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排序方式: 共有163条查询结果,搜索用时 359 毫秒
71.
M Pokorski M Ryba 《European journal of applied physiology and occupational physiology》1982,48(3):361-365
We investigated the effect of intravenous sodium bicarbonate (2 mmol x kg-1) on the arterial blood-spinal fluid PO2 gradient in twelve anaesthetized hyperoxaemic human subjects who were in preparation for surgical procedures The steady-state samples of arterial blood and lumbar fluid were withdrawn for the assessment of the acid-base status and electrolyte content in both fluid compartments before and after NaHCO3 injection. We found that NaHCO3 increased the arterial pH and PCO2, and decreased the blood-spinal fluid PO2 gradient significantly. The latter was a result of an increase in spinal fluid PO2 and a decrease in PaO2. The diminished PO2 gradient can be accounted for by the specific effect of carbamate and bicarbonate, distinct from that of pH, lowering the affinity of haemoglobin for oxygen. This might favor the maintenance of an adequate oxygen supply in the brain tissue under unfavorable conditions. 相似文献
72.
Sub-second turnover of transducin GTPase in bovine rod outer segments. A light scattering study 总被引:1,自引:0,他引:1
A fast, regenerative light scattering signal from bovine ROS, the PA-signal, reflects the light-induced, transient activation of transducin. Its rate of recovery depends on the number of photolysed rhodopsin molecules, indicating that rhodopsin deactivation and not GTPase activity is rate limiting in our in vitro system. When rhodopsin deactivation is accelerated (in the presence of NH2OH), PA-signal recovery is also accelerated. A GTPase turnover number of more than 2 s-1 (at 37 degrees C) can be derived from these experiments. This is more than one order of magnitude faster than the GTPase rates so far described in the literature and is rapid enough for a physiological shut-off mechanism. The fast GTPase is attributed to a highly intact disk stack, which never releases transducin into the free aqueous space. 相似文献
73.
In photoreceptors of the living retina both activation and deactivation of transducin must occur in less than 1 s. In ROS preparations used for in vitro studies, however, deactivation takes minutes. This is due to the fact that activated transducin is released into the free aqueous space, whereby GTPase activity and consequent deactivation of the protein are slowed down, and due to the dilution of soluble ROS proteins involved in the quenching of rhodopsin activity. In this paper, using a convenient, non-invasive light scattering assay, we demonstrate that in an intact stack of disks, where active transducin stays membrane associated and is rapidly deactivated, the activity of rhodopsin can also be quenched in the time range of seconds when soluble ROS proteins are supplemented. Arrestin, the 48 kDa protein of the photoreceptor, is one of the proteins required for rapid recovery, however, it requires the synergistic action of other soluble proteins (besides rhodopsin kinase) in order to exert its effect: When arrestin is included in the reaction mixture without the 'helper protein(s)', it cannot speed recovery, and when a mixture of soluble proteins is added which lacks arrestin, there is also no effect. The nature and identity of this (these) helper protein(s) are still unclear. 相似文献
74.
75.
Cellular mechanisms for diminished scarring with aging 总被引:4,自引:0,他引:4
Marcus JR Tyrone JW Bonomo S Xia Y Mustoe TA 《Plastic and reconstructive surgery》2000,105(5):1591-1599
The study of an age-dependent spectrum of scar formation is driven by the desire to understand and recapitulate scarless healing. Although focus in the past has been directed toward scarring in the fetus, less exuberant scarring is a common clinical observation in the elderly. Cell turnover is a major contributor to the development of scar tissue and is governed by the proliferative and apoptotic cellular fractions within a healing wound. We hypothesize that the balance between cell proliferation and apoptosis during late stages of excisional wound healing is, at least in part, responsible for age-related variations in scarring potential. Full-thickness 7-mm ulcers (four per ear), exposing bare cartilage, were made on the inner surface of the ear on 12 young and 12 aged New Zealand White rabbits. Analyses were performed at days 15, 21, and 28 postwounding. A previously described Scar Elevation Index was derived from histomorphometric analysis, along with the quantification of epithelial ingrowth and total cellularity. Apoptotic cellular fractions were derived from TdT-mediated dUTP nick end-labeling assay-stained histologic sections; proliferative fractions were derived from proliferating cell nuclear antigen-labeled serial sections. Young rabbits demonstrated significantly greater scar elevation/area. Apoptosis was strongly associated with progress of epithelialization in both groups. Significantly higher proliferative indices were seen in the young and were sustained through day 28, by which time levels had substantially declined in the aged. No differences in apoptotic indices were demonstrated between groups at any time point. The clinical observation of less exuberant scarring with aging is supported by this animal model. Apoptosis follows the progression of epithelialization but does not appear to independently influence scar morphology. A diminished proliferative response during later stages of healing is an important contributing mechanism for the decrease in scar formation seen in the elderly. 相似文献
76.
