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