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61.
62.
The stereochemical outcome of the lithium-liquid ammonia reduction of 2,3-dialkyl-4-hydroxy-2-cyclopentenones and 2,3-dialkyl-2-cyclopentenones possessing bulky substituents (i-propyl and t-butyl) is investigated, using different proton donors. The relative configuration of both alkyl groups in the reduction products is interpreted on the basis of the geometry of the transition state for protonation of the intermediate enolate anions formed during the reduction 相似文献
63.
64.
The conformation and configurational assignment of 6,7-disubstituted 2-oxabicyclo[3.3.0]octan-3-ones
The conformational behaviour of 6-alkyl-3-oxo-2-oxabicyclo[3.3.0]octan-7-ols and some derivatives possessing the configurations a (6-endo-7-exo), b (6-endo-7-endo) and c (6-exo-7-endo) is discussed. It is shown that an easy configurational assignment is possible between these three series. 相似文献
65.
66.
Multigram scale, solventless, and diffusion-controlled route to highly monodisperse PbS nanocrystals
Cademartiri L Bertolotti J Sapienza R Wiersma DS von Freymann G Ozin GA 《The journal of physical chemistry. B》2006,110(2):671-673
High-quality PbS nanocrystals were produced in multigram-scale quantities through a solventless, heterogeneous, and relatively green route. The heterogeneous nature of this reaction allows one to limit the diffusion in the system, allowing for unprecedented monodispersity and quality of the product demonstrated by a full-width at half-maximum of the photoluminescence peak (PL fwhm) as low as 52 meV, a Stokes shift as low as 10 meV, and a quantum yield (QY) of 40%. The growth of the nanocrystals is interpreted in the framework of a diffusion-controlled Ostwald growth in conditions of strong supersaturation. 相似文献
67.
In this article, we establish a bijection between the set of mutation classes of mutation-cyclic skew-symmetric integral 3 × 3-matrices and the set of triples of integers (a, b, c) such that 2 ≤ a ≤ b ≤ c and ab ≥ c. We also give an algorithm allowing to verify whether a matrix is mutation-cyclic or not. We prove that given a, b, the two cases depend on whether c is large enough or not. 相似文献
68.
Hannah Schreyer Rene Eckert Sarah Immohr Jacopo deBellis Michael Felderhoff Ferdi Schüth 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(33):11384-11387
Supported catalysts are among the most important classes of catalysts. They are typically prepared by wet‐chemical methods, such as impregnation or co‐precipitation. Here we disclose that dry ball milling of macroscopic metal powder in the presence of a support oxide leads in many cases to supported catalysts with particles in the nanometer size range. Various supports, including TiO2, Al2O3, Fe2O3, and Co3O4, and different metals, such as Au, Pt, Ag, Cu, and Ni, were studied, and for each of the supports and the metals, highly dispersed nanoparticles on supports could be prepared. The supported catalysts were tested in CO oxidation, where they showed activities in the same range as conventionally prepared catalysts. The method thus provides a simple and cost‐effective alternative to the conventionally used impregnation methods. 相似文献
69.
Jerzy Podobiski Mariusz Gackowski Grzegorz Mordarski Katarzyna Samson Micha
liwa Dorota Rutkowska-Zbik Jerzy Datka 《Molecules (Basel, Switzerland)》2021,26(15)
The properties of both Cu2+ and Cu+ ions in zeolite CuY were followed with NO and CO as probe molecules. Cu2+ was found to be located in SII, SII*, and SIII sites, whereas Cu+ was found in SII and SII* sites. The fine analysis of the spectra of Cu2+-NO and Cu+-CO adducts suggests that both in SII and in SII* sites two kinds of Cu cations exist. They differ in the positive charge, which may be related to the varying numbers of AlO4− in close proximity. The experiments of NO and CO adsorption and desorption evidenced that both Cu2+ and Cu+ sites of highest positive charge bind probe molecules most strongly but activate them to a lesser extent than the Cu sites of lowest positive charge. The experiments of reduction with hydrogen evidenced that the Cu ions of higher positive charge are first reduced by hydrogen. On the other hand, Cu sites of the lowest positive charge are first oxidized by oxygen. The experiments with CuNaY zeolites of various Cu contents suggest that the first introduced Cu (at low Cu contents) created Cu+, which was the most neutralized by framework oxygens. Such Cu cations are the most stabilized by framework oxygens. 相似文献
70.
Barbara Fazio Lorenzo Spadaro Giuseppe Trunfio Jacopo Negro Francesco Arena 《Journal of Raman spectroscopy : JRS》2011,42(7):1583-1588
Composite MnOx CeOx catalysts (Mnat: Ceat = 1) synthesized via the redox and coprecipitation routes were comparatively characterized by micro‐Raman spectroscopy using a laser irradiation power ranging between 0.6 and 4.2 mW. A quasi‐molecular dispersion of the oxide species determines a major and irreversible structural rearrangement of the redox MnOx CeOx system because of severe heating effects for laser power in excess of 0.6 mW. The X‐ray diffraction data of samples calcined in the range of 673 1273 K confirm that the micro‐Raman characterization of the composite MnOx CeOx systems requires an adequate minimization of the irradiation power to prevent the strong sintering and restructuring phenomena due to laser‐heating effects. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献