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The Accumulation and Transport of Calcium in Barley Roots 总被引:1,自引:0,他引:1
The accumulation and transport of Ca by various zones of 6-day old barley roots (Hordeum vulgare L.) were examined with special reference to their relationship to the salt status of the root. The initial salt content had a profound effect on Ca transport and a lesser effect on Ca accumulation. High-salt roots transported Ca in much larger amounts than did low salt roots. In low salt roots the apical zone was more active in transporting Ca to the conducting tissue than were the mid or basal zones However, in high salt roots all zones were about equally active in transporting Ca. The metabolic inhibitor, DNP, had little effect on accumulation but inhibited transport very effectively. The effect of DNP was more pronounced on transport from the apical zone than from the other root zones. Calcium applied anywhere along the root length moved only basally and its polarized longitudinal movement was maintained irrespective of the salt status of the root. The movement of Ca was characterized by a rapid release of preabsorbed Ca and a ready exchange of apoplastic Ca. The hypothesis is presented that cellular Ca is in a relatively mobile state. Its entry into the symplasm is the rate limiting step in longitudinal transport and its overall movement is metabolically controlled. 相似文献
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Harvest Refugia in Marine Invertebrate Fisheries: Models and Applications to the Red Sea Urchin, Strongylocentrotus franciscanus 总被引:2,自引:0,他引:2
QUINN JAMES F.; WING STEPHEN R.; BOTSFORD LOUIS W. 《Integrative and comparative biology》1993,33(6):537-550
Benthic marine invertebrates with planktonic larvae may exhibitAllee effects in reproduction or recruitment. Hydrodynamic considerationsand experimental evidence suggest that species broadcastinggametes suffer greatly reduced fertilization efficiencies asdensities decline. There is also evidence for some species,including the red sea urchin, that post-dispersal recruitmentsuccess declines at low densities of adults, if adults provideshelter from predators or other sources of mortality. Speciesdisplaying strong Allee effects may be susceptible to catastrophicpopulation collapses with slight increases in mortality dueto harvesting or natural causes. A simple two patch logisticmodel suggests that the establishment of a harvest refuge isnecessary to prevent collapses and maintain sustainable catchesat high levels of harvesting effort. A more detailed, age structuredmodel based on the biology of the red sea urchin, Strongylocentrotusfranciscanus produces similar results. Effects of harvestingstrategies are sensitive to Allee effects caused by both fertilizationefficiency and the disruption of adult spine canopies. Theoreticalrequirements for the size and spacing of marine reserves dependsupon the dispersal abilities of the target species. Multiplereserves, spaced more closely than the average larval dispersaldistance, appear to be an effective and conservative strategyfor maintaining healthy populations and sustainable levels ofharvest. 相似文献
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Microsporidia 2003: IWOP-8 总被引:1,自引:0,他引:1
LOUIS M. WEISS 《The Journal of eukaryotic microbiology》2003,50(S1):566-568
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SEBASTIEN RIOUX PAQUETTE GARY D. SHORE SANDRA M. BEHNCKE FRANOIS‐JOSEPH LAPOINTE EDWARD E. LOUIS 《Molecular ecology resources》2005,5(3):527-530
The radiated tortoise (Geochelone radiata) is an endangered endemic species from Madagascar that inhabits the semiarid spiny forest of the southern part of the island. Habitat destruction and illegal harvesting greatly threaten this species, as attested by the significant reduction of its distribution area in the past 30 years. In order to undertake appropriate conservation actions, it is essential to acquire a better knowledge of its genetic structure. For this study, 145 blood samples were collected from three populations of radiated tortoises in southwestern Madagascar. Eight microsatellite loci were found to be polymorphic, and allelic diversity and observed heterozygosity were high for all markers. 相似文献
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DIANE GESTY-PALMER LOUIS M. LUTTRELL 《Journal of receptor and signal transduction research》2013,33(1-2):39-58
The discovery that arrestins can function as ligand-regulated signaling scaffolds has revealed a previously unappreciated level of complexity in G protein-coupled receptor (GPCR) signal transduction. Because arrestin-bound GPCRs are uncoupled from G proteins, arrestin binding can be viewed as switching receptors between two temporally and spatially distinct signaling modes. Recent work has established two factors that underscore this duality of GPCR signaling and suggest it may ultimately have therapeutic significance. The first is that signaling by receptor-arrestin “signalsomes” does not require heterotrimeric G protein activation. The second is that arrestin-dependent signals can be initiated by pathway-specific “biased agonists,” creating the potential for drugs that selectively modulate different aspects of GPCR function. Currently, however, little is known about the physiological relevance of G protein-independent signals at the cellular or whole animal levels, and additional work is needed to determine whether arrestin pathway-selective drugs will find clinical application. 相似文献