Can a person cash in their 401K anytime they want? ?

The reason I ask is because, at this time, there isn't much in there and I'm out of work at the moment. Between permanent jobs I am substituting but in the last 2 weeks I haven't been called at all. The small amount I have in my 401K would sustain me until a permanent job comes along. I will be back to work steadily within the next 2 to 2 1/2 weeks.