Perhaps you should try some spelling variations:
bilingual acquisition » biosignal acquisition, signal acquisition, initial acquisition
digital acquisition » signal acquisition, lexical acquisition, biosignal acquisition
language acquistion » language question, language action, language attrition
langage acquisition » image acquisition, land acquisition, planning acquisition

Try widening your search to All Fields.

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: %((((bilingual acquisition) OR (digital acquisition))) OR (((((language acquistion) OR (langage acquisition))) OR (language acquisition)))) AND development%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%((((bilingual acquisition) or (digital acquisition))) or (((((language acquistion) OR (langage acquisition))) or (language acquisition)))) and development%22".
• Adding a wildcard symbol may retrieve word variants: %((((bilingual acquisition) or (digital acquisition))) or (((((language acquistion) OR (langage acquisition))) or (language acquisition)))) and development%22*.