Perhaps you should try some spelling variations:
primary animal » primates animal, primary aims, primary avian
primary tidal » primary total, primary tka, primary tool
pacs worlds » places worlds, laws worlds, class worlds
worlds does » world does, words does, worlds die
2001 pacs » 2000 pacs, 2002 pacs, 2003 pacs

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: 2001 pacs worlds does ((primary tidal) OR (primary animal)) regime.
• Adding a wildcard symbol may retrieve word variants: 2001 pacs worlds does ((primary tidal) or (primary animal)) regime*.