Perhaps you should try some spelling variations:
values research » issues research, changes research
central values » central value, central valley, control values
research nejm » research new, research need, research needs
from surveys » from survey, firm surveys, force surveys
central 2 » central _, central 1, central 7

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

• Performing a fuzzy search may retrieve terms with similar spellings: (( central 2 research nejm series. ) or ( central values research from surveys. ))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (( central 2 research nejm series. ) OR ( central values research from surveys. )).
• Adding a wildcard symbol may retrieve word variants: (( central 2 research nejm series. ) or ( central values research from surveys. ))*.