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排序方式: 共有174条查询结果,搜索用时 15 毫秒
1.
V. A. Astapenko A. S. Kubankin N. N. Nasonov V. V. Polyanskiĭ G. P. Pokhil V. I. Sergienko V. A. Khablo 《JETP Letters》2006,84(6):281-284
The spectra of the collimated polarization bremsstrahlung of 7-MeV electrons intersecting Al, Cu, and Ni polycrystalline films have been measured. Detailed quantitative comparison of the experimental data with theoretical predictions has been performed. It has been shown that the model of a polycrystal as an ensemble of randomly oriented single crystals adequately describes the experimental results. This makes it possible to expect the development of a new method of diagnostics of the atomic structure of partially ordered solids. 相似文献
2.
S. V. Bushin A. K. Khripunov M. A. Bezrukova E. P. Astapenko 《Polymer Science Series A》2007,49(1):71-76
Cellulose myristate samples with a degree of substitution of 230–250 have been studied by the methods of molecular hydrodynamics (viscometry, analytical ultracentrifugation (flotation), and isothermal translational diffusion) in chloroform in the range M = (56–652) × 103. The experimental evidence has been interpreted within the framework of the generalized wormlike Yamakawa-Fuji model with the following parameters: the persistence length a = 115 × 10?8 cm, the chain diameter d = 45 × 10?8 cm, and the molecular mass per unit chain length M L = 270 × 108 cm?1. It has been inferred that the polymer dissolves in chloroform in the form of dimers. 相似文献
3.
Anastacia A. Layeva Galina N. Lipunova Valerii N. Charushin 《Journal of fluorine chemistry》2007,128(7):748-754
A new approach for the synthesis of fluorinated 1H-quinazolin-4-ones and 4-substituted quinazolines has been developed. 6-Fluoro-1H-quinazolin-4-ones were obtained by intramolecular cyclization of fluorine-containing S-ethyl N-benzoylisothioureas. Nucleophilic substitution reactions at positions 2 and 7, as well as alkylation at 1-position of quinazolinones were investigated. In addition, the synthesis of fluorine-containing 4-aminoquinazolines was carried out. 相似文献
4.
5.
Alexander M. Schneider Luyao Lu Eric F. Manley Tianyue Zheng Valerii Sharapov Tao Xu Tobin J. Marks Lin X. Chen Luping Yu 《Chemical science》2015,6(8):4860-4866
We report the properties of a new series of wide band gap photovoltaic polymers based on the N-alkyl 2-pyridone dithiophene (PDT) unit. These polymers are effective bulk heterojunction solar cell materials when blended with phenyl-C71-butyric acid methyl ester (PC71BM). They achieve power conversion efficiencies (up to 5.33%) high for polymers having such large bandgaps, ca. 2.0 eV (optical) and 2.5 eV (electrochemical). Grazing incidence wide-angle X-ray scattering (GIWAXS) reveals strong correlations between π–π stacking distance and regularity, polymer backbone planarity, optical absorption maximum energy, and photovoltaic efficiency. 相似文献
6.
In this study, new biodegradable and biocompatible amphiphilic polymers were obtained by modifying the peripheral hydroxyl groups of branched polyethers and polyesters with organosilicon substituents. The structures of the synthesized polymers were confirmed by NMR and GPC. Organosilicon moieties of the polymers were formed by silatranes and trimethylsilyl blocks and displayed hydrophilic and hydrophobic properties, respectively. The effect of the ratio of hydrophilic to hydrophobic organosilicon structures on the surface activity and biological activity of macromolecules was studied, together with the effect on these activities of the macromolecules’ molecular weight and chemical structure. In particular, the critical micelle concentrations were determined, the effect of the structure of the polymers on their wetting with aqueous solutions on glass and parafilm was described, and the aggregation stability of emulsions was studied. Finally, the effect of the polymer structures on their antifungal activity and seed germination stimulation was examined. 相似文献
7.
Valerii F. Traven Dmitriy A. Cheptsov Zarina Z. Mamirgova Natalya P. Solovjova Vyacheslav M. Martynenko Sergei M. Dolotov Michail M. Krayushkin Ivan V. Ivanov 《Photochemistry and photobiology》2020,96(4):798-804
Photophysical characteristics of new 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins have been measured. These coumarin derivatives are found to be effective fluorophores and show high values of quantum yields of fluorescence both in nonpolar and in polar solvents. The 3-(1-acyl-5-aryl-3-pyrazolinyl)coumarins turned to be photosensitive compounds and undergo photolysis under irradiation in the range of 310–465 nm. Photolysis is suggested to include retro-cyclization and retro-condensation steps. The process is accompanied by a sharp drop of fluorescence that can be of interest for the creation of new media in optical recording of information. 相似文献
8.
Boris N. Kozlov Ivan I. Pilyugin Valerii G. Shchebelin Alexander V. Bulgakov Alexander P. Mayorov Mikhail R. Predtechenskii 《Mikrochimica acta》1995,120(1-4):111-119
A time-of-flight mass spectrometer with electron impact ionization facility was used in investigations of the laser plume structure. Densities and velocity distributions of positively charged and neutral species were measured 12 cm downstream of the target. Velocities of particles in a plume were measured by the retarding potential method. The combination of a skimmer and declining electric field was used to suppress the influence of charged particles during the measurement of the neutral component parameters. In the case of YBaCuO ceramic laser ablation, a strong variation of the laser-induced plume composition was observed from its head to its tail. It seems to be accounted for by the difference of the starting (phase transition) temperatures of various layers of a plume. Ions detected mainly in the head of a plume were followed by atoms, molecules and clusters in inverse succession to their appearance in the plume under the light intensity increase. The characteristic of the number density dependence upon the laser spot diameter make it clear that most of the molecules BaO and YO are the direct product of ablation. In contrast, the detected clusters with masses up to 2000 amu are the product of condensation in the expanding plume under the conditions of the experiments. 相似文献
9.
For plus-operators in a Banach indefinite space, we consider a linear-fractional relation. The classes of operators with the
empty domain of definition for such a relation are described. The sufficient (and necessary, in some meaning) conditions for
the chain rule to be valid are given. 相似文献
10.
The excitation of a two-level system by a chirped laser pulse is analyzed using an analytical approach (in the perturbation-theory limit) that involves the modified rotating-wave approximation and the numerical solution to the Bloch equation. The dependence of the population of the upper energy level on the chirp is studied for various radiation intensities and pulse durations. An exact solution is compared with the result obtained using the modified rotating-wave approximation and the perturbation theory. It is demonstrated that, for a certain range of parameters, the excitation probability of a two-level system can be effectively controlled via a variation in the chirp. 相似文献