In my opinion the @ would usually be spelled out as 'res'. For example, you should be able to search for an Anni with 20@ when you type in 20res instead of 20@.
Here is a list of commonly used terms:
https://forums.d2jsp.org/info.php?p=53Quote (Common Terms Used on d2jsp and battle.net)
4.Diablo II Terms
Res - Resistance
Additional info on the search feature:
https://forums.d2jsp.org/info.php?p=31