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排序方式: 共有100条查询结果,搜索用时 31 毫秒
1.
2.
Optimisation of stir bar sorptive extraction for the analysis of volatile phenols in wines 总被引:2,自引:0,他引:2
An easy, fast and reliable analytical method is proposed for the determination of the concentration of volatile phenols (ethyl- and vinylphenols) in wines. The novel stir bar sorptive extraction (SBSE) technique is employed, following a simple and fast procedure that allows 15 samples to be extracted simultaneously using very small sample volume. Extracts are desorbed in a thermodesorption system (TDS) coupled on-line to a gas chromatograph-mass spectrometry system. The SBSE offers better recovery and linear regression coefficient (r2) for the four volatile phenols than solid-phase extraction (SPE). The mass spectrometric detection in selected ion monitoring mode contributes to the lower detection limit and good sensibility obtained with this method. 相似文献
3.
Luis Friz Francisco Guillén-González M.A. Rojas-Medar 《Comptes Rendus Mathematique》2010,348(15-16):879-883
We treat the existence and uniqueness of reproductive solution (weak time-periodic solution) of a second-grade fluid system for small enough source terms, by using the Galerkin approximation method and compactness arguments. 相似文献
4.
We introduce a parametrisation of the direct correlation function for the square-shoulder fluid and demonstrate that this parametrisation is in quantitative agreement with the numerical solution of the Ornstein–Zernike equation within the Percus–Yevick approximation. Moreover, the radial distribution function obtained from the parametrisation reproduces quantitatively Monte Carlo simulation data. Our results show that the parametrisation is accurate over a large regime of densities for different interaction ranges and potential strengths. 相似文献
5.
A self-consistent approach is used to estimate the internal stresses induced by moisture absorption in composite materials
with a viscoelastic matrix and linear elastic fibers. A strong influence of the behavior of the viscoelastic matrix and humidity
on the internal stresses in the structures at macroscopic and local scales is found to exist. 相似文献
6.
Barbara Zaleska Robert Socha Maria Ciechanowicz-Rutkowska Tulio Pilati 《Monatshefte für Chemie / Chemical Monthly》2000,26(4):1151-1160
An NMR study of the equilibriummixture of two conformers of 2-anilino-2-ethoxy-3-oxothiobutyric acid anilides 3 allows to estimate their population ratio in solvents of increasing polarity. X-Ray analysis as well as IR spectroscopy confirmed that the conformer present in the solid state is stabilized by two hydrogen bonds. The structural basis of the second conformer observed in solution is the 1,4-type S⋯O interaction between the sulfur of the thioanilide moiety and the oxygen of the ethoxy group with a distance of 2.878 ?. 相似文献
7.
Mónica Schwarz M. Carmen Rodríguez Dominico A. Guillén Carmelo G. Barroso 《Journal of separation science》2009,32(11):1782-1790
Brandy and other aged distillates are a rich source of polyphenols. For brandies, contact with wood during ageing makes an important contribution to their polyphenols content. This paper describes the use of a previously devised ultra performance LC (UPLC) method to study the polyphenols content of Brandy de Jerez. UPLC is a new technique in LC offering several potential advantages, especially the reduction of time. Analyses of brandy performed by HPLC were repeated by UPLC. A special UPLC analytical column (Acquity UPLC BEH C18 column, 100×2.1 mm), with a particle size of 1.7 μm, forms part of this system. Using the UPLC system enabled the time needed for analysis to be reduced to one tenth of the time needed in the conventional HPLC system. In conclusion, the separation factor results of the UPLC were compared to those obtained using HPLC methods; this demonstrated that simple, high efficiency UPLC gradients are viable and advantageous substitutes for traditional analysis of polyphenols in brandy by HPLC. The method enabled 14 phenolic compounds to be identified and determined in 33 different commercial brandies, and this allowed them to be differentiated in function of quality. 相似文献
8.
Henrique E. Toma Tulio E. Chavez-Gil Reginaldo C. Rocha Hercílio R. Rechenberg 《Journal of inclusion phenomena and macrocyclic chemistry》1999,34(1):57-68
A novel multibinding species has been obtained by attaching four aliphatic polyamine chains to an iron(II)-polyimine centre, derived from 2,6-diacetylpyridine. Molecular simulations for the complex corroborate the evidence from 1H NMR spectroscopy of a symmetric structure, with the four polyamines displaying a tetrahedral arrangement around the metal centre. The protonated polyamine complex interacts with hexacyanoferrate(II) ions, leading to an inclusion compound which has been characterized based on vibrational and Mössbauer spectroscopy, and on cyclic voltammetry. 相似文献
9.
Christoph Rameshan Werner Stadlmayr Christian Weilach Simon Penner Harald Lorenz Michael Hvecker Raoul Blume Tulio Rocha Detre Teschner Axel Knop‐Gericke Robert Schlgl Norbert Memmel Dmitry Zemlyanov Günther Rupprechter Bernhard Kltzer 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2010,122(18):3292-3296
10.
Santiago Badia Francisco Guillén-González Juan Vicente Gutiérrez-Santacreu 《Journal of computational physics》2011,230(4):1686-1706
In this work, we propose finite element schemes for the numerical approximation of nematic liquid crystal flows, based on a saddle-point formulation of the director vector sub-problem. It introduces a Lagrange multiplier that allows to enforce the sphere condition. In this setting, we can consider the limit problem (without penalty) and the penalized problem (using a Ginzburg–Landau penalty function) in a unified way. Further, the resulting schemes have a stable behavior with respect to the value of the penalty parameter, a key difference with respect to the existing schemes. Two different methods have been considered for the time integration. First, we have considered an implicit algorithm that is unconditionally stable and energy preserving. The linearization of the problem at every time step value can be performed using a quasi-Newton method that allows to decouple fluid velocity and director vector computations for every tangent problem. Then, we have designed a linear semi-implicit algorithm (i.e. it does not involve nonlinear iterations) and proved that it is unconditionally stable, verifying a discrete energy inequality. Finally, some numerical simulations are provided. 相似文献