Sci-Hub is a shadow library website that provides free access to millions of research papers and books, without regard to copyright, by bypassing publishers’ paywalls in various ways. Sci-Hub was founded by Alexandra Elbakyan in 2011 in Kazakhstan in response to the high cost of research papers behind paywalls. The site is extensively used worldwide. In September 2019, the site’s owners said that it served approximately 400,000 requests per day. The number of articles claimed is frequently updated on the site’s home page, being over 85 million in February 2021.
PaperPanda uses some clever logic and the Panda’s detective skills to find you the research paper PDFs you need. Essentially, when you activate PaperPanda it finds the DOI of the paper from the current page, and then goes and searches for it. It starts by querying various Open Access repositories like OpenAccessButton, OaDoi, SemanticScholar, Core, ArXiV, and the Internet Archive. You can also set your university libraries domain in the settings. PaperPanda will then automatically search for the paper through your library. You can also set a different custom domain in the settings.