Perhaps you should try some spelling variations:
"series estudios americanoss." » "series estudios americanos.", "series estados americanos.", "series estudios africanos.", "serie estudios americanoss.", "seis estudios americanoss.", "leyes estudios americanoss."
"tres estudios peruanos." » "tres estudios americanos.", "tres estudios ensayos.", "tres estudios cervantinos.", "otros estudios peruanos.", "los estudios peruanos.", "dios estudios peruanos."
"dos estudios urbanos." » "los estudios urbanos."

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

• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"series estudios americanoss.\") OR (\"dos estudios urbanos.\"))) OR (\"tres estudios peruanos.\"))~".
• Removing quotes may allow a broader search: (((( series estudios americanoss. ) OR ( dos estudios urbanos. ))) OR ( tres estudios peruanos. ))~.
• Adding a wildcard symbol may retrieve word variants: (((("series estudios americanoss.") OR ("dos estudios urbanos."))) OR ("tres estudios peruanos."))*.