Perhaps you should try some spelling variations:
"particle acceleration" » "particle accelerators"
"particle accelerator" » "particle accelerators"
"naturally accelerate" » "naturally regenerated", "partially accelerated"

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