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951.
Gas adsorption techniques have been used to study the pore texture changes occurring in composite SnO2-CeO2 materials of varying Sn: Ce atom ratios on calcination at temperatures up to 1273K. The data show that the uncalcined materials
are largely microporous in nature, but changes in specific surface area, pore sizes and pore volume occur at an early stage
in the calcination process with the formation of mesopores. However, significant changes occur at calcination temperatures>673
K at which point the mesopores are substantially reduced, and at 873 K and above the mean pore size increases greatly finally
giving non-porous solids after calcination at 1273 K. 相似文献
952.
953.
Jan Philip Solovej 《Inventiones Mathematicae》1991,104(1):291-311
Summary The ionization conjecture for atomic models states that the ionization energy and maximal excess charge are bounded by constants independent of the nuclear charge. We prove this for the Hartree-Fock model without the exchange term.Oblatum 3-V-1990Work supported in part by the U.S. National Science Foundation grant DMS-9002416 相似文献
954.
Photoacoustic amplitude and phase measurements have been carried out near the superconducting transition temperature in the
highT
csuperconductor YBa2Cu3O7. In both the samples investigated, the photoacoustic phase undergoes an anomalous step-like decrease aroundT
c≈ 96 K and increases at lower temperatures. A clear temperature hysteresis for the phase change has been noticed. No anomalous
variation has been observed in the amplitude values. Neither phase nor amplitude shows any anomaly in a non-superconducting
sample of the same composition. 相似文献
955.
It is shown that in a current carrying extrinsic semiconductor, a quasi-neutral wave of carrier concentrations evolves into a shock wave(s). Inhomogeneous distribution of impurities causes either amplification (an absolute instability) or depression of these waves. 相似文献
956.
957.
958.
Philip Yaw Boamah Norbert Haider Gottfried Heinisch 《Journal of heterocyclic chemistry》1989,26(4):933-939
Pyrido[3,4-d]pyridazines 2–5, 21 bearing one, two, or three aryl substituents in the pyridine moiety are shown to be conveniently accessible from 4-aroyl-5-methylpyridazines or 4,5-diaroylpyridazines, respectively, by condensation reactions with appropriate C-N fragments. In addition, the novel pyridazine-annelated pyridones 24, 25 were found to be easily available from ethyl 5-methyl-4-pyridazinecarboxylate. 相似文献
959.
Path integral expressions are given for the wave function and for the density matrix in a theory which describes state vector reduction. The magnitude of the contribution of each classical path to the propagator is not unity, as in ordinary quantum theory, but depends upon the path. 相似文献
960.