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Effects of UVB radiation on marine phytoplankton communities 总被引:1,自引:0,他引:1
The impact of enhanced and reduced UVB radiation (UVBR) on pelagic
ecosystems was studied during two mesocosm experiments in May and June/July
1994. The ambient UVBR exposure was either reduced with mylar foil or
artificially enhanced with UVB fluorescent tubes. Developments in the
phytoplankton communities were followed during 11 and 8 day periods using
several structural and functional parameters. In the May experiment,
enhanced UVBR significantly stimulated carbon dioxide fixation, activity of
alkaline phosphatase and content of fatty acids. In the June-July
experiment, the effects induced by changed UVBR were smaller with some
indications of decreased algal biomass with enhanced UVBR. Several of the
measured parameters indicated that the two experiments represented
different stages in the plankton community development. In the May
experiment, the community was in a development stage, moving from
nutrient-replete to nutrient-depleted conditions, while the community in
June/July was depleted of nutrients from the start. The stimulating effects
of UVBR in May are suggested to be the secondary effects of a
photochemically induced breakdown of dissolved organic matter, resulting in
an increase in available nutrients.
相似文献
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Differences in specificity and catalytic efficiency between allozymes of esterase-4 from Drosophila mojavensis 总被引:1,自引:0,他引:1
A more than 10-fold difference in the specificity and catalytic efficiency
for 1-naphthyl esters was measured between two allozymes of esterase-4 from
Drosophila mojavensis. This difference is mainly caused by a difference in
the affinity for the 1-naphthyl esters. The amino acid compositions of the
allozymes are not significantly different, which means that the difference
in primary structure is small. Small differences in primary structure
generally do not result in such a large increase in catalytic efficiency
and such a large shift in substrate specificity as was found in the present
study.
相似文献
247.
.E. Domínguez-Rebolledo M.R. Fernndez-Santos O. García-lvarez A. Maroto-Morales J.J. Garde F. Martínez-Pastor 《Theriogenology》2009,72(8):1073-1084
The effects of routine sperm work are often overlooked. We assessed the effect of washing cryopreserved epididymal spermatozoa from red deer (Cervus elaphus hispanicus, Helzheimer 1909). After thawing, epididymal samples (four stags) were diluted in TALP-HEPES. A split was left untouched, another was centrifuged (300 × g, 5 min) and resuspended, and a third was centrifuged and the supernatant substituted by fresh TALP-HEPES (washing). Each split was supplemented either with nothing, 1 mM of the antioxidant Trolox, 100 μM of the oxidant Fe (with ascorbate), or both. The 3 × 4 treatments were incubated at 37°C and assessed each hour up to 3 h for motility (computer-aided sperm assessment) and viability/apoptosis plus mitochondrial status (YO-PRO-1, propidium iodide, Mitotracker Deep Red; flow cytometry). DNA damage at 4 h was assessed using the terminal deoxynucleotidyl transferase–mediated dUTP nick end-labeling assay. Centrifugation alone affected neither sperm quality nor DNA, and the oxidant had no effect in control or centrifuged samples. Washed samples were not different than control, but oxidant decreased motility, mitochondrial status and viability, and altered the motility subpopulation pattern, being partially suppressed by Trolox. Spermatozoa with damaged DNA dramatically increased in the washed-oxidized sample (from 22.30 ± 3.52% to 67.94 ± 5.07%), but not when antioxidant was present. Although samples from different males behaved similarly, male-to-male variability was detected regarding susceptibility to oxidative damage after washing. We concluded that, although red deer thawed spermatozoa seemed resilient to centrifugation, the vulnerability to oxidative stress after washing makes it advisable to supplement manipulation media with antioxidants, especially taking into account male-to-male variability. 相似文献
248.
Christian Garde Michael Givskov Morten Hentzer Kim Sneppen Thomas Sams 《Journal of molecular biology》2010,396(4):849-857
We present detailed results on the C4-HSL-mediated quorum sensing (QS) regulatory system of the opportunistic Gram-negative bacterium Aeromonas hydrophila. This bacterium contains a particularly simple QS system that allows for a detailed modeling of kinetics. In a model system (i.e., the Escherichia coli monitor strain MH205), the C4-HSL production of A. hydrophila is interrupted by fusion of gfp(ASV). In the present in vitro study, we measure the response of the QS regulatory ahyRI locus in the monitor strain to predetermined concentrations of C4-HSL signal molecules. A minimal kinetic model describes the data well. It can be solved analytically, providing substantial insight into the QS mechanism: at high concentrations of signal molecules, a slow decay of the activated regulator sets the timescale for the QS regulation loop. Slow saturation ensures that, in an A. hydrophila cell, the QS system is activated only by signal molecules produced by other A. hydrophila cells. Separate information on the ahyR and ahyI loci can be extracted, thus allowing the probe to be used in identifying the target when testing QS inhibitors. 相似文献
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