Perhaps you should try some spelling variations:
"tres estudios peruanoss." » "tres estudios peruanos.", "tres estudios urbanos.", "otros estudios peruanoss.", "los estudios peruanoss.", "dos estudios peruanoss."
"series estudios urbano." » "serie estudios urbano.", "leyes estudios urbano.", "sociales estudios urbano.", "series estudios urbanos.", "series estudio urbano.", "series estudios peruanos."
"seis estudios urbano." » "seis estudios urbanos.", "seis estudio urbano.", "seis estudios peruanos.", "los estudios urbano.", "dos estudios urbano.", "dios estudios urbano."

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("tres estudios peruanoss.") or ((("series estudios urbano.") OR ("seis estudios urbano."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("tres estudios peruanoss.") OR ((("series estudios urbano.") OR ("seis estudios urbano.")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"tres estudios peruanoss.\") or (((\"series estudios urbano.\") OR (\"seis estudios urbano.\"))))".
• Removing quotes may allow a broader search: (( tres estudios peruanoss. ) or ((( series estudios urbano. ) OR ( seis estudios urbano. )))).
• Adding a wildcard symbol may retrieve word variants: (("tres estudios peruanoss.") or ((("series estudios urbano.") OR ("seis estudios urbano."))))*.