求翻译：改革开放以来，我国中等职业教育事业有了很大发展，各类职业学校教育和职业培训取得显著成绩，为社会主义现代化建设培养了5000多万高素质劳动者和实用人才，到2005年，中等职业学校总计有14000多所。但是中职学校的管理体制却几经变化。是什么意思？

Since reform and opening up, great development has been China's secondary vocational education, significant achievements in the various types of vocational school education and vocational training, for socialist modernization construction to cultivate practical talents of high quality workers and more than 50 million by 2005, total more than more than 14,000 in secondary vocational schools. But the management system in secondary vocational school after several changes.