Perhaps you should try some spelling variations:
"seis estudios peruanos." » "seis estudios urbanos.", "seis estudios americanos.", "seis estudios ensayos.", "los estudios peruanos.", "dos estudios peruanos.", "dios estudios peruanos."
"tres estudios hispanic." » "tres estudios hispanicos.", "tres estudios hispano.", "tres studies hispanic.", "otros estudios hispanic.", "los estudios hispanic.", "dos estudios hispanic."
"series estudio urbano." » "series estudios urbano.", "serie estudio urbano.", "serie estudios urbano.", "series estudios urbanos.", "series espacio urbano."

Try widening your search to All Fields.

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 peruanos.") or ("series estudio urbano."))) or ("tres estudios hispanic."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("seis estudios peruanos.") OR ("series estudio urbano."))) OR ("tres estudios hispanic.")).
• Removing quotes may allow a broader search: (((( seis estudios peruanos. ) or ( series estudio urbano. ))) or ( tres estudios hispanic. )).
• Adding a wildcard symbol may retrieve word variants: (((("seis estudios peruanos.") or ("series estudio urbano."))) or ("tres estudios hispanic."))*.