Perhaps you should try some spelling variations:
"serie lecturas de clacso." » "serie letras de clacso.", "serie lectura de clacso."
"serie cartas de clase." » "serie actas de clase.", "serie arte de clase.", "serie notas de clase.", "serie carta de clase."
"serie cartas la clase." » "serie actas la clase.", "serie arte la clase.", "serie notas la clase.", "serie cartas a clase.", "serie carta la clase.", "serie cartas una clase."

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

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("serie cartas de clase.") OR ("serie cartas la clase."))) OR ("serie lecturas de clacso."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"serie cartas de clase.\") OR (\"serie cartas la clase.\"))) or (\"serie lecturas de clacso.\"))~".
• Removing quotes may allow a broader search: (((( serie cartas de clase. ) OR ( serie cartas la clase. ))) or ( serie lecturas de clacso. ))~.
• Adding a wildcard symbol may retrieve word variants: (((("serie cartas de clase.") OR ("serie cartas la clase."))) or ("serie lecturas de clacso."))*.