全文获取类型
收费全文 | 124篇 |
免费 | 14篇 |
出版年
2021年 | 1篇 |
2020年 | 3篇 |
2019年 | 1篇 |
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 5篇 |
2015年 | 3篇 |
2014年 | 7篇 |
2013年 | 5篇 |
2012年 | 6篇 |
2011年 | 11篇 |
2010年 | 8篇 |
2009年 | 4篇 |
2008年 | 4篇 |
2007年 | 4篇 |
2006年 | 3篇 |
2005年 | 5篇 |
2004年 | 5篇 |
2003年 | 4篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 4篇 |
1999年 | 9篇 |
1998年 | 4篇 |
1997年 | 4篇 |
1996年 | 3篇 |
1995年 | 1篇 |
1994年 | 4篇 |
1992年 | 2篇 |
1991年 | 2篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1975年 | 2篇 |
1973年 | 2篇 |
1970年 | 1篇 |
排序方式: 共有138条查询结果,搜索用时 15 毫秒
91.
92.
93.
94.
Malate-permeable channels and cation channels activated by aluminum in the apical cells of wheat roots 总被引:27,自引:0,他引:27
Aluminum (Al(3+))-dependent efflux of malate from root apices is a mechanism for Al(3+) tolerance in wheat (Triticum aestivum). The malate anions protect the sensitive root tips by chelating the toxic Al(3+) cations in the rhizosphere to form non-toxic complexes. Activation of malate-permeable channels in the plasma membrane could be critical in regulating this malate efflux. We examined this by investigating Al(3+)-activated channels in protoplasts from root apices of near-isogenic wheat differing in Al(3+) tolerance at a single locus. Using whole-cell patch clamp we found that Al(3+) stimulated an electrical current carried by anion efflux across the plasma membrane in the Al(3+)-tolerant (ET8) and Al(3+)-sensitive (ES8) genotypes. This current occurred more frequently, had a greater current density, and remained active for longer in ET8 protoplasts than for ES8 protoplasts. The Al(3+)-activated current exhibited higher permeability to malate(2-) than to Cl(-) (P(mal)/P(Cl) > or = 2.6) and was inhibited by anion channel antagonists, niflumate and diphenylamine-2-carboxylic acid. In ET8, but not ES8, protoplasts an outward-rectifying K(+) current was activated in the presence of Al(3+) when cAMP was included in the pipette solution. These findings provide evidence that the difference in Al(3+)-induced malate efflux between Al(3+)-tolerant and Al(3+)-sensitive genotypes lies in the differing capacity for Al(3+) to activate malate permeable channels and cation channels for sustained malate release. 相似文献
95.
NH4+ currents across the peribacteroid membrane of soybean. Macroscopic and microscopic properties, inhibition by Mg2+, and temperature dependence indicate a SubpicoSiemens channel finely regulated by divalent cations
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The control of ammonium (NH(4)(+)) transport is critical in preventing futile cycles of NH(4)(+)/ammonia transport. An unusual nonselective cation channel with subpicoSiemens single-channel conductance permeable to NH(4)(+) had previously been identified in the peribacteroid membrane (PBM) of symbiosomes from soybean (Glycine max) nodules. Here, we investigate the proposed channel mechanism and its control by luminal magnesium. Currents carried by NH(4)(+) were measured in inside-out PBM patches by patch clamp. NH(4)(+) transport corresponding to the physiological direction of net transfer showed time-dependent activation and associated single-channel-like events. These could not be resolved to discrete conductances but had the same selectivity as the total current. The voltage dependence of the steady-state current was affected by temperature consistent with the rate constant of channel opening being reduced with decreased temperature. This resulted in steady-state currents that were more temperature sensitive at voltages where the current was only partially activated. When fully activated, the current reflected more the ion conduction through open channels and had an activation energy of 28.2 kJ mol(-1) (Q10 = 1.51, 8 degrees C-24 degrees C). Increased Mg(2+) on the symbiosome lumen side blocked the current (ID(50) = 351 microm, with 60 mm NH(4)(+)). Complete inhibition with 2 mm Mg(2+) was relieved with a small increase in NH(4)(+) on the lumen side of the membrane (shift of 60-70 mm). With Mg(2+) the selectivity of the transport for divalent cations increased. From these features, we propose a divalent-dependent feedback regulation of the PBM-nonselective cation channel that could maintain a constant NH(4)(+) gradient across the membrane. 相似文献
96.
