Perhaps you should try some spelling variations:
"dios estudios etnicos." » "dios estudios criticos.", "dios estudios biblicos.", "los estudios etnicos.", "otros estudios etnicos.", "altos estudios etnicos."
"series estudio urbano." » "series estudios urbano.", "serie estudio urbano.", "serie estudios urbano.", "series estudios urbanos.", "series espacio urbano."
"dos estudios ensayos." » "los estudios ensayos."

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

• Performing a fuzzy search may retrieve terms with similar spellings: (("series estudio urbano.") or ((("dos estudios ensayos.") or ("dios estudios etnicos."))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("series estudio urbano.") OR ((("dos estudios ensayos.") OR ("dios estudios etnicos."))))*.
• Removing quotes may allow a broader search: (( series estudio urbano. ) or ((( dos estudios ensayos. ) or ( dios estudios etnicos. ))))*.