Note 6 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Stock-based compensation expense	$ 297,280	$ 113,444	$ 478,560	$ 304,824
Research and Development Expense [Member]
Stock-based compensation expense	59,567	91,896	92,567	188,426
General and Administrative Expense [Member]
Stock-based compensation expense	$ 237,713	$ 21,548	$ 385,993	$ 116,398

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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