Use OR to find publications that match one or both search terms. OR is used to widen your search (OR=mORe).
Example: exp influenza/ OR influenza.ti,ab,kf. OR flu.ti,ab,kf.
Use AND to find publications that match both search terms.
When looking for articles on gene therapy for Duchenne muscular dystrophy, use: Duchenne muscular dystrophy/ AND exp gene therapy/
or even better: (Duchenne muscular dystrophy/ OR duchenne.ti,ab,kf.) AND (exp gene therapy/ OR gene* therap*.ti,ab,kf.)
Use NOT to exclude all publications that match a certain search term. If you are looking for articles on breast cancer, but not on breast cancer metastases, you could use: exp breast cancer/ NOT breast metastasis/
Note that articles covering both breast cancer (as a primary tumour) and breast cancer metastases will now also be excluded.
ADJn (for expert searchers)
The ADJn (adjacency) operator finds records that contain your search terms (in any order) within a specified number (n) of words of each other. The ADJn operator is useful when there is no exact terminology for a concept.
Example: (quality ADJ1 life) finds 'quality life' and 'life quality'.
ADJ2 allows for one word between the two search terms. (quality ADJ2 life) finds 'life quality', 'quality of life', for instance.
When using multiple boolean operators, make sure that the ( ) are in the correct place. In the example below (to find articles on gene therapy for Duchenne) you can see that placing the brackets in the wrong position will result in a very different number of results.