At this site you can run your search.

The search can be done by Name, Nationality, Military rank, Identification number, Military unit, Branch of the Armed Forces, cause of death, date of death and Gravesite location.

Example:

Search by Name "João", just put the word "João".

Search by Date of death, just put "17 de Junho" or "Junho", for example.

Search by Name and Date of death, just put "João + Junho", for example. 

If you have any questions / suggestions please send an email to ahm@mail.exercito.pt.