全文获取类型
收费全文 | 372篇 |
免费 | 103篇 |
国内免费 | 3篇 |
专业分类
化学 | 476篇 |
物理学 | 2篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 5篇 |
2021年 | 7篇 |
2020年 | 29篇 |
2019年 | 12篇 |
2018年 | 13篇 |
2017年 | 6篇 |
2016年 | 34篇 |
2015年 | 36篇 |
2014年 | 35篇 |
2013年 | 32篇 |
2012年 | 28篇 |
2011年 | 34篇 |
2010年 | 25篇 |
2009年 | 43篇 |
2008年 | 32篇 |
2007年 | 21篇 |
2006年 | 14篇 |
2005年 | 17篇 |
2004年 | 7篇 |
2003年 | 19篇 |
2002年 | 11篇 |
2001年 | 5篇 |
2000年 | 3篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1995年 | 2篇 |
排序方式: 共有478条查询结果,搜索用时 15 毫秒
411.
Construction of Hexahydrophenanthrenes By Rhodium(I)‐Catalyzed Cycloisomerization of Benzylallene‐Substituted Internal Alkynes through C−H Activation 下载免费PDF全文
Yasuaki Kawaguchi Dr. Shigeo Yasuda Prof. Dr. Chisato Mukai 《Angewandte Chemie (International ed. in English)》2016,55(35):10473-10477
The treatment of benzylallene‐substituted internal alkynes with [RhCl(CO)2]2 effects a novel cycloisomerization by C(sp2)?H bond activation to produce hexahydrophenanthrene derivatives. The reaction likely proceeds through consecutive formation of a rhodabicyclo[4.3.0] intermediate, σ‐bond metathesis between the C(sp2)?H bond on the benzene ring and the C(sp2)?RhIII bond, and isomerization between three σ‐, π‐, and σ‐allylrhodium(III) species, which was proposed based on experiments with deuterated substrates. 相似文献
412.
Aromatic Osmacyclopropenefuran Bicycles and Their Relevance for the Metal‐Mediated Hydration of Functionalized Allenes 下载免费PDF全文
Dr. María Batuecas Dr. Ruth Castro‐Rodrigo Prof. Dr. Miguel A. Esteruelas Dr. Cristina García‐Yebra Prof. Dr. Ana M. López Dr. Enrique Oñate 《Angewandte Chemie (International ed. in English)》2016,55(44):13749-13753
The aromatic osmacyclopropenefuran bicycles [OsTp{κ3‐C1,C2,O‐(C1H2C2CHC(OEt)O)}(PiPr3)]BF4 (Tp=hydridotris(1‐pyrazolyl)borate) and [OsH{κ3‐C1,C2,O‐(C1H2C2CHC(OEt)O)}(CO)(PiPr3)2]BF4, with the metal fragment in a common vertex between the fused three‐ and five‐membered rings, have been prepared via the π‐allene intermediates [OsTp(η2‐CH2=CCHCO2Et)(OCMe2)(PiPr3)]BF4 and [OsH(η2‐CH2=CCHCO2Et)(CO)(OH2)(PiPr3)2]BF4, and their aromaticity analyzed by DFT calculations. The bicycle containing the [OsH(CO)(PiPr3)2]+ metal fragment is a key intermediate in the [OsH(CO)(OH2)2(PiPr3)2]BF4‐catalyzed regioselective anti‐Markovnikov hydration of ethyl buta‐2,3‐dienoate to ethyl 4‐hydroxycrotonate. 相似文献
413.
Rhodium‐Catalyzed Diastereoselective Cyclization of Allenyl‐Sulfonylcarbamates: A Stereodivergent Approach to 1,3‐Aminoalcohol Derivatives 下载免费PDF全文
Pierre A. Spreider Dr. Alexander M. Haydl Marc Heinrich Prof. Dr. Bernhard Breit 《Angewandte Chemie (International ed. in English)》2016,55(50):15569-15573
A diastereoselective and stereodivergent rhodium‐catalyzed intramolecular coupling of sulfonylcarbamates with terminal allenes is described and it provides selective access to 1,3‐aminoalcohol derivatives, scaffolds found in bioactive compounds. The reaction is compatible with a large range of different functional groups, thus furnishing products with high diastereoselectivities and yields. Moreover, multigram scale reactions, as well as the application of suitable product transformations were demonstrated. 相似文献
414.
Can substituted allenes be highly efficient leaving groups in catalytic processes? A computational investigation 下载免费PDF全文
There is considerable interest presently in the chemistry of allenes. The current computational investigation looks into the possibility of using allenes and their derivatives as leaving groups. As it is well known, leaving groups are significant in catalytic processes for generating the active site. A full quantum mechanical study using density functional theory shows that allenes and their derivatives can function as excellent leaving groups. Indeed, the calculations show that they can be several orders of magnitude more effective than existing ligands for this purpose. The modification of second generation Grubbs' catalysts with these ligands suggests that the allene ligand cases that would be most effective are those having electron withdrawing groups, especially those that have the potential for supramolecular interactions between the substituent groups in the free state. © 2015 Wiley Periodicals, Inc. 相似文献
415.
