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991.
Factors related to achievement in junior high school science in disadvantaged areas of New York city
Morsley G. Giddings 《科学教学研究杂志》1966,4(2):79-84
More knowledge about socially disadvantaged students must precede curricular changes designed to help them. This report points up differences between high and low achievers in science who come from similar disadvantaged homes. 相似文献
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This paper examines Brazil’s Sector Funds, an emerging research and development policy that seeks to increase public-private research collaboration. The first section sets the context of the ‘policy problem’. The second section discusses the policy’s implementation, and discusses its likely implications for Brazil and beyond. 相似文献
999.
A General Evaluation Framework for Topical Crawlers 总被引：10，自引：0，他引：10
Topical crawlers are becoming important tools to support applications such as specialized Web portals, online searching, and competitive intelligence. As the Web mining field matures, the disparate crawling strategies proposed in the literature will have to be evaluated and compared on common tasks through well-defined performance measures. This paper presents a general framework to evaluate topical crawlers. We identify a class of tasks that model crawling applications of different nature and difficulty. We then introduce a set of performance measures for fair comparative evaluations of crawlers along several dimensions including generalized notions of precision, recall, and efficiency that are appropriate and practical for the Web. The framework relies on independent relevance judgements compiled by human editors and available from public directories. Two sources of evidence are proposed to assess crawled pages, capturing different relevance criteria. Finally we introduce a set of topic characterizations to analyze the variability in crawling effectiveness across topics. The proposed evaluation framework synthesizes a number of methodologies in the topical crawlers literature and many lessons learned from several studies conducted by our group. The general framework is described in detail and then illustrated in practice by a case study that evaluates four public crawling algorithms. We found that the proposed framework is effective at evaluating, comparing, differentiating and interpreting the performance of the four crawlers. For example, we found the IS crawler to be most sensitive to the popularity of topics.Partially supported by National Science Foundation CAREER grant No. IIS-0133124/0348940. 相似文献
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