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"
"drug penetration radar" » "drug penetrating radar", "drug penetrating radars", "drug penetration rate", "drug concentration radar", "a penetration radar"
"cone penetration radar" » "cone penetrating radar", "cone penetrating radars", "cone penetration rate", "a penetration radar"

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 ((("drug penetration radar") OR ("cone penetration radar")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"ground penetration raman\") or (((\"drug penetration radar\") OR (\"cone penetration radar\"))))".
• Removing quotes may allow a broader search: (( ground penetration raman ) or ((( drug penetration radar ) OR ( cone penetration radar )))).
• Adding a wildcard symbol may retrieve word variants: (("ground penetration raman") or ((("drug penetration radar") OR ("cone penetration radar"))))*.