Journal articles can help you delve deeper into your topic than books and encyclopedias. Review articles will give you an overview of the state of a field over a period of time (pay attention to the publication date; they go out-of-date quickly). Research articles tell you exactly how a scientist performed their experiments and interpreted the results.
These resources will help you find journal articles in various fields related to your projects.
Discipline oriented search tools
Citation search tools
Companies tend to file for patents instead of publishing in journals because a patent grants the holder exclusive use of the technology described for a set period of time (usually 20 years). 60-80% of material in the patent literature is published nowhere else. It is important for a company to understand the scope of protected technology to know in which areas they can freely operate.
These patent resources are available at Penn.
These guides provide you with more in-depth information about various types of literature.