Unified Medical Language System® (UMLS®)
Unified Medical Language System (UMLS). MetamorphoSys. Rich Release Format (RRF) Browser: Limit a Search by Source.
The video contains a tutorial.
This video can be seen directly at http://www.nlm.nih.gov/research/umls/user_education/quick_tours/MMSys/limitSearchBySourceN.mp4
The captions are available at http://www.nlm.nih.gov/research/umls/user_education/quick_tours/MMSys/limitSearchBySourceN.srt