景天三七中总黄酮提取条件和含量分析

目的：研究不同提取溶剂对景天三七中总黄酮的含量影响及最佳提取条件下总黄酮的含量。方法：采用盐酸一镁粉法和醋酸铅法对景天三七中总黄酮进行检识,并用不同溶剂对景天三七中总黄酮进行了提取,以分光光度法测定总黄酮含量,以芦丁为标准品,以10％AI（NO2）3-5％NaNO2为显色剂,在508nm波长处进行测定。结果：检识试验证明景天三七中含有黄酮类物质,且最佳提取溶剂为80％乙醇（P〈0．05）。在此提取条件下,测得景天三七中总黄酮的含量为18．39mg·g～,RSD为2．2％（n=5）。总黄酮测定线性范围为15．20-45．60beg·mL^-1。（r=0．9997）,平均回收率为95．74％,RSD为0．98％（n=6）。结论：景天三七中黄酮类物质的最佳提取溶剂为80％乙醇。本法准确可靠,重现性好,结果稳定,适合于景天三七中总黄酮含量分析。     

二语习得关键期假说探讨

本文首先介绍了二语习得关键期假说及其理论背景,之后通过前人的各项研究探讨关键期假说是否具有合理性,希望对教学有启示作用。     

Effect of the geometric shapes of specimens on impact tensile tests

The geometric shapes of specimens are important in impact tensile tests because geometric shapes determine the stress states of the specimens, and precise geometric shapes can obtain proper material properties without non-material factors. The aim of this study was to investigate the 1D form of the stress by changing the length-to-diameter （L/D） ratios of specimens. The experiments were carried out on a split Hopkinson tensile bar （SHTB）-rotating disk indirect bar-bar tensile impact apparatus. The L/D ratios of the LY12CZ specimens used in the test ranged from 1 to 5. Results show that the specimens can be used to obtain exact parameters of materials under the proposed conditions when the L/D ratio is greater than 2. This is because the longer length will reduce or eliminate the effects of the interfaces.     

母语提纲对大一学生二语写作的影响

英语新四级考试作文主要以英语题目加母语提纲为出题方式,大一学生在写作时是否受到母语提纲的负迁移影响？本文将通过对比两个非英语专业的大一班级按照同一题目不同提纲（母语提纲和英语提纲）写的课堂作文,探讨母语提纲对学生作文的影响。     

An Empirical Research on DDL in L2 Writing

L2 （second language） writing teaching and research is greatly influenced by the advent of computer technology. This paper reviews papers, in the field of DDL （data-driven learning） in L2 writing, published in international journals and in Chinese journals, and differences are found in research methodology, research perspective, and research realm. Based on the analysis of the differences, the study aims at finding out the effects of the application of DDL in L2 teaching classroom. The present study, employing semi-structured writing and learning journals, explores how English learners perceive the use of corpora in their writing process. Based on the statistics, it is concluded that DDL in L2 writing is beneficial for vocabulary acquisition. However, corpus consultation does not work well for all learners. Learners＇ attitudes toward the use of corpus are various. The major findings may find application in teaching practice, and implications for teaching are discussed.     

基于单片机的智能测角仪设计

研究了一种基于STC12C5A60S2单片机的智能测角仪。该测角仪由加速度传感器模决MMA7455、时钟模块DS1302、温湿度模块DHT11、语音模块ISD4004组成,实现了角度、时间、温湿度的显示、存储以及语音播报的功能,具有一定的推广价值和实用性。     

基于L2TP／IPSec的企业远程移动办公网的构建

研究了安全的企业远程移动办公网络,首先介绍了L2TP和IPSec的相关概念和工作原理．然后介绍了基于L2TP／IPSec的企业网络方案,最后给出了该方案的具体构建方法。     

认知隐喻学视域下的二语词汇习得研究

词汇是语言大厦的基石,传统的死记法导致词汇学习费时低效。词汇在语音、形态、语义和逻辑等方面存在着理据,化抽象为具体的认知隐喻学在词汇习得方面有着广阔的前景和用武之地,能够帮助学习者深入了解词汇的本源与实质,有助于提高二语词汇学习效果。     

中国高校二语动机策略实证研究

动机被视为影响二语学习成效的一个重要的情感因素。本文用定量研究方法对62位高校英语教师进行了调查,旨在研究动机策略重要性的认识程度以及具体运用程度,并探讨两者之间是否存在显著差异。研究结果表明：教师总体上在动机策略的重要性认识程度和实际课堂运用频率上保持很高的一致性,但在实际教学中也存在策略运用不足,主要体现在学生自主能力、课堂任务及教师层面等策略上。传统的以教师为中心的教学方法、应试教育、基础差和大班教学很大程度上影响和制约了教师的动机策略,并限制了学生动机的形成与维持。