摘要:对Web使用挖掘中数据预处理阶段所采用的技术做了全面的研究,主要包括数据的来源及清理、用户识别、会话识别、路径补充等步骤及其所采用的技术.在现有Web使用挖掘数据预处理的步骤上提出改进,即在路径补充后,利用最大向前序列法(MFR, Max Forward Reference)进行二次会话识别,克服了原有会话识别中最大向前序列法的缺点.最后给出示例及其结果.
摘要:采用三种自行设计的任务考察了小学六年级儿童对估算的概念理解. 从一所普通小学随机抽取的69名被试参加了本实验. 结果表明: ①小学儿童获取的有关估算的概念性知识与程序性知识明显多于条件性知识;②概念性知识与条件性知识的掌握水平之间存在显著正相关;③只有概念性知识的掌握水平明显制约了高、低组儿童的估算表现差异. 文中对上述结果及其在小学数学中的教学含义进行了讨论.%Using three self-designed tasks, this paper investigated the sixth graders' conceptual understanding about computational estimation in Chinese primary school. 69 children randomly sampling from an ordinary primary school participated in this study. The results showed that ① primary school children gained much more conceptual knowledge and procedural knowledge than conditional knowledge about computational estimation;② there was a significant correlation in the level of mastery between conceptual knowledge and conditional knowledge;and ③ only the level of conceptual knowledge contributed significantly to the difference of computational estimation performance between the high-level group and the low-level group. The results and their implications for the instruction of mathematics in primary school were also discussed.
摘要:针对香蕉组织中多糖、多酚等次生物质含量高的特点,以香蕉根、茎、叶、果实为试材,对其总RNA提取进行研究.比较了SDS法、改良SDS法、改良CTAB法和Trizol试剂盒法提取总RNA的效果,结果分析表明:改良SDS法能从香蕉根、茎、叶中获得质量高、完整性较好的总RNA,而改良CTAB法对果实的提取效果较佳,所得A260/A 280均高于1.8,A 260/A 230大于2.0,28 S rRNA带的亮度约是18 S rRNA的2倍.其产率在根、茎、叶中均在400μg·g-1以上,果实中可达49.34μg·g-1.以上2种方法所得的总RNA均能满足RT-PCR、Northern blot和cDNA文库建立等分子生物学研究,且具有快速、简便易行、成本较低的特点,适合于富含多糖、多酚的植物材料.
摘要:运用临界点理论的极小极大方法得到一类次二次Hamilton系统的周期解的可解性条件.%Some solvability conditions of periodic solution are obtained for a class of subquadratic Hamiltonian systems by the minimax methods in critical point theory.