Search and download PDF files for free
搜索功能使用google，需要科学上网
a volunteer-driven effort to produce a collection of high quality, carefully formatted, accessible, open source, and free public domain ebooks that meet or exceed the quality of commercially produced ebooks.
IT电子书
free computer science ebooks
备用域名：wdl.org
需科学，Internet Archive的National Emergency Library （国家紧急图书馆）
