In Windows:
Expand all all in project explorer is Shift+Numpad * (multiplty), as mentioned before.
Collapse all in project explorer is Ctrl+Shift+Numpad - (subtract).
Alternatively, you can just jam on the right arrow to expand to the bottom of a selected tree, or jam on the left arrow to collapse back up to the top.
If you want to see all the shortcuts available for the particular context you are in, type Ctrl+Shift+L.