Perhaps you should try some spelling variations:
integration theory » integration through, information theory, innovation theory
internet services » internet service
duty integration » dutch integration, data integration, why integration
import duty » import duties
13 internet » 1.3 internet, 1 internet, 11 internet
support 13 » support 1.3, support 3, support 1

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( import duty integration theory. ) or ( support 13 internet services. ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( import duty integration theory. ) OR ( support 13 internet services. )).
• Adding a wildcard symbol may retrieve word variants: (( import duty integration theory. ) or ( support 13 internet services. ))*.