There is no special exemption where academic work is unprotected by copyright. You can quote from academic sources to the same extent that you can copy from non-academic sources, without getting permission. In fact, it is legally impossible to tell if a source of "academic" versus "non-academic". Attribution is not particularly relevant for copyright, what matters is permission (when required). It may be that a copyright holder will grant permission for an extensive quote provided you attribute the source, and it may be that academic publishers or authors are more willing to grant permission than other publishers / authors. On the other hand, many academic works are very expensive, so that distributing the text for free may have more "effect on market", and may result in disinclination to grant permission to quote. On the third hand, such quotes are more likely to be squarely directed at the "commentary" motivation behind fair use law. The point here is that there isn't a special law about just academic sources.