Perhaps you should try some spelling variations:
"seis estudios americanoss." » "seis estudios americanos.", "seis estados americanos.", "seis estudios africanos.", "los estudios americanoss.", "dios estudios americanoss.", "pons 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.

• Performing a fuzzy search may retrieve terms with similar spellings: (((("seis estudios americanoss.") or ("dos estudios urbanos."))) or ("tres estudios peruanos."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("seis estudios americanoss.") OR ("dos estudios urbanos."))) OR ("tres estudios peruanos."))*.
• Removing quotes may allow a broader search: (((( seis estudios americanoss. ) or ( dos estudios urbanos. ))) or ( tres estudios peruanos. ))*.