Perhaps you should try some spelling variations:
"seis estudios americanos." » "seis estudios latinoamericanos.", "los estudios americanos.", "dos estudios americanos.", "dios estudios americanos."
"series estudios urbanos." » "serie estudios urbanos.", "leyes estudios urbanos.", "sociales 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.

• Performing a fuzzy search may retrieve terms with similar spellings: (((("series estudios urbanos.") OR ("tres estudios urbanos."))) or ("seis estudios americanos."))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (((("series estudios urbanos.") OR ("tres estudios urbanos."))) OR ("seis estudios americanos."))*.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"series estudios urbanos.\") OR (\"tres estudios urbanos.\"))) or (\"seis estudios americanos.\"))*".
• Removing quotes may allow a broader search: (((( series estudios urbanos. ) OR ( tres estudios urbanos. ))) or ( seis estudios americanos. ))*.