If you have multiple Datasets you can search across all your data and all your Concepts using a federated search.
You can start a federated search from the project homepage, where all its Datasets are listed, by typing into the search bar at the top of the page. This will let you select a Concept, or if you hit return it will invoke a detailed full text search.
Alternatively you can click the arrow button highlighted below without typing in the search bar:
In this case you will be presented with a search page that lets you facet across all your data and build a search from scratch: