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Note 7 - Stockholders' Equity and Common Stock Warrants (Tables)
6 Months Ended
Jun. 30, 2023
Notes Tables  
Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]
   

Outstanding

 

Range of exercise

price per share

 

Expiration dates

Common stock warrants issued related to the May 2019 common stock offering

    27,648   $250.09 - $306.04  

May and December 2024

Common stock warrants issued related to the November 2019 common stock offering

    4,269     $17.51    

May 2024

Common stock warrants issued related to the December 2019 common stock offering

    6,264   $21.68 - $34.92  

December 2024 and June 2025

Common stock warrants issued related to the May 2020 common stock offering

    11,424     $65.65    

March 2025

Common stock warrants issued related to the May 2020 investor warrant exercise

    4,998     $29.7    

November 2025

Common stock warrants issued related to the February 2021 common stock offering

    33,649     $64.08    

February 2026

      88,252