In [33]: a1.getValuesForProperty("http://scigraph.springernature.com/ontologies/core/doi")
Out[33]: []
In [34]: import rdflib
In [35]: a1.getValuesForProperty(rdflib.URIRef("http://scigraph.springernature.com/ontologies/core/doi"))
Out[35]: [rdflib.term.Literal(u'10.1023/B:HIJO.0000045969.52516.59')]