Perhaps you should try some spelling variations:
"mars colonization references" » "mars decolonisation references", "mars polarization references", "mars salinization references", "mrsa colonization references", "its colonization references", "jews colonization references"
"de communication theory" » "de communication technology", "mobile communication theory", "online communication theory"
"_ colonization israel" » "_ communication israel", "_ colonization still", "_ colonization history", "_ decolonization israel", "decolonization _ israel"

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: (((("mars colonization references") OR ("_ colonization israel"))) OR ("de communication theory"))~.
• Removing quotes may allow a broader search: (((( mars colonization references ) or ( _ colonization israel ))) or ( de communication theory ))~.
• Adding a wildcard symbol may retrieve word variants: (((("mars colonization references") or ("_ colonization israel"))) or ("de communication theory"))*.