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排序方式: 共有299条查询结果,搜索用时 93 毫秒
291.
Banerjee A. K. Poon P. S. Laya M. S. Azocar J. A. 《Russian Journal of General Chemistry》2003,73(11):1815-1820
1-Benzyloxy-5-hydroxynaphthalene and 1,6-dimethyl-5-hydroxynaphthalene were prepared from 5-methoxy--tetralone. 6-Methoxy--tetralone was converted to 1,6-dimethoxy-2-isopropylnaphthalene. 相似文献
292.
This year marks the 50th anniversary of the proposal of a double helical structure for DNA by James Watson and Francis Crick. The place of this proposal in the history and development of molecular biology is discussed. Several other discoveries that occurred in the middle of the twentieth century were perhaps equally important to our understanding of cellular processes; however, none of these captured the attention and imagination of the public to the same extent as the double helix. The existence of multiple forms of DNA and the uses of DNA in biological technologies is presented. DNA is also finding increasing use as a material due to its rather unusual structural and physical characteristics as well as its ready availability. 相似文献
293.
Sonier JE Poon KF Luke GM Kyriakou P Miller RI Liang R Wiebe CR Fournier P Greene RL 《Physical review letters》2003,91(14):147002
We report muon-spin rotation and relaxation (muSR) measurements on single crystals of the electron-doped high-T(c) superconductor Pr2-xCexCuO4. In a zero external magnetic field, superconductivity is found to coexist with dilute Cu spins that are static on the muSR time scale. In an applied field, we observe a mu(+)-Knight shift that is primarily due to the magnetic moment induced on the Pr ions. Below the superconducting transition temperature T(c), an additional source of local magnetic field appears throughout the volume of the sample. This finding is shown to be consistent with field-induced antiferromagnetic ordering of the Cu spins. Measurements of the temperature dependence of the in-plane magnetic penetration depth lambda(ab) in the vortex state are also presented. 相似文献
294.
Variations in fiber-cladding diameter on a nanometer scale were measured along millimeter to centimeter lengths by use of whispering-gallery modes (WGMs) in the elastic scattering of the fiber. The fiber was side coupled with a wavelength-tunable Gaussian beam. The scattered light was imaged approximately 1:1 onto a multichannel photodiode array detector. Based on the WGM wavelength shifts along the fiber, the taper of the fiber cladding's diameter was measured on a nanometer/millimeter scale. The fiber's surface roughness amplitude (in nanometers) and granular size ( approximately 100 microm) along centimeter-length fibers could also be revealed by use of higher- Q resonances. 相似文献
295.
G K Poon M Jarman R McCague J H Davies C E Heeremans R A van der Hoeven W M Niessen J van der Greef 《Journal of chromatography. A》1992,576(2):235-244
Liquid chromatography with thermospray mass spectrometry has proved to be an invaluable technique for the study of metabolic degradation of xenobiotics in complex biological fluids. This paper describes the detection of 4-hydroxyandrost-4-ene-3,17-dione and its metabolites in urinary extracts from prostatic cancer patients. Several metabolites were detected including 4 beta,5 alpha-dihydroxyandrostan-3,17-dione, 3,17-dihydroxyandrostan-4-ones and 3 alpha-hydroxy-5 beta-androstan-4,17-dione. 相似文献
296.
Magnetization and resistivity measurements are performed on amorphous La80Au20 alloys doped with Gd impurities. The anomalous behavior observed in the dependence of the superconducting transition temperature on Gd concentration is related to the onset of spin-spin correlations among the Gd impurities. This study suggests the co- existence of superconductivity and spin-glass regime in several previously investigated superconductors doped with Gd. 相似文献
297.
The orientational ordering of the liquid crystal, 3M2CPHOB ((2S, 3S)-3-methyl-2-chloropentanoic acid-4',4'-hexyloxybiphenyl ester) in its smectic A and chiral smectic C phases has been studied by carbon-13 2D N.M.R. The technique used is separated local-field spectroscopy, which produces a first-order splitting for each carbon signal, from which carbon-proton dipolar constants can be determined. The order parameters for different molecular segments of the liquid crystal can then be calculated. The C-H bond order parameter at the chiral centre with a chlorine atom is unusually large, which is a strong indication of hindered rotation of the molecular segment at the chiral centre. The carbon-13 chemical shifts of 3M2CPHOB were also measured as a function of temperature, and the relation between the chemical shifts and the order parameters is discussed. 相似文献
298.
Wai‐Yeung Wong Chun‐Kin Wong Suk‐Yue Poon Albert W.‐M. Lee Tian Mo Xin Wei 《Macromolecular rapid communications》2005,26(5):376-380
Summary: The synthesis and thermal, redox and photoluminescence properties of a soluble donor‐acceptor polyplatinayne with the electron‐accepting silole ring and its model compound are described. The polymer has an optical band gap of 2.10 eV which is much lower than that of thienyl‐ or silyl‐bridged congeners. The incorporation of electron‐accepting silole unit in the metallopolymer main chain creates a new π‐conjugated system that features unique donor‐acceptor characteristics.
299.
Poon Clarice Keriven Nicolas Peyré Gabriel 《Foundations of Computational Mathematics》2023,23(1):241-327
Foundations of Computational Mathematics - Compressed sensing (CS) ensures the recovery of sparse vectors from a number of randomized measurements proportional to their sparsity. The initial theory... 相似文献