1. How is Google Scholar compared to other academic search engines and catalogues such as ScienceDirect, Scopus, and universities' own online catalogues--in terms of the following?

 - **comprehensiveness of search** (i.e. can fetch all the ever published relevant titles, whether the user have access to full-texts or not)
 - **accuracy and precision of results**
 - **advanced search features**
 - **usability**

2. Are there good reasons for (or against) using Google Scholar as the **only** *literature search tool* for PhD research?

3. Does the answer of (2) depend on the research discipline?