East Asian Library
Washington University in St. Louis
Some reference tools are available as mobile apps on iOS and Android devices. This LibGuide page lists selected apps that may be useful for doing research on Korea, such as dictionaries and world fact books.
The National Institute of Korean History provides this database for the Annals of the Choson Dynasty (朝鮮王朝實錄) which include 1,893 books covering 472 years of the history of the Choson Dynasty, from the reign of King Taejo, the founder, to the end of the rule of King Cheoljong.