[{"sf": "DEF", "lfs": [{"lf": "DEFICIENS", "freq": 30, "since": 1984, "vars": [{"lf": "DEFICIENS", "freq": 20, "since": 1995}, {"lf": "deficient", "freq": 6, "since": 1984}, {"lf": "deficiens", "freq": 3, "since": 1990}, {"lf": "deficiency", "freq": 1, "since": 1998}]}, {"lf": "duck embryo fibroblasts", "freq": 16, "since": 1970, "vars": [{"lf": "duck embryo fibroblasts", "freq": 8, "since": 1979}, {"lf": "duck embryo fibroblast", "freq": 7, "since": 1975}, {"lf": "Duck embryo fibroblast", "freq": 1, "since": 1970}]}, {"lf": "dose enhancement factor", "freq": 11, "since": 1976, "vars": [{"lf": "dose enhancement factor", "freq": 7, "since": 1976}, {"lf": "Dose enhancement factor", "freq": 2, "since": 1996}, {"lf": "dose-enhancement factor", "freq": 1, "since": 1982}, {"lf": "dose-enhancement factors", "freq": 1, "since": 1988}]}, {"lf": "dose effect factor", "freq": 11, "since": 1984, "vars": [{"lf": "dose effect factor", "freq": 4, "since": 1984}, {"lf": "dose effect factors", "freq": 3, "since": 1986}, {"lf": "dose-effect factors", "freq": 1, "since": 1984}, {"lf": "dose-effect factor", "freq": 1, "since": 1994}, {"lf": "Dose effect factors", "freq": 1, "since": 1985}, {"lf": "Dose Effect Factor", "freq": 1, "since": 1985}]}, {"lf": "deferoxamine", "freq": 8, "since": 1988, "vars": [{"lf": "deferoxamine", "freq": 8, "since": 1988}]}, {"lf": "Defibrotide", "freq": 7, "since": 1988, "vars": [{"lf": "Defibrotide", "freq": 5, "since": 1989}, {"lf": "defibrotide", "freq": 2, "since": 1988}]}, {"lf": "diethyl fumarate", "freq": 4, "since": 1982, "vars": [{"lf": "diethyl fumarate", "freq": 4, "since": 1982}]}, {"lf": "defensin", "freq": 3, "since": 1993, "vars": [{"lf": "defensin", "freq": 2, "since": 2004}, {"lf": "defensins", "freq": 1, "since": 1993}]}, {"lf": "deformylase", "freq": 3, "since": 1998, "vars": [{"lf": "deformylase", "freq": 3, "since": 1998}]}, {"lf": "deflated", "freq": 3, "since": 2000, "vars": [{"lf": "deflated", "freq": 2, "since": 2000}, {"lf": "deflation", "freq": 1, "since": 2007}]}]}]