Perhaps you should try some spelling variations:
"ground penetration radar" » "ground penetrating radar", "grout penetration radar", "rod penetration radar", "ground penetrating radars", "ground penetration rate"
"ground penetration raman" » "ground penetrating raman", "grout penetration raman", "rod penetration raman", "ground penetration human", "ground penetration rate", "ground penetration bmn"
"cloud penetration raman" » "cloud penetration human", "cloud penetration rate", "cloud penetration bmn", "cloud generation raman", "cloud federation raman", "cloud registration raman"

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