该文件暗示搜索引擎不应搜索某些特殊页面，例如错误页面。
This file hints to the search engine that it should not index particular pages, such as error pages.
这些都是专门设计的搜索引擎只返回PD F文件，以满足您的搜索标准。
These are search engines specifically designed to only return PDF documents that meet your search criteria.
事实上更多的文件甚至会使搜索引擎更糟糕，如果他没有很好的相关性。
Indeed, more documents can make a search engine worse, if it doesn't have good relevancy.
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