fortran 编写的巴特沃斯滤波程序，可以实现低通滤波，高通滤波，带通滤波，作者是李建平。-fortran program written Butterworth filter, can achieve low-pass filtering, high pass filter, band-pass filter, the author is Li Jianping.

SQL.21日自学通，SQL的自学书籍。全文通俗易懂，从简单的入手，慢慢带着我们进入MYSQL的知识殿堂，由浅及深，很适合初学者。-SQL.21 pass on self-learning, SQL self-study books. The full text of user-friendly, from the simple to start slowly with MYSQL knowledge as we enter the hall, by the shallow and deep,