全文获取类型
收费全文 | 666篇 |
免费 | 71篇 |
专业分类
化学 | 597篇 |
晶体学 | 1篇 |
数学 | 41篇 |
物理学 | 98篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 6篇 |
2020年 | 17篇 |
2019年 | 26篇 |
2018年 | 12篇 |
2017年 | 4篇 |
2016年 | 40篇 |
2015年 | 36篇 |
2014年 | 18篇 |
2013年 | 38篇 |
2012年 | 48篇 |
2011年 | 39篇 |
2010年 | 23篇 |
2009年 | 31篇 |
2008年 | 55篇 |
2007年 | 47篇 |
2006年 | 37篇 |
2005年 | 51篇 |
2004年 | 27篇 |
2003年 | 35篇 |
2002年 | 14篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 3篇 |
1996年 | 6篇 |
1995年 | 2篇 |
1994年 | 9篇 |
1993年 | 11篇 |
1992年 | 12篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1987年 | 3篇 |
1986年 | 1篇 |
1985年 | 4篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1982年 | 7篇 |
1981年 | 1篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 5篇 |
1975年 | 1篇 |
1974年 | 3篇 |
1973年 | 1篇 |
1968年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有737条查询结果,搜索用时 15 毫秒
31.
meso-Pentafluorophenyl- substituted [40]nonaphyrin(1.1.1.1.1.1.1.1.1) 3 has been prepared by using a stepwise ring-size-selective synthesis, and has been reduced with NaBH(4) to [42]nonaphyrin(1.1.1.1.1.1.1.1.1) 5. Structurally, 3 is characterized by a figure-of-eight shape, consisting of a porphyrin-like tetrapyrrolic segment and a hexaphyrin-like hexapyrrolic segment, whereas 5 has been found to adopt a distorted nonplanar butterfly-like shape. In the mono-metal complexes 6 and 7, a Zn(II) or Cu(II) ion is bound by the porphyrin-like tetrapyrrolic segment, maintaining the overall structure of 3. Similarly to 3, complexes 6 and 7 are interconvertible with the corresponding complexes 9 and 10 through two-electron reduction with NaBH(4) and oxidation with DDQ. The metal-free hexaphyrin-like segments of 6 and 7 have been shown to serve as a suitable platform for the complexation of two palladium ions, providing hetero-trinuclear metal complexes 11 (Zn(II)-Pd(II)-Pd(II)) and 13 (Cu(II)-Pd(II)-Pd(II)) in high yields, in which the Zn or Cu ion resides at the same porphyrin-like segment, and one Pd ion is bound in an NNCC fashion through double C--H bond activation while the other is bound in an NNC fashion with single C--H bond activation. Multi-metal complexes 11, 12, and 13 exhibit small electrochemical HOMO-LUMO gaps (<0.6 eV), despite their nonplanar conformations. 相似文献
32.
33.
Dr. Tsubasa Nakashima Haruka Fujimori Dr. Kohsuke Ohmatsu Prof. Takashi Ooi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(36):9253-9256
Intermediary radical cations, generated through single-electron oxidation of enol silyl ethers by excited Ir-based photocatalysts, can be exploited as Brønsted acids for the activation of heteroarylcyanides. This strategy enables the direct allylic C−H heteroarylation of enol silyl ethers under visible-light irradiation. 相似文献
34.
Brown MA Fujimori Y Ringleb F Shao X Stavale F Nilius N Sterrer M Freund HJ 《Journal of the American Chemical Society》2011,133(27):10668-10676
The nucleation and electronic structure of vapor-deposited Au on hydroxylated MgO(001) surfaces has been investigated under ultrahigh vacuum conditions. Hydroxylated MgO(001) surfaces with two different hydroxyl coverages, 0.4 and 1 monolayer, respectively, were prepared by exposure to water (D(2)O) at room temperature. Scanning tunneling microscopy experiments show significantly higher gold particle densities and smaller particle sizes on the hydroxylated MgO surface as compared to gold deposited on clean MgO(001). Infrared spectroscopy and X-ray photoelectron spectroscopy experiments were performed to reveal details about the initial nucleation of gold. Gold atoms are found to chemically interact with a specific type of hydroxyl groups on the MgO surface, leading to the formation of oxidized gold particles. The enhanced adhesion of Au particles, which is due to the formation of strong Au-O interfacial bonds, is responsible for the observed higher stability of small Au clusters toward thermal sintering on hydroxylated MgO surfaces. The results are compared to similar studies on Au/TiO(2)(110) model systems and powder samples prepared by the deposition-precipitation route. 相似文献
35.
