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排序方式: 共有152条查询结果,搜索用时 46 毫秒
1.
2.
Veličković Jelena Đ. Andrić Deana Roglić Goran Tešic Živoslav Lj. Milojković-Opsenica Dušanka M. 《平面色谱法杂志一现代薄层色谱法》2004,17(4):255-260
JPC – Journal of Planar Chromatography – Modern TLC - The chromatographic behavior of fourteen 1-arylpiperazine derivatives has been studied by thin-layer chromatography on both silica... 相似文献
3.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献
4.
The dependence of cross sections on the colour state of the colliding hadrons is investigated within the Low-Nussinov model of two-gluon exchange. The total cross sections for colour-octet hadrons are practically constant as functions of the hadronic radii, while they tend to zero when the radii of the colour-singlet hadrons approach zero. The slope parameter of the differential clastic cross sections for small momentum transfers is rather insensitive to the colour structure of the colliding hadrons. The integrated colour exchange cross section is calculated. 相似文献
5.
K. Kriŝtiaková O. Ŝauŝa J. Kriŝtiak Ŝ. Jánoŝ 《Zeitschrift für Physik B Condensed Matter》1989,75(2):197-199
We have measured the ac susceptibility of a wire with a Nb core (1.27 mm diam.) and a Cu cladding (0.37 mm thickness) atT50 K andB0.1 mG. Due to its proximity to Nb, the Cu becomes fully superconducting. From the data we find a breakdown fieldH
b
=1.2 (mG) and a coherence length =2.2T
–1/2 (m) for the Cu, as well as a field penetration depth -34T
1/2 (m) at the Cu/Nb interface. 相似文献
6.
L. Pospíŝil 《Journal of Electroanalytical Chemistry》1981,123(2):323-333
Integrated pulse polarography and similar techniques have been used for study of reduction of bipyridine complexes of Co(II), Ni(II) and partially also Fe(II) in aqueous solutions. By proper choice of pulse and detection intervals, it is possible to confirm or separate the contribution of reactant adsorption. The pulse polarography of the product reoxidation shows a finite charge transfer rate in the case of tris-2,2′-bipyridine cobalt complex. 相似文献
7.
New bent-core liquid crystalline dimers with W-shaped molecular geometry have been prepared and studied. We have modified the dimer shape by variation of the connecting part between two bent-core units and changing the terminal chains (perfluoroalkyl, siloxanealkyl). Additionally, we have altered the inner bend angle value (120°, 60° and 148°) by utilization of different aromatic units. Mesomorphic properties of new dimers were established based on the texture observation in the polarizing microscope and DSC measurements. Moreover, x-ray structural analysis has been performed for selected dimers to confirm phase identification. For most of the studied dimers, nematic or columnar phases have been detected, for several compounds appearing in a nematic-columnar phase sequence on cooling from the isotropic phase. The studied dimers showed richer polymorphism than their monomeric counterparts. 相似文献
8.
Emilia Gîlcă Andrada Măicăneanu Petru Ilea 《Central European Journal of Chemistry》2014,12(8):821-828
The aim of this study was to compare several anion exchangers and to investigate the capacity of Amberlite IRA410 to remove zinc as chloride [ZnCl3]? from hydrochloric solutions (1 M). Influence of the process parameters such as stirring rate, resin quantity and zinc initial concentration over the removal process, was considered. The highest experimental ionic exchange capacity between the considered anionic exchangers, in the same working conditions (500 rpm, 5 g resin and 500 mg L?1), was obtained for Amberlite IRA410, 8.34 mg g?1. With an increase of zinc ions concentration, ionic exchange capacity increased up to 19.31 mg g?1 (1100 mg L?1). The experimental data were analysed using Langmuir, Freundlich, Temkin and Dubinin-Radushkevich isotherm models. The results were also analyzed using sorption kinetics models, pseudo-first-, pseudo-second-order, intra-particle and film diffusion models. From the Dubinin-Radushkevich and Temkin isotherm models the mean free energy and heat of sorption were calculated to be 7.45 kJ mol?1, respectively 1×10?4 kJ mol?1, which indicates that zinc sorption is characterized by a physisorption process. Kinetic studies showed that the adsorption followed a pseudo-second-order kinetic model. 相似文献
9.
