在一般情况下，此类索引内容可通过标准搜索引擎或访问网站本身可见。
In general, such indexed content is available through standard search engines or by visiting the websites themselves.
语义化和遵循标准的编码不只是让你的网站变得清晰，也有助于搜索引擎更好的阅读你的页面。
Semantic and standard coding not only can make your site cleaner, but it also allows the search engines to read your page better.
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.
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