Perhaps you should try some spelling variations:
"series estudios peruanoss." » "series estudios peruanos.", "serie estudios peruanoss.", "leyes estudios peruanoss.", "sociales estudios peruanoss."
"seis estudios urbanos." » "seis estudio urbanos.", "seis estudios peruanoss.", "seis estudios hispanos.", "los estudios urbanos.", "dos estudios urbanos.", "dios estudios urbanos."
"tres estudios urbano." » "tres estudio urbano.", "tres estudios peruanos.", "tres estudios hispano.", "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: (((("series estudios peruanoss.") OR ("seis estudios urbanos."))) OR ("tres estudios urbano."))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"series estudios peruanoss.\") OR (\"seis estudios urbanos.\"))) OR (\"tres estudios urbano.\"))*".
• Removing quotes may allow a broader search: (((( series estudios peruanoss. ) OR ( seis estudios urbanos. ))) OR ( tres estudios urbano. ))*.