Textbooks Algebra 134 Mathematics 87 Chemistry 82 Calculus 76 Psychology 74 Physics 46 Problems, exercises, etc 46 Trigonometry 42 Statistics 36 Research 31 Mathematical statistics 29 Methodology 27 Chemistry, Organic 26 Differential equations 26 Biochemistry 24 History 24 Computer networks 23 Electronics 22 Mathematical models 21 Graphic methods 19 Study and teaching 19 Management 18 Differential equations, Partial 17 Functions 16 Thermodynamics 16 Algebras, Linear 15 Astronomy 14 Counseling 14 Developmental psychology 14