Rare earths 33 History of engineering and technology 23 Technology: general issues 21 Research & information: general 11 Rare earth elements 10 Metal ions 7 Chemistry 6 Physics 6 Research and information: general 6 Binary alloys 5 Biology, life sciences 5 Density functional theory 4 Article 3 Calculations 3 Crystal structure 3 Earth sciences, geography, environment, planning 3 Electronic structure 3 Intermetallics 3 Iron compounds 3 Magnetic anisotropy 3 Magnetism 3 Materials science 3 Mining technology and engineering 3 Rare earth doped 3 Rare earth ions 3 Rare-earths 3 Refractive index 3 Silicon compounds 3 rare earth element 3 recycling 3