Export from the GoldMine search center limits custom fields to 110 characters.
This is a hard limit within the product, if your field is larger that 110 character and you need to export the data of this field you will need to use the GoldMine Export wizard.
To access the Export Wizard, from the GoldMine ToolBar
1) Select "File"
2) Click on Import and Export
3) Select "Export Contact Record"
This will start the export wizard for GoldMine.
If you need instructions from this point, please see knowledge entry 11935 : How to export out of GoldMine to an Microsoft Excel spreadsheet