Similar, but different modeling systems.
SysML vs UML
SysML is heavily based on UML, but it’s smaller. It’s not a strict subset, as there’s native SysML diagrams that do not exist in UML.
Requirements DIagram
Does not exist in UML at all
Structure Diagrams
Package Diagram (same)
Block Definition Diagram (modified)
Internal Block Diagram (modified)
Parametric Diagram (SysML only)
Behavior Diagrams
Sequence Diagram (same)
State Machine Diagram (same)
Use Case Diagram (same)
Activity Diagram (modified)