ref_author: Select only references for which any of the authors
matches the specified name.
ref_pubyr: Select only references published in the specified
year.
pub_title: Select only references that involve the specified
publication.
order: Specifies the order in which the results are
returned. You can specify multiple values separated by commas,
and each value may be appended with .asc or .desc. Accepted
values are: "author", "pubyr", "reftitle", "pubtitle",
"pubtype", "created", "modified", "rank".