If you got to Mono’s Options, at keyboard shortcuts, there is one for opening Unity’s API Reference (ctrl+’ by default). Is there some way to get the same result in Visual Studio? This has been asked before (here), but I don’t know if Unity started to support VS more since 2011.
If anyone still cares, there is a free Visual Studio extension called Unity VS that does this apart from other stuff.
You need VS Community edition or Pro +.