Both LionSearch and Google scholar allow you to search across a wide range of disciplines. Since homeland security is broad and is influenced by many forces, LionSearch or Google Scholar can be good starting points. LionSearch allows you to refine you search in ways not possible in Google Scholar, and it will connect you to Penn State full text resources in many formats. Google Scholar can connect you to full text journal articles available through the University Libraries by adding Penn State University under Settings > Library Links on the Google Scholar page.
These sources will help you locate both books and journal articles. LionSearch will also recomend subject databases to allow you to explore your subject in more depth.
For full text items, click the "full text online" link to go to the full text of the article.