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991.
微型化有机合成实验的实践 总被引:1,自引:0,他引:1
1前言微型化有机化学实验有降低学生实验费用、节约时间、减少实验的污染物排放、有利于学生实验技能提高等诸多好处,因此,有机化学实验教学工作者一直为微型化有机实验在努力,比较有机化学实验的新老教材,许多有机合成实验的试剂用量都已大大减少[’,’],但是,真正毫克级的微型化实验对学生来说因操作难度过大而不易实用化。但随着实验技术的发展,在科研中毫克级的合成己广泛应用,因此,对学生进行毫克级的合成反应实验训练已是迫切需要。本文建立了一套在学生实验中实用的薄层色谱操作,并用之于分析、监测反应、判断产物纯度… 相似文献
992.
S. Shanmuga Sundara Raj Hoong‐Kun Fun Jing Zhang Ren‐Geng Xiong Xiao‐Zeng You 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(6):e274-e275
In the crystal structure of the title compound, C12H10N4, the pyridine ring makes a dihedral angle of 1.12 (9)° with the mean plane of the complete almost planar and crystallographically centrosymmetric molecule. There are stacks of parallel molecules along the a‐axis direction, with alternate stacks having a herring‐bone arrangement relative to each other and an interplanar spacing of 3.551 Å. 相似文献
993.
Many applications of histogram-based techniques for the purposes of image enhancement are well known. However, these techniques often fail to produce satisfactory results for a broad variety of low-contrast images (e.g., X-ray images). In this paper, we propose a new form of histogram for image contrast enhancement. The input image is first divided into several equal-sized regions according to the intensities of gradients, their corresponding statistical values of gray levels are then modified respectively, and finally the processed histogram for the whole image is obtained by the summation of all the weighted values of regions. The fundamental characteristic of this new form of histogram is that the amplitudes of its components can objectively reflect the contribution of the gray levels to the representation of image information. Accordingly, this new histogram is called gray-level information histogram. The performance of many histogram-based enhancement techniques might be improved dramatically using the proposed histogram. Testing on the X-ray images validates the effectiveness of the new histogram. 相似文献
994.
995.
In this paper, the robust filter design problem is studied for a class of uncertain dynamical systems with finite-step correlated
process noises and missing measurements. The dynamical system under consideration is subject to both deterministic norm-bounded
uncertainties in the measurement output and stochastic uncertainties on the system states. The process noises are assumed
to be finite-step correlated. The missing measurement phenomenon is modeled as a binary switching sequence. Based on the min-max
game theory, a recursive robust filter is designed that is suitable for online application. A particular feature is that,
as the proposed robust filters work in a recursive fashion, there is no need to investigate the existence issue of the filters.
A simulation example is presented to illustrate the usefulness of the proposed filter. 相似文献
996.
Lu Han Yan-Ru Ma Lai-Chen Chen Shu-Min Huo Tao-Run Qiu Rong-Hua Zeng Qun-Hui Meng Yi-Fan Luo 《Journal of chemical crystallography》2011,41(4):596-600
Abstract
A new 4d–4f coordination polymer, [AgGd(pyzc)2(ox)·H2O)] (1) [pyzc = Pyrazine-2-carboxylate, ox = oxalate] has been successfully synthesized under hydrothermal conditions and structurally determined by single-crystal X-ray diffraction, and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis and power X-ray diffraction. Single-crystal X-ray analysis reveals that it crystallizes in the monoclinic space group P2 1 /c with a = 10.0746(1) ?, b = 18.642(1) ?, c = 8.0525(2) ?, β = 112.470(1)°, Mr = 617.34, Z = 4, V = 1505.6(2) ?3, μ = 5.732, F(000) = 1164. The Gd(III) ion is nine-coordinated by two O-donors and two N-donors of two different chelating pyzc ligands, four O-donors of two different chelating oxalate ligands, and one O-donor of another carboxylate group of one pyzc ligand. The compound represents a 3D microporous polymeric network constructed by gadolinium–oxalate chains and Ag-pyzc subunits. 相似文献997.
998.
999.
You-Jun Fu Zhang-Shou Gao Xun Sun Shen-Lai Wang Yi-ping Li Hong Zeng Jian-Ping Luo Ai-Dong Duan Ji-Yang Wang 《Progress in Crystal Growth and Characterization of Materials》2000,40(1-4):211-220
The synthesis of KDP from its raw material has been found exist in the growth solution. In the crystal growth experiment, significant extension of specific faces was observed at low dopant concentration. At high doping concentration, the growth rate of the whole crystal decreased with no significant habit modification. The inhibiting effects of phosphite and other H-bonding anionic ions on the growth of pyramidal faces are discussed. Rapid growth rate experiments have been carried out with purified material and an averaged growth rate of 18.6mm/day was obtained. 相似文献
1000.
陷阱型双通带声表面波滤波器的设计 总被引:1,自引:1,他引:0
研究比较了几种陷阱型双通带声表面波滤波器的设计方法。实验表明,采用组合式均匀叉指换能器及变形多条耦合器元件可有效提高对陷阱频率的抑制。 相似文献