WHO COVID-19 Global literature on coronavirus disease
The global literature cited in the WHO COVID-19 database is updated daily (Tuesday through Saturday) from searches of bibliographic databases, hand searching, and the addition of other expert-referred scientific articles. This database represents a comprehensive multilingual source of current literature on the topic. While it may not be exhaustive, new research is added regularly.
Help guide can be accessed here https://www.who.int/docs/default-source/coronaviruse/who-covid-19-database/bireme-who-covid-19-quick-search-guide-for-who-covid-19-database.pdf?sfvrsn=7e8bb418_3&download=true