@article{Thelwall2018, author = "Mike Thelwall", title = "{Headings used by articles and documents in the PMC Open Access collection}", year = "2018", month = "12", url = "https://figshare.com/articles/dataset/Headings_used_by_articles_and_documents_in_the_PMC_Open_Access_collection/7445603", doi = "10.6084/m9.figshare.7445603.v1" }