https://sci-hub.ru/database 大，大数据 Sci-Hub collected a database of 88,343,822 research documents, freely available for download. Around 80% of the collection are research articles published in journals, 6% are papers from conference proceedings, 5% are book chapters, the rest are other types of documents. 77% of the documents available through Sci-Hub were published between 1980 and 2020, and 36% between 2010 and 2020. The coverage is > 95% for all major scientific publishers. The total size of Sci-Hub database is about 100 TB.