One of the two Tübingen catalogues, the "Catalog Plus", allows the search for different aspects to be more and more restricted. You can take advantage of this by starting relatively generally and then restricting it thematically under "subjects". It is also quite useful to get an overview of the available e-books with the help of this catalogue: Just enter "sociology" once. More than 100,000 entries. Not very useful? Simply select then the item "Electronic Resource" under "Types of Media" and there will be a little more than 5,000 entries, sorted chronologically. Even this listing is quite useful - if you want to narrow it down further, then the "Subjecs" are available again below.