Which of the following are the types of columns encountered in gas chromatography?(1) flat plates (2) packed columns (3) plastic strips (4) open tubular, or capillary columns
A: 1,2
B: 3, 4
C: 1, 3
D: 2,4
A: 1,2
B: 3, 4
C: 1, 3
D: 2,4
举一反三
- If it is known that A is a 3×5 matrix, after executing A(:,1:2:3)=[], ( ). A: A becomes row vector B: A becomes 3 rows and 3 columns C: A becomes 3 rows and 2 columns D: A becomes 2 rows and 3 columns
- Capillary<br/>columns are open tubular columns constructed from which of the<br/>following materials? ( ) A: Glass B: Metal C: Stainless<br/>steel D: Fused<br/>silica
- If a is known to be a 2×3 matrix, then after executing a=a(:), ( ). A: a transforms to a column vector B: a transforms to 3 rows and 2 columns C: a transforms to 3 rows and 3 columns D: a transforms to 2 rows 3 and columns
- df1 = pd.DataFrame([[5, 2, 3], [4, 5, 6],[7,8,9]], index=['A', 'B','D'], columns=['C1', 'C2', 'C3']) ，其中 df1.loc[2:1]=8（）
- 设集合A={1 , 2 , 3 , 4}上的二元关系 R = {(1 , 1)，(2 , 2)，(2 , 3)，(3,4),(2,4),(3,3),(4 , 4)}， S = {(1 , 1)，(2 , 2)，(2 , 3)，(3 , 2)，(3,3),(4 , 4)}， T = {(1 , 1)，(2 , 2)，(3, 3)，(3 , 2)，(2,4), (2,3),(4,2),(4 , 4)}， 是相容关系， 是等价关系，是偏序关系