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空间Bézier曲线的挠率在几何造型中被广泛应用. 文中利用笛卡尔符号法则讨论了两种特殊三次空间Bézier曲线的挠率单调性问题, 最后得出当空间三次Bézier曲线的控制边相等且中间控制边和相邻两控制边的夹角相等时, 挠率仅有一个极小值; 而当两夹角相等但控制边长成等差数列时, 文中给出了挠率单调及极值存在的充分条件. 相似文献
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1 INTRODUCTION Zeolites have attracted much attention in both scientific and industrial areas for their special characteristics and multiple uses. Zeolites are composed of TO4 (T = Si, Al, Ga, P, etc.) tetrahedra which are connected with each other by sharing oxygen atoms to produce a complex and repetitive three-dimensional atom network with regular molecular dimension cavities joined by channels. Shape selectivity is the most important property of zeolites. Combined with the possib… 相似文献
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手性噁唑硼烷催化α-和β-氨基酮不对称还原反应立体选择性的AM1过渡态模型研究 总被引:1,自引:0,他引:1
AM1 transition state (TS) models were developed for the enanfioselecfivifies in the reductions of α-and β-aminoketones catalyzed by (S)-4-benzyl-5,5-diphenyl-1,3,2-oxazaborolidine. The result showed that β-aminoketone gave better enanfioselectivity than its α-analog. Different chiralifies of the final products were obtained, R for the former and S for the latter. These semiempirical TS models are consistent with the experimental data. 相似文献
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通过对我国外贸吞吐量2001年1月至2009年6月的时间序列数据进行分析,建立干预分析模型,研究金融危机对我国外贸的影响,结果显示该模型具有较好的模拟与预测效果. 相似文献