Scientific principles often deal with universal features of existence but a scientific experiment only deals with particular instances of those laws. So how can scientific laws be deduced purely from experiment? Aren't there always going to be a priori deducible scientific principles?
You are right that scientific laws cannot be deduced from experiment. They can't be deduced a priori (from pure reason) either. Deduction is only one form of inference, however. Usually both induction (generalization) and abduction (inference to the best explanation) are used in science. Induction and abduction are more fallible than deduction. Although scientific theories can be confirmed and disconfirmed, they can't be proven deductively like a theorem in mathematics.