Giulia Lavarda Daiki Shimizu Toms Torres Atsuhiro Osuka 《Angewandte Chemie (International ed. in English)》2020,59(8):3127-3130
Peripherally metalated porphyrinoids are promising functional π‐systems displaying characteristic optical, electronic, and catalytic properties. In this work, 5‐(2‐pyridyl)‐ and 5,10,15‐tri(2‐pyridyl)‐BIII‐subporphyrins were prepared and used to produce cyclometalated subporphyrins by reactions with [Cp*IrCl2]2, which proceeded through an efficient C?H activation to give the corresponding mono‐ and tri‐IrIII complexes, respectively. While the mono‐IrIII complex was obtained as a diastereomeric mixture, a C3‐symmetric tri‐IrIII complex with the three Cp*‐units all at the concave side was predominantly obtained in a high yield of 90 %, which displays weak NIR phosphorescence even at room temperature in degassed CH2Cl2, differently from the mono‐IrIII complexes. 相似文献
36.
37.
Sato H Tashiro K Shinmori H Osuka A Aida T 《Chemical communications (Cambridge, England)》2005,(18):2324-2326
Upon complexation with 4,4[prime or minute]-bipyridine, a cyclic dimer of a fused porphyrin zinc complex, having two pi-electronically coupled binding sites, shows a strong negative cooperativity in the second guest binding, to allow stepwise formation of 1 : 1 and 1 : 2 inclusion complexes. 相似文献
38.
5,10,15‐Tris(pentafluorophenyl)tetrapyrromethane was efficiently prepared through a route involving stepwise diaroylation of 5‐pentafluorophenyldipyrromethane. A2B6‐type [36]octaphyrins were prepared by the cross condensation of the tetrapyrromethane with aryl aldehydes in moderate yields. A2B6‐type [36]octaphyrins bearing 2,4,6‐trifluorophenyl, 2,6‐dichlorophenyl, and phenyl substituents underwent CuII‐metalation‐induced fragmentation to give two molecules of AB3‐type CuII porphyrins. A2B6‐type [36]octaphyrin bearing 3‐thienyl substituents underwent thermal N‐thienyl fusion reactions to provide a modestly aromatic [38]octaphyrin, which, upon treatment with MnO2, underwent further N‐thienyl fusion and subsequent oxidation to give a nonaromatic doubly N‐thienyl fused [36]octaphyrin. 相似文献
39.
Koji Naoda Young Mo Sung Jong Min Lim Prof. Dr. Dongho Kim Prof. Atsuhiro Osuka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7698-7705
A cross‐conjugated hexaphyrin that carries two meso‐oxacyclohexadienylidenyl (OCH) groups 9 was synthesized from the condensation of 5,10‐bis(pentafluorophenyl)tripyrrane with 3,5‐di‐tert‐butyl‐4‐hydroxybenzaldehyde. The reduction of 9 with NaBH4 afforded the Möbius aromatic [28]hexaphyrin 10 . Bis‐rhodium complex 11 , prepared from the reaction of 10 with [{RhCl(CO)2}2], displays strong Hückel antiaromatic character because of the 28 π electrons that occupy the conjugated circuit on the enforced planar structure. The oxidation of 11 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) yielded complexes 12 and 13 depending upon the reaction conditions. Both 12 and 13 are planar owing to bis‐rhodium metalation. Although complex 12 bears two meso‐OCH groups at the long sides and is quinonoidal and nonaromatic in nature, complex 13 bears 3,5‐di‐tert‐butyl‐4‐hydroxyphenyl and OCH groups and exhibits a moderate diatropic ring current despite its cross‐conjugated electronic circuit. The diatropic ring current increases upon increasing the solvent polarity, most likely due to an increased contribution of an aromatic zwitterionic resonance hybrid. 相似文献
40.
Pictet–Spengler Synthesis of Quinoline‐Fused Porphyrins and Phenanthroline‐Fused Diporphyrins 下载免费PDF全文
Dr. Ke Gao Norihito Fukui Seok II Jung Prof. Dr. Hideki Yorimitsu Prof. Dr. Dongho Kim Prof. Dr. Atsuhiro Osuka 《Angewandte Chemie (International ed. in English)》2016,55(42):13038-13042
Doubly and quadruply quinoline‐fused porphyrins were effectively synthesized through a reaction sequence consisting of Suzuki–Miyaura coupling of β‐borylated porphyrins with 2‐iodoaniline and subsequent Pictet–Spengler cyclization. These quinoline‐fused porphyrins display red‐shifted absorption bands and higher electron‐accepting abilities. This synthetic protocol also allowed the synthesis of phenanthroline‐fused porphyrin dimers, which bound either a NiII or ZnII cation. The resultant metal complexes displayed further red shifted absorption spectra and molecular twists to effect an almost perpendicular arrangement of the two porphyrins. 相似文献