全文获取类型
收费全文 | 201篇 |
免费 | 9篇 |
国内免费 | 54篇 |
专业分类
化学 | 259篇 |
晶体学 | 3篇 |
物理学 | 2篇 |
出版年
2023年 | 6篇 |
2022年 | 8篇 |
2021年 | 11篇 |
2020年 | 14篇 |
2019年 | 9篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 15篇 |
2015年 | 7篇 |
2014年 | 7篇 |
2013年 | 36篇 |
2012年 | 8篇 |
2011年 | 8篇 |
2010年 | 12篇 |
2009年 | 5篇 |
2008年 | 13篇 |
2007年 | 14篇 |
2006年 | 16篇 |
2005年 | 7篇 |
2004年 | 11篇 |
2003年 | 10篇 |
2002年 | 6篇 |
2001年 | 5篇 |
2000年 | 4篇 |
1999年 | 2篇 |
1998年 | 3篇 |
1997年 | 3篇 |
1996年 | 2篇 |
1995年 | 1篇 |
1994年 | 1篇 |
1993年 | 1篇 |
1992年 | 2篇 |
排序方式: 共有264条查询结果,搜索用时 15 毫秒
211.
212.
I. Nobeli S. L. Price J. P. M. Lommerse R. Taylor 《Journal of computational chemistry》1997,18(16):2060-2074
The directionality and relative strengths of hydrogen bonds to monocyclic aromatic heterocycles were investigated using crystal structure data and theoretical calculations. Surveys of the Cambridge Structural Database for hydrogen bonds between C(sp3)(SINGLE BOND)O(SINGLE BOND)H and aromatic fragments containing one or more nitrogen and/or oxygen heteroatoms showed that hydrogen bonds to nitrogen atoms are much more abundant than to oxygen. Distinct preferred orientations were also revealed in these surveys. Theoretical calculations were performed on the interaction of methanol with pyridine, pyrimidine, pyrazine, pyridazine, oxazole, isoxazole, 1,2,4-oxadiazole, and furan as models for the heterocyclic fragments. The intermolecular potential surface was thoroughly scanned using a model potential that accurately described the electrostatic forces (derived from distributed multipole analysis) with empirical parameters for the repulsion and dispersion terms. Minima on this surface agreed well with the observed orientations in the data base and they were typically deeper for nitrogen than for oxygen acceptors, although the hydrogen bond strength and geometry was influenced by other heteroatoms in the ring. These results were confirmed by highly accurate intermolecular perturbation theory calculations, which also estimated the deviations from hydrogen bonding in the traditional nitrogen lone pair direction that could occur with negligible reduction in the interaction energy. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 2060–2074, 1997 相似文献
213.
Sandra Fusco Domenica Capasso Roberto Centore Sonia Di Gaetano Emmanuele Parisi 《Acta Crystallographica. Section C, Structural Chemistry》2019,75(10):1398-1404
A study of three isomeric compounds containing a phenolic moiety attached to the nitrogen‐rich triazolo–triazole bicycle is presented. In the three isomers, the phenolic OH group is in the ortho, meta and para positions. The crystal structure analysis of the meta isomer (C10H9N5O) shows that the 2H‐tautomer is present in the crystal and that the molecule adopts a substantially planar geometry. However, the conformation found in the crystal is different compared to the monoprotonated cation of the same compound previously investigated in several salts. The packing of the meta isomer is driven by the formation of strong hydrogen bonds and shows the formation of infinite planar ribbons, parallel to a, formed around 21 crystallographic axes. The three isomers were tested against some cancer cell lines and also against normal cell lines. The ortho isomer shows a weak antiproliferative activity, the meta isomer shows significant antiproliferative activity against some cancer lines and no activity against healthy cell lines, and the para isomer is active against all the tested cell lines. 相似文献
214.
