Perhaps you should try some spelling variations:
"serie retratos teoricos." » "serie retratos heroicos.", "serie textos teoricos.", "serie debates teoricos.", "ferre retratos teoricos.", "serie letras teoricos.", "sobre retratos teoricos."
"serie tesis teoricos." » "serie textos teoricos.", "serie sus teoricos.", "serie ejes teoricos."
"serie retos teoricos." » "serie textos teoricos.", "serie retos eticos.", "serie aspectos teoricos.", "serie reinos teoricos.", "serie riesgos teoricos."

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("serie tesis teoricos.") or ((("serie retos teoricos.") OR ("serie retratos teoricos."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("serie tesis teoricos.") OR ((("serie retos teoricos.") OR ("serie retratos teoricos.")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"serie tesis teoricos.\") or (((\"serie retos teoricos.\") OR (\"serie retratos teoricos.\"))))".
• Removing quotes may allow a broader search: (( serie tesis teoricos. ) or ((( serie retos teoricos. ) OR ( serie retratos teoricos. )))).
• Adding a wildcard symbol may retrieve word variants: (("serie tesis teoricos.") or ((("serie retos teoricos.") OR ("serie retratos teoricos."))))*.