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Note 7 - Stockholders' Equity and Common Stock Warrants (Tables)
3 Months Ended
Mar. 31, 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