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131.
Luciano Luciani Federico Milani Roberto Zannetti Vito Di Noto 《Macromolecular Symposia》1993,66(1):55-70
Among many precursors and catalysts for alpha-olefins polymerization, one seems to be particularly interesting, because it has not been completely clarified yet. We refer especially to precursors obtained via reaction between Mg-alkyls and SiCl4. The products of this reaction are not well known; in fact, under some operating conditions, a special form of MgCl2 is obtained, showing x-ray diffraction peaks in the angular region lower than 15° (2 theta), which corresponds to the 5.9 A interplanar spacing, characteristic of alpha-MgCl2. Under other conditions, MgCl2 is obtained in the well known and strongly disordered delta structure. By employing these precursors, some catalytic systems for alpha-olefins polymerization have been prepared. In this paper, the peculiar aspects of these precursors and catalysts are described, particularly focusing on the correlation between structure and performances in ethylene and propylene polymerization. 相似文献
132.
A preconcentration method for subsequent determination of rare earth elements (REE) by X-ray fluorescence (XRF) spectrometry
was developed. The method is based on using (o-[3,6-disulfo-2-hydroxy-1-naphthylazo]-benzenearsonic acid) (Thorin) as a complexing
agent which is retained on a polyamide membrane by a chemofiltration process. The pH dependence of the chemofiltration of
these metal ions on the membrane and other variables, such as flow-rate, contact time, kinetic of complex formation, etc.
were determined. The membrane containing the chemofiltrate formed a thin film, which eliminated the interelemental effects
when measured by XRF. The detection limits were 23, 23 and 49 ng/mL for Sm(III), Eu(III) and Gd(III), respectively. High enrichment
factors were obtained. The method was successfully applied to the preconcentration of Sm(III), Eu(III) and Gd(III) from different
samples.
Received: 8 March 2000 / Revised: 9 May 2000 / Accepted: 15 May 2000 相似文献
133.
134.
In the past few years the literature on supply chain management has widely emphasized that cooperation among supply chain (SC) firms is a key source of competitive advantage. This paper explores the topic in a particular context, i.e. the industrial district (ID), which constitutes a specific production model where complex SC networks can be identified. SC cooperation may take on several forms in IDs and may produce several benefits (e.g. upgrading quality and reducing costs) so this paper also analyzes the benefits of a specific form of SC cooperation in different competitive scenarios and for diverse ID organizational structures. An agent-based model of SC cooperation in IDs has been developed and a simulation analysis carried out. 相似文献
135.
David Kenning Iztok Golobič Huijuan Xing Matej Bašelj Vito Lojk Jost von Hardenberg 《Heat and Mass Transfer》2006,42(6):511-527
Correlations for nucleate boiling heat transfer should be improved, or in the long term possibly be replaced, by the development
of mechanistic simulations that include the non-uniform spacing and variable characteristics of the nucleation sites and non-linear
interactions between the sites. This paper discusses the interactions that should be included in simulations and some lessons
from a first attempt to validate a particular simulation against experimental spatio-temporal data for wall temperature. Input
data for nucleation site positions and characteristics are a particular problem and the prospects for obtaining this data
from measurements that are independent of boiling are discussed. 相似文献
136.
Héctor Rosas Leidy Erika Sarmiento Vito Lubes María Goncalves Mary Lorena Araujo Felipe Brito 《Journal of solution chemistry》2008,37(5):701-711
The complex species formed between vanadium(III) cysteine and small blood serum bioligands: lactic, oxalic, citric and phosphoric
acids were studied in aqueous solution by means of electromotive force measurements, Emf(H), at 25 °C and 3.0 mol⋅dm−3 KCl as the ionic medium. The ternary complexes were studied by potentiometric measurements and the data analyzed using the
least-squares computational program LETAGROP to obtain the respective stability constants and stoichiometric coefficients.
The UV-Vis spectrophotometric measurements were done in order to make a qualitative characterization of the complexes formed
in aqueous solution. 相似文献
137.
Capriati V Florio S Luisi R Perna FM Barluenga J 《The Journal of organic chemistry》2005,70(15):5852-5858
A diastereo- and enantiospecific formation of tetrasubstituted cyclopropane carbene complexes and cyclopropanecarboxylates from lithiated aryloxiranes and alpha,beta-unsaturated Fischer carbene complexes is described. 相似文献
138.
It is probably redundant to stress how extensive are nowadays the attempts to reduce the diesel particulate emissions from automotive and stationary sources. The present paper looks into a technology relied on a catalytic trap based on a SiC wall-flow monolith lined with suitable catalysts for the sake of promoting a more complete and faster regeneration after particulate capture. All the major steps of the catalytic filter preparation are dealt with, including: the synthesis and choice of the proper catalyst and trap materials, the development of an in situ catalyst deposition technique, the bench testing of the derived catalytic wall-flow. The best catalyst selected was the perovskite La0.9K0.1Cr0.9O3-delta. The filtration efficiency and the pressure drop of the catalytic and non-catalytic monoliths were evaluated on a diesel engine bench under various operating conditions. 相似文献
139.
Starting from 3-bromo-, 1-iodo- and 4-iodo-9-oxo-fluorene three symmetrical bifluorenonyls and the corresponding hydrocarbons 3,3′-, 1,1′- and 4,4′-bifluorenyls are prepared. An attempt to obtain the non-symmetrical 1,2′-bifluorenyl is also described. 相似文献
140.
Guido Barone Giuseppina Castronuovo Vittorio Elia Vito Savino 《Journal of solution chemistry》1984,13(3):209-219
The excess Gibbs free energies of four -methyl-D-aldopyranosides in water were determined at 25°C from isopiestic measurements. The excess entropies were obtained by subtracting the free energy values from the enthalpy data. The results show a remarkable enthalpy-entropy compensation. The positive sign of the excess free energies is interpreted as due to the favorable solute-solvent interactions that prevent the favorable solute-solute interaction. The signs and magnitudes of the pair interaction coefficients are attributed to the release of water from the hydration cospheres during the concentration process. The excess properties seem to depend, however, on the stereochemistry of the solutes. This effect is discussed and attributed to the different specific stabilities of the hydration shells. 相似文献