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861.
Si WANG Pei Cheng ZHANG Ruo Yun CHEN De Quan YU* Institute of Materia Medica Chinese Academy of Medical Sciences 《中国化学快报》2001,(9)
Goniothalamus cheliensis Hu (Annonaceace) is a small tree or shrub in Yunnan Province, southwest of China. Acetogenins, styryllactones and alkaloids1-3 from the genus were reported in the previous literature and many of them showed strong cytotoxic activities against a number of human cancer cell lines4. The titled plant has been the subject of our investigation due to the impressive cytotoxicity of its organic extract against mouse lymphocytic leukemia cells in preliminary pharmacological s… 相似文献
862.
§ 1 IntroductionA graph-theoretic approach for investigating basis transformations in a linear pro-gramming has been historically developed.Let V be the setof all bases with respectto thecolumn vectors of a matrix A.Two bases are called adjacentifthey can be transformed intoeach other by a pivot operation.Denote by E the set of edges each of which is incidentwith a pair of adjacentbases.Then G=(V,E) is called the basisgraph of matrix A(or ofthe corresponding LP) .Tucker[1 ] first called… 相似文献
863.
Two novel fluorescent calix[4]arene derivatives 1a and 1b with benzoxazole or benzothiazole units in 1,3-alternate conformation have been synthesized and characterized by IR,~1H NMR,~(13)C NMR and MS.Their complexation properties to different heavy and transition metal ions have been studied by UV-vis spectroscopy and fluorescence spectrometer.Compounds 1a and 1b show selective recognition to Fe~(3+) and Cr~(3+). 相似文献
864.
An alternative approach to synthesize pedamide,a key building block of pederin was described.Iodine-induced asymmetric heterocyclization was used as the key step to construct the skeleton,a tetrahydropyran ring with three chiral centers.Brown's asymmetric allylation and Lewis acid-mediated allylation were investigated to introduce chains and chiral alcohols.Sharpless dihydroxylation decorated the side chain.And high optically pure target was obtained by removing the epimers formed in these reactions on c... 相似文献
865.
A new macrolide glycoside,cuneataside F was isolated from the n-butanol extract of the stem of Sargentodoxa cuneata. The structure was elucidated on the basis of extensive 1D and 2D NMR as well as HRESI-MS spectroscopic analysis. 相似文献
866.
AA Yan LI Kai CAO ZhongHua & HU WenRui Key Laboratory of Microgravity 《中国科学:物理学 力学 天文学(英文版)》2011,(2)
The dependency of the critical Marangoni number on the geometrical aspect ratio of the floating half zone is essential to predict the onset of oscillatory thermocapillary convection.The experimental studies in the microgravity conditions on floating half zones of several centimeters in diameter have predicted that the critical Marangoni number increases with the increasing aspect ratio,and the terrestrial experimental studies have predicted the contradictory conclusion for floating half zones of several mil... 相似文献
867.
LI GuangShun ZHOU XiaoHong ZHANG ShuangQuan ZHANG YuHu & MENG Jie Institute of Modern Physics Chinese Academy of Sciences Lanzhou China Graduate University of Chinese Academy of Sciences Beijing School of Physics SK Laboratory of Nuclear Physics & Technology Peking University Beijing 《中国科学:物理学 力学 天文学(英文版)》2011,(Z1)
Theoretical calculations have been performed for the ν9/2+[624](i13/2) and ν7/2-[503](f7/2) bands of 185Pt in the framework of particle-rotor model. The band properties of signature splitting and configuration mixing have been analyzed. The level energy and signature splitting before the band crossing can be well interpreted by introducing triaxiality. The positive-parity yrast band is pro posed to be dominated by the ν9/2+[624](i13/2) component, while the negative-parity band shows strong mixing of ν7/2-[5... 相似文献
868.
LI HaoJun TANG GuiFeng HE Feng WU Bin HU XiaoGong CHEN YanLing 《中国科学:物理学 力学 天文学(英文版)》2013,(8):1591-1597
A new strategy to realize precise absolute positioning for a single-frequency user is presented. In the presented strategy, the receiver clock and ambiguities are removed using the satelliteand epoch-differenced (SDED) algorithm. As a further development of the SDED algorithm, a regional augmentation network is used to generate the SDED atmospheric delays at the user. The weakened mathematic property due to the epoch-differenced operation is improved by adding the generated atmospheric delays and applying the robust estimation. To test the new approach, the 24-h data at 5 Continuous Operation Reference Station (CORS) stations in Shanghai is processed. The results show a more than 96% success rate, defined as the case where three directions achieve the desired positioning accuracy of 10 cm, when the observation is longer than 20 min. The 20-min static results show that the new method can reach an accuracy of 3.42, 4.76 and 9.26 cm in the North, East and Up directions, respectively. An experiment was carried out to assess the kinematic positioning. The results show that the kinematic positioning accuracy is 4.11, 5.31 and 4.05 cm in the north-south, east-west and height directions,respectively. 相似文献
869.
XIE XiaoPing & XU JinChao School of Mathematics Sichuan University Chengdu China 《中国科学 数学(英文版)》2011,(7)
We consider mixed finite elements for the plane elasticity system and the Stokes equation. For the unmodified Hellinger-Reissner formulation of elasticity in which the stress and displacement fields are the primary unknowns, we derive two new nonconforming mixed finite elements of triangle type. Both elements use piecewise rigid motions to approximate the displacement and piecewise polynomial functions to approximate the stress, where no vertex degrees of freedom are involved. The two stress finite element ... 相似文献
870.
SHANG Li & ZHANG HePing School of Information Science Engineering Lanzhou University Lanzhou China School of Mathematics Statistics 《中国科学 数学(英文版)》2010,(4)
It has been shown that a λ m-connected graph G has the property λ m (G)≤ξ m (G) for m≤3.But for m≥4,Bonsma et al.pointed out that in general the inequality λ m (G)≤ξ m (G) is no longer true.Recently Ou showed that any λ 4-connected graph G with order at least 11 has the property λ 4 (G)≤ξ 4 (G).In this paper,by investigating some structure properties of a λ m-connected graph G with λ m (G) ξ m (G),we obtain easily the above result.Furthermore,we show that every λ m-connected graph G with order greater than m(m-1) satisfies the inequality λ m (G)≤ξm (G) for m≥5.And by constructing some examples,we illustrate that our conditions are the best possible. 相似文献