Perhaps you should try some spelling variations:
"parallel acceleration" » "particle acceleration", "parallel generation", "parallel application"
"particle accelerator" » "particle acceleration"
"particle accelerators" » "particle accelerations", "particle accelerated", "particle accelerate", "particle accelerating"

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