TP Chemical technology 147 Nitrogen 123 Research & information: general 102 Biology, life sciences 98 QD Chemistry 80 nitrogen 74 Article 61 Technology: general issues 61 Soils 60 China 59 TA Engineering (General). Civil engineering (General) 55 Ecosystems 49 Research and information: general 43 TJ Mechanical engineering and machinery 41 nonhuman 41 Forestry 40 Nitrogen oxides 40 Nutrients 36 controlled study 35 History of engineering and technology 34 Water quality 34 Biomass 32 Organic carbon 32 Ammonia 30 human 29 Carbon 28 biomass 27 metabolism 27 Bacteria 25 Climate change 24