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排序方式: 共有412条查询结果,搜索用时 15 毫秒
1.
Dirk Lützenkirchen‐Hecht Kay Rohrmann Thomas Stöcker Wolfgang Thiel 《Surface and interface analysis : SIA》2007,39(11):845-851
Different ink‐jet printed paper materials were investigated using X‐ray photoelectron spectroscopy (XPS) yielding the elemental composition of the near‐surface region of the papers. We found significant differences with respect to the detected elements and their atomic concentrations in the different inks studied here. Two different groups of inks could be identified by means of a lower ratio of the O and C atomic concentrations and lower concentrations in specific trace elements like Mg, Na and Si. High‐resolution spectra of C 1s and O 1s core levels allowed a detailed determination of the chemical state of the respective elements. On the basis of a detailed deconvolution of these XPS signals, significant differences between all the investigated ink‐jet printed papers were found, thereby allowing their discrimination. The applicability of the measurements and, more generally, the XPS technique for forensic investigations of paper are discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
2.
Summary Electrophoretic mobility measurements in the pH 2‐10 range are described for several commercial HPLC silica microparticles
and a laboratory-produced product. The content of metal impurities for the silicas was also determined by AAS. An acidic/hydrothermal
treatment was used to generate a more homogenous surface for some of the silicas. The zero points of charge (zpc) for both
a native and a treated silica plus several commercial HPLC silicas were compared. The electrophoretic mobility method may
be useful in predicting the utility of certain types of silica supports for chromatographic separations. 相似文献
3.
A stochastic (Monte Carlo) simulation is used to investigate thermodynamic and kinetic contributions from the reversible A <--> B reaction in capillary electrophoresis (CE). The effects of equilibrium constant, rate constant, and electrophoretic mobility on the molecular zone profiles and the corresponding statistical moments are evaluated. As the reaction approaches steady state, the velocity of the zone is governed by the equilibrium constant and the electrophoretic mobilities of the reacting molecules. When the equilibrium constant is less than unity, the mean zone velocity is more similar to that of the reactant A. Conversely, when the equilibrium constant is greater than unity, the velocity is more similar to that of the product B. The extent of zone-broadening and asymmetry at steady state is dependent upon the equilibrium constant, the characteristic reaction lifetime, and the electrophoretic mobility difference between reacting molecules. If all other parameters are held constant, the plate height is greatest and skew is least when the equilibrium constant is unity. The plate height increases linearly with the characteristic reaction lifetime and electrophoretic mobility difference, whereas the skew is independent of these parameters. These conclusions have important implications for the elucidation of thermodynamic and kinetic information from experimental data. 相似文献
4.
Hideya Kawasaki Hiroshi Maeda 《Colloids and surfaces. A, Physicochemical and engineering aspects》2004,250(1-3):479-483
Effects of the surfactant concentration Cd and the NaCl concentration Cs on the electrophoretic mobilities U of the well-characterized polymer-like micelles have been investigated by the electrophoretic light scattering, using tetradecyldimethylamine oxide hemihydrochloride (C14DMAO·1/2HCl). At the high ionic strength of 0.1 mol kg−1 NaCl, the electrophoretic mobilities were independent of Cd (5 mM < Cd < 100 mM), despite the concentration-dependent micelle growth of the polymer-like micelles. This suggests that the electrophoretic mobility of the polymer-like micelle at high ionic strengths is independent of the contour length (i.e., the molecular weight), as found on linear polyelectrolytes. Somewhat surprisingly, the entanglements of the polymer-like micelles gave small effect on the electrophoretic mobilities in the examined range of the surfactant concentration above an overlap concentration. The mobilities of the polymer-like micelle decreased with √Cs in a single exponential manner in the range of Cs from 0.02 to 0.3 mol kg−1. It is suggested that the cylinder model can be applied to the electrophoretic mobilities of the polymer-like micelles at high ionic strengths (i.e. a free-draining behavior), since the persistence length of the polymer-like micelle (20 nm) is much larger than the Debye length at high ionic strength. 相似文献
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7.
Mauro A. La-Scalea Carla M. Souza Menezes Elizabeth I. Ferreira 《Journal of Molecular Structure》2005,730(1-3):111-120
Diffusion coefficients and electrophoretic mobility are two important physicochemical parameters used in mass transport phenomenon studies. The volume of the solute is required to determine or estimate these parameters. Classical methods, such as the LeBas method are commonly used. However, although valid, this method may represent a boring and time-consuming task, depending on the nature and number of compounds to be calculated. In this study, the volumes of a series of neutral and charged substances of the main functional groups present in organic molecules, amino acids, drugs and diverse compounds, such as cytosine and glucose, were calculated according to the LeBas method (VM) and the AM1 semi-empirical method, VW(AM1). The latter showed to be statistically coincident with the former. Employed as a pure value or corrected by the LeBas molar volume, the AM1 molecular volume was also demonstrated to estimate the diffusion coefficients in infinite aqueous dilution within an acceptable average error, according to the Othmer–Thakar, Wilke–Chang and Hayduk–Laudie methods, as well as the electrophoretic mobility of charged substances, such as carboxylates and protonated amines. According to these results, the AM1 method was seen to be statistically valid to calculate molecular volume. Many advantages in the construction of most diverse structures were noted, as well as a reduction in time and an increase in the quality of the information, when run on molecular modeling software. 相似文献
8.
《Journal of separation science》2003,26(11):1045-1049
Differences in the surface charges of bacteria can be exploited for their separation by capillary electrophoresis. Because of their low electrophoretic mobility, the separation is not always easy to perform, especially in the presence of the electroosmotic flow. Elimination of electroosmotic flow by capillary wall modification with γ‐(trimethoxysilyl)propyl methacrylate followed by acrylamide bonding permits separation over a distance of 8.5 cm. 相似文献
9.
Paul Becher 《Journal of Dispersion Science and Technology》2013,34(4):513-514
Room temperature glass containing copper nitrate was produced using the microemulsion-gel method. Ultraviolet-visible spectroscopy and x-ray diffraction spectra were used to demonstrate the presence of copper nitrate in the gel samples. The samples were examined using optical microscopy, with and without polarized filters, and scanning electron microscopy with energy dispersive x-ray analysis, before and after the extraction of the surfactant with an organic solvent. The results indicated that copper nitrate was present throughout the silicate network formed and was associated with the microemulsion components, i.e., the interstitial liquid, remaining in the bulk material. 相似文献
10.