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排序方式: 共有71条查询结果,搜索用时 31 毫秒
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Mixtures of CaHPO4, CaCO3, and Na2CO3 were heated at 870°C under steam or under dry CO2 until phase composition and weight were constant. According to chemical analysis and X-ray diffractometry the stability field of the β-Ca3(PO4)2 phase is limited by the molar P/Ca ratio of 0.664 ± 0.003 and 0.675 ± 0.010 irrespective of the partial water vapour pressure. A continuous series of solid solutions was found between β-Ca3(PO4)2 and a new whitlockite with the composition Ca10Na(PO4)7. The IR spectrum of these solid solutions shows that the point symmetry of the PO4 groups and their environment increases with increasing sodium content. This is in agreement with data published about the structure of β-Ca3(PO4)2 and whitlockite. The composition of these solid solutions suggests that Na+ ions can replace H+ ions in the whitlockite structure. Carbonate and pyrophosphate ions are not incorporated in these whitlockites. 相似文献
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O. I. Lebedev † J. Verbeeck G. Van Tendeloo N. Hayashi T. Terashima M. Takano 《哲学杂志》2013,93(36):3825-3841
Thin films of SrFeO3??? x (0?≤?x?≤?0.5) (SFO) grown on a (LaAlO3)0.3 (SrAl0.5Ta0.5O3)0.7 (LSAT) substrate by pulsed laser deposition have been structurally investigated by electron diffraction and high resolution transmission electron microscopy for different post-deposition oxygen treatments. During the deposition and post-growth oxidation, the oxygen-reduced SFO films accept extra oxygen along the tetrahedral layers to minimize the elastic strain energy. The oxidation process stops at a concentration SFO2.875 and/or SFO2.75 because a zero misfit with the LSAT substrate is reached. A possible growth mechanism and phase transition mechanism are suggested. The non-oxidized films exhibit twin boundaries having a local perovskite-type structure with a nominal composition close to SFO3. 相似文献
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Oxidative Addition of Haloheteroarenes to Palladium(0): Concerted versus SNAr‐Type Mechanism
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Prof. Bert U. W. Maes Dr. Stefan Verbeeck Dr. Tom Verhelst Audrey Ekomié Niklas von Wolff Dr. Guillaume Lefèvre Dr. Emily A. Mitchell Prof. Anny Jutand 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(21):7858-7865
The kinetics of the oxidative additions of haloheteroarenes HetX (X=I, Br, Cl) to [Pd0(PPh3)2] (generated from [Pd0(PPh3)4]) have been investigated in THF and DMF and the rate constants have been determined. In contrast to the generally accepted concerted mechanism, Hammett plots obtained for substituted 2‐halopyridines and solvent effects reveal a reaction mechanism dependent on the halide X of HetX: an unprecedented SNAr‐type mechanism for X=Br or Cl and a classical concerted mechanism for X=I. These results are supported by DFT studies. 相似文献
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Lhoëst G Zey T Verbeeck RK Wallemacq P Maton N De Houx JP Latinne D 《Journal of mass spectrometry : JMS》1999,34(1):28-32
It was demonstrated that rapamycin is metabolized in vitro by pig liver microsomes under the influence of the cytochrome P450-dependent mixed function oxygenase system to a rapamycin tris-epoxide metabolite, as demonstrated by electrospray tandem mass spectrometry. The in vitro immunosuppressive activity of this metabolite was found to be lower than that of rapamycin, probably because the rapamycin effector sector was structurally modified. The effector region of rapamycin was recognized to include the conjugated double bonds of this compound and metabolic reactions affecting this region may change the binding affinity of the rapamycin-FKBP binary complex towards another pharmacological receptor bound to the binary complex. Moreover, metabolic modifications in the effector region are probably able to induce a change in the binding affinities of the rapamycin-FKBP binary complex, including the pipecolic acid moiety and the lactone function of the parent drug. 相似文献
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P. D. W. Moens F. J. Callens E. R. Boesman R. M. H. Verbeeck 《Applied magnetic resonance》1995,9(1):103-113
The isotropic EPR signal atg=2.0007 in X-irradiated carbonated apatites, precipitated from aquaeous solutions and dried at 25°C, is investigated with Electron Nuclear Double Resonance (ENDOR). The23Na,31P and1H ENDOR results indicate that the precursor of this radical is most probably located in an aqueous phase entrapped between the crystallites (the so-called occluded water). Other experimental features, such as the correlation between the appearance of the signal in the EPR spectrum and the presence of some residual (adsorbed and/or occluded) water in the sample seem to strengthen our hypothesis. 相似文献
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We prove that in the construct PRAP of pre-approach spaces the class of exponential objects completely determines the exponential objects in certain subconstructs. We show that Exp B Exp PRAP for every coreflective subconstruct B and from this inclusion we deduce the equality Exp B = B Exp PRAP for every subconstruct B that is coreflective and finitely productive. We prove that the same equality holds for non-trivial quotient reflective subconstructs. These results induce well known answers to similar questions on the construct of pretopological spaces and are compared to the topological situation. 相似文献
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Subbiah Meenakshisundaram RM. Sockalingam 《Journal of molecular catalysis. A, Chemical》2000,160(2):269-275
Catalytic activity of Os(VIII) in the oxidation of some twenty organic sulfides with sodium salt of N-chlorobenzenesulfonamide (CAB) has been investigated in alkaline (pH8.7) t-butanol–water (1:1 v/v) medium. Significant retarding influence of [OH−] on the reactivity is exhibited. The catalysed reaction is strongly accelerated in the presence of Hg(II). Imperfections are observed in the linear Hammett relationship in the case of –NO2 substituents. 相似文献