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在数据库应用中,根据用户提交的查询请求,如何才能精炼又高效地得到查询结果?从多个角度描述怎样优化SQL语句。实验结果表明,SQL优化能够减轻系统资源的占用,满足用户的要求。 相似文献
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A new method for estimating the degree of [SiO4]4-polymerization of coal gangue is presented. The method uses the relative bridging oxygen number （RBO） based on nuclear magnetic resonance （NMR） techniques. X-ray diffraction （XRD） and ^29Si NMR techniques have been used to study phase transitions and silicate polymerization of coal gangue calcined at different temperatures or co-calcined. It has been found that phase transition of clay minerals causes silicate polymerization to change with temperature. In this study, cementing activity and RBO were determined to be inversely related. Generally, activated coal gangue with lower RBO had better cementitious activity. 相似文献
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