Both Google Books and Amazon offer previews or selected pages of many books online. While these are hardly substitutes for a complete e-book, they can be helpful in a couple of ways:
These previews usually include the tables of contents of books. That can be helpful in identifying chapters or sections of books that will be most useful to a particular need. It is sometimes possible to obtain individual chapters via interlibrary loan even if we cannot obtain the full book. (Publisher's sites often include tables of contents for their books as well.)
It is always possible, of course, that the selection or portion of a particular book that is made available will at least partially provide information useful to your needs.
ProQuest Dissertations & Theses
Many scholarly books have their roots in the authors' doctoral dissertations. While not the same thing as an edited, curated, book, such dissertations can contain useful information on the same topic. The BU database ProQuest Dissertations & Theses contains PDFs of thousands of such dissertations. Search for a book's author by name to see if there is something there that will be of use to you
Ask a Librarian
If a resource you would like to access is not available, Ask a Librarian. Our BU Librarians may be able to point you to other resources that will help fulfill your information need.