Perhaps you should try some spelling variations:
training resources » learning resources, teaching resources
training sources » training courses, training resource, training course
learning survey » learning curve, learning curves, hearing survey
survey series » surveys series
4 learning » 2 learning, 3 learning

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( wbi ((training sources) OR (training resources)) series. ) or ( 4 learning survey series. ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( wbi ((training sources) OR (training resources)) series. ) OR ( 4 learning survey series. )).
• The words AND, OR and NOT may confuse the search; try adding quotes: "(( wbi ((training sources) OR (training resources)) series. ) or ( 4 learning survey series. ))".
• Adding a wildcard symbol may retrieve word variants: (( wbi ((training sources) OR (training resources)) series. ) or ( 4 learning survey series. ))*.