Perhaps you should try some spelling variations:
"ferre retratos de clacsos." » "ferre retrats de clacsos.", "serie retratos de clacsos.", "sobre retratos de clacsos.", "ferre retrato de clacsos.", "ferre contratos de clacsos.", "ferre retratos de clacso.", "ferre retratos de casos.", "ferre retratos de clases."
"serie cartas a clase." » "serie actas a clase.", "serie arte a clase.", "serie notas a clase.", "serie cartas de clase.", "serie cartas la clase.", "serie cartas a case.", "serie cartas y clase."
"serie detras de bases." » "serie letras de bases.", "serie lecturas de bases.", "serie retratos de bases.", "serie detras de base."

Try widening your search to All Fields.

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• Performing a fuzzy search may retrieve terms with similar spellings: (("serie cartas a clase.") or ((("ferre retratos de clacsos.") or ("serie detras de bases."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("serie cartas a clase.") OR ((("ferre retratos de clacsos.") OR ("serie detras de bases.")))).
• Removing quotes may allow a broader search: (( serie cartas a clase. ) or ((( ferre retratos de clacsos. ) or ( serie detras de bases. )))).
• Adding a wildcard symbol may retrieve word variants: (("serie cartas a clase.") or ((("ferre retratos de clacsos.") or ("serie detras de bases."))))*.