jing-Yu Li Chang-Long Tan Ming-Yu Qi Prof. Dr. Zi-Rong Tang Prof. Dr. Yi-Jun Xu 《Angewandte Chemie (International ed. in English)》2023,62(22):e202303054
Photocatalytic epoxide alcoholysis through C−O bond cleavage and formation has emerged as an alternative to synthesizing anti-tumoral pharmaceuticals and fine chemicals. However, the lack of crucial evidence to interpret the interaction between reactants and photocatalyst surface makes it challenging for photocatalytic epoxide alcoholysis with both high activity and regioselectivity. In this work, we report the hierarchical ZnIn2S4@CdS photocatalyst for epoxide alcoholysis with high regioselectivity nearly 100 %. Mechanistic studies unveil that the precise activation switch on exposed Zn acid sites for C−O bond polarization and cleavage has a critical significance for achieving efficient photocatalytic performance. Furthermore, the establishment of Z-scheme heterojunction facilitates the interface charge separation and transfer. Remarkably, the underlying regioselective photocatalytic reaction pathway has been distinctly revealed. 相似文献