Given a DOI number…
$ doi2bib 10.1038/s41524-017-0032-0
You can easily append a bib into a bibfile, just do
$ doi2bib 10.1038/s41524-017-0032-0 >> file.bib
You also can generate a bibtex from a txt file containing a list of DOIs
$ doi2bib --input file_with_dois.txt --output refs.bib