The period from year 1990 to 1999; almost the same period as the 10th (and last) decade of the 20th century, which, however, was from 1991 to (the end of) year 2000
1967 February 16, Space Seed (Star Trek), season 1, number 22 (Science Fiction), Paramount Domestic Television:
KIRK: We're reading it, Lieutenant. I thought you said it couldn't possibly be an Earth vessel. SPOCK: I fail to understand why it always gives you pleasure to see me proven wrong. KIRK: An emotional Earth weakness of mine. There it is. KIRK: An old Earth vessel, similar to the DY-500 class. SPOCK: Much older. DY-100 class, to be exact. Captain, the last such vessel was built centuries ago, back in the 1990s. KIRK: Then it's a derelict, its signal left on automatic. SPOCK: Or an old Earth ship being used by aliens.
2008, Jack F. Williams, Ch’ang-yi David Chang, “Back from the brink: resolving Taiwan's environmental problems”, in Taiwan's Environmental Struggle: Toward a Green Silicon Island, →ISBN, →OCLC, page 108: