The Congressional Research Service publishes research reports on a wide variety of topics. The Congressional Research Service itself does not make these reports publicly available. There’s a relatively new website that makes available every CRS report, called, appropriately EveryCRSReport.com.
The Digital Library of the University of North Texas also maintains a library of CRS reports.
There is also another archive at CRSreports.com.
npm says
The above was true for many years, but in March, Congress required CRS to make reports public (https://fas.org/blogs/secrecy/2018/03/crs-publication/)
The official site recently went live: https://crsreports.congress.gov/