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81.
Robert J Bond 《Journal of Number Theory》1981,13(2):246-254
Let K be an unramified abelian extension of a number field F with Galois group G. K corresponds to a subgroup H of the ideal class group of F. We study the subgroup J of ideal classes in H which become trivial in K. There is an epimorphism from the cohomology group H?1(G, ClK) to J which is an isomorphism if G is cyclic; ClK is the ideal class group of K. Some results on the structure of J and ClK are obtained. 相似文献
82.
L.J. Bond 《Ultrasonics》1979,17(2):71-77
Surface acoustic waves are under active investigation in three fields of study: geophysics, electronics and non-destructive testing. While the mathematical features are the same for all three fields, the wavelengths, as well as the dimensions of the features, range over at least ten orders of magnitude.In this paper a brief review of available numerical techniques is presented and this is followed by discussion of a series of models which use finite difference methods to predict the reflected and transmitted signals from wide band pulses of ultrasonic Rayleigh waves incident on various surface-breaking features. The paper concludes with a comparison of analytical, numerical and experimental results. 相似文献
83.
84.
Nada Miljević Dusan Golobočanin Nives Ogrinc Ana Bondžić 《Isotopes in environmental and health studies》2013,49(2):137-148
Stable hydrogen and oxygen isotopes were analysed in water samples from the River Danube and its tributaries during a longitudinal survey performed in August 2005 on Serbian territory. Danube river water data ranged from?80‰ to?66‰ for δ2H, and from?11.2‰ to?9.3‰ for δ18O with δ values increasing downstream. The isotopic signatures of the adjacent tributaries (the Tisza, the Sava and the Velika Morava) sampled at the locations close to their confluence with the Danube (Titel, Ostru?nica and Ljubi?evski most, respectively) just about the time of the campaign were enriched (?67‰ and?63‰ for δ2H, and?9.3‰ and?8.9‰ for δ18O) with respect to the Danube water because of their catchment effects. Hydrogen and oxygen stable isotope values were used in combination with measured physico-chemical and biological parameters to trace hydrological and transport processes in these river systems. The mixing relationships between the Danube main stream and its tributaries were estimated using the mass balance for isotopic composition and electrical conductivity as conservative parameters. Evidence of an incomplete mixing process at the ?enta location, 8 km below the confluence of the Tisza river, with its participation of 88% was shown by its oxygen-18 content. The correlations between river water isotope composition and physico-chemical and biological parameters are discussed. 相似文献
85.
Controllable Synthesis of Few‐Layer Bismuth Subcarbonate by Electrochemical Exfoliation for Enhanced CO2 Reduction Performance 下载免费PDF全文
Ying Zhang Xiaolong Zhang Yunzhi Ling Fengwang Li Prof. Alan M. Bond Dr. Jie Zhang 《Angewandte Chemie (International ed. in English)》2018,57(40):13283-13287
Two‐dimensional (2D) engineering of materials has been recently explored to enhance the performance of electrocatalysts by reducing their dimensionality and introducing more catalytically active ones. In this work, controllable synthesis of few‐layer bismuth subcarbonate nanosheets has been achieved via an electrochemical exfoliation method. These nanosheets catalyse CO2 reduction to formate with high faradaic efficiency and high current density at a low overpotential owing to the 2D structure and co‐existence of bismuth subcarbonate and bismuth metal under catalytic turnover conditions. Two underlying fast electron transfer processes revealed by Fourier‐transformed alternating current voltammetry (FTacV) are attributed to CO2 reduction at bismuth subcarbonate and bismuth metal. FTacV results also suggest that protonation of CO2.? is the rate determining step for bismuth catalysed CO2 reduction. 相似文献
86.
Diverged Plant Terpene Synthases Reroute the Carbocation Cyclization Path towards the Formation of Unprecedented 6/11/5 and 6/6/7/5 Sesterterpene Scaffolds 下载免费PDF全文
Dr. Ancheng C. Huang Dr. Young J. Hong Dr. Andrew D. Bond Prof. Dr. Dean J. Tantillo Prof. Anne Osbourn 《Angewandte Chemie (International ed. in English)》2018,57(5):1291-1295
Sesterterpenoids are a relatively rare class of plant terpenes. Sesterterpene synthase (STS)‐mediated cyclization of the linear C25 isoprenoid precursor geranylfarnesyl diphosphate (GFPP) defines sesterterpene scaffolds. So far only a very limited number of STSs have been characterized. The discovery of three new plant STSs is reported that produce a suite of sesterterpenes with unprecedented 6/11/5 and 6/6/7/5 fused ring systems when transiently co‐expressed with a GFPP synthase in Nicotiana benthamiana. Structural elucidation, feeding experiments, and quantum chemical calculations suggest that these STSs catalyze an unusual cyclization path involving reprotonation, intramolecular 1,6 proton transfer, and concerted but asynchronous bicyclization events. The cyclization is diverted from those catalyzed by the characterized plant STSs by forming unified 15/5 bicyclic sesterterpene intermediates. Mutagenesis further revealed a conserved amino acid residue implicated in reprotonation. 相似文献
87.
The leading asymptotic term for the function that counts theeigenvalues of the Stokes operator is determined for fairlygeneral underlying bounded domains. Moreover, the remainderis estimated in terms of the fractality of the boundary of thedomain. The results obtained resemble corresponding ones forthe Dirichlet Laplacian. 1991 Mathematics Subject Classification:35P20. 相似文献
88.
Robin D. Rogers Michael J. Adrowski Andrew H. Bond 《Journal of chemical crystallography》1994,24(10):711-714
The crystals of Pt(S2COEt)2 are orthorhombic, Pbca, with (at 20°C)a=7.799(3),b=7.368(6),c=20.588(7) Å.D
cale=2.46g cm–3 forZ=4. The platinum atom resides on a crystallographic center of inversion and is bound to the four sulfur atoms of the xanthato ligand in a square planar geometry. The Pt–S distances are 2.313(6) and 2.320(7)Å with an intraligand S–Pt–S angle of 75.1(2)°. 相似文献
89.
Andrew D. Bond John E. Davies Simon Parsons 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(10):o543-o546
The crystal structures of the cyclic amines azetidine (C3H7N), pyrrolidine (C4H9N) and hexamethyleneimine (homopiperidine, C6H13N), of the series (CH2)nNH, with n = 3, 4 and 6, respectively, have been determined at 170 K, following in situ crystallization from the melt. These structures provide crystallographic data to complete the homologous series of cyclic amines (CH2)nNH, for n = 2–6. Azetidine and pyrrolidine contain chains propagating along 21 screw axes, in which the molecules are linked by co-operative N—H...N hydrogen bonds. Azetidine has two molecules in its asymmetric unit, while pyrrolidine has only one. Hexamethyleneimine contains tetrameric hydrogen-bonded rings formed about crystallographic inversion centres, with two molecules in its asymmetric unit. The observation of crystallographically distinct molecules in the hydrogen-bonded chains of azetidine and cyclic hydrogen-bonded motifs in hexamethyleneimine is consistent with expectations derived from comparison with monoalcohols forming chains or rings by co-operative O—H...O hydrogen bonds. The next member of the cyclic amine series, heptamethyleneimine, forms a cubic plastic phase on cooling from the melt. 相似文献
90.