The National Digital Library is a digital library that aims to provide convenient online reading and borrowing services for the public. Its main feature is to realize the remote access and utilization of digital resources through Internet technology, including books, journals, newspapers, electronic documents, technical standards and other digital resources. The digital resources of the National Digital Library could be accessed in many ways, including mobile applications, websites, clients, and so on. Through these channels, users could obtain the reading rights of various resources in the digital library and read according to their own needs. However, if a user encounters the problem of not being able to access books in the digital library, it may be due to one of the following reasons: 1. The book has been collected by the National Digital Library, but the user does not have the right to read it. 2. The user's region does not have the service of the National Digital Library. You need to visit the local digital library. 3. The user encountered network problems when using the digital library and could not access it. If users encounter the above problems, they can contact the local digital library staff for help and solutions.