APIs for titles and abstracts for most or all published articles? Are there any APIs that index and capture the titles and abstracts most or all published scientific journals?

If not, what about only for pharmaceutical or health fields?

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Edits: I came across CrossRef api, but wonder if there are other options.
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.