The ability to search the archive of an alert is a feature available to Readers as well as Administrators. 

1. Login to Linex
2. From the My Alerts page (Under your name in the top navigation bar > My Alerts) click on the title of the alert that you want to search across. You will get a pop up showing you the most recent alert, with a drop down menu giving you access to the last twenty publishes of that alert.
3. In the top right is a Search button, select this.
4. You are now in the Linex search page, where you can apply keyword searches and filters across all the items that have been published in that alert for the past few months.