Perhaps you should try some spelling variations:
"particle concentrations" » "particle concentration", "particle correlations", "particle penetration"
"particle accelerator" » "particle acceleration"
"particle accelerators" » "particle accelerations", "particle accelerated", "particle acceleration", "particle accelerate"

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: (("particle accelerator") OR ((("particle accelerators") OR ("particle concentrations")))).
• Removing quotes may allow a broader search: (( particle accelerator ) or ((( particle accelerators ) or ( particle concentrations )))).
• Adding a wildcard symbol may retrieve word variants: (("particle accelerator") or ((("particle accelerators") or ("particle concentrations"))))*.