query: #publications prof.voit
  SELECT DISTINCT ?item ?itemLabel ?publicationDate (COUNT(?citations) AS ?count)
  WHERE 
  {
    ?item wdt:P31 wd:Q13442814.
    ?item wdt:P50 wd:Q21256003.
    ?item wdt:P577 ?publicationDate.
    optional {
      ?item wdt:P2860 ?citations.
    }
    SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
  } GROUP BY ?item ?itemLabel ?publicationDate ?count ORDER BY ?publicationDate