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排序方式: 共有1810条查询结果,搜索用时 15 毫秒
1.
2.
以ESR、UV和IR表征Cu(2+)离子与PVAC的配位反应。根据CUCl2·2H2O乙醇溶液与PVAc-CuCl2·2H2O乙醇溶液的电导率差值随Cu(2+)离子摩尔浓度变化的明显转析点得知,1个Cu(2+)离子大约能与PVAc4个链节单元配位。证实MMA在Cu(Ⅱ)-PVAc配合物/Na2SO3体系的聚合体是无规PMMA,得率为70%。讨论了MMA在Cu(Ⅱ)-PVAc配合物/Na2SO3体系络合催化引发下的游离基反应历程。 相似文献
3.
合成了4种-N(2-羟基乙基)水杨醛亚胺合铜(Ⅱ)类配合物,其结构经红外光谱、元素分析,原子吸收证实,并对其抑菌活性进行了试验。结果表明,配合物Ⅰ、Ⅱ对4种革兰氏阳性菌和一种革兰氏阴性菌有抑菌活性。 相似文献
4.
用K.S熵(一种信息熵)判别林业系统中生态和经济的协调关系,并提出了控制和改进现有林业系统的有效途径。 相似文献
5.
Michael P. Stryker Peter H. Schiller 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1975,23(1):103-112
Summary In unrestrained animals of many species, electrical stimulation at sites in the superior colliculus evokes motions of the head and eyes. Collicular stimulation in monkeys whose heads are rigidly fixed is known to elicit a saccade whose characteristics depend on the site stimulated and are largely independent of electrical stimulation parameters and initial eye position.This study examined what role the colliculus plays in the coding of head movements. A secondary aim was to demonstrate the effects of such electrical stimulation parameters as pulse frequency and intensity. Rhesus monkeys were free to move their heads in the horizontal plane; head and eye movements were monitored. As in previous studies, eye movements evoked by collicular stimulation were of short latency, repeatable, had a definite electrical threshold, and did not depend on the initial position of the eye in the orbit. By contrast, evoked head movements were extremely variable in size and latency, had no definite electrical threshold, and did depend on initial eye position. Thus when the eyes approached positions of extreme deviation, a head movement in the same direction became more likely. These results suggest that the superior colliculus does not directly code head movements in the monkey. 相似文献
6.
C. Strazielle P. Krémarik J.-F. Ghersi-Egea R. Lalonde 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,121(1):35-45
Lurcher mutant mice are characterized by massive degeneration of cerebellar Purkinje cells and granule cells and by deficits in motor
coordination. Regional brain variations of cytochrome oxidase (CO) activity were analyzed to identify those brain regions
with abnormal metabolic activity as a secondary consequence of the cerebellar atrophy and to establish the relationship between
CO activity and motor deficits. Lurcher mutants had higher CO activity in all three cerebellar deep nuclei than normal littermate controls of the same background
strain. Higher CO activity was also found in Lurcher mutants in brain regions directly connected to the cerebellum, such as the lateral vestibular nucleus, the cochlear nucleus,
the red nucleus, the ventrolateral thalamus, the dorsal raphe, the interpeduncular nucleus, and the inferior colliculus. By
contrast, there was a sharp decrease in CO activity in the inferior olive. As for brain regions not directly connected to
the cerebellum, higher CO activity was observed in the trigeminal motor nucleus and the CA1 molecular layer of the hippocampus,
which highlights probable transsynaptic alterations as a secondary consequence of cerebellar atrophy. A positive correlation
between CO activity in the red nucleus and latencies before falling in two motor-coordination tests indicates that a compensatory
increase of metabolic activity in a cerebellar efferent region is associated with improved behavior.
Received: 15 September 1997 / Accepted: 3 March 1998 相似文献
7.
