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排序方式: 共有120条查询结果,搜索用时 211 毫秒
51.
Inversionless light amplification in sodium 总被引:1,自引:0,他引:1
Jin-Yue Gao Han-Zhuang Zhang Hai-Feng Cui Xiu-Zhen Guo Yun Jiang Qing-Wen Wang Guang-Xu Jin Jin-Song Li 《Optics Communications》1994,110(5-6):590-594
Light amplification without population inversion in sodium vapor is reported. The result of this work is the amplification of a weak probe beam at a wavelength of 589.0 nm when the atoms are driven coherently by a long pulse at 589.6 nm, and the amplification of a weak probe beam at 589.6 nm when the atoms are driven coherently at 589.0 nm. The population contributions in the upper and lower lasing levels are calculated through the absorption spectra. 相似文献
52.
Dong M Cong B Yu SH Sauriol F Huo CH Shi QW Gu YC Zamir LO Kiyota H 《Organic letters》2008,10(5):701-704
Echinopines A (1) and B (2), novel sesquiterpenoids with an unprecedented rearranged skeleton named echinopane, were isolated from the roots of Echinops spinosus. The structures were elucidated by extensive spectroscopic analysis. The relative configuration of 1 was assigned by a combination of NOESY correlations and a simulation analysis. A plausible biosynthetic pathway for echinopane was discussed. 相似文献
53.
Qi Liqun Luo Ziyan Wang Qing-Wen Zhang Xinzhen 《Journal of Optimization Theory and Applications》2022,193(1-3):621-648
Journal of Optimization Theory and Applications - The class of quaternion matrix optimization (QMO) problems, with quaternion matrices as decision variables, has been widely used in color image... 相似文献
54.
Jian Gao Qing-Wen Song Liang-Nian He Chang Liu Zhen-Zhen Yang Xu Han Xue-Dong Li Qing-Chuan Song 《Tetrahedron》2012,68(20):3835-3842
A polystyrene-supported Lewis acidic iron-containing ionic liquid was proved to be recyclable and efficient heterogeneous catalyst for converting CO2 into cyclic carbonate without utilization of any organic solvent or additive. Excellent yields and selectivity were obtained under mild reaction conditions. Notably, the catalyst could be readily recovered and reused over five times without appreciable loss of catalytic activity. A possible catalytic cycle was proposed. The present protocol has successfully been applied to reactions of aziridines/propargyl amines with CO2. This kind of the catalyst presented herein would have great potential in industrial application thanks to its featured advantages. 相似文献
55.
56.
Zhao BX Wang Y Zhang DM Huang XJ Bai LL Yan Y Chen JM Lu TB Wang YT Zhang QW Ye WC 《Organic letters》2012,14(12):3096-3099
Two new Securinega alkaloids, virosaines A (1) and B (2), were isolated from the twigs and leaves of Flueggea virosa. The structures and absolute configurations were elucidated by means of NMR, X-ray diffraction, and CD analyses. Compounds 1 and 2 represent the first examples of Securinega alkaloids bearing a 7-oxa-1-azabicyclo[3.2.1]octane ring system, whose plausible biogenetic pathways were also proposed. 相似文献
57.
Investigation of a 4H-SiC metal-insulation-semiconductor structure with an Al2O3/SiO2 stacked dielectric
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Atomic layer deposited(ALD) Al2O3 /dry-oxidized ultrathin SiO2 films as a high-k gate dielectric grown on 8°off-axis 4H-SiC(0001) epitaxial wafers are investigated in this paper.The metal-insulation-semiconductor(MIS) capacitors,respectively with different gate dielectric stacks(Al2O3/SiO2,Al2O3,and SiO2) are fabricated and compared with each other.The I-V measurements show that the Al2O3/SiO2 stack has a high breakdown field(≥12 MV/cm) comparable to SiO2,and a relatively low gate leakage current of1×10-7A/cm2 at an electric field of4 MV/cm comparable to Al2O3.The 1-MHz high frequency C-V measurements exhibit that the Al2O3/SiO2 stack has a smaller positive flat-band voltage shift and hysteresis voltage,indicating a less effective charge and slow-trap density near the interface. 相似文献
58.
Isolation and structure revision of 10-deacetyltaxinine from the seeds of the Chinese yew, Taxus mairei 总被引:3,自引:0,他引:3
A new taxoid was isolated from the methanol extract of the seeds of Taxus mairei. Its structures were established as 2alpha,9alpha-diacetoxy-10beta-hydroxy-5alpha-cinnamoyloxytaxa-4(20), 11-dien-13-one (l0-deacetyltaxinine) on the basis of spectral analysis including (1)H-NMR, (13)C-NMR, HMQC, HMBC, NOESY, and HR-FABMS. The structure of previously reported 10-deacetyltaxinine is 9-deacetyltaxinine. 相似文献
59.
60.
It has recently been reported that dopamine may show some biological activities in antitumor and cell apoptosis. We have thoroughly investigated the interaction between dopamine and DNA by CD, UV, fluorescence and electrochemical methods. The results of spectroscopic measurements have indicated that a binding event occurs in a dopamine-DNA system. Besides the electronstatic interaction between a negatively charged DNA molecule and a positively charged dopamine molecule, other binding modes, such as hydrogen-bond and intercalation may also exist in this system. The interaction parameters, including the equilibrium constant and binding numbers, were estimated by an electrochemical method based on the redox current and formal potentials. Both of the two calculation methods showed that the 1:1 type of complex was formed in the dopamine-DNA system and that its equilibrium constant was about 5.85 x 10(6) M(-1). Based on the results of UV, fluorescence and electrochemical experiments in the present study, dopamine may be employed as an effective probe for a DNA assay. 相似文献