Perhaps you should try some spelling variations:
"seis estudios americanos." » "seis estudios latinoamericanos.", "los estudios americanos.", "dos estudios americanos.", "dios estudios americanos."
"seis estudios peruanos." » "seis estudios ensayos.", "seis estudios cervantinos.", "los estudios peruanos.", "dos estudios peruanos.", "dios estudios peruanos."
"series estudios urbanos." » "serie estudios urbanos.", "tres estudios urbanos.", "leyes 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 urbanos.") or ((("seis estudios peruanos.") OR ("seis estudios americanos."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("series estudios urbanos.") OR ((("seis estudios peruanos.") OR ("seis estudios americanos."))))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"series estudios urbanos.\") or (((\"seis estudios peruanos.\") OR (\"seis estudios americanos.\"))))*".
• Removing quotes may allow a broader search: (( series estudios urbanos. ) or ((( seis estudios peruanos. ) OR ( seis estudios americanos. ))))*.