On advantages and limitations of computer-assisted language learning

Computer-assisted language learning(CALL)is used increasingly in foreign language teaching.Compared with the traditional teaching method,computer-assisted language learning has unparallel advantages,but in fact it does have some limitations in some aspects.     

农药使用负面影响管理中的政府、市场与组织

中国以国家干预、政府主导为特征的农药管理政策,在维护国家粮食安全、环境影响控制和农产品质量安全方面已经取得了较大进展,但目前政府主导、事前监管为主的农药负面影响管理忽视了市场和组织的力量及其在事中和事后监管中的优势,效率亟待提高。文章构建了一个政府监督、调控衣药负面影响的分析框架,应用这一新的分析框架加强和改善政府对农药负面影响的管理和调控,就需要以政府为主体,创新农药管理体制;同时重视发挥、培育市场和组织的力量。     

试论现行财务分析的局限性

作为企业的核心运作源泉财务,只有很好的把握企业运作过程,并总结过去经济活动经验,预测其未来走向,对信息使用者来说无疑是作出决策的根据。文章将从对现行财务分析的框架进行剖析,找出其局限性,以便信息使用者能根据其不足作进一步分析,最终做出正确的决策判断。     

固相萃取-气相色谱法测定三七中38种农药残留

三七中药材产品经乙腈提取,盐析,采用C18和硅胶固相萃取柱净化后,用气相色谱仪检测38种有机氯、拟除虫菊酯农药残留含量。结果表明:C18和硅胶固相萃取柱净化能够有效除去三七药材中挥发油、有机酸、皂苷等大部分共萃物和干扰组分,获得较好的净化效果;3个不同浓度水平添加回收率在78.6%~120.3%之间,相对标准偏差为0.1%~12.5%;校准曲线线性相关系数均大于0.999。该方法操作简单、快速稳定、除杂效果明显,适用于三七中药材产品中多种农药残留的日常检测工作。     

采用QuEChERS-气相色谱-质谱法快速测定农产品中143种农药及代谢物残留

为了适应农药残留分析高灵敏度和快速性的趋势与要求,本方法选取农产品中具有代表性的苹果、梨、木耳、黄瓜、土豆、菠菜、西红柿作为基质,用QuEChERS-气相色谱-质谱法测定其中的有机磷、有机氯、拟除虫菊酯、氨基甲酸酯类等143种农药及其代谢物残留量。检出限LOD为0.002 mg/kg,定量限LOQ为0.005 mg/kg;各农药标准溶液在0.005 mg/L0.1 mg/L范围内与响应值(定量离子峰面积)有良好的线性关系;采用各基质进行了3个添加水平10平行的回收率试验,回收率为81.4%103.9%,RSD≤10.4%。本方法快速简便、经济高效,且具有较高的灵敏度,适用于农产品中农药残留的日常检测和快速筛查。     

西方经济学的三个学科基础缺陷

本文指出并分析了西方经济学的自然科学基础局限性、社会时空基础局限性和逻辑基础缺陷，由此说明，我们不能盲目崇拜西方经济学，更不能将其作为我国经济发展与改革的指导思想。     

The residual market factor,the APT,and mean-variance efficiency

The rapidly increasing volume of both published and unpublished work on the arbitrage pricing theory (APT) of Ross (1976) has given rise to a number of misunderstandings at the interface of theoretical and econometric work. In this article we extend the theoretical structure of our previous work (McElroy and Burmeister, 1985, 1988; Burmeister and McElroy, 1987, 1988) to provide a broad yet rigorous framework both for econometric estimation and for better economic interpretation of new empirical results. We begin with the case where allK factors are observed, and then present the second case ofK−1≡J observed APT factors and one unobserved factor, theresidual market factor introduced in McElroy and Burmeister (1985). The economic interpretations for equivalent specifications of this model are discussed, and we enumerate several immediate payoffs to these specifications. The main new results are concerned with the sometimes intricate relationships among APT models withK factors and APT models withK factors that are constrained to satisfy mean-variance efficiency restrictions. These results are not only of theoretical interest, but more importantly they provide the basis for econometric estimation and testing of nested hypotheses. These econometric issues are discussed in detail.     

Covariance formulas via marginal martingw

Prenctice and Cai recently introduced and studied the function C defined as the covariance function of the two marginal counting process martingales of a pair of dependent survival times (T₁, T₂ ). They show that the function C together with the marginal distributions determines the joint survival function F of (T₁, T₂ ). In this note we show how the key characterizing equation of Prentice and Cai yields a formula for the covariance of T₁ and T₂ in termsof the marginal mean residual life functions and C. The resulting formula generalizes a formula for the variance of a one-dimensional random variable Tdueto Pyke (1965). We also explore several generalizations of the covariance formula, and obtain a valid k-dimensional version of the Prentice and Cai formula.     

基于灰色残差模型的中国税收收入预测

税收是国家财政收入的重要来源,准确的税收预测结果对于制定各项经济政策具有非常重要的意义。为提高中国税收收入的预测精度,适应资源配置、收入再分配和宏观经济调控的需求,在传统灰色预测技术的基础上,建立了残差灰色预测模型,并通过实例分析验证了该模型的实用性和精确性。     

石家庄市农药行业现状和发展对策

通过对石家庄市农药企业现状调查研究,并结合国内国际的农药行业的现状及发展趋势,有针对性的提出了在环境危机下石家庄市实施产业结构调整、建立研发中心、促进企业合作升级、组建农药三废处理和包装回收中心系统等一系列具体措施,真正实现石家庄市农药行业的可持续发展。