Joanne L Fothergill Stavroula Panagea Charles A Hart Martin J Walshaw Tyrone L Pitt Craig Winstanley 《BMC microbiology》2007,7(1):45
Background
Some isolates of the Liverpool cystic fibrosis epidemic strain of Pseudomonas aeruginosa exhibit an unusual virulence-related phenotype, characterized by over-production of quorum sensing-regulated exoproducts such as pyocyanin and LasA protease. Our aim was to determine the prevalence of this unusual phenotype amongst isolates of the epidemic strain, and to study other intraclonal phenotypic and genotypic variations. 相似文献77.
Characterization of human angiogenin variants implicated in amyotrophic lateral sclerosis 总被引:1,自引:0,他引:1
Crabtree B Thiyagarajan N Prior SH Wilson P Iyer S Ferns T Shapiro R Brew K Subramanian V Acharya KR 《Biochemistry》2007,46(42):11810-11818
Human angiogenin (ANG), the first member of the angiogenin family (from the pancreatic ribonuclease A superfamily) to be identified, is an angiogenic factor that induces neovascularization. It has received much attention due to its involvement in the growth of tumors and its elevated expression level in pancreatic and several other cancers. Recently the biological role of ANG has been shown to extend to the nervous system. Mutations in ANG have been linked with familial as well as sporadic forms of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disorder characterized by selective destruction of motor neurons. Furthermore, mouse angiogenin-1 has been shown to be expressed in the developing nervous system and during the neuronal differentiation of pluripotent stem cells. We have now characterized the seven variants of ANG reported in ALS patients with respect to the known biochemical properties of ANG and further studied the biological properties of three of these variants. Our results show that the ribonucleolytic activity of six of the seven ANG-ALS implicated variants is significantly reduced or lost and some variants also show altered thermal stability. We report a significant reduction in the cell proliferative and angiogenic activities of the three variants that we chose to investigate further. Our studies on the biochemical and structural features of these ANG variants now form the basis for further investigations to determine their role(s) in ALS. 相似文献
78.
N J Ryba 《Current biology : CB》1999,9(13):R472-R474
Recent studies of the projection pattern made by sensory neurons involved in mammalian pheromone reception have shown that there is a map of activation in the brain, but this pheromone map appears far more complex than the equivalent map in the main olfactory system responsible for the sense of smell. 相似文献
79.
Distribution of biomass of species differing in photosynthetic pathway along an altitudinal transect in southeastern wyoming grassland 总被引:4,自引:1,他引:4
Summary Based on the physiological characteristics and responses of C3, C4, and CAM plants to environmental factors, it is generally predicted that C4 and CAM plants will become more abundant with increasing temperature and decreasing precipitation. To test this prediction, the relative contribution of each photosynthetic type to total plant community biomass was examined at seven study areas along an altitudinal transect in southeastern Wyoming grassland. In going from high (2,652 m) to low (1,405 m) elevation along this transect, mean annual temperature increased and annual precipitation decreased.The percentage of C4 biomass composing each study area decreased with increasing elevation, while the percentage of C3 biomass increased. All elevations had a significantly higher percentage of C4 biomass in August than in June, reflecting the warm season growth characteristic of C4 plants. Regressions of relative abundance of photosynthetic types on climatic variables showed that both mean annual temperature and annual precipitation were equally reliable as predictors of C3–C4 biomass, although we feel that temperature is of primary importance in explaining our observations. CAM species were present at all elevations, but showed no trends in biomass distribution with respect to elevation. 相似文献
80.
Katherine H. Karlsgodt Tena Rosser Evan S. Lutkenhoff Tyrone D. Cannon Alcino Silva Carrie E. Bearden 《PloS one》2012,7(10)
Neurofibromatosis (NF1) represents the most common single gene cause of learning disabilities. NF1 patients have impairments in frontal lobe based cognitive functions such as attention, working memory, and inhibition. Due to its well–characterized genetic etiology, investigations of NF1 may shed light on neural mechanisms underlying such difficulties in the general population or other patient groups. Prior neuroimaging findings indicate global brain volume increases, consistent with neural over-proliferation. However, little is known about alterations in white matter microstructure in NF1. We performed diffusion tensor imaging (DTI) analyses using tract-based spatial statistics (TBSS) in 14 young adult NF1 patients and 12 healthy controls. We also examined brain volumetric measures in the same subjects. Consistent with prior studies, we found significantly increased overall gray and white matter volume in NF1 patients. Relative to healthy controls, NF1 patients showed widespread reductions in white matter integrity across the entire brain as reflected by decreased fractional anisotropy (FA) and significantly increased absolute diffusion (ADC). When radial and axial diffusion were examined we found pronounced differences in radial diffusion in NF1 patients, indicative of either decreased myelination or increased space between axons. Secondary analyses revealed that FA and radial diffusion effects were of greatest magnitude in the frontal lobe. Such alterations of white matter tracts connecting frontal regions could contribute to the observed cognitive deficits. Furthermore, although the cellular basis of these white matter microstructural alterations remains to be determined, our findings of disproportionately increased radial diffusion against a background of increased white matter volume suggest the novel hypothesis that one potential alteration contributing to increased cortical white matter in NF1 may be looser packing of axons, with or without myelination changes. Further, this indicates that axial and radial diffusivity can uniquely contribute as markers of NF1-associated brain pathology in conjunction with the typically investigated measures. 相似文献