Yes, there are generally no strict professional restrictions on applying for a doctorate. At present, the entrance examination for doctoral students in most universities and research institutes in China is generally three courses, 1 foreign language +2, and the examination subjects are entirely independent propositions of the schools, so the policies of different schools may be very different. Candidates with the same academic ability generally have to take the professional course of 1-2. A few schools also require interdisciplinary students to take 1-2 related professional courses, depending on the school you apply for. It is recommended that you read the enrollment brochure and precautions before the exam, and you must contact your tutor in advance to ask about relevant matters. If you succeed in studying for a doctorate, it seems like three years; if you fail, it seems like five years, such as failing a thesis. I wish the landlord all the best!