It is possible to do full text searching several ways in the Digital Library.
The example below searches for documents that mention Security Council resolution 1325 (2000) on women, peace and security.
After a simple search for keywords, toggle the Fulltext Search ON
Alternatively, in the simple search, use the command fulltext:"key words"
Another option: in the advanced search, select fulltext from the dropdown then click the Search button (NOTE: this is not working well)
More information on Fulltext searching can be found in the Help text.