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251.
Carbon screen-printed electrodes (CSPE) modified with gold nanoparticles present an interesting alternative in the determination of antimony using differential pulse anodic stripping voltammetry. Metallic gold nanoparticles deposits have been obtained by direct electrochemical deposition. Scanning electron microscopy measurements show that the electrochemically synthesized gold nanoparticles are deposited in aggregated form. Any undue effects caused by the presence of foreign ions in the solution were also analyzed to ensure that common interferents in the determination of antimony by ASV. The detection limit for Sb(III) obtained was 9.44 × 10−10 M. In terms of reproducibility, the precision of the above mentioned method in %R.S.D. values was calculated at 2.69% (n = 10). The method was applied to determine levels of antimony in seawater samples and pharmaceutical preparations. 相似文献
252.
We present a dynamic density functional theory (dDFT) which takes into account the advection of the particles by a flowing solvent. For potential flows, we can use the same closure as in the absence of solvent flow. The structure of the resulting advected dDFT suggests that it could be used for nonpotential flows as well. We apply this dDFT to Brownian particles (e.g., polymer coils) in a solvent flowing around a spherical obstacle (e.g., a colloid) and compare the results with direct simulations of the underlying Brownian dynamics. Although numerical limitations do not allow for an accurate quantitative check of the advected dDFT both show the same qualitative features. In contrast to previous works which neglected the deformation of the flow by the obstacle, we find that the bow wave in the density distribution of particles in front of the obstacle as well as the wake behind it are reduced dramatically. As a consequence, the friction force exerted by the (polymer) particles on the colloid can be reduced drastically. 相似文献
253.
Jaime Charris Arthur Barazarte JosÉ Domínguez Gricela Lobo JosÉ Camacho Rosa Ferrer Neira Gamboa Juan Rodrigues Mario V. Capparelli 《Journal of heterocyclic chemistry》2007,44(3):639-643
254.
Peris-Vicente J Garrido-Medina R Simó-Alfonso E Gimeno-Adelantado JV Doménech-Carbó MT 《Rapid communications in mass spectrometry : RCM》2007,21(6):851-856
Mass spectrometry methodology to characterize drying oil used as binding media and varnishes in pictorial artworks, prior to conservation or restoration treatment, is proposed. The analytical treatment requires prior basic hydrolysis of the samples to release the fatty acids: caprylic, pelargonic, capric, sebacic, azelaic, suberic, eicosanoic, lauric, mirystic, palmitic, linolenic, linoleic, oleic and stearic, followed by separation from the matrix by a hexane/water extraction. After removing the solvent, the remaining solid is dissolved in potassium hydroxide, propanol and methanol. The mixture is directly infused into a mass spectrometer without any previous derivatization or separation steps. The detector is operated in electrospray negative ion mode and the [M-H](-) ions of the fatty acids enable identification of the acids. Obtained data for fatty acid ion abundances are analyzed by linear discriminant analysis. The drying oils studied (linseed, poppy seed and walnut) were satisfactorily distinguished. The analytical method shows adequate sensitivity, reproducibility, speed and ease. The proposed methodology has been successfully applied to samples from artistic samples belonging to the Cultural Heritage of Valencia (Spain). 相似文献
255.
We propose a new robust method for the computation of scattering of high-frequency acoustic plane waves by smooth convex objects
in 2D. We formulate this problem by the direct boundary integral method, using the classical combined potential approach.
By exploiting the known asymptotics of the solution, we devise particular expansions, valid in various zones of the boundary,
which express the solution of the integral equation as a product of explicit oscillatory functions and more slowly varying
unknown amplitudes. The amplitudes are approximated by polynomials (of minimum degree d) in each zone using a Galerkin scheme. We prove that the underlying bilinear form is continuous in L
2, with a continuity constant that grows mildly in the wavenumber k. We also show that the bilinear form is uniformly L
2-coercive, independent of k, for all k sufficiently large. (The latter result depends on rather delicate Fourier analysis and is restricted in 2D to circular domains,
but it also applies to spheres in higher dimensions.) Using these results and the asymptotic expansion of the solution, we
prove superalgebraic convergence of our numerical method as d → ∞ for fixed k. We also prove that, as k → ∞, d has to increase only very modestly to maintain a fixed error bound (d ∼ k
1/9 is a typical behaviour). Numerical experiments show that the method suffers minimal loss of accuracy as k →∞, for a fixed number of degrees of freedom. Numerical solutions with a relative error of about 10−5 are obtained on domains of size for k up to 800 using about 60 degrees of freedom. 相似文献
256.
