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排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
B. G. Tagiev U. F. Kasumov N. N. Musaeva R. B. Dzhabbarov 《Physics of the Solid State》2003,45(3):426-432
The current-voltage characteristics of Ca4Ga2S7: Eu3+ single crystals are measured for the first time, and the processes affecting these characteristics are analyzed theoretically. It is demonstrated that Ca4Ga2S7: Eu3+ single crystals are high-resistance semiconductors with a resistivity of ~109 Ω cm and a relative permittivity of 10.55. The electrical properties of the studied materials are governed by traps with activation energies of 0.13 and 0.19 eV and a density ranging from 9.5×1014 to 2.7×1015 cm?3. The one-carrier injection is observed in weak electric fields. In electric fields with a strength of more than 4×103 V/cm, traps undergo thermal field ionization according to the Pool-Frenkel mechanism. At low temperatures and strong fields (160 K and 5×104 V/cm), the electric current is most likely due to hopping conduction by charge carriers over local levels in the band gap in the vicinity of the Fermi level. 相似文献
982.
Hong‐Qing Wang Zhao‐Jie Liu Li‐Min Yang Ming‐Wu Ding 《Journal of heterocyclic chemistry》2004,41(3):393-397
A series of new 1H‐pyrazolo[3,4‐d]pyrimidin‐4(5H)‐one Derivatives 5 has been designed and regio‐selectively synthesized via a tandem aza‐Wittig reaction. The structures of all compounds prepared have been confirmed by 1H NMR, IR, EI‐MS spectroscopy and elemental analyses. The results of preliminary bioassay indicate that most compounds 5 possess an inhibition effect against Botrytis cinereapers and Pyricularia oryzae at the concentration of 50 mg/L. 相似文献
983.
完全Rees矩阵半群的分解及性质 总被引:1,自引:0,他引:1
用等价关系Q^~出了完全Rees矩阵半群的一种分解.而且得到了它的每个Q^~一类的表示. 相似文献
984.
S. B. Krupanidhi 《Journal of Chemical Sciences》2003,115(5-6):775-788
Relaxor properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) and non-lead perovskite thin films have been analysed in terms of large frequency dispersion of dielectric response
at low temperatures. A wide spectrum of dielectric relaxation was observed in the frequency-dependent response of the imaginary
part of the dielectric permittivity. Transformation from normal ferroelectric to relaxor behaviour has been observed in the
case of the Ca substituting the BaTiO3 thin films. A number of techniques were exploited to investigate the wide spectrum of relaxation times in pulsed laser ablated
thin films.ac anddc electric field induced complex dielectric properties of 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 (PMN-PT) thin films were studied as function of frequencies at different temperatures. Nonlinear behaviour of dielectric
susceptibility with respect to the amplitude of theac drive was observed at lower temperatures. The frequency dependence of transition temperatureT
m
(temperature of the maximum of dielectric constant) was studied using the Vogel-Fulcher relation.
Dedicated to Professor C N R Rao on his 70th birthday 相似文献
985.
A gravitational field can be seen as the anholonomy of the tetrad fields. This is more explicit in the teleparallel approach, in which the gravitational field-strength is the torsion of the ensuing Weitzenböck connection. In a tetrad frame, that torsion is just the anholonomy of that frame. The infinitely many tetrad fields taking the Lorentz metric into a given Riemannian metric differ by point-dependent Lorentz transformations. Inertial frames constitute a smaller infinity of them, differing by fixed-point Lorentz transformations. Holonomic tetrads take the Lorentz metric into itself, and correspond to Minkowski flat spacetime. An accelerated frame is necessarily anholonomic and sees the electromagnetic field strength with an additional term. 相似文献
986.
I.V. Markevich V.I. Kushnirenko L.V. Borkovska B.M. Bulakh 《Solid State Communications》2005,136(8):475-478
The mechanism of formation of a thin highly conductive layer, which is known to be present on ZnO surface, has been proposed. This process has been assumed to consist in accumulation of mobile shallow donors at crystal surface due to their drift in band-bending electric field caused by adsorbed oxygen. Experimental results that confirm this mechanism have been obtained. 相似文献
987.
A surface-mounted device assembly technique for small optics based on laser reflow soldering 总被引:4,自引:0,他引:4
L. Stauffer A. Würsch B. Gchter K. Siercks I. Verettas S. Rossopoulos R. Clavel 《Optics and Lasers in Engineering》2005,43(3-5):365
The three-dimensional miniaturized optical surface-mounted device (TRIMO-SMD) is a new flexible and automated assembly technique for small optical components (maximum diameter for a lens is 2 mm) based on laser reflow soldering technique. This technology can be compared to the electronic SMD technique but applied to micro-optical devices. We present some recent developments of TRIMO-SMD in its application to industrial products. 相似文献
988.
Jean-Pierre Changeux Alain Connes M. B. DeBevoise Jean Petitot Mark Anspach 《Mathematical Intelligencer》2005,27(4):48-56
Conclusion The debate between Jean-Pierre Changeux and Alain Connes is one of the most, interesting to take place in recent years. It
re-frames in a very up-to-date context a whole series of traditional and difficult questions from the standpoint of the knowledge
and experience of two of the leading protagonists of contemporary science. To the choice presented by the neurobiologist between
a Platonist ontology and a neurocognitive psychology of mathematical activity, the mathematician replies with a conception
that is objective (neither ontological nor psychological) of the thoroughly consistent universe of mathematical idealities.
It is indeed in this three-sided arena that the major difficulties play themselves out. One of the great virtues of the book
is to cast a spotlight on this confrontation. 相似文献
989.
990.
Tetraalkyltin complexes, SnR4 (R = Me, Et, Pr, Bu) could react with Pt/HY at 193, 243, 273 and 333 K, respectively. The reactions occurred on the surface of the zeolite and the organotin grafted zeolites were characterized in detail. The framework and the microporous structure of the grafted Pt/HY zeolites were retained. However, the modified zeolites showed better size selectivity in the absorption of hydrocarbons. 相似文献