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991.
The first phytochemical investigation on stems of Mitrephora thorelii led to the isolation of three new lignanamides, thoreliamides A–C ( 1 – 3 ), and a new sesquiterpenoid, thorelinin ( 4 ), together with ten known compounds. The structures of the new compounds were established on the basis of extensive spectroscopic analyses. Thoreliamide C is the first trimer derived from cinnamic acid amide units. 相似文献
992.
993.
Tülin Coşkun 《Proceedings Mathematical Sciences》2000,110(4):357-362
In this work we obtain, under suitable conditions, theorems of Korovkin type for spaces with different weight, composed of
continuous functions defined on unbounded regions. These results can be seen as an extension of theorems by Gadjiev in [4]
and [5]. 相似文献
994.
M. Ionescu-Bujor A. Iordăchescu E. A. Ivanov G. Pascovici D. Ploştinaru V. Sabaiduc 《Zeitschrift für Physik A Hadrons and Nuclei》1990,336(3):291-296
The two short-lived isomeric states in112In have been reinvestigated by means of the112Cd(d, 2n) and109Ag (α, n) reactions. Measurements of delayed X- andγ-ray, lifetime and TDPAD spectra have been performed. A 6.32(3) keVγ-ray has been identified in the isomeric decay and anM1 multipolarity has been assigned to it on the basis of the measured internal conversion coefficients:α L =196(39) andα tot=231(35). TheE1+M2(δ =+0.24(4)) andE2 multipolarities have been determined for the 263 and 188 keV transitions deexciting the 8?(T 1/2=2.82(2) μs) and 7+ (T 1/2=0.93(2) μs) isomeric states, respectively. A revised isomeric decay scheme is presented. 相似文献
995.
New conditions for a planar homoclinic loop to have cyclicity two under multiple parameter perturbations have been obtained. As an application it is proved that a homoclinic loop of a nongeneric cubic Hamiltonian has cyclicity two under arbitrary quadratic perturbations. 相似文献
996.
Yun‐Sheng Ye Ying‐Chieh Yen Wen‐Yi Chen Chih‐Chia Cheng Feng‐Chih Chang 《Journal of polymer science. Part A, Polymer chemistry》2008,46(18):6296-6304
This article describes a new and simple method for preparing polyimide nanocomposites that have very low dielectric constants and good thermal properties: simply through blending the polyimide precursor with a fluorinated polyhedral oligomeric silsesquioxane derivative, octakis(dimethylsiloxyhexafluoropropyl) silsesquioxane (OF). The low polarizability of OF is compatible with polyimide matrices, such that it can improve the dispersion and free volume of the resulting composites. Together, the higher free volume and lower polarizability of OF are responsible for the lower dielectric constants of the PI‐OF nanocomposites. This simple method for enhancing the properties of polyimides might have potential applicability in the electronics industry. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6296–6304, 2008 相似文献
997.
In this paper we studied the general properties of Bertrand curves and their characterizations in Riemann–Otsuki space. 相似文献
998.
The flows that occur in the solution, in the linear approximation, of the problem of the failure of a dam for the model of two-layer shallow water with a free boundary are analysed qualitatively. It is shown that, apart from symmetry, four basic processes and four transients exist. They are distinguished by the type of jumps in the levels on the lines of discontinuity and by the direction of the velocities in the liquid layers. Examples of the profiles of all these flows are presented. 相似文献
999.
Ayşe Kalkanli 《International Journal of Theoretical Physics》1987,26(11):1085-1092
It is shown that the Gürses-Nutku equations have a finite prolongation algebra for any value of the parameterK. The Painlevé property of these equations is also examined.The research reported in this paper is supported in part by the Scientific and Technical Research Council of Turkey. 相似文献
1000.
Ying Zhao Ying‐Wu Luo Changhuai Ye Bo‐Geng Li Shiping Zhu 《Journal of polymer science. Part A, Polymer chemistry》2009,47(1):69-79
Methyl methacrylate (MMA)/tert‐butyl methacrylate (tBMA) gradient copolymers having linear and hyperbolic composition profiles were synthesized. These special copolymer products were achieved via a model‐based computer‐controlled semibatch atom transfer radical copolymerization (ATRcoP) process. A simple ATRcoP model was developed based on the terminal model. The equilibrium constants in the ATRP of MMA and tBMA were estimated by the data correlation. The model was verified by batch experiments and was found to give good correlation for the polymerization rate, molecular weight, and copolymer composition data. The model coupled with a reactor model was then applied to the semibatch ATRcoP and was used to calculate comonomer feeding rates for the targeted gradient composition profiles. It was found that the experimental monomer conversion, molecular weight, and cumulative copolymer composition were in good agreement with their targeted theoretical values. The gradient copolymers had low polydispersities close to 1.1. This work demonstrated the feasibility of the model‐based semibatch ATRcoP in fine‐tuning gradient copolymer composition profiles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 69–79, 2009 相似文献