Letter Z (1979-1996)
	Z39.50 Access to MEDLINE and MEDLINE Backfiles. 1995 Sep-Oct:23 ZIDOVUDINE AZT, a new entry version. 1990 Sep-Oct:5 Clinical Alert. 1994 Mar-Apr:3 ZIP CODE, NLM. 1979 Mar:3 Zip Codes. changed for NLM and NIH. 1985 Aug:3 SDILINE availability for U.S. 1985 Apr:3 ZN (Mesh Z Tree Number for Country of Publication) Changes for 1991. 1991 Sep-Oct:Appendix D Year-End Processing1991 Sep-Oct:11 ZN (Country of Publication) Field Changes. 1992 Nov-Dec:23 ZN (MeSH Z Tree Number) Field Replaced. 1993 Sept-Oct:13,18

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