5	NATURAL SCIENCES. MATHEMATICS. MEDICINE
50	NATURAL SCIENCES
50.1	Environmental protection. Nature conservation
50.11	Endangered species. Natural reserves
50.12	Air protection
50.13	Water protection
50.14	Soil protection
50.19	Animal protection
51	MATHEMATICS
51.1	Theory of numbers. Arithmetic. Algebra
51.2	Geometry
51.3	Analysis
51.4	Probability calculus
51.5	Special calculation methods
51.8	Mathematics as a hobby and pastime
52	ASTRONOMY. GEODESY
52.1	Theoretical astronomy. Celestial mechanics
52.2	Universe. Stars. Stellar systems
52.21	The solar system
52.3	Astronomical instruments
52.4	Space research. Space flights
52.6	Geodesy. Land surveying. Mapping
52.8	Chronology
53	PHYSICS
53.1	General and theoretical physics
53.11	Theory of relativity
53.12	Nuclear physics. Atomic physics. Molecular physics
53.13	Quantum theory. Quantum mechanics
53.3	Mechanics
53.4	Acoustics. Mechanical vibrations
53.5	Thermology
53.6	Optics. Radiology
53.66	Chromatics
53.7	Electricity. Magnetism
53.8	Physics as a hobby and pastime
54	CHEMISTRY
54.1	Theoretical and physical chemistry
54.2	Inorganic chemistry
54.3	Organic chemistry. Chemistry of plastics
54.4	Analytical chemistry
54.8	Chemistry as a hobby and pastime
55	PHYSICAL GEOGRAPHY. GEOLOGY
55.2	Geology. Geomorphology
55.3	Mineralogy. Petrology. Crystallography
55.4	Palaeontology
55.5	Meteorology. Climatology
55.6	Hydrology
56	BIOLOGY
56.1	Cytology. Cell biology
56.2	Biochemistry. Biophysics. Molecular biology
56.3	General microbiology
56.4	Genetics
56.41	Theory of evolution. Evolutionary biology
56.411	Biological anthropology
56.8	Nature handbooks
56.9	Ecology. Biogeography
57	BOTANY
57.1	Vascular plants
57.11	Trees. Bushes
57.3	Algae. Lichen. Fungi. Bryophytes
57.8	Plant anatomy. Plant physiology. Plant morphology
57.9	Plant ecology. Plant geography
58	ZOOLOGY
58.1	Vertebrates
58.11	Mammals
58.12	Birds
58.13	Reptiles. Amphibians
58.14	Fishes
58.2	Invertebrates
58.21	Insects
58.8	Animal anatomy. Animal physiology. Animal morphology
58.9	Animal ecology. Etology. Animal geography
59	MEDICINE. HEALTH CARE
59.1	Medical biology
59.11	Human anatomy
59.12	Human physiology
59.13	Medical microbiology. Immunology
59.2	General health care
59.21	Nursing science. Nursing work. Nursing staff
59.22	Care institutions
59.221	Hospital technology
59.23	Prevention of accidents. First aid
59.24	Social medicine. Environmental medicine
59.241	Occupational health. Student health. The work of a school nurse
59.27	Forensic medicine
59.28	Sports medicine
59.3	Personal health care
59.31	Beauty care. Looks
59.32	Baths. Sauna
59.33	Relaxation. Sleep. Insomnia
59.34	Nutrition. Diets
59.35	Sexology
59.4	Methods of treatment
59.41	Physiotherapy. Physiological treatments
59.411	Acupuncture. Acupressure. Zone therapy
59.42	Aids and equipment for sick and disabled persons
59.43	Pharmacotherapy. Pharmacology
59.48	Surgery. Surgical treatment
59.49	Terminal care
59.5	Organs. Diseases
59.51	Infectious diseases
59.511	Venereal diseases
59.52	The skeleto-muscular system. Skeleto-muscular diseases
59.53	Viscera. Internal diseases
59.532	Respiratory organs. Respiratory diseases
59.533	Endocrinal glands. Metabolic diseases.
59.534	Blood. Blood diseases. The circulatory system. Diseases of the circulatory system
59.535	The digestive system. Diseases of the digestive system
59.536	Urinary organs. Diseases of the urinary system
59.54	Cancerous diseases
59.55	Nervous system. Neurology
59.56	Psychiatry
59.561	Mental health disorders
59.5612	Eating disorders
59.562	Psychotherapy. Mental health care
59.5622	Psychoanalysis
59.5623	Family, group and relational therapy
59.5624	Creativity and activity therapy
59.563	Mental health. Emotional disorders
59.564	Crisis psychology. Disaster psychology. Grief work
59.565	Suicides and their prevention
59.567	Use of intoxicants and stimulants
59.5671	Smoking
59.5672	Alcoholism. Alcohol use
59.5673	Narcotic addiction
59.57	Gynaecology
59.571	Pregnancy. Foetal development. Delivery
59.58	Allergies. Skin. Skin diseases
59.59	Sensory organs. Eye diseases. Ear, nose and throat diseases
59.6	Children's health care. Children's diseases
59.8	Health care for the elderly. Geriatric diseases
59.9	Odontology