You can't use Find/Replace for changing the display text of URLs - you need to edit the hyperlink's display text property. You could automate that with a macro such as:
Code:
Sub Demo()
Application.ScreenUpdating = False
Dim Hlnk As Hyperlink
For Each Hlnk In ActiveDocument.Hyperlinks
With Hlnk
If InStr(.TextToDisplay, "http://dx.doi") > 0 Then
.TextToDisplay = Split(.TextToDisplay, "http://dx.doi")(0) & "Full Text"
End If
End With
Next
Application.ScreenUpdating = True
End Sub
For PC macro installation & usage instructions, see:
http://www.gmayor.com/installing_macro.htm
For Mac macro installation & usage instructions, see:
http://word.mvps.org/Mac/InstallMacro.html