全文获取类型
收费全文 | 130篇 |
免费 | 1篇 |
专业分类
化学 | 123篇 |
晶体学 | 1篇 |
力学 | 3篇 |
数学 | 1篇 |
物理学 | 3篇 |
出版年
2022年 | 2篇 |
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 2篇 |
2018年 | 1篇 |
2017年 | 2篇 |
2016年 | 3篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 4篇 |
2012年 | 5篇 |
2011年 | 16篇 |
2010年 | 4篇 |
2009年 | 7篇 |
2008年 | 5篇 |
2007年 | 8篇 |
2006年 | 11篇 |
2005年 | 2篇 |
2004年 | 10篇 |
2003年 | 6篇 |
2002年 | 7篇 |
2001年 | 5篇 |
2000年 | 6篇 |
1999年 | 2篇 |
1998年 | 1篇 |
1997年 | 4篇 |
1995年 | 4篇 |
1994年 | 2篇 |
1993年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
排序方式: 共有131条查询结果,搜索用时 0 毫秒
61.
Stereoselective synthesis of 2,4,5-trisubstituted piperidines by carbonyl ene and Prins cyclisations
An approach to 2,4,5-trisubstituted piperidines is reported, in which the key step is the Prins or carbonyl ene cyclisation of aldehydes of the type 1. Prins cyclisation catalysed by concentrated hydrochloric acid in CH(2)Cl(2) at -78 degrees C afforded good yields of two of the four possible diastereomeric piperidines, with the 4,5-cis product 7 predominating in a diastereomeric ratio of up to 94:6. The diastereoselectivity of the cyclisation decreased as the 2-substituent increased in size, becoming unselective for very bulky 2-substituents. In contrast, cyclisation catalysed by MeAlCl(2) in CH(2)Cl(2) or CHCl(3) at temperatures of between 20-60 degrees C, favoured the 4,5-trans diastereomer 8, in a diastereomeric ratio of up to 99:1. The low-temperature cyclisations catalysed by HCl proceed under kinetic control via a mechanism involving the development of significant carbocationic character, in which the 4,5-cis cation is more stable than the 4,5-trans cation as a result of overlap with the neighbouring oxygen. The cyclisations catalysed by MeAlCl(2) proceed under thermodynamic control, affording the product in which both the 4- and 5-substituents are equatorial. 相似文献
62.
The syntheses of three new ligands (L1-3), which are based upon a DO3A core and appended with additional receptor sites for metal cations, are described, together with their corresponding Eu(III) complexes (Eu-L1-3). The complexes are visibly luminescent in aqueous solution, following sensitization via the pyridine chromophore, showing characteristic narrow line-like emission from Eu(III). The luminescence properties show that water is effectively excluded from the inner coordination sphere of europium (q = 0). Each of the complexes showed perturbed luminescence properties upon addition of a variety of d-block metal ions. For example, emission quenching was observed for each complex following addition of Cr(III) and Cu(II). Selectivity towards Hg(II) (over Cd(II), Cu(II) and Zn(II)) was demonstrated with Eu-L3, which possesses a receptor site incorporating a softer thiophene moiety. More specifically, Hg(II) binding resulted in changes in the form of the steady state emission spectrum, together with a corresponding reduction of the luminescence lifetime in water, which can be attributed to an increase in inner sphere hydration (q = 2) and thus enhanced non-radiative deactivation of the 5D0 state by proximate O-H oscillators. 相似文献
63.
The Synthesis of Organic Molecules of Intrinsic Microporosity Designed to Frustrate Efficient Molecular Packing 下载免费PDF全文
Dr. Rupert G. D. Taylor Dr. C. Grazia Bezzu Dr. Mariolino Carta Dr. Kadhum J. Msayib Dr. Jonathan Walker Dr. Rhys Short Dr. Benson M. Kariuki Prof. Neil B. McKeown 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(7):2466-2472
Efficient reactions between fluorine‐functionalised biphenyl and terphenyl derivatives with catechol‐functionalised terminal groups provide a route to large, discrete organic molecules of intrinsic microporosity (OMIMs) that provide porous solids solely by their inefficient packing. By altering the size and substituent bulk of the terminal groups, a number of soluble compounds with apparent BET surface areas in excess of 600 m2 g?1 are produced. The efficiency of OMIM structural units for generating microporosity is in the order: propellane>triptycene>hexaphenylbenzene>spirobifluorene>naphthyl=phenyl. The introduction of bulky hydrocarbon substituents significantly enhances microporosity by further reducing packing efficiency. These results are consistent with findings from previously reported packing simulation studies. The introduction of methyl groups at the bridgehead position of triptycene units reduces intrinsic microporosity. This is presumably due to their internal position within the OMIM structure so that they occupy space, but unlike peripheral substituents they do not contribute to the generation of free volume by inefficient packing. 相似文献
64.
