全文获取类型
收费全文 | 211篇 |
免费 | 33篇 |
国内免费 | 66篇 |
专业分类
化学 | 308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 | 19篇 |
2012年 | 18篇 |
2011年 | 13篇 |
2010年 | 19篇 |
2009年 | 10篇 |
2008年 | 25篇 |
2007年 | 12篇 |
2006年 | 15篇 |
2005年 | 19篇 |
2004年 | 18篇 |
2003年 | 15篇 |
2002年 | 4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310条查询结果,搜索用时 31 毫秒
61.
Total Synthesis of Mycinamicin IV as Integral Part of a Collective Approach to Macrolide Antibiotics
Georg Späth Prof. Alois Fürstner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(11):e202104400
The total synthesis of the 16-membered macrolide mycinamicin IV is outlined, which complements our previously disclosed, largely catalysis-based route to the aglycone. This work must also be seen in the context of our recent conquest of aldgamycin N, a related antibiotic featuring a similar core but a distinctly different functionalization pattern. Taken together, these projects prove that the underlying blueprint is integrative and hence qualifies for a collective approach to this prominent class of natural products. In both cases, the final glycosylation phase mandated close attention and was accomplished only after robust de novo syntheses of the (di)deoxy sugars of the desosamine, chalcose, mycinose and aldgarose types had been established. Systematic screening of the glycosidation promoter was also critically important for success. 相似文献
62.
Kefeng Wan Jiangui Zhao Song Qin Xueli Zheng Haiyan Fu Ruixiang Li Hua Chen Jijun Yang Chunji Yang 《应用有机金属化学》2020,34(10):e5863
Three bidentate phosphoramidite ligands were synthesized, characterized, and employed in Rh-catalyzed hydroformylation of vinyl ethers. The complex Rh(acac)(2,2′-bis{(di[1H-indol-1-yl]phosphanyl)oxy}-1,1′-binaphthalene} (acac = acetylacetone) (Rh- L4 ) was also synthesized and characterized. Rh- L4 showed good regioselectivity for the hydroformylation of vinyl ethers under mild reaction conditions: 2 MPa of syngas, 1:1 (H2/CO) substrate/catalyst molar ratio 1000:1, and 60 °C. The linear selectivity was up to 98%, and in most cases was about 80%, with no hydrogenation product formation observed, which could be a potential way to synthesize 1,3-propanediol. A mechanism study including density functional theory computational analysis showed that both Rh–H and CO insertion steps in the hydroformylation of vinyl ether were linear-preferred in our catalyst system. 相似文献
63.
This work reports rhodium catalyzed selective hydroformylation of natural olefins like eugenol, estragole, anethole, prenol and isoprenol using biphenyl based Buchwald phosphine ligands (S‐Phos ( L 1 ), t‐Bu XPhos ( L 2 ), Ru‐Phos ( L 3 ), Johnphos ( L 4 ) and DavePhos ( L 5 ). Ru‐Phos ( L 3 ) ligand exhibited high impact on the hydroformylation of eugenol providing high selectivity (90%) of linear aldehyde as major product. In addition, internal natural olefins like anethole and prenol provided moderate to high selectivity (65% and 85% respectively) of branched aldehydes as a major products. The various reaction parameters such as influence of ligands, P/Rh ratio, syngas pressure, temperature, time and solvents have been studied. A high activity and selectivity gained on the way to the linear aldehydes it may be due to the bulky, steric cyclohexyl and isopropoxy groups present in L 3 phosphine ligand. Moreover, this catalytic system was smoothly converting natural olefins into corresponding linear and branched aldehydes with higher selectivity under the mild reaction conditions. 相似文献
64.
Back Cover: Hydroformylation of Olefins by a Rhodium Single‐Atom Catalyst with Activity Comparable to RhCl(PPh3)3 (Angew. Chem. Int. Ed. 52/2016) 下载免费PDF全文
65.
合成了四个从葡萄糖及半乳糖衍生的手性芳基双膦配体,制备了手性双膦-铑(Ⅰ)配合物催化剂,并将其用于苯乙烯不对称氢甲酰化反应中.结果表明,葡萄糖骨架手性中心与联萘基之间有协同作用,对映体过量值和转化率受配体C-4骨架立体中心的绝对构型影响,而产物的绝对构型则主要由联萘单元控制;配体4-双{[(S)-1,1′-联萘基-2,2′-双基]-磷}-苯基-3,6-脱水-β-D-葡萄糖的吡喃糖苷基和联萘基的匹配组合,给出41%的对映体选择性和74∶26(异构/正构)区域选择性. 相似文献
66.
Xi Yang Haoran Liang Haiyan Fu Xueli Zheng Maolin Yuan Ruixiang Li Hua Chen 《应用有机金属化学》2016,30(5):335-340
The organic/aqueous biphasic hydroformylation of 2,5‐norbornadiene (NBD) was investigated for the first time using HRh(CO)(TPPTS)3 (TPPTS: trisodium salt of tri(m‐sulphonylphenyl)phosphine) as the catalyst precursor. A comparison was made of homogeneous and biphasic systems. The optimum reaction parameters are discussed and the reaction mechanism is presented. In order to ensure the process attained high activity under moderate conditions, the effect of various cationic surfactants was tested in the biphasic hydroformylation of NBD. The results indicated that the hydroformylation of NBD in the biphasic system exhibited high activity and high selectivity to dialdehyde products under mild conditions. The addition of cationic surfactants markedly accelerated the reaction. A single long‐chain surfactant seemed to exert a greater impact on the hydroformylation of NBD than a double long‐chain surfactant. Moreover, the recycling of aqueous solution containing catalyst with or without surfactant was investigated. In the absence of the surfactant, the aqueous catalyst could be recycled six times without a significant decrease in activity and selectivity. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
67.
68.
Probing o‐Diphenylphosphanyl Benzoate (o‐DPPB)‐Directed CC Bond Formation: Total Synthesis of Dictyostatin 下载免费PDF全文
Sebastian Wünsch Prof. Dr. Bernhard Breit 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2358-2363
Herein, we report a robust total synthesis of dictyostatin. This polyketide natural product has attracted much attention because of its impressive antiproliferative activity against several human cancer‐cell lines. We accomplished its synthesis in a highly convergent manner from three fragments of equal complexity, which were prepared on multigram scale. The southern and northwestern subunits were constructed through application of our o‐DPPB‐directed hydroformylation and allylic substitution methodology, respectively. These methods generated the C6 and C14 stereocenters of dictyostatin with good diastereoselectivities and simultaneously allowed further elaboration of the fragments by Wittig olefination and Sharpless asymmetric epoxidation, respectively. The compelling performance of the hydroformylation and allylic substitution with regard to practicability, selectivity, and scale underline their value for the construction of propionate motifs. 相似文献
69.
70.