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381.
We unfold a rapid synthetic protocol for the preparation of imidazo[1,2-a]pyridine in cyclohexane. This methodology includes several advantages like shorter reaction time, catalyst free, broader substrate scope, and good yields of the desired products. Late stage functionalization of imidazo[1,2-a]pyridine has also been performed through C–H bond activation and C–C cross-coupling reactions. 相似文献
382.
Tusharkumar Menapara Raj kumar Tak S. Saravanan Rukhsana I. Kureshy Noor-ul H. Khan B. Ganguly Mrinal Kanti Si 《Tetrahedron》2018,74(49):7000-7008
Chiral Cu-1B generated in situ was used as an efficient catalyst for the synthesis of β-nitroamines in high yield (88%) with excellent enantioselectivity (ee up to 99%) at RT in absence of co-catalyst via asymmetric aza-Henry reaction of various isatin derived N-Boc ketimines with nitromethane. This catalytic system did not work well with other nitroalkanes under the above optimized reaction conditions. To examine this catalytic behaviour, quantum chemical DFT calculations were performed with the nucleophiles (CH2NO2? and CH3CHNO2?) for the conversion of 1a to 2a using macrocyclic Cu-1B complex. The DFT calculated results have shown that the reaction with CH2NO2? is more favourable than the corresponding CH3CHNO2?. The calculated activation barriers suggest that the reaction with CH2NO2? is ~8.0?kcal/mol energetically favoured than CH3CHNO2?. This catalytic protocol was further used to obtain chiral β-diamines (a building block for pharmaceuticals) at gram scale. In order to elucidate the reaction mechanism of asymmetric aza Henry reaction kinetic experiments were performed with different concentrations of the catalyst Cu-1B, nitromethane and 1g as the representative substrate. The reaction of isatin N-Boc ketimine was first order with respect to the concentration of the catalyst and the nitromethane but did not depend on the initial concentration of the substrate. A possible mechanism for the aza Henry reaction was proposed. 相似文献
383.
The electronic transport properties of a-(Si,Ge):H alloys across the range of Ge content (0-40%) grown using PECVD technique have been investigated in detail by employing the microwave photomixing technique. Strong evidence for the existence of long-range potential fluctuations in a-(Si,Ge):H alloys has been found from the measurements of electric field dependence of the drift mobility. It was observed that the film transport properties degrade monotonically with increasing Ge content, where the strongest potential fluctuations occur as a result of a significant increase in the charged defect density. The potential fluctuations whose effect is enhanced by adding Ge to the alloy system result in deterioration of the transport properties of a-(Si,Ge):H alloys. Our present results demonstrate that the increased charged scattering centers and compositional disorder upon adding Ge to the alloys play an important role in the potential fluctuations. 相似文献
384.
I.K. Gopalakrishnan N. Bagkar R. Ganguly S.K. Kulshreshtha 《Journal of Crystal Growth》2005,280(3-4):436-441
Nanocrystalline Mn3O4 has been synthesized by ultrasonic irradiation of Mn acetate solution in water. Analysis of its X-ray diffraction data shows formation of a phase-pure compound with an average particle size of about 15 nm. DC magnetization measurements as a function of temperature and field show a reduced ferrimagnetic transition temperature as compared to those reported for the bulk , and a subsequent observation of superparamagnetic behavior at 40 K. The observed magnetic properties are suggestive of formation of a single domain magnetically ordered Mn3O4 nanoparticles below their ferrimagnetic transition temperature. 相似文献
385.
Abstract Abstract Infrared spectra of La2?xSrxCuO4 and YBa2Cu3O7?δ are discussed, specially with respect to the disappearance of the high-frequency (~650 cm) band of the superconducting compositions at 300K. Some of the bands persist at 300K eventhough the materials are fairly conducting. YBa2Cu3O7?δ does not show evidence in the far IR spectrum for the presence of an optical gap. 相似文献
386.
Considerable changes are observed in the spectra of the valence band and O(ls) regions in YBa2Cu3O7, when the temperature is lowered from 300K to 80K. The results are interpreted in terms of a progressive formation of O2- 2-like species with decreasing temperature. This is accompanied by the transformation of Cu to Cu. It is suggested that the holes generated at the top of the valence band forming the O2- 2-like species may play a crucial role in the superconductivity of the oxide. 相似文献
387.
The bubble model, which is conventionally used to fit the observed characteristics of the pickoff component of ortho-Positronium decay in liquids, is subjected in this study to a critical assessment. It is demonstrated that in its present form (namely that of a bubble with a sharp boundary) the model is untenable when confronted jointly with experimental data on the lifetime and angular correlation of the decay gammas. A modified version of the model, free from such shortcomings, is presented. Further, the dramatic turnover in the temperature dependence of the rate for the formation of positronium–acceptor complex in the case of nitro-benzene in different solvents is interpreted as a Kramers’ turnover in the context of the improved Bubble Model. 相似文献
388.
Ajay K. Bose Maghar S. Manhas Subhendu N. Ganguly Suhas Pednekar Arun Mandadi 《Tetrahedron letters》2005,46(17):3011-3013
A water-based biphasic reaction process has been developed for conducting exothermic reactions without organic solvents. This procedure is rapid, simple, and suitable for small scale synthesis as well as larger (multi-molar) scale reactions. The preparation of several hundred grams of clofibric acid and analogues by this eco-friendly and energy-efficient procedure is described. Smaller amounts of these compounds were prepared by the friction-activated ‘Grindstone Chemistry’ method described previously. 相似文献
389.
Using modified Baker-Venkataraman reaction a novel class of 3-acyl flavones and chromones have been synthesised. Reaction mechanism for their formation have been elucidated. The properties of 3-acyl flavonoids indicate them to be precursors for the synthesis of flavones. 相似文献
390.
The First Synthesis of the Sterically Encumbered Adamantoid Phosphazane P4(NtBu)6: Enabled by Mechanochemistry 下载免费PDF全文
Yan X. Shi Dr. Kai Xu Dr. Jack K. Clegg Dr. Rakesh Ganguly Dr. Hajime Hirao Prof. Dr. Tomislav Friščić Prof. Dr. Felipe García 《Angewandte Chemie (International ed. in English)》2016,55(41):12736-12740
All reported attempts to synthesize the tert‐butyl‐substituted adamantoid phosph(III)azane P4(NtBu)6 have failed, leading to the classification of this molecule as inaccessible and a literature example of steric control in chemistry of phosphorus‐nitrogen compounds. We now demonstrate that this structure is readily accessible by a solvent‐free mechanochemical milling approach, highlighting the importance of mechanochemical reaction environments in evaluating chemical reactivity. 相似文献