Summary of significant accounting policies (Details 3)	12 Months Ended
Dec. 31, 2025 USD ($)	Dec. 31, 2025 CNY (¥)	Dec. 31, 2024 CNY (¥)	Dec. 31, 2023 CNY (¥)
Disaggregation of Revenue [Line Items]
Total revenues	$ 60,045,146	¥ 422,045,319	¥ 541,487,420	¥ 580,016,414
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Total revenues	40,504,749	284,699,784	414,763,523	580,016,414
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Total revenues	$ 19,540,397	¥ 137,345,535	¥ 126,723,897

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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