Call numbers seem strange to most library users. Here is a guide to understanding them in the area of physics. You can also refer to this if you wish to browse the stacks.
Q1-390 Science (General)
Q1-295 General
Q300-390 Cybernetics
Q350-390 Information theory
Subclass QA
QA1-939 Mathematics
QA1-43 General
QA47-59 Tables
QA71-90 Instruments and machines
QA75-76.95 Calculating machines
QA75.5-76.95 Electronic computers. Computer science
QA76.75-76.765 Computer software
QA101-(145) Elementary mathematics. Arithmetic
QA150-272.5 Algebra
QA273-280 Probabilities. Mathematical statistics
QA299.6-433 Analysis
QA440-699 Geometry. Trigonometry. Topology
QA801-939 Analytic mechanics
Subclass QB
QB1-991 Astronomy
QB1-139 General
QB140-237 Practical and spherical astronomy
QB275-343 Geodesy
QB349-421 Theoretical astronomy and celestial mechanics
QB455-456 Astrogeology
QB460-466 Astrophysics
QB468-480 Non-optical methods of astronomy
QB495-903 Descriptive astronomy
QB500.5-785 Solar system
QB799-903 Stars
QB980-991 Cosmogony. Cosmology
Subclass QC
QC1-999 Physics
QC1-75 General
QC81-114 Weights and measures
QC120-168.85 Descriptive and experimental mechanics
QC170-197 Atomic physics. Constitution and properties of matter (Including molecular physics, relativity, quantum theory, and solid state physics
QC221-246 Acoustics. Sound
QC251-338.5 Heat
QC310.15-319 Thermodynamics
QC350-467 Optics. Light
QC450-467 Spectroscopy
QC474-496.9 Radiation physics (General)
QC501-766 Electricity and magnetism
QC501-(721) Electricity
QC669-675.8 Electromagnetic theory
QC676-678.6 Radio waves (Theory)
QC701-715.4 Electric discharge
QC717.6-718.8 Plasma physics. Ionized gases
QC750-766 Magnetism
QC770-798 Nuclear and particle physics. Atomic energy. Radioactivity
QC793-793.5 Elementary particle physics
QC794.95-798 Radioactivity and radioactive substances
QC801-809 Geophysics. Cosmic physics
QC811-849 Geomagnetism
QC851-999 Meteorology. Climatology (Including the earth's atmosphere)
QC974.5-976 Meteorological optics
QC980-999 Climatology and weather
QC994.95-999 Weather forecasting