Perhaps you should try some spelling variations:
economics experiments » economic experiments, proteomics experiments, dynamics experiments
economic instruments » economics investments, astronomical instruments
boarding papers » working papers, boarding pass, boarding passes

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: oecd ((economics experiments) OR (economic instruments)) boarding papers.
• Adding a wildcard symbol may retrieve word variants: oecd ((economics experiments) or (economic instruments)) boarding papers*.