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目前,以计算机网络为基础的现代远程教育在我国得到了长足的发展.但是作为一个新生事物,在具体应用中还存在一些问题.比较突出的就是学习支持服务问题,由此引发了高辍学率、低及格率、毕业时间延长等问题.基于我国远程教育的发展现状,以提高远程教学质量为出发点,提出增强学习支持服务意识、使用统一制作的课件形式、实行“教师-课程-学生”绑定制度以及提供更多共享资源等提高远程教育质量的实施策略. 相似文献
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Radially oriented Nd-Fe-B rings are prepared by backward extrusion of fine grained melt-spun powder. Melt-spun powder with the nominal composition of Nd30.5Febal.Co6.0Ga0.6Al0.2B0.9 (wt%) is used as starting material. The effects of process variables, such as deformation temperature (Td), strain rate (ε) and height reduction (Δh%), on the magnetic properties of the rings are investigated. A scanning electron microscope (SEM) equipped with an energy spectrum device is used to study the metallograph and microfracture of the extruded rings. The Br and (BH)max reach the optimum values at Td=800℃, ε =0.01 mm/s, and Δh% =70%. It is found by SEM observations that the particle boundaries, which seemingly correspond to the interfaces of the starting melt-spun powders, emerge after the corrosion of metallography specimens. This is helpful for studying the effects of powder-powder interface on the local deformation and deformation homogeneity in the rings. For different spatial positions of the extruded rings, there are characteristic metallographies and microfractures. The upper end of the rings has the least deformation and worst texture, and therefore the worst magnetic properties. The magnetic properties in the radial direction increase slightly along the axis from the bottom to the middle, then steeply decrease at the upper end of the ring. The deformation and the formation-of-texturing processes are discussed. The deformation and the texturing formation of melt-spun Nd-Fe-B alloys probably involve grain boundary sliding and grain rotation, the solution-precipitation process and preferential growth of Nd2Fe14B nanograins along the easy growth a-axis. 相似文献
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广告英语是英语文体学研究的一个重要方面。修辞在广告文体中起着重要作用。本文结合大量实例,主要从拟人、双关、排比等七个方面论述了现代广告英语中使用的主要修辞手法及其功能进行描述与分析。 相似文献
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对从同一磁体上切取的取向方向不同的三组烧结Sm2Co17试样的抗弯强度进行测定,对其抗弯断口进行宏观观察和扫描电镜观察.对烧结Sm2Co17型永磁材料的力学性能和断裂行为的各向异性进行了研究.研究结果表明:烧结Sm2Co17型永磁材料的抗弯强度和断裂行为具有明显的各向异性,烧结Sm2Co17型永磁材料断裂的微观机制为解理断裂,材料易于沿密排面(0001)面或沿与密排面的夹角大约为60°的晶面解理断裂
关键词:
Sm2Co17型永磁
抗弯强度
解理断裂
各向异性 相似文献
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李安华 《数学的实践与认识》1989,(4)
大系统里,具有一类指定关系的系统结构常常表现为十分复杂的有向网络,它对应着一个模糊的非对称阵.本文给出了一组满足于计算机搜索算法的命题,以使纷乱的逻辑结构在偏序决策链的前提下相对地清晰化.设二元序偶 G=(X,(?))是一个有实际背景的系统结构.X={x_1,x_2,…,x_m;m<∞} 为有限节点集,(?)=(a_(ij))_((?)x(?)),a_(ij)=(x_i,x_j) 为从 x_i 到 x_j 的赋权,{(x_i,x_j)}(?)X×X.有以下命题:1.设(?)是一个自反的非对称模糊矩阵.令 A~((0))=(?),(?)~((k))=(?)~(k-1)_。(?)~(k-1),“。”:(?)k,a_(ij)~(k)=(?)(a_(il)~(k-1)∧a_(li)~(k-1)).则只要(?),(?)即为(?)的传递闭包. 相似文献