Perhaps you should try some spelling variations:
"seis estudios cervantinos." » "seis estudios mercantiles.", "seis estudios criticos.", "seis estudios andinos.", "los estudios cervantinos.", "dos estudios cervantinos.", "dios estudios cervantinos."
"series estudios urbanos." » "serie estudios urbanos.", "tres estudios urbanos.", "sociales estudios urbanos."
"leyes estudios urbanos." » "los estudios urbanos.", "tres estudios urbanos."

Try widening your search to All Fields.

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