Indeed, the WWW is certainly the largest communal document store in human history, and its informal organization probably makes it the set of documents most in need of good search engine.
的确，WWW 肯定是人类有史以来最大的公共文档库，它的非正规组织结构使其非常需要有好的搜索引擎。
At present no-one search engine has been able to cover all WWW resources, moreover the majority of search engines can commonly index only about 5%-20% of the entire WWW resources.
目前没有一个搜索引擎能够覆盖所有的WWW资源，而且大部分搜索引擎的索引平均只能涉及到整个WWW资源5% - 20%左右。
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