The symbiosome of nitrogen fixing root nodules mediates metabolite exchange between endosymbiotic rhizobia bacteria and the legume host. In the present study, the ion currents of the symbiosome membrane of the model legume Lotus japonicus were analyzed by patch-clamp recording. Both excised and symbiosome-attached patches exhibited a large inward (toward the cytosolic side of the membrane) current that is activated in a time-dependent manner by negative (on the cytosolic side) potentials. Based on reversal potential determinations and recordings with the impermeant cation N-methyl-glucamine, this current shows a high permeability for monovalent cations with no apparent permeability for anions. The current also showed a finite Ca(2+) permeability. However, the currents were predominantly carried by univalent cations with a slightly greater selectivity for NH(4)(+) over K(+). Increased Ca(2+) concentration inhibited the current with a K(0.5) for inhibition of 0.317 mM. The current showed strong rectification that is mediated by divalent cations (either Mg(2+) or Ca(2+)). The influence of divalent cations is symmetrical in nature, because rectification can be exerted in either direction depending upon which side of the membrane has the highest concentration of divalent cations. However, based on observations with symbiosome-attached patches, the direction of the current in vivo is proposed to be toward the cytosol with cytosolic Mg(2+) acting as the putative gating regulator. The findings suggest that L. japonicus possesses a voltage-dependent cation efflux channel that is capable of exporting fixed NH(4)(+), and may also play an additional role in Ca(2+) transport. 相似文献
97.
The functional significance of water channels in wheat (Triticum aestivum L.) root membranes was assessed using light scattering to measure vesicle shrinking in response to osmotic gradients rapidly imposed in a stopped flow apparatus. Vesicles were obtained from both a plasma membrane fraction and a plasma membrane-depleted endomembrane fraction including tonoplast vesicles. Osmotic water permeability (Pos) in the endomembrane fraction was high (Pos= 86.0 [mu]m s-1) with a low activation energy (EA= 23.32 kJ mol-1 [plus or minus] 3.88 SE), and was inhibited by mercurials (K1= 40 [mu]M HgCl2, where K1 is the inhibition constant for half-maximal inhibition), suggesting participation of water channels. A high ratio of osmotic to diffusional permeability (Pd) (using D2O as a tracer, Pos/Pd = 7 [plus or minus] 0.5 SE) also supported this view. For the endomembrane fraction there was a marked decrease in Pos with increasing osmotic gradient that was not observed in the plasma membrane fraction. Osmotic water permeability in the plasma membrane fraction was lower (Pos= 12.5 [mu]m s-1) with a high activation energy (EA= 48.07 kJ mol-1 [plus or minus] 3.63 SE) and no mercury inhibition. Nevertheless, Pos/Pd was found to be substantially higher than one (Pos= 3 [plus or minus] 0.2 SE), indicating that water channels mediated water flow in this fraction, too. Possible distortion of the Pos/Pd value by unstirred layer effects was shown to be unlikely. 相似文献
98.
Chromosomal DNA from 23 closely related, pathogenic strains of Escherichia
coli was digested and probed for the insertion sequences IS1, IS2, IS4,
IS5, and IS30. Under the assumption that elements residing in DNA
restriction fragments of the same apparent length are identical by descent,
parsimony analysis of these characters yielded a unique phylogenetic tree.
This analysis not only distinguished among bacterial strains that were
otherwise identical in their biochemical characteristics and enzyme
electrophoretic mobilities, but certain aspects of the topology of the tree
were consistent across several unrelated insertion elements. The
distribution of IS elements was then reexamined in light of the inferred
phylogenetic relationships to investigate the biological properties of the
elements, such as rates of insertion and deletion, and to discover apparent
recombinational events. The analysis shows that the pattern of distribution
of insertion elements in the bacterial genome is sufficiently stable for
epidemiological studies. Although the rate of recombination by conjugation
has been postulated to be low, at least two such events appear to have
taken place.
相似文献
99.
Homologues of glucosephosphate isomerase (GPI, EC 5.3.1.9) were purified to
homogeneity and kinetically characterized from Mytilus edulis and Isognomon
alatus, two bivalve molluscs experiencing contrasting thermal environments.
The enzyme isolated from I. alatus functions at warmer temperatures (25-35
C) than GPI from M. edulis, a species that inhabits colder marine littoral
habitats (5-20 C). The former exhibits apparent first-order (with respect
to substrate) catalytic rate constants (Vmax/KM) in vitro that become
progressively greater than the mussel enzyme as the assay temperature is
raised. Apparent zero-order catalytic rate constants (Vmax) are relatively
less differentiated. Catalytic efficiency, defined as the rate at which a
catalytic event occurs in either reaction direction for reference standard
states (substrate concentrations), is greater for the enzyme from the
tropical species (I. alatus) at all realistic combinations of temperature
and substrate concentration except for the lowest temperatures and highest
substrate concentrations, where the GPI from the boreal/temperate M. edulis
is more efficient. This pattern of catalytic divergence appears to be due
primarily to differentiation in Vmax/KM. These results and other published
data are reviewed and shown to be inconsistent with claims that adaptation
of enzymes to higher cell temperatures requires a loss in catalytic
efficiency.
相似文献
100.