Probably the best database to use to get started on your biology research is ScienceDirect.
Before you get started searching for science articles, it's important to make a distinction between reference sources and research sources.
A reference resource can give you basic, known information about a subject.
Example: Search for 'enzyme' in AccessScience. You'll see there are many results explaining how an enzyme works, the chemical structure, classifications, etc.
Peer-reviewed research articles offer us some new insight into biology, and often do not contain the basic information you might find in reference resources.
Example: Search in ScienceDirect for 'enzyme'. You'll see that your results list gives you both 'Review' articles and 'Research' articles.
Review articles typically synthesize the information on a topic (sometimes very narrow or specific topics.)
Research articles convey the hypothesis, method, and conclusion from specific experiments.
Each will provide you with a collection of citations. If you see a citation reference you think will be useful in your own work, look it up in Spartan Search