APIs for titles and abstracts for most or all published articles?
For healthcare, you'll want to check out what the NIH has to offer. NCBI has a bunch of a free APIs, and also allows download of the index data directly. I used to download PubMed Central for local indexing via rsync, but I'm not sure if they still operate that service. In any event, PMC is a key tool that is familiar to health/medical researchers and very popular.