[求一篇关于科技的英语作文]Science and technology have changed our life thoroughly throughout the history, especially in the last century. There is a prevailing understanding about scienc...+阅读

关键词是从论文的题名、提要和正文中选取出来的，是对表述论文

的中心内容有实质意义的词汇。关键词是用作计算机系统标引论文内容

特征的词语，便于信息系统汇集，以供读者检索。 每篇论文一般选取

3-8个词汇作为关键词，另起一行，排在“提要”的左下方。

主题词是经过规范化的词，在确定主题词时，要对论文进行主题分

析，依照标引和组配规则转换成主题词表中的规范词语。（参见《汉语

主题词表》和《世界汉语主题词表》）。

不论国内还是国外的论文，关键字的选取都是遵循一定规范的，是为了满足文献标引或检索工作的需要而从论文中选取出的词或词组。 关键词包括主题词和自由词2个部分：主题词是专门为文献的标引或检索而从自然语言的主要词汇中挑选出来并加以规范了的词或词组；自由词则是未规范化的即还未收入主题词表中的词或词组。

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