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【简答题】
图示两端铰支细长压杆的截面为矩形,横截面尺寸如图所示,其中 h>b ,杆轴线为 x 轴,当其失稳时挠曲轴位于 平面内。(填xoy、xoz或yoz)
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【单选题】在电子商务条件下，买方应当承担的义务不包括（ ）
A.
买方应承担按照网络交易规定方式支付价款的义务
B.
准确、及时地进行电子资金的划拨义务
C.
买方应承担按照合同规定的时间、地点和方式接受标的物的义务
D.
买方应当承担对标的物验收的义务
【多选题】How do mitogens stimulate cell proliferation by inhibiting the Rb protein?
A.
As a general rule, mammalian cells will multiply only if they are stimulated to do so by extracellular signals, called mitogens, produced by other cells. If deprived of such signals, the cell cycle arrests in G 1 ; if the cell is deprived of mitogens for long enough, it will withdraw from the cell cycle and enter a nonproliferating state, in which the cell can remain for days or weeks, months, or even for the lifetime of the organism, as we discuss shortly.
B.
Escape from cell-cycle arrest—or from certain nonproliferating states—requires the accumulation of cyclins. Mitogens act by switching on cell signaling pathways that stimulate the synthesis of G 1 cyclins, G 1 /S cyclins, and other proteins involved in DNA synthesis and chromosome duplication. The buildup of these cyclins triggers a wave of G 1 /S-Cdk activity, which ultimately relieves the negative controls that otherwise block progression from G 1 to S phase.
C.
One crucial negative control is provided by the Retinoblastoma (Rb) protein. Rb was initially identified from studies of a rare childhood eye tumor called retinoblastoma, in which the Rb protein is missing or defective. Rb is abundant in the nuclei of all vertebrate cells, where it binds to particular transcription regulators and prevents them from turning on the genes required for cell proliferation.
D.
Mitogens release the Rb brake by triggering the activation of G 1 -Cdks and G 1 /S-Cdks. These complexes phosphorylate the Rb protein, altering its conformation so that it releases its bound transcription regulators, which are then free to activate the genes required for entry into S phase.
【单选题】在电子商务条件下,买方应当承担的义务不包括( )
A.
买方应承担按照网络交易规定方式支付价款的义务
B.
选完商品就立即就付款
C.
买方应承担按照合同规定的时间、地点和方式接受标的物的义务
D.
买方应当承担对标的物验收的义务
【多选题】下列关于洪泽湖的说法中，正确的是?( )
A.
洪泽湖是我国第四大淡水湖。
B.
洪泽湖是淮河流域的湖泊型水库。
C.
洪泽湖是南水北调东线工程调节水库。
D.
洪泽湖是淮河干流上的人工湖。
【多选题】在电子商务条件下,买方应当承担的义务包括
A.
按照网络交易规定方式支付价款的义务
B.
按照合同规定的时间，地点和方式接受标的物的义务
C.
对标的物的质量承担担保义务
D.
对标的物验收的义务
【简答题】设函数F(x)为定义在凸集R上且具有连续二阶导数的函数,则,F(x)在R上为凸函数的充要条件是海森矩阵在R上处处 。
相关题目：
【多选题】下列关于洪泽湖的说法中，正确的是?( )
A.
洪泽湖是我国第四大淡水湖。
B.
洪泽湖是淮河流域的湖泊型水库。
C.
洪泽湖是南水北调东线工程调节水库。
D.
洪泽湖是淮河干流上的人工湖。