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