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排序方式: 共有271条查询结果,搜索用时 15 毫秒
71.
Tai Sheng LU Yang Hua YI* Shi Long MAO Da Zheng ZHOU Qiang Zhi XU Hai Feng TANG Shu Yu ZHANG Center of Marine Drug Research School of Pharmacy Second Military Medical University Shanghai 《中国化学快报》2001,(8)
Cassia siamea Lam. (CSL) is a common tree in the southern part of China. It has been used as folk medicine for aperient, antiarthritic and swellings1. We report here the isolation and structural elucidation of a new chromone glucoside, 2-methyl-5-propyl-7, 12-dihydroxy chromone-12-O-(-D-glucopyranoside (1), from the n-butanol-soluble fraction of CSL extract . 1The 80% ethanolic extract of CSL was dissolved in water and partitioned with petroleum ether, dichloromethane and n-butanol. The … 相似文献
72.
XUE Zhixin YANG Guipeng CHEN Dianbao MA Xiaomei ZHANG Xiqin QUAN Zhenlan College of Chemical Engineering Environment Qingdao University Qingdao China Key Laboratory of Marine Chemistry Theory Technology Ministry of Education Ocean University of China Qingdao P.R.China Fullerenes Materials Group Qingdao University of Science Technology Qingdao China 《Chinese Journal of Reactive Polymers》2006,(1)
1. INTRODUCTION1. INTRODUCTIONOne of the most widely discussed subjects these days is the energy crisis, i.e. the oil shortage and the oil price rising, which encouraged us to research and develop new green energy-hydrogen energy in the 21st century. Therefore, hydrogen produced from water splittingwith photocatalyst has been extensively studied from the viewpoint of photo energy, such as solar energy conversion to chemical and electricity energy, and environmental concerns. To date, … 相似文献
73.
Femtosecond ablation of ultrahard materials 总被引:4,自引:0,他引:4
G. Dumitru V. Romano H.P. Weber M. Sentis W. Marine 《Applied Physics A: Materials Science & Processing》2002,74(6):729-739
Several ultrahard materials and coatings of definite interest for tribological applications were tested with respect to their
response when irradiated with fs laser pulses. Results on cemented tungsten carbide and on titanium carbonitride are reported
for the first time and compared with outcomes of investigations on diamond and titanium nitride. The experiments were carried
out in air, in a regime of 5–8 J/cm2 fluences, using the beam of a commercial Ti:sapphire laser. The changes induced in the surface morphology were analysed with
a Nomarski optical microscope, and with SEM and AFM techniques. From the experimental data and from the calculated incident
energy density distributions, the damage and ablation threshold values were determined. As expected, the diamond showed the
highest threshold, while the cemented tungsten carbide exhibited typical values for metallic surfaces. The ablation rates
determined (under the above-mentioned experimental conditions) were in the range 0.1–0.2 μm per pulse for all the materials
investigated.
Received: 31 August 2001 / Accepted: 3 December 2001 / Published online: 20 March 2002 相似文献
74.
A new procedure based on hydrophilic interaction chromatography coupled to tandem mass spectrometry (ionisation process by pneumatically assisted electrospray in negative ion mode), is developed and validated for the simultaneous determination of underivatised taurine and methionine in beverages rich in carbohydrates such as energy drinks. No initial clean-up procedure and no sample derivatisation are required. Satisfactory analysis was obtained on an Astec apHera NH2 (150 mm x 4.6 mm; 5 microm) column with methanol-water (60/40) as mobile phase. The method was validated in terms of specificity, detection limits, linearity, accuracy, precision and stability, using threonine as internal standard. The potential effects of matrix and endogenous amino acid content were also examined. The limits of detection in the beverage varied from 20 microg L(-1) for taurine to 50 micro L(-1) for methionine. 相似文献
75.
Kohut-Svelko N Reynaud S Dedryvère R Martinez H Gonbeau D François J 《Langmuir : the ACS journal of surfaces and colloids》2005,21(4):1575-1583
A simple way to obtain a conducting nanocomposite is described, and the conducting particles are characterized. Core-shell particles [polystyrene-polyaniline (PANI)] have been obtained by the dispersion process from three types of polystyrene latexes: a no-cross-linked core stabilized by a nonylphenolethoxylate (NP40) and two cross-linked cores stabilized by NP40 and a mixture NP40/Surfamid (a surfactant bearing an amide group). The surface of these particles has been extensively characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and scanning electron microscopy. A maximum coverage of 94% was obtained for the high PANI content as revealed by XPS analysis. A better coverage was obtained for the cross-linked polystyrene latex stabilized by the Surfamid. The amide group of this surfactant allows the H-bonding formation with the PANI backbone and, thus, improves the conductivity. It was shown that a uniform coverage of the core particles was not required to ensure a good conductivity. 相似文献
76.
77.
E. Giacobino C. Fabre A. Heidmann R. Horowicz S. Reynaud D. Grandclément G. Grynberg M. Pinard 《Hyperfine Interactions》1987,37(1-4):109-124
It is shown that oscillators using nearly degenerate parametric conversion or four-wave mixing in the phase conjugation geometry
generate pairs of highly correlated photons. The intensity difference of the two corresponding light beams is then expected
to be below the shot noise limit. This property can be used to produce intensity stabilized light beams below the quantum
limit.
The phases of the twin beams also exhibit interesting correlation properties which will be discussed. Moreover, the combination
of the twin beams gives a squeezed state, which has been observed by other authors when the device is below the oscillation
threshold. We will describe preliminary results of experiments performedabove oscillation threshold. 相似文献
78.
A modification of perturbation theory, known as the delta expansion (variationally improved perturbation), gave rigorously
convergent series in some D=1 models (oscillator energy levels) with factorially divergent ordinary perturbative expansions. In a generalization of the
variationally improved perturbation technique appropriate to renormalizable asymptotically free theories, we show that the
large expansion orders of certain physical quantities are similarly improved, and prove the Borel convergence of the corresponding
series for , with the new (arbitrary) mass perturbation parameter. We argue that non-ambiguous estimates of quantities relevant to dynamical
(chiral) symmetry breaking in QCD are possible in this resummation framework.
Received: 25 February 2002 / Published online: 8 May 2002 相似文献
79.
80.
Stable Isotope Labeling by Amino acid in Vivo (SILAV): a new method to explore protein metabolism
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