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排序方式: 共有422条查询结果,搜索用时 328 毫秒
1.
Lipase from Mucor miehei (MML) has been selected as the most suitable enzyme to catalyze the efficient monobenzoylation of 1,4-diols using vinyl benzoate as acyl transfer reagent in tert-butyl methyl ether. The regioselectivity of the monobenzoylation of 2-substituted-1,4-diols has been studied as well. 相似文献
2.
Scopo del lavoro è di studiare la stabilità asintotica per le soluzioni di problemi di evoluzione astratti. Si considerano
operatori differenziali quali ilp-Laplaciano, e il poliarmonico, termini smorzanti e fortemente smorzanti, potenziali di richiamo o di sorgente.
相似文献
3.
Fabio Martinelli Enzo Olivieri Elisabetta Scoppola 《Journal of statistical physics》1990,61(5-6):1105-1119
We present a proof of the exponential convergence to equilibrium of single-spin-flip stochastic dynamics for the two-dimensional Ising ferromagnet in the low-temperature case with not too small external magnetic fieldh uniformly in the volume and in the boundary conditions. 相似文献
4.
Fabio Martinelli Enzo Olivieri Elisabetta Scoppola 《Journal of statistical physics》1989,55(3-4):477-504
We apply previous results on the pathwise exponential loss of memory of the initial condition for stochastic differential equations with small diffusion to the problem of the asymptotic distribution of the first exit times from an attracted domain. We show under general hypotheses that the suitably rescaled exit time converges in the zero-noise limit to an exponential random variable. Then we extend the results to an infinite-dimensional case obtained by adding a small random perturbation to a nonlinear heat equation. 相似文献
5.
Francesco Ghetti Giuliano Colombetti Francesco Lenci Enzo Campani Erseo Polacco Maurizio Quaglia 《Photochemistry and photobiology》1985,42(1):29-33
Abstract— The spectroscopic characterization of the photoreceptor pigment is one of the main questions in the study of the photosensory transduction chains in photomotile microorganisms. One of the possible techniques that can be used is in vivo microspectrofluorometry. By means of a tunable dye-laser microspectrofiuorometer developed by us, we have investigated some of the spectroscopic properties of the photoreceptor pigment of the green flagellate Euglena gracilis. The in vivo fluorescence excitation spectrum has been determined and the fluorescence quantum yield has been measured. The results show that flavins are indeed present in the paraflagellar body of E. gracilis and that their fluorescence quantum yield is much lower than that of a free flavin. An estimate of the order of magnitude of the rate constants for primary molecular reactions is tentatively given. 相似文献
6.
Gabriele Proietti Stefano Corsano Enzo Castagnino 《Journal of heterocyclic chemistry》1981,18(2):415-416
The synthesis of cis- and trans-2-methyl-3-phenyl-1,4-benzodioxans 4 and 5 , from 1-phenyl-2-[2-(hydroxy)-phenoxy]propanols threo 2 and erythro 3 are described. 相似文献
7.
Silvestrini E Michelozzi M Skroppa T Brancaleoni E Ciccioli P 《Journal of chromatography. A》2004,1034(1-2):183-189
Head-space sampling (HS) has been combined with enantioselective gas chromatography (GC) for the analysis of chiral and non-chiral monoterpenes present in the cortical tissues of five different Norway spruce clones. (1S)-(-)-alpha-Pinene, (1S,5S)-(-)sabinene, (1S)-(-)-beta-pinene, and (4S)-(-)limonene dominated over (1R)-(+)-alpha-pinene, (1R,5R)-(+)-sabinene, (1R)-(+)-beta-pinene, and (4R)-(+)-limonene. Results showed a large variation in the enantiomeric composition of cortical tissues between different clones. The development of HS-GC greatly increased the speed of precise analyses of chiral monoterpenes in small samples and therefore offer excellent opportunities in studies on the ecophysiological and chemotaxomic roles of these chiral components. 相似文献
8.
Summary. This review reveals that, in contrast to the general opinion, the aqueous speciation of nickel is poorly known. Besides the
fairly well established first hydrolysis constant, data are scarce and only poor estimates can be derived for higher Ni hydrolysis
constants from a few solubility studies. The situation is even worse in the case of aqueous carbonate complexes. No reliable
experimental study has been published so far and almost all numbers reported in thermodynamic databases are unacceptable estimates.
In this review we scrutinise all these published estimates and propose expectation ranges of nickel carbonate complex stability
through correlation with other known thermodynamic constants. Solubility constants for a few simple nickel solids are known
or have been estimated from thermochemical data. However, none of these simple solids is of geochemical relevance at ambient
conditions. Based on field evidence, classes of solids are identified which potentially govern nickel concentrations in ground
and surface waters. Recent spectroscopic data indicate that magnesium clay minerals and layered double hydroxides are the
most prominent candidates for nickel-bearing solids at ambient conditions.
Corresponding author. E-mail: wolfgang.hummel@psi.ch
Dedicated to the memory of Prof. Rolf Grauer
Received January 14, 2003; accepted January 24, 2003
Published online May 15, 2003 相似文献
9.
Measurement of labile Cu in soil using stable isotope dilution and isotope ratio analysis by ICP-MS 总被引:1,自引:0,他引:1
Isotope dilution is a useful technique to measure the labile metal pool, which is the amount of metal in soil in rapid equilibrium (<7 days) with the soil solution. This is normally performed by equilibrating soil with a metal isotope, and sampling the labile metal pool by using an extraction (E value), or by growing plants (L value). For Cu, this procedure is problematic for E values, and impossible for L values, due to the short half-life of the 64Cu radioisotope (12.4 h), which makes access and handling very difficult. We therefore developed a technique using enriched 65Cu stable isotope and measurement of 63Cu/65Cu ratios by quadrupole inductively coupled plasma mass spectrometry (ICP-MS) to measure labile pools of Cu in soils using E value techniques. Mass spectral interferences in detection of 63Cu/65Cu ratios in soil extracts were found to be minimal. Isotope ratios determined by quadrupole ICP-MS compared well to those determined by high-resolution (magnetic sector) ICP-MS. E values determined using the stable isotope technique compared well to those determined using the radioisotope for both uncontaminated and Cu-contaminated soils. 相似文献
10.
Magnani A Marchettini N Ristori S Rossi C Rossi F Rustici M Spalla O Tiezzi E 《Journal of the American Chemical Society》2004,126(37):11406-11407
The present work deals with the spatially extended oscillatory Belousov Zhabotinsky reaction-diffusion system carried out in an anisotropic environment of phosphatidylcholines/water binary system, which presents layered aqueous domains separated by lipid bilayers. We report the occurrence of stable Turing patterns, spiral waves, and other exotic structures in phospholipids bilayers that are generally used as a models for cell plasma membranes. 相似文献