Jana ic
labur Marko Brajer Sandra Voa Ante Gali Sanja Radman Suzana Rimac-Brn
i Qiang Xia Zhenzhou Zhu Nabil Grimi Francisco J. Barba Nataa Hulak 《Molecules (Basel, Switzerland)》2021,26(7)
Spices are a popular food of plant origin, rich in various phytochemicals and recognized for their numerous properties. The aim of the study was to evaluate the antioxidant and antimicrobial activity, as well as the content of specialized metabolites, of aqueous extracts of three spice species––garlic (Allium sativum L.), ginger (Zingiber officinalle L.) and turmeric (Curcuma longa L.)––prepared by green extraction methods. Ultrasound treatment increased the chromaticity parameter b value of turmeric and ginger extracts, thus indicating a higher yellow color predominantly due to curcuminoids characteristic of these species. Ultrasound-assisted extraction significantly increased the content of total soluble solids, phenolic compounds, total carotenoids and vitamin C. The temperature of the system was also an important factor, with the highest (70 °C) conditions in ultrasound-assisted extraction having a positive effect on thermolabile compounds (vitamin C, phenolics, total carotenoids). For example, turmeric extract treated with ultrasound at 70 °C had up to a 67% higher vitamin C content and a 69.4% higher total carotenoid content compared to samples treated conventionally at the same temperature, while ginger extracts had up to 40% higher total phenols. All different concentrations of spice extracts were not sufficient for complete inhibition of pathogenic bacterial strains of Salmonella, L. monocytogenes and S. aureus; however, only garlic extracts had an effect on slowing down the growth and number of L. monocytogenes colonies. Spice extracts obtained by ultrasonic treatment contained a significantly higher level of bioactive compounds and antioxidant capacity, suggesting that the extracts obtained have significant nutritional potential and thus a significant possibility for phytotherapeutic uses. 相似文献
10.
Edina Vranić Daris Grizić Odon Planinšek Stanko Srčič Erem Bilensoy 《Journal of inclusion phenomena and macrocyclic chemistry》2014,80(1-2):139-146
Cyclodextrins are cyclic oligosaccharides, capable of forming inclusion complexes with many active substances. This way, the aqueous solubility and rate of dissolution of active substances can be changed. For this research we have selected celecoxib as the model active substance, due to its low water solubility, high lipophilicity, and high intestinal permeability. Usually, the amount of cyclodextrin complex that can be incorporated into a pharmaceutical dosage form is limited. The usage of hydrophilic polymers can overcome this problem. In this study, we wanted to point out the potential of various types of hydrophilic polymers for enhancing the complex formation efficiencies, and to highlight the possible use of alginate as a solubility stabilizer/enhancer and as a microsphere matrix polymer. The phase solubility investigation showed greater stability constants (> 250 M?1) in ternary complexes than in the binary complex, which is a good indicator of the complex formation enhancer properties of these hydrophilic polymers. The relative solubilizing efficiency decreased in the next order: PVP K25 (6.49) > Sodium alginate (6.26) > PEG 6000 (5.72) > without polymer (4.81). The DSC curves showed that all samples that were prepared with β-cyclodextrin (both complexes and physical mixtures) had lower melting endotherms at 160 °C than pure celecoxib. XRD confirmed the complex formation by partial celecoxib amorphisation. The dissolution studies of the prepared microspheres revealed that all samples had different release rates (shown by the similarity factor f2, which was 36.37, 42.46 and 38.11 % respectively) and that the use of β-cyclodextrin increased the dissolution rate of celecoxib from alginate microspheres in a controlled manner. We concluded that sodium alginate could act as a complex stabilizing/enhancing agent and as a microsphere matrix polymer, at the same time. 相似文献