National Academies Press offers about 8000 titles in science, engineering, and medicine. They are monographs, reports, studies, proceedings.
Almost all of these PDFs can be downloaded for free by the chapter or the entire book. The ebooks which you have full-text access to are supplied on a Digital Rights Management (DRM) Free basis, allowing you to print or save PDF of each chapter/section within the book. or up to 100% of the ebook for your own use.
You can find the NAP ebooks in the library catalog, on EDS, or by visiting their website, at your convenience, the link is included in the list of databases.