Perhaps you should try some spelling variations:
"tres estudios americanos." » "tres estudios latinoamericanos.", "otros estudios americanos.", "los estudios americanos.", "dios estudios americanos."
"series estudios peruanoss." » "series estudios peruanos.", "serie estudios peruanoss.", "seis estudios peruanoss.", "leyes estudios peruanoss."
"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: (((("series estudios peruanoss.") or ("dos estudios urbanos."))) or ("tres estudios americanos."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("series estudios peruanoss.") OR ("dos estudios urbanos."))) OR ("tres estudios americanos."))*.
• Removing quotes may allow a broader search: (((( series estudios peruanoss. ) or ( dos estudios urbanos. ))) or ( tres estudios americanos. ))*.