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81.
Hopf bifurcation analysis of a density predator-prey model with crowley-martin functional response and two time delays 下载免费PDF全文
In this paper, a delayed density dependent predator-prey model with Crowley-Martin functional response and two time delays for the predator is considered. By analyzing the corresponding characteristic equations, the local stability of each of the feasible equilibria of the system is addressed and the existence of Hopf bifurcation at the coexistence equilibrium is established. With the help of normal form method and center manifold theorem, some explicit formulas determining the direction of Hopf bifurcation and the stability of bifurcating period solutions are derived. Finally, numerical simulations are given to illustrate the theoretical results. 相似文献
82.
Jianming Zhang Shuming Li Hongpeng Geng 《Journal of Applied Analysis & Computation》2016,6(4):1205-1210
Using the method of dynamical systems for the the generalized Radhakrishnan, Kundu, Lakshmanan equation, the existence of soliton solutions, uncountably infinite many periodic wave solutions and unbounded wave solution are obtained. Exact explicit parametric representations of the above travelling solutions are given. To guarantee the existence of the above solutions, all parameter conditions are determined. 相似文献
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分析了三角枫成熟叶的挥发油化学成分。实验采用同时蒸馏萃取法提取三角枫成熟叶的挥发油,利用气相色谱-质谱(GC-MS)对其化学成分进行分析,并以面积归一化法测定各个成分的相对含量。从三角枫成熟叶的挥发油中分别分离鉴定出了79个化合物,占其挥发油总量的94.30%,主要成分为柠檬烯、石竹烯、α-蒎烯、β-蒎烯、大根香叶烯、叶绿醇等。结果表明,三角枫成熟叶的挥发性成分非常丰富,其中,许多化学成分具有芳香性或药理药效作用,在香精香料或医疗领域具有一定的利用价值。 相似文献
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87.
《Polyhedron》2002,21(5-6):587-598
Dihypersilylstannylene [(Me3Si)3Si]2Sn (1) and dihypersilylplumbylene [(Me3Si)3Si]2Pb (2) are Lewis-amphoteric compounds, i.e. they may behave as Lewis-acid and/or as Lewis-base. Quantum-chemical calculations indicate that their Lewis-acidity is strongly enhanced compared with their diorganyl substituted relatives by the electropositive silyl substituents present. Furthermore silyl substituents are expected to migrate more easily than organyl groups, due to relatively weak ESi bonds formed to the heavier Group 14 congeners (tetrels) leading to different reaction patterns. Here I will give a brief report about our recent investigations on the chemical behavior of the title compounds towards other Lewis-acidic or Lewis-basic or Lewis-amphoteric species. 相似文献
88.
Bing-Jie Zhang Wen-Na Xiao Jing Chen Mei-Fen Bao Johann Schinnerl Qi Wang Xiang-Hai Cai 《Tetrahedron》2019,75(38):130515
Continued interest in Erythrina alkaloids resulted in the isolation of 38 alkaloids including 7 undescribed ones from the leaves of Erythrina arborescens Roxburgh. Among the new compounds, erythrivarines H-I were two dimeric alkaloids, while others were Erythrina alkaloid glucosides. Dimeric Erythrina alkaloids and monomers, turcomanidine and isoboldine, showed medium xanthine oxidase inhibition. 相似文献
89.
《Tetrahedron letters》2019,60(31):2078-2083
A metal-free p-toluenesulfonic acid (TsOH·H2O) mediated synthesis of 3-ketoquinolines from anilines, enaminones and DMSO has been developed. In this transformation, DMSO was activated by TsOH·H2O and provided the one-carbon unit of the 3-ketoquinolines. A plausible mechanism involving an electrophilic sulfenium ion intermediate was proposed. 相似文献
90.
《Tetrahedron letters》2019,60(41):151136
A tandem reaction of heterocyclic ketene aminals (HKAs) with diazoesters in the presence of a Cu catalyst is demonstrated for the efficient synthesis of pyrimidopyrrolidone derivatives. The reaction shows a broad substrate scope and excellent functional group tolerance. Our method provides rapid access to diverse pyrimidopyrrolidones in moderate to excellent yields under mild reaction conditions. 相似文献