Jones JE Kariuki BM Ward BD Pope SJ 《Dalton transactions (Cambridge, England : 2003)》2011,40(14):3498-3509
The syntheses of four new ligands based upon 3-picolyl functionalised amino anthraquinone (AQ) chromophores are described via a one-pot reductive amination procedure giving the desired ligands L1-L4 (L1, 1-(3-picolylamino)anthracene-9,10-dione; L2, 1-hydroxy-4-(3-picolylamino)anthracene-9,10-dione; L3, 1,4-bis(3-picolylamino)anthracene-9,10-dione; L4, 1,5-bis(3-picolylamino)anthracene-9,10-dione). Each ligand was characterised in solution via(1)H and (13)C{(1)H} NMR, with three examples giving single crystal X-ray diffraction data. The structures confirmed the proposed formulations and also revealed the presence of intramolecular H-bonding between the quinone and secondary amine units. The electronic characteristics of the ligands were investigated using a combined experimental/theoretical approach, revealing that in each case absorption in the visible region constitutes significant charge transfer (CT) character, originating from N-(amine)-to-quinone transitions, and is solvent sensitive. Density functional theory (DFT) calculations also suggest that the position of amino-substitution at the AQ core influences the wavelength of the lowest energy feature, by modulation of the HOMO, rather than the LUMO energy. The coordination chemistry of the ligands was probed through reaction with fac-[Re(CO)(3)(di-imine)(MeCN)](BF(4)) where di-imine = 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmp). Combined structural and spectroscopic studies confirmed that the ligands coordinate to Re(i) exclusively via the pyridyl units, however in the case of L3 only monometallic complexes were isolated. The optical properties of the complexes are dominated by AQ-centred (>425 nm) absorptions superimposed upon (1)MLCT features, as well as diimine-based intra-ligand (<350 nm) transitions. The luminescence properties of the complexes generally display dual emission, which was dependent upon the wavelength of sensitisation, with short-lived AQ fluorescence superimposed upon long-lived (3)MLCT phosphorescence. 相似文献
65.
The synthesis and characterisation of two binaphthyl trisilanes is described. Reaction between 2,2′-dilithio-1,1′-binaphthyl and 1,3-dichlorohexamethyltrisilane gave 3,3,4,4,5,5-hexamethyl-4,5-dihydro-3H-3,4,5-trisilacyclohepta[2,1-a;4,3-a′]binaphthalene (3). Compound 3 was characterised by 1H, 13C and 29Si NMR spectroscopy and a crystal structure analysis. Reaction between 2,2′-dilithio-1,1′-binaphthyl and 1,3-bis(trifluoromethanesulfonyloxy)-1,1,2,3,3-pentamethyltrisilane, generated in situ by treatment of 1,3-diphenyl-1,1,2,3,3-pentamethyltrisilane with trifluormethanesulfonic acid, gave 3,3,4,5,5-pentamethyl-4,5-dihydro-3H-3,4,5-trisilacyclohepta[2,1-a;4,3-a′]binaphthalene (7). Analysis by 1H, 13C and 29Si NMR spectroscopy revealed that 7 had a very similar structure to 3. 相似文献
66.
Benson M. Kariuki Ludovic G. Bonnet John E. Warren 《Journal of chemical crystallography》2009,39(10):693-697
Abstract Investigation of the thermal properties of triphenylphosphonium p-toluenesulfonates, which are high temperature ionic liquids, reveals that they solidify to a noncrystalline material on fast
cooling from the melt. During the study, a second crystalline form of [1-(methoxycarbonyl) ethyl] triphenylphosphonium p-toluenesulfonate (form II) has been obtained. Form II is monoclinic P21/c, with a = 11.002(5)?, b = 12.793(5)?, c = 18.805(5)?, and β = 102.498(5)°. Comparison with form I reveals the existence
of a common robust structural feature involving interactions between cations and anions.
Graphical Abstract Investigation of thermal properties of ionic liquids has revealed a second crystalline form of [1-(methoxycarbonyl) ethyl]
triphenylphosphonium p-toluenesulfonate.
相似文献
67.
A diimidazolium salt incorporating a secondary amine moiety has been used to prepare a palladium(II) di-N-heterocyclic carbene amino complex that can be deprotonated with NaH to give the first example of a transition metal NHC-amide. 相似文献
68.
Smith CB Constable EC Housecroft CE Kariuki BM 《Chemical communications (Cambridge, England)》2002,(18):2068-2069
Reaction of the heterotritopic ligand L, which contains one bipy and two terpy metal-binding domains linked by a flexible spacer with iron(II) chloride results in the formation of a [1 + 1] metallomacrocycle. 相似文献
69.
Tedesco E Turner GW Harris KD Johnston RL Kariuki BM 《Angewandte Chemie (International ed. in English)》2000,39(24):4488-4491
70.
Walker SM Williams JT Russell AG Kariuki BM Snaith JS 《Organic & biomolecular chemistry》2007,5(18):2925-2931
The thermal or Lewis acid-catalysed ene cyclisation of a variety of 4-aza-1,7-dienes afforded 3,4-disubstituted or 3,4,5-trisubstituted piperidines. Activation of the enophile with a single ester facilitated a thermal ene cyclisation, although the reaction was not amenable to Lewis acid catalysis. With other activating groups on the enophile it was found that Lewis acid catalysis was facile, although there was a fine balance between the desired ene cyclisation and the competing hetero-Diels-Alder reaction, with the product distribution being influenced by the activating group on the enophile, the nature of the ene component, and the Lewis acid used. Activation of the enophile with an oxazolidinone function facilitated Lewis acid-catalysed cyclisation to afford mixtures of ene and hetero-Diels-Alder products. Activating the enophile with two ester groups gave a substrate that underwent a very facile ene cyclisation catalysed by MeAlCl(2) to give the corresponding trans 3,4-disubstituted piperidines with diastereomeric ratios of >200 : 1. 相似文献