Note 13 - Capital Stock (Details Textual) - USD ($)					12 Months Ended
	Oct. 27, 2021	Apr. 08, 2021	Mar. 19, 2021	Sep. 23, 2020	Jul. 31, 2021	Jul. 31, 2020	Apr. 30, 2021	Jul. 31, 2019
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)					$ 1.90	$ 2.03		$ 1.94
Share Price (in dollars per share)				$ 0.96
Class of Warrant or Right, Fair Value Per Share (in dollars per share)				$ 0.23
Proceeds from Warrant Exercises					$ 3,588,291	$ 0
Warrant Issued with September 2020 Offering [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)				1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)				$ 1.80
Warrants and Rights Outstanding, Term (Month)				2 years
Warrant Issued to Agents [Member]
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)		1
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)		$ 4.125		$ 1.80
Warrants and Rights Outstanding, Term (Month)		5 years		2 years
Class of Warrant or Right, Number of Securities Called by Warrants or Rights (in shares)		181,818		583,333
Class of Warrant or Right, Fair Value Per Share (in dollars per share)							$ 1.80
September 2020 Offering [Member]
Number of Units Issued During Period (in shares)				12,500,000
Shares Issued, Price Per Share (in dollars per share)				$ 1.20
Proceeds from Issuance or Sale of Equity, Total				$ 15,000,000
Number of Shares per Unit Issued (in shares)				1
Number of Warrants per Unit (in shares)				0.5
The 2020 At-the-market Offering [Member]
Stock Issued During Period, Shares, New Issues (in shares)					13,668,906
Proceeds from Issuance of Common Stock, Net					$ 29,320,949
The 2020 At-the-market Offering [Member] | Weighted Average [Member]
Shares Issued, Price Per Share (in dollars per share)					$ 2.19
Direct Offering [Member]
Shares Issued, Price Per Share (in dollars per share)		$ 3.30	$ 3.05
Stock Issued During Period, Shares, New Issues (in shares)		3,636,364	10,000,000
Proceeds from Issuance of Common Stock, Net		$ 11,315,966	$ 29,083,710
The 2021 At-the-market Offering [Member]
Shares Issued, Price Per Share (in dollars per share)					$ 2.78
Stock Issued During Period, Shares, New Issues (in shares)					2,265,700
Proceeds from Issuance of Common Stock, Net					$ 6,156,690
The 2021 At-the-market Offering [Member] | Subsequent Event [Member]
Shares Issued, Price Per Share (in dollars per share)	$ 3.09
Stock Issued During Period, Shares, New Issues (in shares)	20,743,878
Proceeds from Issuance of Common Stock, Net	$ 62,671,103