National Academies Press
The National Academies Press (NAP) was created by the National Academy of Sciences to publish the reports of the National Academies of Sciences, Engineering and Medicine, operating under a charter granted by the Congress of the United States. The NAP publishes more than 200 books a year on a wide range of topics in science, engineering, and medicine, providing authoritative information on important matters in science and health policy. They offer more than 5,000 titles in PDF format. Almost all of these PDFs can be downloaded for free by the chapter or the entire book.