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."
"serie estudios peruanos." » "serie estudios americanos.", "serie estudios ensayos.", "serie estudios cervantinos."
"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 ("serie estudios peruanos."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("dos estudios urbanos.") OR ("tres estudios hispanicos."))) OR ("serie estudios peruanos."))*.
• Removing quotes may allow a broader search: (((( dos estudios urbanos. ) or ( tres estudios hispanicos. ))) or ( serie estudios peruanos. ))*.