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排序方式: 共有60条查询结果,搜索用时 218 毫秒
21.
Laurynas Staišiūnas Konstantinas Leinartas Meilutė Samulevičienė Povilas Miečinskas Asta Grigucevičienė Remigijus Juškėnas Eimutis Juzeliūnas 《Journal of Solid State Electrochemistry》2013,17(6):1649-1656
Nanocrystalline Mg–Nb and Mg–Nb–Al–Zn alloy films were deposited by dc magnetron sputtering on glass and quartz substrates in a wide range of niobium concentrations from 6 to 80 at.%. Structural, electrochemical and corrosion properties of the films were studied by X-ray diffraction, dc voltammetry, electrochemical impedance spectroscopy and electrochemical quartz crystal microbalance. Development of body-centred cubic Nb structure in the Mg–Nb alloy matrix yielded the effects of lattice contraction, grain refining and electrochemical passivity. The measurements showed high corrosion resistance of the films in alkaline solutions when niobium content was one third or more. An increased corrosion resistance was achieved by introducing minor amounts of Al (ca. 2 at.%). In particular, such Al effect was pronounced at lower Nb concentrations (20 to 30 at.%). Semiconductor properties of spontaneously formed oxide on Mg–Nb alloy were studied by Mott–Schottky plots, which indicated highly doped n-type oxide structures on Mg–Nb surface. The paper fills some gap in understanding of niobium–magnesium systems, which show potential for applications in hydrogen storage, switchable mirrors and corrosion protection. 相似文献
22.
J. Macutkevic D. Seliuta G. Valusis J. Banys P. Kuzhir S. Maksimenko V. Kuznetsov S. Moseenkov O. Shenderova Ph. Lambin 《Solid State Sciences》2009,11(10):1828-1832
Dielectric analysis of a novel polymer composite based on onion-like carbon (OLC) has been carried out by varying the temperature between 240 and 460 K within a wide frequency range (20 Hz–1 MHz). A small effect of the OLC inclusions on the beta transition of OLC/polymethylmethacrylate (PMMA) composite has been observed, which indicates a weak affinity of the OLC to the host matrix. At the same time, an increase in concentration of the OLC has been found to strongly influence the glass and melting temperatures of the nanocomposites. These structural properties of the OLC/PMMA composite materials should be taken into account when a new family of effective wide-band electromagnetic materials are designed and fabricated. 相似文献
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Milda M. Burbuliene Rita Mazeikaite Povilas Vainilavicius 《Journal of heterocyclic chemistry》2008,45(2):607-610
26.
The dielectric spectra of ferroelectric hydrogen bonded betaine phosphate0.05 betaine phosphite0.95 (DBP0.05DBPI0.95) was investigated in the very wide temperature (300–20 K) and frequency (20–35 GHz) regions. The dielectric dispersion was analyzed in terms of distribution of relaxation times, using Tichonov regularization method. Strongly asymmetric and broad distribution of relaxation times below ferroelectric phase transition temperature T c?≈?253 K clearly differs from the one that is usually observed in ferroelectrics. The observed disorder in deuterons system close to ferroelectric phase transition temperature is an embryo of coexistence ferroelectric order and dipolar glass disorder observed at low temperatures. 相似文献
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Romualdas Smicius Virginija Jakubkiene Milda M. Burbuliene Povilas Vainilavicius 《Monatshefte für Chemie / Chemical Monthly》2002,7(1):173-181
Treatment of 5-(6-methyl-2,4-dioxo-1,2,3,4-tetrahydro-3-pyrimidinyl)-methyl-1,3,4-oxadiazole-2-thione with haloalkanes yielded oxadiazole S-alkyl derivatives, whereas its reaction with formaldehyde and amines resulted in formation of oxadiazole N(3)-aminomethyl derivatives. The alkylation of 2-alkylsulfanyl-5-(6-methyl-2,4-dioxo-1,2,3,4-tetrahydro-3-pyrimidinyl)-methyl-1,3,4-oxadiazoles with methyl bromoacetate proceeded at the N(1)-position of pyrimidine to give 2-alkylsulfanyl-5-(1-methoxycarbonylmethyl-6-methyl-2,4-dioxo-1,2,3,4-tetrahydro-3-pyrimidinyl)-methyl-1,3,4-oxadiazoles, whereas aminomethylation, bromination, or nitration took place at position 5 of pyrimidine ring and afforded the corresponding 5-pyrimidine substituted derivatives. 相似文献
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Povilas Vainilavicius Romualdas Smicius Virginija Jakubkiene Sigitas Tumkevicius 《Monatshefte für Chemie / Chemical Monthly》2001,132(7):825-831
Summary. In the reaction of 5-(6-methyl-2,4-dioxo-1,2,3,4-tetrahydro-3-pyrimidinyl)-methyl-1,3,4-oxadiazole-2-thione with hydrazine
hydrate, 5-(6-methyl-2,4-dioxo-1,2,3,4-tetrahydro-3-pyrimidinyl)-methyl-4-amino-1,2,4-triazole-3-thione was formed. The reactions
of the latter with ethyl bromoacetate and chloroacetonitrile in the presence of triethylamine proceeded under formation of
the corresponding S-alkylated derivatives, whereas from its reaction with ω-bromoacetophenone and ethyl 4-chloroacetoacetate
triazolothiadiazines were obtained. Treatment of the title compound with ethyl 2-chloroacetoacetate led to the formation of
5-(6-methyl-2,4-dioxo-1,2,3,4-tetrahydro-3-pyrimidinyl)-methyl-4-N-acetylamino-(3-ethoxy-carbonylmethylthio)-1,2,4-triazole.
Performing of the latter reaction without basic catalyst gave a triazolothiadiazine. Treatment of the S-alkylated derivatives
with sodium methoxide resulted in triazolothiadiazines via a cyclocondensation reaction.
Received November 20, 2000. Accepted January 15, 2001 相似文献