Im assuming you have manual, not power brakes. But yes you should be able to lock them up but it does take a good hard stomp on the pedal to do so.
This may sound stupid but have you tried to lock them up on wet pavement?
Can you give us more info? Did you do a brake job? What did you replace?
If you didn't do a brake job then it could be the condition of your shoes and drums, Air in the lines, Old gummed up brake fluid, Old brake hoses that could expand when you apply the brakes.
If you give more info we can go from there.