Yes this is possible with the following steps:
- Set up a keyword search on 'X-ray' and save the hitlist before running the search by entering a name in the Save in hitlist box.
- Conduct a second keyword search on 'NMR' and again save the hitlist.
- Click on the "Hitlists" button in the top menu bar. Go to "Protein Set 1" and select the X-ray hitlist, then for "Protein Set 2" select the NMR hitlist. Change the hitlist operation to "MINUS". This then gives a hitlist consisting of proteins containing the word X-ray and not NMR.