排序方式: 共有69条查询结果,搜索用时 15 毫秒
41.
An efficient, mild, chemoselective, and convenient protocol for synthesis of isothiocyanate derivatives. This protocol was applied successfully in the novel synthesis of anthelmintic drug 4-isothiocyanato-4′-nitrodiphenyl ether and its analogs. 相似文献
42.
Infrared-to-visible wave-length conversion in the Yb3+−Er3+ doped phosphors system has been described by a simple three level model based on two ions mechanism. The excitation in the
range of 900–1000 nm of an IR-photon is first absorbed by Yb3+ ion as a sensitizer attributed to the resonant energy transition in Er3+ ion from 4
I
3/2 → 4
S
15/2 and 1
F
9/2 → 4
I
15/2, respectively for green and red emission. The essential energy transfer processes in this system i.e. upconversion from 4
I
11/2 and 1
I
13/2, cross-relaxation from 4
S
3/2 and 1
F
9/2 are taken into account. The limitations of the rate-equation approach are examined with a focus on the underlying dynamics
of this rare-earth system. 相似文献
43.
APPLICATION OF GENETIC ALGORITHM IN PARTICLE SIZE ANALYSIS BY MULTISPECTRAL EXTINCTION MEASUREMENTS 总被引:1,自引:0,他引:1
Gerard Grhan 《中国颗粒学报》2004,2(6):235-240
Both dependent and independent model algorithms are designed with genetic algorithm (GA) to retrieve aerosol size data from multispectral extinction measurements. Compared with the traditional dependent model algorithm, e.g., simplex, GA can locate the global optimized solution instead of local ones. As an independent model algonthm, when combined with B-splines, GA gives consistent results with Chahine and Phillip-Twomey-NNLS algorithms. Numerical simulations also show that GA has high stability and good resistance to relatively higher error levels. For a population size of 50 in the present paper, the feasible ranges for genetic operators Pc and pm are found to be [0.01, 0.5] and [0.01, 0.15], respectively, and the generation number Gen_Max should be larger than 250. 相似文献
44.
Babasaheb P. Bandgar Suhas P. Kasture 《Monatshefte für Chemie / Chemical Monthly》2000,131(8):913-915
Summary. The Friedel-Crafts arylmethylation of aromatics with benzyl halides or bis-(bromomethyl)-benzene in the presence of Envirocat EPZ10? affords selectively para-arylmethylated products in good yields. Isolation of pure products involving an eco-friendly procedure and recyclability
of the catalyst are important features of this method.
Received January 17, 2000. Accepted (revised) March 2, 2000 相似文献
45.
2, 4-Dichlorophenoxy acetic acid anion supported on anion exchange resin (Tulsion A-27 Chloride form) was treated with appropriate dihalide in acetonitrile at 25°C or 80 – 85°C to give corresponding diesters of 2, 4-dichlorophenoxy acetic acid as effective herbicides. 相似文献
46.
Chemoselective protection of carbonyl compounds as acetals has been carried out by using Envirocat EPZG as a novel heterogeneous catalyst. 相似文献
47.
Condensation of α-cyanothioacetamide with aldehydes has been carried out in excellent yield under mild conditions by using Envirocat EPZG as a heterogenous reusable catalyst. 相似文献
48.
NaIO4, KIO4 and anhydrous CaCl2 catalyzed selective transesterification of β‐keto esters is described. Neutral reaction conditions and inexpensive catalysts are important features of this method. 相似文献
49.
50.
LI YingQiu HU YangLi & LIU QuanSheng College of Mathematics Computing Sciences Changsha University of Science Technology Changsha China College of Mathematics Computer Sciences Hunan Normal University Changsha LMAM University of Bretgne-Sud BP Vannes France 《中国科学 数学(英文版)》2011,(7)
Let W be the limit of the normalized population size of a supercritical branching process in a varying or random environment. By an elementary method, we find sufficient conditions under which W has finite weighted moments of the form EWpl(W), where p > 1, l 0 is a concave or slowly varying function. 相似文献