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71.
Construction of the side chain of brassrnolide and its related compounds by the aldolreaction of lithofuran with 22-steroidal aldehyde obtained from hyodeoxycholic acid isdescribed. A key intermediate, 22R, 23R-γ-hydroxy-α, β-unsaturated lactone (16) wassynthesized. 相似文献
72.
Bang-yen Chen 《Annals of Global Analysis and Geometry》1993,11(4):345-359
In this article we obtain the best possible estimates of the type number of tensor product immersions and investigate tensor product immersions with lowest possible type. Several classification theorems in this respect are then proved. 相似文献
73.
74.
One of the central problems in the theory of ordered sets is to describe the orientations of the covering graph of an ordered set. We show that the particular operation called inversion, together with the classical constructions of retraction and product, provide a context for the classification of all such orientations.
AMS subject classifications (1980). 06A10, 05C75, 05C20. 相似文献
75.
在H-ZSM-5沸石上甲醇转化为汽油的初始产物分布姜玄珍(浙江大学化学系,杭州310027)R.F.Howe(新南威尔士大学物理化学系,澳大利亚)关键词H-ZSM-5沸石,甲醇转化汽油,产物分布以氢型ZSM-5沸石作催化剂转化甲醇为汽油(MTG),在... 相似文献
76.
77.
For an arbitrary poset P, subposets {P
i
: 1ik} form a transitive basis of P if P is the transitive closure of their union. Let u be the minimum size of a covering of P by chains within posets of the basis, s the maximum size of a family of elements with no pair comparable in any basis poset, and a the maximum size of an antichain in P. Define a dense covering to be a collection D of chains within basis posets such that each element belongs to a chain in D within each basis poset and is the top of at least k-1 chains and the bottom of at least k-1 chains in D. Dense coverings generalize ordinary chain coverings of poset. Let d=min {|D|–(k–1)|P|}. For an arbitrary poset and transitive basis, a convenient network model for dense coverings yields the following: Theorem 1: da, with equality iff P has a minimum chain decomposition in which every pair of consecutive elements on each chain are comparable in some basis poset. Theorem 2: usda. Theorem 3: s=d iff s=a. The most interesting special case is where the transitive basis expresses P as the product of two posets, in which case u and s measure the minimum and maximum sizes of unichain coverings and semiantichains. 相似文献
78.
Kinetic equations for a multistage electrode process complicated by the transfer of intermediates between the near-electrode layer and bulk solution are derived and analyzed. Computer-aided modeling of the kinetics of processes of this kind is performed. Conditions under which the share of diffused intermediates is no longer vanishingly small are determined. Effect of various factors on the individual stages is established. Techniques of processing experimental data for determining kinetic parameters of separate stages are suggested. 相似文献
79.
西松烷型二萜类化合物是一大类广泛分布于松脂、烟草、陆地动物及海洋生物体中的具有十四元碳环骨架的化合物.其结构新颖复杂,且大多具有显著和广谱的生物活性.近几十年来,有关这类化合物的研究已引起了人们的极大兴趣.因此,开展这类天然产物及其类似物的全合成及构效关系的研究不仅具有重要的学术价值,而且具有潜在的应用前景. 相似文献
80.
A comparative study for the fitting of X‐ray photoelectron spectra (XPS) using different model functions is presented. Synthetically generated test spectra using Gaussian/Lorentzian convolution and a real measured spectrum are fitted with the three commonly used models: product, sum and Gaussian/Lorentzian convolution functions. In these limited tests, it was found that the sum function is superior to the product function, particularly for low‐noise spectra. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献