全文获取类型
收费全文 | 3012篇 |
免费 | 428篇 |
国内免费 | 223篇 |
专业分类
化学 | 3628篇 |
晶体学 | 4篇 |
综合类 | 7篇 |
物理学 | 24篇 |
出版年
2024年 | 4篇 |
2023年 | 51篇 |
2022年 | 58篇 |
2021年 | 86篇 |
2020年 | 126篇 |
2019年 | 103篇 |
2018年 | 100篇 |
2017年 | 85篇 |
2016年 | 146篇 |
2015年 | 135篇 |
2014年 | 248篇 |
2013年 | 348篇 |
2012年 | 140篇 |
2011年 | 200篇 |
2010年 | 163篇 |
2009年 | 178篇 |
2008年 | 200篇 |
2007年 | 184篇 |
2006年 | 172篇 |
2005年 | 151篇 |
2004年 | 173篇 |
2003年 | 189篇 |
2002年 | 74篇 |
2001年 | 55篇 |
2000年 | 57篇 |
1999年 | 29篇 |
1998年 | 34篇 |
1997年 | 34篇 |
1996年 | 27篇 |
1995年 | 25篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 19篇 |
1991年 | 8篇 |
1990年 | 7篇 |
1989年 | 5篇 |
1988年 | 5篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有3663条查询结果,搜索用时 218 毫秒
151.
152.
(+)-Decytospolides A and B, natural products containing the tetrahydropyran skeleton, were synthesized via Prins cyclization as the key step. 相似文献
153.
154.
Debayan Roy Dr. Beeraiah Baire 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(12):4009-4015
Design and development of a domino cyclative approach for the synthesis of new polycyclic γ-butenolides from β-aryl-Z-enoate propargylic alcohols, through the interception of an intermediate of the Z-enoate-assisted Meyer–Schuster rearrangement, has been reported. A systematic NMR analysis of various derivatives of this class revealed and supported the potential atropisomerism associated with them. These molecules represent first examples of butenolide ring-based atropisomeric compounds in organic chemistry. The synthetic process involves a synchronous construction of both rings with concurrent creation of the potential stereogenic rotational axis. 相似文献
155.
《Mendeleev Communications》2021,31(5):664-666
Novel 3-azaxanthenes have been synthesized via acid-catalyzed one-pot Friedel–Crafts reaction of pyridoxal/pyridoxal-5'-phosphate with naphthols followed by dehydration of the intermediate bis(2-hydroxyaryl)-(pyridin-4-yl)methane derivatives. The cytotoxicity of the obtained 3-azaxanthenes against M-HeLa and HuTu-80 tumor cell lines is comparable to that of tamoxifen, whereas the cytotoxicity against normal cell line is absent in the tested concentrations range, which makes this class of compounds interesting for further studies. 相似文献
156.
Edyta M. Greer Christopher V. Cosgriff Olga Lavinda 《Journal of Physical Organic Chemistry》2012,25(12):1293-1298
Pentamethylene chain conformational effects for the Bergman cyclization of the 11‐membered ring enediyne, (3Z)‐3‐cycloundecene‐1,5‐diyne, 2, are examined theoretically with unrestricted Becke, three‐parameter, Lee–Yang–Parr/6‐31 G(d,p) calculations. A C1 symmetric enediyne conformation was found to be the global minimum, where its nonsymmetric pentamethylene chain prevented π‐orbital alignment of the acetylene groups for C–C σ bond product formation. The Bergman cyclization of 2 was found to be conformationally dependent. In a Curtin–Hammett type process, the C1 symmetric 2 inverts to one of the CS or C2 symmetric conformers required for the Bergman cyclization, which produced a CS or C2 symmetric 1,4‐diradical intermediate. The activation energy for the cyclization is slightly higher to reach the C2 symmetry diradical compared with the CS symmetry diradical. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
157.
Wei-Chen Cui Wenxuan Zhao Ming Gao Wei Liu Dr. Shaozhong Wang Prof. Yong Liang Prof. Zhu-Jun Yao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16506-16510
A visible-light-driven radical silylative cyclization of aza-1,6-dienes featuring an acrylonitrile or acrylate moiety and an electron-neutral olefin was developed, which allows for stereoselective synthesis of densely functionalized piperidines in a highly atom-economical manner. Depending on the substitution pattern of the electron-neutral olefin, poor-to-excellent diastereoselectivity was observed. It was suggested that the 6-exo-trig cyclization was initiated by a chemoselective addition of silyl radical toward electron-deficient olefin and the geometry of the remaining olefin is closely associated with the cis-stereoselectivity. DFT calculations supported that a transition state with a cyano group locating at the axial position of the forming piperidine ring might be involved, in which either the increase of 1,3-diaxial repulsion or the lack of hydrogen bonding interaction will diminish diastereoselectivity. 相似文献
158.
Ludmila A. Oparina Oksana V. Vysotskaya Lidiya N. Parshina Nina K. Gusarova Boris A. Trofimov 《Phosphorus, sulfur, and silicon and the related elements》2013,188(9):2087-2093
Under acid- or base-catalyzed conditions, thiols add regio- and chemos-electively either to vinyloxy or methacrylate group of vinyloxyalkyl-methacrylates to give polyfunctional methacrylates or polyfunctional vinyl ethers, respectively. 相似文献
159.
Rolf Appel Peter Schulte Falk Knoch 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):195-198
Abstract Two imino(bismethylene)phosphat-ions can be synthesized via reaction of phenylamino- and α-naphthylaminobismethylenephosphorane with n-butyllithium in tetrahydrofuran. Anions containing [sgrave]3λ6-bounded phosphorus are stabilized in the crystal with THF-solvated lithium-kations. Zwei Imino(bismethylen)phosphat-ionen werden durch Umsetzung des Phenylamino- und des α-Naphthylaminobismethylenphosphorans mit n-Butyllithium in Tetrahydrofuran erhalten. Die Anionen mit [sgrave]3λ6-gebundenem Phosphor werden im Kristall durch THF-solvatisierte Lithium-Kationen stabilisiert. 相似文献
160.
Xu‐Wen Li Alexandre Ear Lukas Roger Dr. Nassima Riache Alexandre Deville Dr. Bastien Nay 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(48):16389-16393
A bio‐inspired strategy was used to complete the formal synthesis of the antitubercular hirsutellone B and congeners A and C, through construction of its decahydrofluorene core from a linear polyene strand activated at both ends by a silyl enol ether and an allyl acetate. Our synthesis features a key electrophilic cyclization, starting with the remote activation (by [Yb(OTf)3] or BF3 ? OEt2) of the allyl acetate and stereoselectively affording the C ring. This was followed by an intramolecular Diels–Alder reaction to get the tricyclic core of the natural product. The stereoselective reduction of the resulting ketone towards the formal intermediate was critical to the success of this strategy. 相似文献