1, courseware download website of China University:/
This is an all-round book website launched by the state, which not only supports the PDF version of university textbooks, but also finds periodicals, newspapers, papers, ancient books, music, movies and television.
3. Turing Community:/
This is a computer-based book website, where you can find books on Python, computers, mathematics, C language, algorithms and so on.
4、pdf drive:x.org/
This is a foreign e-book website, where you can find many foreign textbooks and courseware, such as e-books on mathematics, astronomy, biology and physics.
9. Science Library:/
This is a completely free PDF e-book website. The books it provides include: mathematics, chemical materials, resources and environment, agriculture and forestry, medicine, information, engineering, management, economy and so on.
10, Renmin University of China Press:/szjc/index.html.
This is a university course website, and all the courses are from the top schools in China. Including politics, sociology, economics, finance, finance and taxation, law, education and so on.
Source of PDF file
Each PDF file contains a complete description of a flat document with a fixed layout, including text, glyphs, graphics and other information that needs to be displayed. 199 1 year, Adobe Systems*** by John? Warnock's system named "Camelot" evolved into PDF.
PDF file format was developed in the early 1990' s to share documents including text format and built-in video. It can be operated across platforms, even if the computer platforms are completely different, the receiver does not need to adapt to related or shared application software interfaces. At that time, those competing with PDF for cross-platform file formats included DjVu (still under development), Envoy, Common Ground Digital Paper, Farallon Replica and Adobe's own PostScript (. Ps) format.