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941.
942.
对单变量情形下的牛顿-莱布尼兹公式借助于定向体积化和外微分形式,给出了统一、简明的多变量情形下的Newton-Leibniz公式。 相似文献
943.
Silicon nitride (Si3N4) powders were prepared by the direct nitridation of silicon powders diluted with α-Si3N4 at normal pressure. Silicon powders of 2.2 μm in average diameter were used as the raw materials. The nitriding temperature was from 1623 to 1823 K, and the reaction time ranged from 0 to 20 min. The phase compositions and morphologies of the products were analyzed by X-ray diffraction and scanning electron microscopy, respectively. The effects of nitriding temperature and reaction time on the conversion rate of silicon were determined. Based on the shrinking core model as well as the relationship between the conversion rate of silicon and the reaction time at different temperatures, a simple model was derived to describe the reaction between silicon and nitrogen. The model revealed an asymptotic exponential trend of the silicon conversion rate with time. Three kinetic parameters of silicon nitridation at atmospheric pressure were calculated, including the pre-exponential factor (2.27 cm·s?1) in the Arrhenius equation, activation energy (114 kJ·mol?1), and effective diffusion coefficient (6.2×10?8 cm2·s?1). A formula was also derived to calculate the reaction rate constant. 相似文献
944.
945.
Integrating IP and WDM is an attractive direction for research.Many solutions have been presented but it is noted that the existing switching technologies still need more concern. Since optical packet switching is not practical yet, there are just two possible solutions left. One is wavelength routing(WR), which is circuit switching in essence and the other is newly proposed optical burst switching (OBS). In this paper, characteristics of WR and OBS are first described, then, compared in several aspects. It is notice that in many aspects, the wavelength routing and burst switching are complement. This stimulates us to propose a new switching architecture, which may be considered as “mixture” of WR and OBS. We beleve the network built on new switching structure can accommodate the requirements of practicability, flexibility, robustness, effciency and etc. simultaneously. However, many related problems still need to be further researched. 相似文献
946.
基于铝(Ⅲ)5′-硝基水杨基荧光酮的荧光具有猝灭的特性,拟定了一种测定铝的新方法。该方法的激发波长为246nm,发射波长为552nm,线性范围为1.6-28ng/ml,检出限为1.6ng/ml。本方法灵敏度高、选择性好,用于多种茶叶中微量铝的测定,获得了满意的结果。 相似文献
947.
芾吟 《浙江万里学院学报》2000,13(4):51-52,90
古代诗歌中有一种人们屡见不鲜的现象,常常以为是写作技法,至多被认为是一种句法结构,从《诗经》始,这种回环结构就已存在,历代诗家自觉不自觉地运用着,心有灵犀地丰富着,使这种回环结构成为诗的一种基本结构。现代诗更是借鉴和延伸了这种结构。词语破碎处,万物皆存。 相似文献
948.
949.
Search engine is an effective approach to promote the service quality of the World Wide Web. On terms of the analysis of search engines at home and abroad, the developing principle of search engines is given according to the requirement of Web information for chemical fiber engineering. The implementation method for the communication and dynamic refreshment of information on home page of the search engines are elaborated by using programming technology of Active Server Page 3.0 (ASP3.0). The query of chemical fiber information and automatic linking of chemical fiber Web sites can be easily realized by the developed search engine under Internet environment according to users' requirement. 相似文献
950.
为克服超薄注塑充模的困难,定义了主、次相剪切的概念,分析了超薄注塑剪切场.根据泊肃叶方程,通过狭缝流变实验,重点讨论了超薄注塑过程中次相剪切对表观黏度、表观剪应力的影响,分析了次相剪切与粘性升温、入口压力的关系,发现次相剪切能有效改善超薄注塑中的熔体充模.文中还提出了超薄导光板的表面微特征混排设计方法,使熔体在流动平面内形成次相剪切,有效提高了制件填充率,验证了次相剪切效应的理论正确性. 相似文献