Perhaps you should try some spelling variations:
"particles acceleration" » "particle acceleration", "particle accelerators", "parallel acceleration"
"particle accelerator" » "particle accelerators", "particle acceleration"
"particle penetration" » "particle generation", "particle concentration", "particle separation"

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