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811.
812.
Simon G. Bott Alan P. Marchand Dongxia Xing Rajesh Shukla Stephen James Obrey K. Venkatesan J. Narasimha Moorthy 《Journal of chemical crystallography》1994,27(11):661-665
NaBH4 reduction of a cage dione proceeds in a stereospecific fashion to give theendo,endo-diol. This reactivity is related to the crystal structure. 相似文献
813.
K. Subramanian S. Lakshmi K. Rajagopalan Thomas Steiner Evgeni B. Starikov 《Journal of chemical crystallography》1998,28(7):581-584
In the X-ray crystal structure of the alkynol 5-hydroxy-5-(prop-2-ynyl)-10-methyl-1(9)-octalin-2-one [C14H18O2, Pca2
1, a = 13.559(1), b = 7.960(2), c = 21.748(3) Å], the hydroxyl and propynyl groups form a hydrogen bond chain C---C-HO-HO which is supposed to be a cooperative arrangement. Quantum chemical calculations estimate cooperativity enhancement within the array to be 0.4 kcal/mol, which is only a small (but recognizable) effect. 相似文献
814.
An efficient three-component coupling of aldehydes, amines and alkynes to prepare propargylamines, in nearly quantitative yields using nanocrystalline CuO as a catalyst is described. Structurally divergent aldehydes and amines were converted to the corresponding propargylamines. The reaction does not require any co-catalyst. After completion of the reaction, the catalyst was recovered by centrifugation and reused several times with only a slight decrease of activity observed under the same reaction conditions. 相似文献
815.
Even if numerical simulation of the Burgers’ equation is well documented in the literature, a detailed literature survey indicates that gaps still exist for comparative discussion regarding the physical and mathematical significance of the Burgers’ equation. Recently, an increasing interest has been developed within the scientific community, for studying non-linear convective–diffusive partial differential equations partly due to the tremendous improvement in computational capacity. Burgers’ equation whose exact solution is well known, is one of the famous non-linear partial differential equations which is suitable for the analysis of various important areas. A brief historical review of not only the mathematical, but also the physical significance of the solution of Burgers’ equation is presented, emphasising current research strategies, and the challenges that remain regarding the accuracy, stability and convergence of various schemes are discussed. One of the objectives of this paper is to discuss the recent developments in mathematical modelling of Burgers’ equation and thus open doors for improvement. No claim is made that the content of the paper is new. However, it is a sincere effort to outline the physical and mathematical importance of Burgers’ equation in the most simplified ways. We throw some light on the plethora of challenges which need to be overcome in the research areas and give motivation for the next breakthrough to take place in a numerical simulation of ordinary / partial differential equations. 相似文献
816.
817.
Y. Kalyana Lakshmi 《Journal of magnetism and magnetic materials》2009,321(9):1240-1245
With a view to understand the structural, magnetic and electrical properties of La1−xAgxMnO3 (x=0.05-0.3), a series of samples were prepared by polyvinyl alcohol (PVA) gel route. It has been found that both the metal-insulator and ferro- to paramagnetic transition temperatures after increasing up to the composition x=0.20, are found to remain constant thereafter. The electrical resistivity vs. temperature plot of the sample x=0.10 is found to exhibit an insulating behavior below 36 K, while the sample, x=0.20 exhibits two peaks, and the observed behavior is explained on the basis of the phase separation model. The low-temperature (T<TP), electrical resistivity data were analyzed by a theoretical model, ρ=ρ0+ρ2T2+ρ4.5T4.5, indicating the importance of grain/domain boundary effects, electron-electron and two-magnon scattering processes. The low-temperature resistivity data (T<50 K) were fitted to an equation, which is based on the combined effect of weak localization, electron-electron and electron-phonon scattering. 相似文献
818.
Gnana Sutha Siluvai Babu Varghese Narasimha N. Murthy 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(6):o380-o382
In the title salt, 1,3‐bis{[2‐(2‐pyridinio)ethyl][2‐(2‐pyridyl)ethyl]amino}benzene diperchlorate dihydrate, C34H38N62+·2ClO4−·2H2O, the cation contains two ethylpyridyl and two ethylpyridinium pendant pairs anchored to the two N atoms of 1,3‐phenylenediamine. The pyridyl and pyridinium N atoms are flanked by a molecule of water through strong hydrogen‐bonding interactions [N—H⋯O = 2.762 (6) and 2.758 (6) Å, and O—H⋯N = 2.834 (6) and 2.839 (6) Å]. The water molecules have weak hydrogen‐bonding interactions with the perchlorate anions as well. One of the perchlorate anions is severely disordered. 相似文献
819.
With a view to understand the magnetic and electrical behavior of monovalent substituted lanthanum manganites, a series of materials were prepared by sol-gel route by sintering at 1200 °C. The X-ray diffraction data were analyzed using Rietveld refinement technique and it has been found that all the samples were found to crystallize into rhombohedral structure with R3¯c space group. The values of ferro to paramagnetic (TC) and metal-insulator transition (TP) temperatures were obtained using ac susceptibility and electrical resistivity data, respectively. It has been found that sodium-, potassium- and rubidium-doped samples exhibit two peaks in the electrical resistivity vs. temperature plots. The observed behavior has been explained on the basis of oxygen deficiency present in the samples. The electrical resistivity data were analyzed using various theoretical models and it has been concluded that the electrical resistivity data in the low-temperature regime (T<TP) can be explained using the equation ρ(T)=ρ0+ρ2T2+ρ4.5T4.5, signifying the importance of the grain/domain boundary, electron-electron and two magnon scattering processes. On the other hand, the high-temperature resisitivity data (T>TP) were explained using variable range and small polaron hopping mechanisms. 相似文献
820.
We study the sample-size dependence of the strength of disordered materials with a flaw, by numerical simulations of lattice models for fracture. We find a crossover between a regime controlled by the disorder and another controlled by stress concentrations, ruled by continuum fracture mechanics. The results are formulated in terms of a scaling law involving a statistical fracture process zone. Its existence and scaling properties are revealed only by sampling over many configurations of the disorder. The scaling law is in good agreement with experimental results obtained from notched paper samples. 相似文献