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991.
2,5-Disubstituted tetrahydrofurans were obtained from lactones and organozinc halides in moderate to high yield in the presence of Lewis acids. 相似文献
992.
设计了微波辅助合成和水解乙酰水杨酸的新型大学有机化学实验。该方法具有反应时间短、试剂用量少和产率高等特点。将乙酰水杨酸回收进行微波辅助水解实验,得原料水杨酸,减少了物耗和废弃物的污染。 相似文献
993.
994.
A generalized strong external difference family (briefly \((v, m; k_1,\dots ,k_m; \lambda _1,\dots ,\lambda _m)\)-GSEDF) was introduced by Paterson and Stinson in 2016. In this paper, we give some nonexistence results for GSEDFs. In particular, we prove that a \((v, 3;k_1,k_2,k_3; \lambda _1,\lambda _2,\lambda _3)\)-GSEDF does not exist when \(k_1+k_2+k_3< v\). We also give a first recursive construction for GSEDFs and prove that if there is a \((v,2;2\lambda ,\frac{v-1}{2};\lambda ,\lambda )\)-GSEDF, then there is a \((vt,2;4\lambda ,\frac{vt-1}{2};2\lambda ,2\lambda )\)-GSEDF with \(v>1\), \(t>1\) and \(v\equiv t\equiv 1\pmod 2\). Then we use it to obtain some new GSEDFs for \(m=2\). In particular, for any prime power q with \(q\equiv 1\pmod 4\), we show that there exists a \((qt, 2;(q-1)2^{n-1},\frac{qt-1}{2};(q-1)2^{n-2},(q-1)2^{n-2})\)-GSEDF, where \(t=p_1p_2\dots p_n\), \(p_i>1\), \(1\le i\le n\), \(p_1, p_2,\dots ,p_n\) are odd integers. 相似文献
995.
In this paper, we define two homogenous q-Laguerre polynomials, by introducing a modified q-differential operator, we prove that an analytic function can be expanded in terms of the q-Laguerre polynomials if and only if the function satisfies certain q-partial differential equations. Using this main result, we derive the generating functions, bilinear generating functions and mixed generating functions for the q-Laguerre polynomials and generalized q-Hahn polynomials. Cigler’s polynomials and its generating functions discussed in [J. Cao, D.-W. Niu, A note on q -difference equations for Cigler’s polynomials, J. Difference Equ. Appl. 22 (2016), 1880–1892.] are generalized. At last, we obtain an q-integral identity involving q-Laguerre polynomials. These applications indicate that the q-partial differential equation is an effective tool in studying q-Laguerre polynomials. 相似文献
996.
在不同pH值的条件下,多氧霉素B的吸收光谱会发生变化。为此选择无干扰的吸收波长,优化测定条件,建立液相色谱—二极管阵列检测器定量及定性检测多氧霉素B的方法。本方法快速简便,准确可靠。 相似文献
997.
Xiaohui Yu Xiaogang Zhao Changwei Liu Zewei Bai Daming Wang Guodong Dang Hongwei Zhou Chunhai Chen 《Journal of polymer science. Part A, Polymer chemistry》2010,48(13):2878-2884
A series of polyimides containing ether and ketone moieties were synthesized from 1,3‐bis(4‐fluorobenzoyl) benzene and several commercially available dianhydrides via a conventional two‐step polymerization. The inherent viscosities of Polyamide acids ranged from 0.46 to 0.73 dL/g. Thermal properties, mechanical properties, and thermalplasticity of the obtained polimide films were investigated by focusing on the chemical structures of their repeat units. These films were amorphous, flexible, and transparent. All films displayed low Tgs (184–225 °C) but also excellent thermal stability, the 5% weight loss temperature was up to 542 °C under nitrogen. The films showed outstanding mechanical properties with the modulus up to 3.0 GPa and the elongation at break in the range of 8–160%. The uniaxial stretching of PI‐a at high temperature was studied owing to its excellent flexibility. The PI‐a had an elongation at break up to 1600% at 245 °C and the uniaxially stretched film exhibited a much higher modulus (3.9 GPa) and strength (240 MPa) than undrawn film. The results indicated that PI‐a can potentially be used to prepare materials such as fiber, ultra‐thin film or ultra‐high modulus film. All the obtained films also demonstrated excellent thermoplasticity (drop of E′ at Tg > 103) which made the polyimides more suitable for melt processing. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2878–2884, 2010 相似文献
998.
Z. P. Niu D. Y. Xing 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,78(1):83-86
The lattice dynamics in the CuIr2S4 system have been
investigated through Raman spectroscopy and the induced-pressure
effect. Four Raman active modes are observed experimentally. Upon
cooling, these Raman spectra undergo changes due to the
Peierls-like phase transition. In addition, the substitution of Ag
for Cu affects the amplitude of the Raman spectra while keeping
their wave number unchanged. Furthermore, the positive and
negative pressure effects are induced by shrinking and expanding
the lattice. It is suggested that the pressure effect is an
effective proof of the orbital-induced Peierls state mechanism. 相似文献
999.
Shu Rong Ban Cong Wei Niu Wen Bin Chen Zhi Hong Yu Si Wu Chen Wang Zhen Xi State-Key Laboratory of Elemento-Organic Chemistry Department of Chemical Biology Nankai University Tianjin China School of Pharmaceutical Science Shanxi Medical University Taiyuan China 《中国化学快报》2007,18(2)
Some new sulfonylureas and their hydroxylation products had been synthesized from 2-amino-4-methylpyrimidine. Their bioactivities against E. coli AHAS II in vitro were tested and the results indicated that the hydroxylation decreased the inhibition activities of sulfonylureas significantly. Subsequently herbicidal tests against stem-growth of barnyard grass and root-growth of rape confirmed the above conclusion. The preliminary molecular docking studies were also carried out to investigate the binding modes of non-hydroxylated and hydroxylated sulfonylureas with AHAS. 相似文献
1000.
Jia-Xiao Niu Qi Zhang Xi-Lang Zhou Zhi-Yong Shan 《International Journal of Infrared and Millimeter Waves》2008,29(5):519-526
A compact two-dimension (2-D) finite-difference frequency-domain (FDFD) method is used to analyze the dispersion characteristics
of single and double trapezoidal-ridge waveguides. The general 2-D FDFD formulation under orthogonal curvilinear coordinate
system is derived from the difference form of Maxwell’s equations, and modified difference formulas at the trapezoidal-ridge
section are built. After implementing the boundary conditions, the 2-D FDFD formulation is concluded as an eigen equation
and then constructed by a highly sparse matrix. By solving the matrix-eigen equation, the dispersion characteristics of the
ridged waveguides can be obtained. Computed results are in good agreements with the previously published and simulated ones,
which prove the correctness of the method. 相似文献