排序方式: 共有66条查询结果,搜索用时 15 毫秒
41.
Liang Yuanwei Huang Weiting Situ Qianyi Su Weiming Qiu Wenhua Li Shixiao He Luxin Chen Jianping 《Russian Journal of General Chemistry》2022,92(4):725-731
Russian Journal of General Chemistry - A series of 2,2′:6′,2′-terpyridine conjugated nitrogen mustard derivatives with structurally symmetrical character and rather small... 相似文献
42.
Yuanwei?Qi Gao-Feng?ZhengEmail author 《Calculus of Variations and Partial Differential Equations》2018,57(5):133
In this paper, we study the parabolic Allen–Cahn equation, which has slow diffusion and fast reaction, with a potential K. In particular, the convergence of solutions to a generalized Brakke’s mean curvature flow is established in the limit of a small parameter \( \varepsilon \rightarrow 0\). More precisely, we show that a sequence of Radon measures, associated to energy density of solutions to the parabolic Allen–Cahn equation, converges to a weight measure of an integral varifold. Moreover, the limiting varifold evolves by a vector which is the difference between the mean curvature vector and the normal part of \({\nabla K}/{2K}\). 相似文献
43.
Shengxiang Huang Lianwen DengKesheng Zhou Zhaowen HuShuyuan Sun Yuanwei MaPeng Xiao 《Journal of magnetism and magnetic materials》2012
La1−xAgxMnO3 perovskites with different doping Ag-content were prepared by the sol–gel method. The electromagnetic characteristics and microwave loss behavior of these ion-doped rare-earth manganites were studied in the 2–18 GHz frequency range. The microstructure and morphology of the samples were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM) techniques. The complex permittivity spectra, the complex permeability spectra and microwave reflection loss were measured by a microwave vector network analyzer system. The XRD patterns show that the crystalline perovskite main phase ABO3 is formed and impurity phases disappear when calcined at 1100 °C, and Ag metal as an impurity phase appears when excessive Ag+ is doped. The SEM image indicates that many of the La0.85Ag0.15MnO3 particles are fiber-like or ellipsoidal. Magnetic loss and dielectric loss coexist and cooperate in microwave attenuation by moderate substitution of Ag+ for La3+. The microwave absorption property of the La0.85Ag0.15MnO3 sample is enhanced with the bandwidth below −10 dB at about 6 GHz and the peak value of reflection loss is near −25.0 dB at the layer thickness of 2 mm. 相似文献
44.
Phosphorylcholine‐containing poly(L‐lactide) (PLLA‐PC) was synthesized by ring‐opening polymerization of L‐lactide in the presence of glycerophosphorylcholine originated from egg lecithin. Self‐assembling micelles were then obtained by film hydration, ultrasonication and stirring. Transmission electron microscopy and confocal laser scanning microscopy confirmed the micellar structure with hydrophobic core and hydrophilic shell. The critical micellar concentration (CMC) value of PLLA‐PC was only 1/50 that of naturally occurring PC, in agreement with a better surfactant property of the former. Dynamic light scattering showed that the size and size distribution of micelles varied with dilution, but the CMC was independent of the concentration of NaCl solution within 0.9 wt%, indicating that the micelles could be stable upon intravenous injection. In addition, the micelle solution could be stored at 4 °C over 30 days without any noticeable changes, whereas at 37 °C, the size, size distribution and the number of micelles decreased over time due to degradation. The solubility of clofazimine, a highly hydrophobic drug, was found to be 11.9 µg/ml in the PLLA‐PC micellar solution, which was 40 times that in pure water. This preliminary study suggests that PLLA‐PC micelles present a great potential as delivery system for hydrophobic drugs. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
45.
