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991.
992.
Xiaowen Cui 《European Polymer Journal》2004,40(6):1111-1118
A series of novel even-odd nylons were synthesized through step-heating melting-polycondensation of undecanedioic acid with various diamines. The synthesized polyamides were characterized comprehensively by means of elements analysis, intrinsic viscosity, Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), Raman spectra, thermogravimetry analysis (TGA) and differential scanning analysis (DSC). The obtained products except nylons 4 11 and 2 11 have intrinsic average molecular weights ranging from 1.3 × 104 to 2.5 × 104. Nylons 4 11 and 2 11 have intrinsic average molecular weights of 8400 and 7200, respectively. The melting temperatures of this series of even-odd nylons decrease with declining the concentration of hydrogen bonds. Furthermore, the dynamic mechanical analysis (DMA) was performed for nylons 12 11, 10 11, 8 11 and 6 11. The glass transition temperatures of nylons 12 11, 10 11, 8 11 and 6 11 are in the range of 40.1-45.7 °C. 相似文献
993.
994.
In this paper, on basis of [O.A. Oleinik, A.S. Shamaev, G.A. Yosifian, Mathematical Problems in Elasticity and Homogenization, North-Holland, Amsterdam, 1992], we present a local error estimate of the method of multi-scale asymptotic expansions for second order elliptic problems with rapidly oscillatory coefficients. 相似文献
995.
该文研究根据Byrne和Chaplain的思想建立的一个描述抑制物作用下无坏死核肿瘤生长的数学模型, 这个模型是一个非线性反应扩散方程组的自由边界问题. 作者运用反应扩散方程理论中的上下解方法结合自由边界问题的迭代技巧, 研究了解的渐近性态, 在营养物消耗函数f、抑制物消耗函数g和肿瘤细胞繁衍函数S的一些一般条件下,证明当常数c1,c2(肿瘤细胞分裂速率和营养物、抑制物扩散速率的比值)都非常小时,在一定的初边值条件下肿瘤趋于消失,在另外一些初边值条件下肿瘤半径趋于一个常数,进而时变解将趋于一个稳态解. 相似文献
996.
1IntroduInthispaperwestudyill(.)(l}xlsl(.)ll(:()noTI-1)ega,t]v(3s(>1lltionsfort,h(i1,woilo]lit,boundaryvalueproblemsu\ry;l;(:i.t>(v,>\,:t),:j:=fti-i'...ifn(j)>l),A>0isdcollstanta,f,dj'e(!'l,.,ti,fi<,,f(())<0(l.:i)111.of)i(lfllsifs{.1.l:)-(.I.2)havel,ecnsi… 相似文献
997.
998.
Xin Cui Juan Li Lei Liu Qing Xiang Guo Department of Chemistry University of Science Technology of China Hefei China 《中国化学快报》2007,18(6):625-628
Some 1,3-dicarbonyl compounds (such as pentane-2,4-dione and 3-oxo-N-phenylbutanamide) were found to constitute highly efficient, yet low-priced and phosphine-free ligands for the Pd-catalyzed Heck and Suzuki reactions of aryl bromides and iodides with very high turnover numbers (ca. 103-104). 相似文献
999.
1000.
Asymmetric triphenylene imidazolium salts with different spacer lengths were successfully synthesized through quarternization of ω-bromo-substituted triphenylenes with 1-methyl imidazole. The asymmetry in ω-bromo-substituted triphenylenes tended to destroy liquid crystallinity in the sample. However, highly ordered columnar mesophases with a lamellar microphase segregation were induced by ionic interactions among the imidazolium salts, and the lamellar morphology was visualized by transmission electron microscopy. On the basis of an X-ray diffraction study on shear oriented samples, a novel rectangular columnar phase with a plane group of pm was observed for a triphenylene imidazolium salt with a spacer length of C11, while an oblique columnar phase was determined for a triphenylene imidazolium salt with a C8 spacer. Due to the asymmetric molecular shape and ionic interactions in the triphenylene imidazolium salts, the columnar liquid crystalline phase was extended to below room temperature (c. -20°C) for samples with spacer lengths of C8 and C11. 相似文献