query: SELECT ?doi (COUNT(DISTINCT ?article) as ?count) WHERE {
    VALUES ?journal { wd:Q5535339 }  
    ?article wdt:P1433 ?journal ;
             wdt:P356 ?doi .
    FILTER (REGEX(?doi, "\\(")).
    FILTER (!REGEX(?doi, "<"))
    }
  GROUP BY ?doi
  HAVING (?count > 1)
  ORDER BY DESC(?count)