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41.
Enantioselective partitioning of ibuprofen enantiomers in a biphasic recognition chiral extraction system was studied. A combination of hydrophobic L‐isobutyl tartrate in organic phase and hydrophilic β‐cyclodextrin derivative in aqueous phase is necessary to establish a biphasic recognition chiral extraction system. The studies performed involve an enantioselective extraction in a biphasic system, where ibuprofen enantiomers form four complexes with the β‐cyclodextrin derivative in aqueous phase and the D(L)‐isobutyl tartrate in organic phase, respectively. In these biphasic resolutions, the types and the concentrations of the extractants, pH and temperature all exert a considerable influence on the biphasic recognition process. Good enantioselectivities for ibuprofen enantiomers were obtained at pH≦2.5 and a ratio of 2:1 of [L‐isobutyl tartrate] to [HP‐β‐CD]. Biphasic recognition chiral extraction is of strong chiral separation ability, and may be very helpful to optimize the extraction systems and realize the large‐scale production of enantiomers. 相似文献
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本文研究了一类独立重尾随机变量随机和S(t)∧=∑k=1^N(t)Xk,t≥0的大偏差概率,其中{N(t),t≥0}是一放大晨负整数值随机变量;{Xn,n≥1}是非负,独立随机变量序列,并与{N(t),t≥0}独立。本文的结果将{Xn,n≥1}为独立同分布情形推广到了独立不同分布情形。 相似文献
45.
Hydrophilic β-cyclodextrin (β-CD) and its derivatives are not soluble in organic liquids but they are highly soluble in water and can interact with enantiomers
selectively to form diastereomeric complexes which enable their use as chiral selectors in chiral solvent extraction. In this
paper, terbutaline enantiomers were extracted by hydrophilic β-CD derivatives in an aqueous/organic biphasic solvent system with racemic terbutaline in the organic phase and β-CD in the aqueous phase. Five β-CD derivatives, namely: methyl-β-cyclodextrin (Me-β-CD), hydroxyethyl-β-cyclodextrin (HE-β-CD), 2-hydroxyethyl-β-cyclodextrin (2-HE-β-CD), (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD) and (4-sulfobutylether)-β-cyclodextrin (SBE-β-CD) were used as hydrophilic selectors, respectively. Process variables affecting extraction efficiency were investigated,
namely influence of the type of organic solvents and β-CD derivatives, concentrations of selectors and terbutaline enantiomers, pH, and temperature. Experimental results show that
the efficiency of extraction depends, often strongly, on process variables. All five β-CD derivatives studied preferentially extract the more biologically active (R)-terbutaline from the organic phase; HP-β-CD has the strongest recognition ability. The maximum enantioselectivity (α) of 1.42 was achieved under optimal conditions: pH 7.0 and temperature of 5°C. Utilization of the extraction method for separation
of terbutaline enantiomers is expected to be cheap and easy to scale up to commercial scale. 相似文献
46.
Tiju Thomas Xiaomei Guo MVS Chandrashekhar Carl B. Poitras William Shaff Mark Dreibelbis Jesse Reiherzer Kewen Li Francis J. DiSalvo Michal Lipson M.G. Spencer 《Journal of Crystal Growth》2009,311(19):4402-4407
Eu:GaN powder synthesized using a high temperature ammonothermal process is known to be dark in appearance due to presence of Eu-containing absorbing particles. Improvement of the visual quality of the Eu:GaN powder is achieved by rinsing in dilute acids. Acid-rinsed Eu:GaN has photoluminescence (PL) enhanced by a factor of 3 when compared to as-prepared Eu:GaN. Such visually clear powders are used for making Eu:GaN nanoparticles of sizes 30–50 nm using a soft ball-milling technique. The particle size was determined using X-ray diffraction, scanning electron microscopy and a dynamic light scattering system. Longer durations of a “soft” ball-milling technique results in particle size reduction. These nanopowders show significant photoluminescence intensity with no yellow luminescence, and have a reduced PL intensity with increasing ball-milling time. Eu:GaN nanopowder embedded in a KBr matrix shows at least a 10× improvement in transmittance when compared to as-prepared powders. The improvement of transmittance depends on both the concentration and particle size. This improved transmittance suggests that such a transparent matrix could be used as a laser gain medium. 相似文献
47.
A model has been derived theoretically to correlate capillary pressure and resistivity index based on the fractal scaling
theory. The model is simple and predicts a power law relationship between capillary pressure and resistivity index (P
c
= p
e
· I
β) in a specific range of low water saturation. To verify the model, gas-water capillary pressure and resistivity were measured
simultaneously at a room temperature in 14 core samples from two formations in an oil reservoir. The permeability of the core
samples ranged from 0.028 to over 3000 md. The porosity ranged from less than 8 to over 30. Capillary pressure curves were
measured using a semi-permeable porous-plate technique. The model was tested against the experimental data obtained in this
study. The results demonstrated that the model could match the experimental data in a specific range of low water saturation.
The experimental results also support the fractal scaling theory in a low water saturation range. The new model developed
in this study may be deployed to determine capillary pressure from resistivity data both in laboratories and reservoirs, especially
in the case in which permeability is low or it is difficult to measure capillary pressure. 相似文献
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Separation of phenylsuccinic acid enantiomers using biphasic chiral recognition high‐speed countercurrent chromatography 下载免费PDF全文
Genlin Sun Kewen Tang Panliang Zhang Weijun Yang Guoqing Sui 《Journal of separation science》2014,37(14):1736-1741
High‐speed countercurrent chromatography (HSCCC) combined with biphasic chiral recognition was successfully applied to the resolution of phenylsuccinic acid enantiomers. d ‐Isobutyl tartrate and hydroxypropyl‐β‐cyclodextrin were employed as lipophilic and hydrophilic selectors dissolved in the organic stationary phase and aqueous mobile phase, respectively. The two‐phase solvent system was made up of n‐hexane/methyl tert‐butyl ether/water (0.5:1.5:2, v/v/v). Impacts of the type and concentration of chiral selectors, the pH value of the aqueous phase solution as well as the temperature on the separation efficiency were investigated. By means of preparative HSCCC, pure enantiomer was obtained by separating 810 mg of racemate with a purity >99.5% and a recovery rate between 82 and 85%. The experimental results indicate that biphasic recognition HSCCC provide a promising means for efficient separation of racemates. 相似文献
50.