Talvez deva tentar algumas variações de ortografia:
negative level » relative level (Expandir a Pesquisa), negative liver (Expandir a Pesquisa), negative levy (Expandir a Pesquisa)
disease liver » disease like (Expandir a Pesquisa), disease linked (Expandir a Pesquisa), disease living (Expandir a Pesquisa)
drug negative » erg negative (Expandir a Pesquisa), during negative (Expandir a Pesquisa)
does develop » boys develop (Expandir a Pesquisa), loss develop (Expandir a Pesquisa), does developing (Expandir a Pesquisa)
develop them » develop type (Expandir a Pesquisa), develop age (Expandir a Pesquisa)
drug disease » drug release (Expandir a Pesquisa)
liver ther » liver other (Expandir a Pesquisa), liver rather (Expandir a Pesquisa), live rather (Expandir a Pesquisa)
level ther » level theory (Expandir a Pesquisa), level rather (Expandir a Pesquisa), levels other (Expandir a Pesquisa)
drug does » drug doses (Expandir a Pesquisa), drugs does (Expandir a Pesquisa), drug dose (Expandir a Pesquisa)

You can also try:

• Europeana
• Digital Public Library of America
• CORE

Pode obter mais resultados ajustando a pesquisa.

• "As palabras AND, OR e NOT podem gerar pesquisas incorrectas; tente utilizar aspas": "(( drug does develop them ) OR ((( drug disease liver ther ) OR ( drug negative level ther ))))~".
• Se adicionar um carácter universal pode recuperar variações da palavra pesquisada: (( drug does develop them ) OR ((( drug disease liver ther ) OR ( drug negative level ther ))))*.