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现今所谓的“第四媒体“,即网络传媒,已经对印刷出版物构成了威胁,其内容的广泛性、大容量,势不可挡地从纸媒体手中夺走读者群。而其快捷性和低成本优势,更令纸媒体望尘莫及。 就拿报道北约导弹袭击我驻南大使馆事件来说,网络传媒充分展现了其天生的优势。北京时间1999年5月8日凌晨5时45分,北约的3枚导弹悍然袭击我驻南大使馆。仅仅42分钟后,中国的普通老百姓即从互联网上知道了这一骇人听闻事件。和1998年的美国空袭伊拉克 相似文献
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The changes of grindability, grading and wettability of recycled plaster(R-P)and the mechanisms of these changes were studied by using vickers hardness, particle size distribution(PSD), scanning electron microscope (SEM) and nitrogen adsorption porosimetry to reveal that R-P was obviously different from plaster of Paris(POP). At the same milling time, R-P had the characteristics of high specific surface area, fine particle diameter and uneven size distribution compared with POP, so R-P possessed both good grindability and poor grading. The water absorption, dissolution rate and mass loss in dry-wet cycle of the hardened recycled gypsum(hardened RG) increased, while the water saturated strength and dry-wet cycle strength decreased significantly compared with the hardened virgin gypsum(hardened VG). Therefore, poor wettability could be seen in R-P. The analyses indicated that the changes of grindability and grading could be attributed to the reduction in hardness and the increase in the porosity of hardened RG and that the poor wettability of R-P was caused by the increase of large pores and the changes of microstructure of hardened RG. 相似文献
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