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