COVID-19 Open Research Dataset (CORD-19)
Download from MANY sources
Apparently cannot search the sources as a whole
Must first download each of them
Probably have to download each set daily to keep up to date
I hope that many of these limitations will soon be eliminated
https://www.semanticscholar.org/ has a wealth of medical studies, which are nicely indexed/accessed by AI aided techniques - seems much better than PubMed
You can easily set up your own personal notification service based on a neat set of criteria which include publicaion downloads, reads, references, etc,