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排序方式: 共有1818条查询结果,搜索用时 15 毫秒
861.
862.
狄艳媚 《浙江大学学报(理学版)》2004,31(4):369-372
采用Hardy空间的原子分解理论、Riesz-Thorin内插定理以及调和分析中的一些基本方法讨论了粗糙核奇异积分算子TΩ,βf(x)=p.v.∫Rnb(|y|)Ω(y′)|y|-n-βf(x-y)dy,当Ω∈Hr(Sn-1)(r=n-1/n-1+β)时,是从Herz型Sobolev空间到Herz型空间有界的.其中b(?)是一个有界函数,β≥0,Ω是Sn-1上满足某些消失性条件的分布. 相似文献
863.
通过在18t钢包上进行的钢包密闭喷粉脱硫脱氮新工艺的试验表明:第1阶段脱硫率达到50%,脱氮率达到30%;第2阶段脱硫率达到65%,脱氮率达到40%.该工艺钢液中硫质量分数为4×10,氮质量分数为12×10-6. 相似文献
864.
探讨楼梯间采暖是否节能,规范中有关楼梯间的计算方法是否合理等问题.在2006年1月对西安市一幢塔式高层住宅楼梯间的温度场进行了测试和计算,结果表明,对于严寒地区及寒冷地区,住宅楼梯间可以不采暖,通过加强建筑物整体保温等手段,以改善楼梯间的热环境. 相似文献
865.
D. G. Hwang J. K. Kim S. W. Kim S. S. Lee H. Koo S. H. Chung M. Dreyer R. D. Gomez 《Journal of magnetism and magnetic materials》2003,260(3):400-405
The dependence on nickel oxide thickness in unidirectional and isotropic exchange-coupled NiO/NiFe bilayer films was investigated by magnetic force microscopy to better understand exchange biasing at microscopic length scales. As the NiO thickness increased, the domain structure of unidirectional biased films formed smaller and more complex in-plane domains. By contrast, for the isotropically coupled films, large domains generally formed with increasing NiO thickness including a new cross type domain with out-of-plane magnetization orientation. The density of the cross domain is proportional to exchange biasing field, and the fact that the domain mainly originated from the strongest exchange coupled region was confirmed by imaging in an applied external field during a magnetization cycle. 相似文献
866.
Seung-Jin Han Seung Koo Shin 《Journal of the American Society for Mass Spectrometry》1997,8(4):319-326
Space-charge effects were studied by monitoring Fourier transform ion cyclotron resonance spectra while scanning the laser wavelength near the origin of a two-photon resonant 3s ← n Rydberg transition of acetaldehyde. The rotational contour of the origin band permits the experimental control of space-charge density. Both the frequency shift and the inhomogeneous line broadening were observed as a function of space-charge density. Three-dimensional ion trajectories in the presence of Coulomb interactions between ions were simulated under the quadratic and exact trapping potentials. The simulated Fourier transform ion cyclotron resonance spectra were obtained from the image-charge signals induced by a uniform field of chirp or impulse excitation. Comparisons of experiments with three-dimensional simulations reveal that the inhomogeneous line broadening observed in experiments is most likely due to both large-amplitude oscillations of ions and Coulomb interactions between different m/q ions. 相似文献
867.
868.
Faheem Ahmed Nishat Arshi M. S. Anwar Bon Heun Koo 《Journal of Sol-Gel Science and Technology》2014,71(1):1-7
Localized surface plasmon resonance (LSPR) of gold nanoparticles (AuNPs) has been used for biosensing and chemical sensing applications because the LSPR peak wavelength depends on the dispersion state and local refractive index of the surrounding medium. In this study, AuNP-loaded silica gels were prepared as sensing chips with high transparency and solution holding capability. The silica gels were prepared at various sintering temperatures from 500 to 900 °C, and the AuNPs precipitated in the gels by using a subsequent thermal reduction process. At sintering temperatures of 700, 800, and 900 °C, transparent and crack-free AuNP-loaded silica gels were obtained. Transmission electron microscopy observation revealed the AuNP size to be approximately 20 nm, and they were highly dispersed in all the silica gel samples. However, the sintering temperature of the silica gels strongly affected the LSPR property of the AuNPs and the porous property of the silica gel. The samples sintered at higher temperature exhibited a lower LSPR sensing ability against the refractive index of immersing solvents. The low sensing ability was considered as a result of a decrease in the contact area between the AuNPs and immersing solvent caused by an increase in the silica gel density with sintering temperature. 相似文献
869.
Baeck Kyoung Lee Hwan Geun Choi Eun Joo Roh Won Koo Lee Taebo Sim 《Tetrahedron letters》2013,54(6):553-556
An efficient synthesis of (?)-8-epi-swainsonine, starting from a commercially available 1-(R)-α-methylbenzylaziridine-2-methanol, was developed. The synthetic route utilizes stereocontrolled Sharpless asymmetric dihydroxylation governed by AD-mix-β followed by an aziridine ring opening-cyclization sequence to generate the five membered N-heterocyclic ring system present in the bicyclic target. A subsequent stereoselective allylation and piperidine ring forming cyclization then produced a precursor that was converted into (?)-8-epi-swainsonine. 相似文献
870.
A highly efficient method for the synthesis of 1,4-dideoxy-1,4-imino-d- and l-arabinitol (d-AB1, 1 and l-AB1, 3) and 1,4-dideoxy-1,4-imino-d- and l-xylitol (d-DIX, 2 and l-DIX, 4) starting from commercially available chiral aziridines was developed. The general strategy employs a sequence involving two-carbon homologation, dihydroxylation, and regioselective aziridine ring opening/intramolecular five-membered iminosugar ring formation. The facile use of recrystallization to generate pure diastereomers makes the routes more amenable to large-scale synthesis. 相似文献