Note 6 - Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($)	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Stock-based compensation expense	$ 91,204	$ 324,667
Research and Development Expense [Member]
Stock-based compensation expense	13,596	16,372
General and Administrative Expense [Member]
Stock-based compensation expense	$ 77,608	$ 308,295

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
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