Perhaps you should try some spelling variations:
closed environment » cloud environment, crowded environment, cloud environments
field environment » food environment, world environment, lipid environment
policy papers » policy paper, policy part

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: ((field environment) OR (closed environment)) policy papers.
• Adding a wildcard symbol may retrieve word variants: ((field environment) or (closed environment)) policy papers*.