Research on the entrepreneurship of returning migrant workers in the Three Gorges Reservoir area 并列题名：Research on the entrepreneurship of returning migrant workers in the Three Gorges Reservoir area research on urban entrpreneurship of migrant workers in transition period Study on the "public security space units"in urban area of the three gorges reservoir area Mechanism of entrepreneurship growth for returning migrant workers under the perspective of location difference 并列题名：Mechanism of entrepreneurship growth for returning migrant workers under the perspective of location difference