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