Perhaps you should try some spelling variations:
"class communication issues" » "class community issues", "class communication india", "class communication united", "mass communication issues", "plans communication issues", "crisis communication issues"
"city cooperation studies" » "city cooperation series", "city cooperation sources", "city cooperation implies", "city corporation studies", "china cooperation studies", "city corporations studies"
"mars colonization still" » "mars colonization failed", "mars colonization israel", "mars colonization songs", "mrsa colonization still", "its colonization still", "jews colonization still"

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: (("class communication issues") or ((("mars colonization still") or ("city cooperation studies"))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: (("class communication issues") OR ((("mars colonization still") OR ("city cooperation studies")))).
• Removing quotes may allow a broader search: (( class communication issues ) or ((( mars colonization still ) or ( city cooperation studies )))).
• Adding a wildcard symbol may retrieve word variants: (("class communication issues") or ((("mars colonization still") or ("city cooperation studies"))))*.