WinPhone 8.1 Project does not Support System.Web ? System.Threading;

Hello everyone,

We are adding to our projects Windows 8.1 Phone support but after create the project i am surprise with the point that WP8.1 does not Support many many libs like:

System.Web,
System.Threading,
System.IO.FILE,
System.IO.Path,
System.Type,
System.Environment.SpecialFolder, GetFolderPath
string.Normalize,

and many many others...

i am using a SHARED PROJECT....
someone know how can i work?

Thank you all