Specifically academic alternative to LinkedIn It is well-known that LinkedIn is used by scholars too, but I think that the business-friendly structure of your profile-page makes it markedly less suitable for academic purposes. Is there a specifically academic website that includes the same characteristics as LinkedIn plus the possibility to add some more scholarly elements in your profile?
ResearchGate is more academic. It allows you to add your research publications, not just papers. It also has a stackexchange like section and a Jobs section, that features listings to research and advanced positions (PHD, Post-Doc) in academic institutions and in business.

As @StephanKolassa noted you should scout Research Gate before joining (follow the link in his comment), as any other alternative.