Complex sentence: Since 1879, the National Library of Medicine (NLM) has published the Index Medicus, a monthly guide to medical articles in thousands of journals, the huge volume of bibliographic citations were manually compiled at a cost of millions of dollars annually.
Split into simpler sentences: Since 1879, the National Library of Medicine (NLM) has published Index Medicus, a monthly guide to medical articles in thousands of journals. The huge volume of bibliographic citations were manually compiled at a cost of millions of dollars annually.