In Wikidata, we have at the moment around 36 million citations. It is not much compared to Google Scholar, but you can query them in flexible ways with the Wikidata Query Service, - a SPARQL endpoint.
In Scholia, a website that uses Wikidata Query Service, we have implemented a query that shows "all papers that cite both A and B". You can see an example for "Protein measurement with the Folin phenol reagent" and "Novel method for detection of beta-lactamases by using a chromogenic cephalosporin substrate" here: https://tools.wmflabs.org/scholia/works/Q20900776,Q24564458.
Scholia will also show results for more than two papers, see, e.g., https://tools.wmflabs.org/scholia/works/Q20900776,Q24564458,Q39309940.
Following the link "Edit on query.Wikidata.org" gets you to the SPARQL query at the Wikidata Query Service interface. The SPARQL query currently reads:
SELECT ?date ?work ?workLabel
WITH {
SELECT (MIN(?dates) AS ?date) ?work
WHERE {
?work wdt:P2860 wd:Q20900776 . ?work wdt:P2860 wd:Q24564458 .
OPTIONAL {
?work wdt:P577 ?datetimes .
BIND(xsd:date(?datetimes) AS ?dates)
}
}
GROUP BY ?work
ORDER BY DESC(?date)
LIMIT 1000
} AS %results
WHERE {
INCLUDE %results
SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en,da,es,fr,nl,no,ru,sv,zh". }
}
ORDER BY DESC(?date)
You can read more about the approach of using Wikidata and SPARQL for citation analysis work in this paper: "Scholia and scientometrics with Wikidata", https://arxiv.org/abs/1703.04222