These tools can help you determine if there are free online (legal!) versions of scholarly articles you want.
Limit by domain name to see results only from .gov sites. Example: robotics site:.gov
Use quotation marks to search for logical phrases. Example: "lesson plan"
Be specific. If you want a curriculum aligned with standards, include those terms in your search. Example: robotics curriculum "standards-aligned" OR robotics curriculum NGSS
Many government agencies have resources for educators (selections linked below). All federal agencies are required to have a website for youth.