animal experiment nonhuman 1,220 controlled study 937 article 922 Animals 843 priority journal 788 male 542 Male 522 animal tissue 521 mouse 499 rat 494 female 471 animal model 463 Female 459 animal cell 418 Rats 405 Mice 403 animal 306 Animal 270 protein expression 238 unclassified drug 237 Article 228 metabolism 216 Animalia 207 Support, Non-U.S. Gov't 199 in vitro study 196 enzyme activity 160 Humans 144 human 139 physiology 137