Lorena del Torno‐de Román M. Asunción Alonso‐Lomillo Olga Domínguez‐Renedo M. Julia Arcos‐Martínez 《Electroanalysis》2015,27(2):302-308
Acetylcholinesterase (ACh) and acid phosphatase (AcP) have been simultaneously cross‐linked onto an array of SPCEs, which was set up by a Ag/AgCl reference electrode, a carbon counter electrode and two carbon working electrodes. The detection of As(III) and As(V) is based on their enzymatic inhibitory effect. Different immobilization conditions, substrates, supporting electrolytes and chronoamperometric experimental conditions have been studied for the sensitive and selective detection of both species of arsenic in complex matrices, such as tap water and wine, at once. 相似文献
257.
Application of the Generalized Molar‐Ratio Method to the Determination of the Stoichiometry and Apparent Binding Constant of Nanoparticle‐Organic Capping Systems
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Antonio Doménech‐Carbó María González‐Béjar Julia Pérez‐Prieto 《Electroanalysis》2015,27(10):2302-2312
A generalization of the molar‐ratio method is applied to the determination of the stoichiometry and apparent binding constant of metal nanoparticle‐organic capping complexes (MmLx) using voltammetric data for the oxygen reduction reaction (ORR) in air‐saturated aqueous phosphate buffer solutions. The method is applied to the formation of binary nanohybrids consisting of gold nanoparticles (AuNPs) capped with a rigid spacer, cucurbit[7]uril (CB), termed AuNP@CB, as well as to the formation of their ternary complexes (MmLxBz) with methylene blue (MB), termed AuNP@CB@MB. The obtained stoichiometries correspond to binding of four Au surface atoms for each CB unit. 相似文献
258.
Dr. Giampaolo Barone Prof. Dr. José M. Leal Prof. Dr. Fernando Domínguez Dr. Lisandro J. Giovanetti Prof. Dr. Félix G. Requejo Prof. Dr. Begoña García Prof. Dr. M. Arturo López‐Quintela 《Angewandte Chemie (International ed. in English)》2015,54(26):7612-7616
Subnanometric samples, containing exclusively Ag2 and Ag3 clusters, were synthesized for the first time by kinetic control using an electrochemical technique without the use of surfactants or capping agents. By combination of thermodynamic and kinetic measurements and theoretical calculations, we show herein that Ag3 clusters interact with DNA through intercalation, inducing significant structural distortion to the DNA. The lifetime of Ag3 clusters in the intercalated position is two to three orders of magnitude longer than for classical organic intercalators, such as ethidium bromide or proflavine. 相似文献
259.
As reported in the companion paper, part I, the creep behaviour of two silicon nitride ceramics is governed by a stress exponent n?=?0.6?±?0.1. It is known that, under certain conditions, silicon nitride ceramics may undergo a transition n?=?1?→?n<1 (the ‘shear-thickening transition’) at a well-defined stress σ*. This transition has not been observed, which, together with considerations regarding the value of the transition stress σ*, leads us to reject the shear-thickening phenomenon as an explanation for the creep behaviour of the materials investigated. Instead, it may be understood in terms of a particular grain boundary sliding mechanism accommodated by solution–precipitation. 相似文献
260.
Doménech-Carbó MT Silva MF Aura-Castro E Fuster-López L Kröner S Martínez-Bazán ML Más-Barberá X Mecklenburg MF Osete-Cortina L Doménech A Gimeno-Adelantado JV Yusá-Marco DJ 《Analytical and bioanalytical chemistry》2011,399(9):2921-2937
This work proposes a multi-method approach that combines advanced microscopy (SEM/EDX, AFM) and spectroscopy (UV-vis and FTIR) techniques. This approach not only characterises the behaviour of the additives of two commercial poly(vinyl acetate) (PVAc) and acrylic emulsion paints but also simultaneously characterises the changes in chemical composition and morphology observed in the paint films as a result of ageing due to the paints being exposed to an intense source of simulated daylight. In parallel, a series of mechanical tests were performed that correlate the chemical changes in composition and the changes observed in the films' mechanical properties. This work was a comparative study between both types of acrylic and PVAc paints. The results obtained are of great interest for the modern paint conservation field as they provide valuable information on the mid- and long-term behaviours of these synthetic paints. 相似文献