Stereospecific and Stereoselective Rhodium(I)‐Catalyzed Intramolecular [2+2+2] Cycloaddition of Allene‐Ene‐Ynes: Construction of Bicyclo[4.1.0]heptenes 下载免费PDF全文
Yuu Ohta Dr. Shigeo Yasuda Yuka Yokogawa Kei Kurokawa Prof. Dr. Chisato Mukai 《Angewandte Chemie (International ed. in English)》2015,54(4):1240-1244
Treatment of the allene‐ene‐yne substrates with [{RhCl(CO)2}2] effected the intramolecular [2+2+2]‐type ring‐closing reaction to produce various of tri‐ and tetracyclic derivatives containing a cyclopropane ring. The reaction is highly stereoselective as well as stereospecific with good to excellent yields. 相似文献
416.
Dr. Guoyong Song Dr. Baoli Wang Dr. Masayoshi Nishiura Prof. Dr. Zhaomin Hou 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(23):8394-8398
The catalytic C?H addition of pyridines to allenes has been achieved for the first time by using a half‐sandwich scandium catalyst, thus constituting a straightforward and atom‐economical route for the synthesis of alkenylated pyridine derivatives. The reaction proceeded regio‐ and stereoselectively, affording a new family of alkenylated pyridine compounds which are otherwise difficult to synthesize. A cationic Sc‐η2‐pyridyl species was isolated and confirmed to be a key catalyst species in this transformation. 相似文献
417.
Lukas Körner Dr. Luong Phong Ho Dr. Ralph Puchta Prof. Dr. Amnon Stanger Prof. Dr. Matthias Tamm 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(65):e202202737
The new diaminoacetylene (DAA) dimorpholinoacetylene ( 3 ) was prepared from 1,1-dimorpholinoethene ( 1 ) by bromination to form the dibromoketene aminal 2 , which upon lithiation afforded 3 through a Fritsch-Buttenberg-Wiechell rearrangement. Heating 3 at elevated temperatures resulted in a complete conversion into the dimer 1,1,2,4-tetramorpholino-1-buten-3-yne ( 4 ), which was used for the synthesis of four-membered cyclic bent allene (CBA) transition-metal complexes of the type [(CBA)MLn] ( 5 - 7 ; MLn=AuCl, RhCl(COD), RhCl(CO)2; CBA=1,3,4,4-tetramorpholino-1,2-cyclobutadiene; COD=1,5-cyclooctadiene). The reaction of 3 with tetraethylammonium bromide gave 1,2,3,4-tetramorpholinocyclobutenylium bromide ( 8 ), which reacted with bromine to form 1,2,3,4-tetra(morpholino)cyclobutenediylium bis(tribromide) ( 9 ). Compound 9 represents the first fully characterized compound containing a tetraaminocyclobutadiene dication and displays a nearly planar C4N4 core as shown by X-ray diffraction analysis. Detailed quantum chemical calculations were performed to assess the aromaticity of tetraaminocyclubutadiene dications by employing the Nucleus Independent Chemical Shift (NICS) method and current density analysis. 相似文献
418.
Direct Synthesis of Chiral Allenoates from the Asymmetric CH Insertion of α‐Diazoesters into Terminal Alkynes 下载免费PDF全文
Yu Tang Quangang Chen Prof. Dr. Xiaohua Liu Gang Wang Dr. Lili Lin Prof. Dr. Xiaoming Feng 《Angewandte Chemie (International ed. in English)》2015,54(33):9512-9516
The asymmetric C? H insertion of α‐diazoesters into 1‐alkynes was achieved using chiral cationic guanidinium salts and copper(I) complexes. Optically active 2,4‐disubstituted allenoates were generated under mild reaction conditions from various α‐diazoesters and 1‐alkynes in high yield (up to 99 %) and enantioselectivity (up to 97:3 e.r.). Control experiments excluded the possibility of an asymmetric isomerization of alkynoates. 相似文献
419.
Eileen G. Burke Prof. Jennifer M. Schomaker 《Angewandte Chemie (International ed. in English)》2015,54(41):12097-12101
Regioselectivity in the aziridination of silyl‐substituted homoallenic sulfamates is readily diverted to the distal double bond of the allene to yield endocyclic bicyclic methyleneaziridines with excellent stereocontrol. Subsequent reaction with electrophilic oxygen sources initiates facile rearrangement to densely functionalized, fused azetidin‐3‐ones in excellent d.r., effectively transferring the axial chirality of the allene to central chirality in the products. The steric nature of the silyl group dictates which of the two rings of the fused azetidin‐3‐one will undergo further functionalization, providing an additional element of diversity for the preparation of enantioenriched azetidine scaffolds with potential biological activity. 相似文献
420.
Efficient Access to Bicyclo[4.3.0]nonanes: Copper‐Catalyzed Asymmetric Silylative Cyclization of Cyclohexadienone‐Tethered Allenes 下载免费PDF全文
Zhi‐Tao He Xiao‐Qi Tang Li‐Bo Xie Mian Cheng Ping Tian Prof. Guo‐Qiang Lin 《Angewandte Chemie (International ed. in English)》2015,54(49):14815-14818
The creation of three consecutive chiral carbon centers in one step is achieved using Cu‐catalyzed asymmetric silylative cyclization of cyclohexadienone‐tethered allenes. Through regioselective β‐silylation of the allene and subsequent enantioselective 1,4‐addition to cyclohexadienone, this tandem reaction could afford cis‐hydrobenzofuran, cis‐hydroindole, and cis‐hydroindene frameworks with excellent yields (80–98 %) and enantioselectivities (94–98 % ee) bearing vinylsilane and enone substructures. Meanwhile, this mild transformation is generally compatible with a wide range of functional groups, which allows further conversion of the bicyclic products to bridged and tricyclic ring structures. 相似文献