How to include angular service and controller files dynamically?

I want to make service and controller in seperate files but I don't want to load those scripts all time in index.html. If I have 20 controllers and 20 services, I need to write 40 lines of script tag in index html to be able to use services and controllers in angular. How can I load them without writing too many script tags in index.html? Am I wrong to seperate those files?

Sorry for not good English.