Carbon–carbon bond forming reactions, such as aldol reaction and condensation, belong to extremely desired transformations as manifested by >25,000 entries in SciFinder. Their stereoselective variant requires the use of an appropriate catalyst with a strictly defined structure. Hence, chiral 2-azabicycloalkane-based catalysts were designed, synthesized and tested in a stereoselective aldol reaction between cyclic/acyclic ketone and p-nitrobenzaldehyde both in organic and aqueous media. Among catalysts containing a chiral bicyclic backbone, amide based on 2-azabicyclo[3.2.1]octane and pyrrolidine units showed the best catalytic activity and afforded aldol product in excellent chemical yields (up to 95%) and good diastereo- and enantioselectivity (dr 22:78, ee up to 63%). 相似文献
215.
216.
以苯基嘧啶/吡啶基嘧啶为母核, 同时引入2个三氟甲基(CF3)合成了2-[3,5-二(三氟甲基)苯基]-5-氟基嘧啶(tfmphfppm)和2-[2,6-二(三氟甲基)-4-吡啶基]-5-氟基嘧啶(tfmpyfppm)主配体, 并以2-(5-苯基-1,3,4-噁二唑-2-)苯酚(pop)为辅助配体合成了2种铱(III)配合物Ir(tfmphfppm)2(pop)和Ir(tfmpyfppm)2(pop), 其发射光谱峰分别位于484和504 nm, 分别属于蓝绿光和绿光发射, 发光量子效率分别达到76%和89%. 由于氮杂环和2,5-二苯基-1,3,4-噁二唑基团的存在, 配合物具有较低的最低未占据分子轨道(LUMO)能级和较高的电子迁移率. 以2种 铱(III)配合物为发光中心制备的有机电致发光器件(OLED)显示了较好的器件性能, 其最大亮度(Lmax)、 最大电流效率(ηc, max)、 最大功率效率(ηp, max)和最大外量子效率(EQEmax)分别为33379 cd/m2, 76.55 cd/A, 31.59 lm/W和26.7%; 并且该器件显示了比较小的效率滚降, 在亮度为1000 cd/m2时, 器件的ηc仍然可以达到72.71 cd/A. 本文结果表明, 氮杂环、 2,5-二苯基-1,3,4-噁二唑和三氟甲基基团可以有效提高铱(Ⅲ)配合物的发光性能和电子迁移率, 从而提高器件的性能. 相似文献
217.
218.
Bo‐Wen Hu Wen‐Qi Zhu Wei‐Wei Shi Peng Chen Quan‐Wen Li Ge‐Ping Yin 《无机化学与普通化学杂志》2019,645(16):1062-1066
A series of heterometallic NiII/CoII coordination polymers with 2D networks were synthesized by tetrazole‐1‐acetate ligands and structurally characterized. With increasing concentration of cobalt(II), another different connectivity patterns have been observed. The influence of cobalt(II) is not only on the crystallization, but also on the variation of magnetic properties. 相似文献
219.
Alessio Baccalini Prof. Giuseppe Faita Prof. Giuseppe Zanoni Prof. Debabrata Maiti 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(44):9749-9783
Sequential, domino and tandem reactions could be defined as a sequence of synthetic transformations that occur one after the other, in the same reaction flask. This Review highlights recent advances at the overlap of two worlds: transition-metal mediated C−H activation as a trigger of cascade reaction, for the heterocycles synthesis. To shed some light on this intricate “middle-earth”, focus was put on the reaction mechanism rather than the type of metal or the chronological order of the reaction. The aim is to separate, and then highlight, the true domino reactions initiated by C−H activation, compared to other examples of C−H functionalization for heterocycle syntheses. 相似文献
220.
Hiroto Uno Daichi Fujimoto Kyosuke Harada Chika Tanaka Prof. Dr. Norio Shibata 《ChemistryOpen》2021,10(5):518-522
Efficient synthesis of N,O-heterocyclic tetra-substituted trifluoromethyl-3,1-benzoxazines via a transition-metal-catalyzed decarboxylative intramolecular cyclization was achieved. The decarboxylation of N-benzoyl trifluoromethyl-benzoxazinones generated the amide oxygen nucleophile, allowing a selective internal C1-attack on Pd- or Cu-coordinated zwitterions, affording medicinally attractive tetra-substituted vinyl- or ethynyl-trifluoromethyl-3,1-benzoxazines. This protocol can be applied to the synthesis of perfluoroalkyl- and non-fluorinated 3,1-benzoxazines. 相似文献