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."
"leyes estudios urbanos." » "series estudios urbanos.", "los estudios urbanos."
"tres estudios urbanos." » "otros estudios urbanos.", "los estudios urbanos.", "dos estudios urbanos."

You may be able to get more results by adjusting your search query.

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