Perhaps you should try some spelling variations:
"ground penetration raman" » "ground penetrating raman", "grout penetration raman", "cloud penetration raman", "ground penetration human", "ground penetration rate", "ground penetration bmn"
"a penetration radar" » "a penetrating radar", "a penetrating radars", "a penetration rate", "_ penetration radar"
"cone penetration radar" » "cone penetrating radar", "cone penetrating radars", "cone penetration rate"

Try widening your search to All Fields.

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: (("ground penetration raman") OR ((("a penetration radar") OR ("cone penetration radar")))).
• Removing quotes may allow a broader search: (( ground penetration raman ) or ((( a penetration radar ) or ( cone penetration radar )))).
• Adding a wildcard symbol may retrieve word variants: (("ground penetration raman") or ((("a penetration radar") or ("cone penetration radar"))))*.