If you are looking for a free product, this guide considers Microsoft Academic Search to be a better choice than Google Scholar or Google Books. It is more accurate, more reliable, and the universe of publications is better defined.
".... a free service... find academic content, researchers, institutions, and activities.... indexes not only , it also surfaces key relationships between and among subjects, content, and authors..." This is a subset of the content available in Bing, and concentrates exclusively on scholarly works.
Use "Advanced Search" or the results may be nonsense.
One strong point of this tool is that there is some attempt to resolve the author disambiguation issue (see "Considerations"). If you choose "Advanced Search" and enter an author's name, you will be given a list of variants of the name--e.g., first/last, first/middle/last, first initial/last, first/different middle/last, etc. Each of these names is also affiliated with an "Interest" which eliminates the need to weed out Brett Blaze, the Nanotechnology scientist, from B. Blaze, the scholar in Musicology. It is possible, though, for the same relevant author to be listed more than once (see below).
Another advantage of this tool is that the results are easy to manipulate, the display is clear and clean, it has good sorting features, export capabilities to bibliographic software, and is in general easy to use.
Some cautionary notes: