Ask HN: How do you find free academic/scientific material?

Over the years, copywriting, SEO, and other factors have made it increasingly difficult to find quality material on the internet. It takes more effort than ever to find what you're looking for. When I need to learn about a new topic, I usually search for scientific articles. A few years ago, I discovered that I often got good results by searching for "KEYWORD PDF," as this led to static PDF files that aren't easily changed. Very often, they are written by academics or produced by government agencies. Lately, however, I've gotten the feeling that the results more and more often lead to "zombie sites" that just redirect to ads and other junk.