Gribova A Donchin O Bergman H Vaadia E Cardoso De Oliveira S 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》2002,144(3):322-335
It has been established that repeated presentation of a transient target motion stimulus such as a constant-velocity ramp leads to the build up of steady state (SS), anticipatory smooth pursuit eye movements after two or three presentations. Each SS response is then composed of the anticipatory component of nonvisual origin, a visual component associated with the stimulus presentation and another nonvisual component that represents the decay of the response after extinction of the stimulus. Here we investigated the interactions that occur when each motion stimulus was itself a sequence containing more than one ramp component. Ramp components had a velocity of 15 degrees /s or 30 degrees /s to left or right and were separated by gaps of 200 ms duration. In an initial experiment, responses to 2-ramp stimuli were examined and compared with responses to the single-ramp stimuli from which they were constituted. We present evidence that the anticipatory, nonvisual components of the double-ramp response result from the linear summation of the nonvisual components of the responses to the constituent single-ramp components. In a 2nd experiment, we examined responses to a wide variety of 4-ramp sequences and again found evidence that, in the SS, the responses were formed from the linear summation of the constituent single-ramp components. Regression analysis performed on the velocity at onset of each ramp component indicated that this nonvisual part of the response was predictive of the upcoming ramp component. To confirm this, unexpected changes were introduced into single ramp components of the 4-ramp sequence after at least five prior presentations of the sequence had allowed a SS response to be established. Subjects continued to initiate a response to the modified component that was appropriate in velocity and direction for the corresponding part of the previous sequence and inappropriate for the newly modified stimulus. This preprogrammed response persisted unmodified for more than 170 ms after onset of the modified ramp component. In contrast, in the second presentation of the new sequence, the anticipatory component of the response was highly correlated with the SS response of the new sequence, but not with that of the prior sequence, showing that the preprogrammed response had been modified very rapidly. Similar behaviour was observed whichever of the 4-ramp components was modified, indicating that the velocity and direction of the anticipatory response to each component had been preprogrammed. The results suggest that velocity information related to at least four elements of a sequence can be temporarily stored and subsequently released with appropriate temporal order to form an anticipatory response throughout the whole sequence. 相似文献
8.
Ines Santisteban Francisco X. Arredondo-Vega Susan Kelly Marianne Debre Alain Fischer Jean Louis Prignon Bettina Hilman Jane Eldahr David H. Dreyfus Erwin W. Gelfand P. Lynne Howell Michael S. Hershfield 《Human mutation》1995,5(3):243-250
Three new missense mutations (H15D, A83D, and A179D) and a new splicing defect (573 + 1G→A) in the 5′ splice site of intron 5 were among six mutant adenosine deaminase (ADA) alleles found in three unrelated patients with severe combined immunodeficiency disease, the most common phenotype associated with ADA deficiency. When expressed in vitro, the H15D, A83D, and A179D proteins lacked detectable ADA activity. The splicing defect caused skipping of exon 5, resulting in premature termination of translation and a reduced level of mRNA. H15D is the first naturally occurring mutation of a residue that coordinates directly with the enzyme-associated zinc ion. Molecular modeling based on the atomic coordinates of murine ADA suggests that the D15 mutation would create a cavity or gap between the zinc ion and the side chain carboxylate of D15. This could alter the ability of zinc to activate a water molecule postulated to play a role in the catalytic mechanism. A83 and A179 are not directly involved in the active site, but are conserved residues located respectively in a helix 4 and β strand 4 of the α/β barrel. Replacement of these small hydrophobic Ala residues with the charged, more bulky Asp side chain may distort ADA structure and affect enzyme stability or folding.© 1995 wiley-Liss, Inc. 相似文献
9.
H. Heuer Will Spijkers Thomas Kleinsorge Hanno van der Loo Christoph Steglich 《Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale》1998,118(3):381-392
We investigated the time course of the amplitude specification of rapid bimanual reversal movements (lateral displacements
on two digitizers). To this end we used the timed-response paradigm in which the response has to be initiated synchronously
with an auditory signal. Information about the required amplitudes was presented at various times before the synchronization
signal. Consistent with previous results, the progression of amplitude specification was reflected in the dependence of the
amplitudes of the reversal movements on the time interval between amplitude information and synchronization signal. Same or
different amplitudes for the hands were used to examine cross-talk at the programming level of the two-level model of intermanual
interference. The results indicate the existence of cross-talk in particular at short intervals between information about
amplitude and movement initiation. This is consistent with the notion that cross-talk between concurrent processes of amplitude
specification is transient and vanishes as the time available for motor programming increases.
Received: 28 August 1996 / Accepted: 10 July 1997 相似文献
10.
The relation between movement amplitude and the strength of interlimb interactions was examined by comparing bimanual performance at different amplitude ratios (1:2, 1:1, and 2:1). For conditions with unequal amplitudes, the arm moving at the smaller amplitude was predicted to be more strongly affected by the contralateral arm than vice versa. This prediction was based on neurophysiological considerations and the HKB model of coupled oscillators. Participants performed rhythmic bimanual forearm movements at prescribed amplitude relations. After a brief mechanical perturbation of one arm, the relaxation process back to the initial coordination pattern was examined. This analysis focused on phase adaptations in the unperturbed arm, as these reflect the degree to which the movements of this arm were affected by the coupling influences stemming from the contralateral (perturbed) arm. The thus obtained index of coupling (IC) reflected the relative contribution of the unperturbed arm to the relaxation process. As predicted IC was larger when the perturbed arm moved at a larger amplitude than did the unperturbed arm, indicating that coupling strength scaled with movement amplitude. This result was discussed in relation to previous research regarding sources of asymmetry in coupling strength and the effects of amplitude disparity on interlimb coordination. 相似文献