Perhaps you should try some spelling variations:
"serie retratos de clacso." » "ferre retratos de clacso.", "serie letras de clacso.", "sobre retratos de clacso.", "serie retrato de clacso.", "serie contratos de clacso."
"serie detras de clase." » "serie letras de clase.", "serie lecturas de clase.", "serie actas de clase."
"serie parte la clase." » "serie arte la clase.", "serie art la clase.", "serie parte de clase.", "serie parte ii clase.", "serie parte i clase."

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 parte la clase.") or ((("serie retratos de clacso.") or ("serie detras de clase."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("serie parte la clase.") OR ((("serie retratos de clacso.") OR ("serie detras de clase.")))).
• Removing quotes may allow a broader search: (( serie parte la clase. ) or ((( serie retratos de clacso. ) or ( serie detras de clase. )))).
• Adding a wildcard symbol may retrieve word variants: (("serie parte la clase.") or ((("serie retratos de clacso.") or ("serie detras de clase."))))*.