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481.
An analytical solution is given for a time-decay Rankine vortex profile due to viscous effects. The vortex filament is assumed
to be isolated, strong, concentrated and having zero-meridional flow (i.e. radial and axial velocities are equal to zero).
Zero-meridional renders the governing equations for an unsteady, incompressible and axisymmetric vortex in a simple form.
Based on the tangential momentum equation, the spatial-temporal distributions of the swirl velocity are given in terms of
Fourier-Bessel series by using separation of variables technique. A general formula is derived by total differentiation of
the swirl velocity with respect to time, depicting the viscous dissipation for Oseen and Taylor-like vortex profiles. This
analysis is validated by comparison with previous experimental data.
The English text was polished by Yunming Chen. 相似文献
482.
Konstantinos Tsiantas Thalia Tsiaka Georgios Koutrotsios Eleni Siapi Georgios I. Zervakis Nick Kalogeropoulos Panagiotis Zoumpoulakis 《Molecules (Basel, Switzerland)》2021,26(7)
In recent years, mushrooms have drawn the attention of agro-industries and food-industries as they were considered to be valuable natural sources of health promoting compounds such as β-glucans, ergothioneine, and lovastatin. The detection and quantification of such compounds by implementing reliable analytical approaches is of the utmost importance in order to adjust mushrooms’ cultivation conditions and maximize the production in different species. Toward this direction, the current study focuses on the comparison of ultraviolet–visible (UV–Vis) spectrometry and liquid chromatography–mass spectrometry (LC–MS) methods (a) by evaluating the content of ergothioneine and lovastatin in mushrooms and (b) by highlighting any possible substrate-based interferences that hinder the accurate determination of these two compounds in order to propose the technique-of-choice for a standardized bioactive compounds monitoring. For this purpose, mushrooms produced by three species (i.e., Agaricus bisporus, Pleurotus ostreatus, and P. citrinopileatus) on various cultivation substrates, namely wheat straw (WS), winery (grape marc (GM)), and olive oil (OL) by-products, were examined. Among the two applied techniques, the developed and validated LC–MS methods, exhibiting relatively short analysis time and higher resolution, emerge as the methods-of-choice for detecting ergothioneine and lovastatin in mushrooms. On the contrary, UV–Vis methods were hindered due to co-absorbance of different constituents, resulting in invalid results. Among the studied mushrooms, P. citrinopileatus contained the highest amount of ergothioneine (822.1 ± 20.6 mg kg−1 dry sample), whereas A. bisporus contained the highest amounts of lovastatin (1.39 ± 0.014 mg kg−1 dry sample). Regarding the effect of different cultivation substrates, mushrooms produced on OL and WS contained the highest amount of ergothioneine, while mushrooms deriving from GM-based substrates contained the highest amount of lovastatin. 相似文献
483.
Georgios N. Tsigaridas Aristides I. Kechriniotis Christos A. Tsonos Konstantinos K. Delibasis 《Annalen der Physik》2023,535(4):2200647
In this work, a general method is described for obtaining degenerate solutions of the Dirac equation, corresponding to an infinite number of electromagnetic 4-potentials and fields, which are explicitly calculated. More specifically, using four arbitrary real functions, one can automatically construct a spinor that satisfies the Dirac equation for an infinite number of electromagnetic 4-potentials, defined by those functions. An interesting characteristic of these solutions is that, in the case of Dirac particles with nonzero mass, the degenerate spinors should be localized, both in space and time. The method is also extended to the cases of massless Dirac and Weyl particles, where the localization of the spinors is no longer required. Finally, two experimental methods are proposed for detecting the presence of degenerate states. 相似文献
484.
Novel pyrrones were synthesized by one-stage polycondensation in polyphosphoric acid of 2,3,5,6-tetraamino-l,4-benzoquinone with pyromellitic anhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, or 3,4,9,10-perylenetetracarboxylic dianhydride. The prepared polymers showed a considerable percentage of imide linkages, so they were heated at 350°C under high vacuum to increase the ring closure to the pyrrone structure. The polymers were insoluble in all common polar aprotic solvents, even in dimethylacetamide-water mixture, after reduction with sodium dithionite, but were slightly soluble in concentrated sulfuric and methanesulfonic acid. The thermal decomposition of the polymers (weight loss 5%) started above 400°C both under nitrogen and in air. 相似文献
485.
