Perhaps you should try some spelling variations:
"retardo mental en educacion especial" » "retardo mental en educacion aspectos", "retardo mental en educacion espana", "retraso mental en educacion especial", "retardo mental de educacion especial", "retardo ambiental en educacion especial"
"retardo mental la educacion especial" » "retardo mental la educacion aspectos", "retardo mental la educacion espana", "retraso mental la educacion especial", "retardo menta la educacion especial", "retardo mental a educacion especial", "retardo mentales la educacion especial"

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: (("retardo mental en educacion especial") OR ("retardo mental la educacion especial"))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"retardo mental en educacion especial\") OR (\"retardo mental la educacion especial\"))".
• Removing quotes may allow a broader search: (( retardo mental en educacion especial ) OR ( retardo mental la educacion especial )).
• Adding a wildcard symbol may retrieve word variants: (("retardo mental en educacion especial") OR ("retardo mental la educacion especial"))*.