How can I retrieve the number of citations of a paper in a given year?
I had a look at Scopus Citation Overview API but the pybliometrics documentation says the API key needs to be approved by Elsevier for this purpose, and in fact it is returning error 403.
Are there other data sources from which I can retrieve the number of citations?
The rcrossref package provides a function cr_citation_count which seems to get the number of citation today.
I need the number of citation at a given year (for instance, if a paper was published in 2010, I may need the number of citation in 2015, not as of today at 2021).
First, access the OpenCitations API with a given DOI.
Second, fetch the DOIs of all the citing papers.
Third, use these newly fetched DOIs and loop them through the CrossRef API to obtain the respective publication dates.
Example:
You are interested in obtaining all citations from the year 2020 to the paper with the DOI 10.1080/17512786.2019.1682940.
First, access OpenCitations via https://opencitations.net/index/coci/api/v1/citations/10.1080/17512786.2019.1682940 (which finds 6 citations in total).
Second, fetch the values in the field citing -- they show the DOIs of the citing papers. For example, the second citing DOI is 10.17645/mac.v8i3.3019.
Third, access CrossRef with the help of these DOIs, such as via https://api.crossref.org/works/10.17645/mac.v8i3.3019, and look at the published-field (which is 2020-07-10). Keep only those values that start with the year 2020.
Note - - maybe you could omit the third step if you fetch the creation-field in OpenCitations during the second step (it seems to be identical to the published-field in CrossRef). I haven't tested that systematically.
Be aware that the citation counts between OpenCitations and CrossRef can vary (OpenCitaions usually shows less citations than CrossRef).