486.
Larisa Muravleva Ekaterina Muravleva Georgios C. Georgiou Evan Mitsoulis 《ournal of non Newtonian Fluid Mechanics》2010,165(9-10):544-550
The augmented Lagrangian/Uzawa method has been used to study benchmark one-dimensional cessation flow problems of a Bingham fluid, such as the plane Couette flow, and the plane, round, and annular Poiseuille flows. The calculated stopping times agree well with available theoretical upper bounds for the whole range of Bingham numbers and with previous numerical results. The applied method allows for easy determination of the yielded and unyielded regions. The evolution of the rigid zones in these unsteady flows is presented. It is demonstrated that the appearance of an unyielded zone near the wall occurs for any non-zero Bingham number not only in the case of a round tube but also in the case of an annular tube of small radii ratio. The advantages of using the present method instead of regularizing the constitutive equation are also discussed. 相似文献
487.
The seven-step synthesis of a novel structural isomer of VPA-985, N-[3-chloro-4-(5H-pyrrolo[1,2-c][1.3]benzodiazepin-6(11H)-ylcarbonyl)phenyl]-5-fluoro-2-methylbenzamide, is described. (2-Aminophenyl)(1H-pyrrol-2-yl)methanone was converted with thiophosgene into (2-isothiocyanatophenyl)(1H-pyrrol-2-yl)methanone which was cyclised in the presence of base to 5-thioxo-5,6-dihydro-11H-pyrrolo[1,2-c][1.3]benzodiazepin-11-one. The latter underwent desulfurisation with Raney nickel followed by reduction with lithium aluminium hydride in the presence of aluminium trichloride and the resulting 6,11-dihydro-5H-pyrrolo[1,2-c][1.3]-benzodiazepine acylated with 2-chloro-4-nitrobenzoyl chloride to afford 6-(2-chloro-4-nitrobenzoyl)-6,11-dihydro-5H-pyrrolo[1,2-c][1.3]benzodiazepine. The nitro group in the latter compound was reduced with zinc and ammonium chloride to give the corresponding aniline derivative which was then acylated with 2-methyl-5-fluorobenzoyl chloride to provide the final product. 相似文献
488.
In this paper, the basic frequency and time response functions of the three-parameter Poynting–Thomson solid and Jeffreys
fluid are revisited. The two rheological models find application in several areas of rheology, structural mechanics, and geophysics.
The relation between the analyticity of a frequency response function and the causality of the corresponding time response
function is established by identifying all singularities at ω = 0 after applying a partial fraction expansion to the frequency response functions. The strong singularity at ω = 0 in the imaginary part of a frequency response function in association with the causality requirement imposes the addition
of a Dirac delta function in the real part in order to make the frequency response function well defined in the complex plane.
This external intervention, which was first discovered by PAM Dirac, has not received the attention it deserves in the literature
of viscoelasticity and rheology. The addition of the Dirac delta function makes possible the application of time domain techniques
that do not suffer from violating the premise of causality. 相似文献
489.
Vlasoula Bekiari Maria Sotiropoulou Georgios Bokias Panagiotis Lianos 《Colloids and surfaces. A, Physicochemical and engineering aspects》2008,312(2-3):214-218
Poly(N,N-dimethylacrylamide-co-sodium acrylate) hydrogel, which bears negatively charged –COO− groups was used to extract organic or inorganic solutes from water. Some model dyes and metal ions have been studied. Cationic dyes are strongly adsorbed and retained by the polymer while adsorbance of hydrophobic dyes was very low and that of anionic dyes was negligible. Both maximum adsorption and equilibrium binding constant varied from one cationic species to the other depending on the chemical structure of the dye, the presence of functional chemical groups and the hydrophobic–hydrophilic balance. In the case of metal cations, adsorption depended on valence. The hydrogel can be regenerated in an aqueous phase of low pH and thus be reused in several adsorption procedures. 相似文献
490.