With the WikiCite project, the bibliographic information on Wikidata is increasing rapidly with Wikidata describing 9.3 million scientific articles and 36.6 million citations. As far as I can determine most of the work is currently done by James Hare and Daniel Mietchen. Mietchen’s Research Bot is over 11 million edits on Wikidata while Hare has 15 million edits. For entering data into Wikidata from PubMed you can basically walk your way through PMID starting with “1” with the Fatameh tool. Hare’s reference work can take advantage of a webservice provided by National Institute of Health. For instance, a URL such https://eutils.ncbi.nlm.nih.gov/entrez/eutils/elink.fcgi?dbfrom=pmc&linkname=pmc_refs_pubmed&retmode=json&id=5585223 will return a JSON formatted result with citation information. This specific URL is apparently what Hare used to setup P2860 citation information in Wikidata, see, e.g., https://www.wikidata.org/wiki/Q41620192#P2860. CrossRef may be another resource.
Beyond these resources, we could potentially use Google Scholar. A former terms of service/EULA of Google Scholar stated that: “You shall not, and shall not allow any third party to: […] (j) modify, adapt, translate, prepare derivative works from, decompile, reverse engineer, disassemble or otherwise attempt to derive source code from any Service or any other Google technology, content, data, routines, algorithms, methods, ideas design, user interface techniques, software, materials, and documentation; […] “crawl”, “spider”, index or in any non-transitory manner store or cache information obtained from the Service (including, but not limited to, Results, or any part, copy or derivative thereof); (m) create or attempt to create a substitute or similar service or product through use of or access to any of the Service or proprietary information related thereto“. Here is “create or attempt to create a substitute or similar service” a stopping point.
The Google Scholar terms document seems now to have been superseded by the all embracing Google Terms of Service. This document seems less restrictive: “Don’t misuse our Services” and “You may not use content from our Services unless you obtain permission from its owner or are otherwise permitted by law.” So it may be or may not be ok to crawl and/or use/republish the data from Google Scholar. See also a StackExchange question. and another StackExchange question.
The Google robots.txt limits automated access with the following relevant lines:
Disallow: /scholar Disallow: /citations? Allow: /citations?user= Disallow: /citations?*cstart= Allow: /citations?view_op=new_profile Allow: /citations?view_op=top_venues Allow: /scholar_share
“/citations?user=” means that you are allowed to bot access the user profiles. Google Scholar user identifiers may be recorded in Wikidata by a dedicated property, so you could automatically access Google Scholar user profiles from the information in Wikidata.
So if there is some information you can get from Google Scholar is it worth it?
python -m scholia.googlescholar get-user-data gQVuJh8AAAAJ
It is worth remembering that Wikidata has the P4028 property to link to Google Scholar articles. There ain’t no many items using it yet though: 31. It was suggested by Vladimir Alexiev back in May 2017, but it seems that I am the only one using the property. Bot access to the link target provided by P4028 is – as far as I can see from the robots.txt – not allowed.