Summary of significant accounting policies (Details 2)	6 Months Ended
Jun. 30, 2026 USD ($)	Jun. 30, 2026 CNY (¥)	Jun. 30, 2025 CNY (¥)
Disaggregation of Revenue [Line Items]
Total revenues	$ 20,071,752	¥ 136,706,698	¥ 188,112,127
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Total revenues	10,903,118	74,260,052	142,800,304
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Total revenues	$ 9,168,634	¥ 62,446,646	¥ 45,311,823

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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+ Details

- 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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+ Details