Should I apply for a visa before leaving Beijing or I can obtain a visa when entering ISTANBUL ?

Dear Sir

I will be traveling to ISTANBUL on the 21st of March (from Beijing to Istanbul / Transit on the 22nd March ) and will spend 3 days there on the way back to Beijing (from 01 to 03 APRIL 2012).
I am a Mauritian Citizen from MAURITIUS ISLAND, and hold a Mauritian Passport.

Should I apply for a visa before leaving Beijing or I can obtain a visa when entering ISTANBUL ?

I Live in Beijing and have a resident and work permit.

Thanks beforehand and waiting for your reply.

Best regards