Li Gao Le-Le Li Xiaolong Wang Peiwen Wu Yang Cao Bo Liang Xin Li Yuanwei Lin Yi Lu Xuefeng Guo 《Chemical science》2015,6(4):2469-2473
Many metal ions are present in biology and in the human body in trace amounts. Despite numerous efforts, metal sensors with ultrahigh sensitivity (<a few picomolar) are rarely achieved. Here, we describe a platform method that integrates a Cu2+-dependent DNAzyme into graphene–molecule junctions and its application for direct detection of paramagnetic Cu2+ with femtomolar sensitivity and high selectivity. Since DNAzymes specific for other metal ions can be obtained through in vitro selection, the method demonstrated here can be applied to the detection of a broad range of other metal ions. 相似文献
46.
The palladium-catalyzed tandem arylation of O-homoallylhydroxylamines with 2 equiv of aryl bromides was examined. With Pd2(dba)3 (1 mol %) as the catalyst, Xantphos (2 mol %) as the ligand, and NaOt-Bu as the base, the reactions of O-homoallylhydroxylamines with aryl bromides via sequential N-arylation/cyclization/C-arylation in toluene afforded the corresponding N-aryl-3-arylmethylisoxazolidines in good yields with excellent diastereoselectivity. 相似文献
47.
Miao Zhan Hongxia Jiang Xuehai Pang Tao Zhang Ruixue Xu Lifeng Zhao Yu Liu Yu Gong Yuanwei Chen 《Tetrahedron letters》2014
A highly effective and operationally practical method for the regioselective deuteration of N-alkyl-substituted anilines employing Ru3(CO)12 (?1 mol %) as catalyst and D2O as deuterium source was described. A variety of N-alkyl-substituted anilines were efficiently deuterated (up to 98%) at the ortho and/or para position with respect to the nitrogen at neutral conditions. Under the present conditions, deuterated anilines can be easily obtained with simple extraction and evaporation. Substituents with aromatic methoxy groups would not influence the selectivity compared to previous method. 相似文献
48.
疏水星形PCL与PCL-b-PEG两亲共聚物的自组装研究 总被引:1,自引:0,他引:1
用疏水星形聚合物模拟疏水性药物,研究其与两亲聚合物的自组装,探讨两亲性聚合物包载疏水性药物的机理.用开环聚合合成了5种两亲聚己内酯-聚乙二醇两嵌段共聚物(PCL-b-PEG)和4种疏水星型聚己内酯(star-branched polycaprolactone,SPCL),使用相分离法使PCL-b-PEG与SPCL进行自组装.浊度、SEM、动态光散射(dynamic light scattering,DLS)和FTIR结果表明,PCL-b-PEG与SPCL能够进行自组装,而且PCL-b-PEG中PEG长度和PCL含量对自组装有影响;PCL-b-PEG/SPCL形成的自组装体的粒径与SPCL的臂长、臂数和加入量有关. 相似文献
49.
In this paper we study the existence and non-existence of travelling wave to parabolic system of the form at=axx−af(b), bt=Dbxx+af(b), with f a degenerate nonlinearity. In the context of an auto-catalytic chemical reaction, a is the density of a chemical species called reactant A, b that of another chemical species B called auto-catalyst, and D=DB/DA>0 is the ratio of diffusion coefficients, DB of B and DA of A, respectively. Such a system also arises from isothermal combustion. The nonlinearity is called degenerate, since f(0)=f′(0)=0. One case of interest in this article is the propagating wave fronts in an isothermal auto-catalytic chemical reaction of order with 1<n<2, and D≠1 due to different molecular weights and/or sizes of A and B. The resulting nonlinearity is f(b)=bn. Explicit bounds v∗ and v∗ that depend on D are derived such that there is a unique travelling wave of every speed v?v∗ and there does not exist any travelling wave of speed v<v∗. New to the literature, it is shown that v∗∝v∗∝D when D<1. Furthermore, when D>1, it is shown rigorously that there exists a vmin such that there is a travelling wave of speed v if and only if v?vmin. Estimates on vmin improve significantly that of early works. Another case in which two different orders of isothermal auto-catalytic chemical reactions are involved is also studied with interesting new results proved. 相似文献
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