Perhaps you should try some spelling variations:
"critical issues in environmental degradation" » "critical issues in environmental education", "practical issues in environmental degradation"
"Critical issues in environmental regulation" » "Critical issues in environmental education", "Critical issues in environmental remediation"
"Critical issues in environmental radiation" » "Critical issues in environmental remediation", "Critical issues in environmental evaluation", "Critical issues in environmental adaptation"
"critical issues in environmental taxation" » "critical issues in environmental variation", "critical issues in environmental action", "critical issues in environmental evaluation", "practical issues in environmental taxation"

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: (("critical issues in environmental taxation") OR ((((("Critical issues in environmental radiation") OR ("Critical issues in environmental regulation"))) OR ("critical issues in environmental degradation")))).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((\"critical issues in environmental taxation\") or (((((\"Critical issues in environmental radiation\") OR (\"Critical issues in environmental regulation\"))) or (\"critical issues in environmental degradation\"))))".
• Removing quotes may allow a broader search: (( critical issues in environmental taxation ) or ((((( Critical issues in environmental radiation ) OR ( Critical issues in environmental regulation ))) or ( critical issues in environmental degradation )))).
• Adding a wildcard symbol may retrieve word variants: (("critical issues in environmental taxation") or ((((("Critical issues in environmental radiation") OR ("Critical issues in environmental regulation"))) or ("critical issues in environmental degradation"))))*.