Earlier this year, we introduced the Search Options panel in web search, making it easier to perform queries that limit results to a particular type of content- such as videos, forums, and reviews. We are now making it even easier to find books and magazines by making all of the content on Google Books searchable using the Search Options panel.
This will provide easier access to books and magazines by letting you slice and dice your results with certain characteristics. For example, you can now search for only books or magazines or for only content that you can preview in Google Books.
Try this yourself when you search the web using Google by clicking "Show options..." and selecting "Books".
Please note that this is currently only available in the United States, but we look forward to making this available elsewhere in the future.