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41.
42.
P Kubes K A Nesbitt S M Cain C K Chapler 《Canadian journal of physiology and pharmacology》1991,69(10):1399-1404
We questioned whether carbon monoxide hypoxia (COH) would affect peripheral blood flow by neural activation of adrenoceptors to the extent we had found in other forms of hypoxia. We studied this problem in hindlimb muscles of four groups of anesthetized dogs (untreated, alpha 1-blocked, alpha 1 + alpha 2-blocked, and beta 2-blocked). Cardiac output increased, but hindlimb blood flow (QL) and resistance (RL) remained at prehypoxic levels during COH (O2 content reduced 50%) in untreated animals. When activity in the sciatic nerve was reversibly cold blocked, QL doubled and RL decreased 50%. These changes with nerve block were the same during COH, suggesting that neural activity to hindlimb vasculature was not increased by COH. In animals treated with phenoxybenzamine (primarily alpha 1-blocked), RL dropped (approximately 50%) during COH, an indication that catecholamines played a significant role in maintaining tone to skeletal muscle. Animals with both alpha 1 + alpha 2-adrenergic blockade (phenoxybenzamine and yohimbine added) did not survive COH. RL was higher in beta 2-block than in the untreated group during COH, but nerve cooling indicated that beta 2-adrenoceptor vasodilation was accomplished primarily by humoral means. The above findings demonstrated that adrenergic receptors were important in the regulation of QL and RL during COH, but they were not activated by sympathetic nerve stimulation to the limb muscles. 相似文献
43.
A flux analysis of glucose metabolism in the filamentous fungus Rhizopus oryzae was achieved using a specific radioactivity curve-matching program, TFLUX. Glycolytic and tricarboxylic acid cycle intermediates labeled through the addition of extracellular [U-14C]glucose were isolated and purified for specific radioactivity determinations. This information, together with pool sizes and the rates of glucose utilization and end product production, provided input for flux maps of the metabolic network under two different experimental conditions. Based upon the flux analysis of this system, a mutant of R. oryzae with higher lactate and lower ethanol yields than the parent was sought for and found. 相似文献
44.
Detailed examination of abdominal tip extracts from adult female Heliothis armigera revealed the presence of two components which elicit electroantennographic responses from the male moth. These olfactory stimulants have been fully identified as (Z)-11-hexadecenal (I) and (Z)-11-hexadecen-1-ol(II), and detected in airborne volatiles from a ‘calling’ female moth. A third olfactory stimulant was detected only in female tip extracts from some moths of Malawi origin, and this was tentatively identified as (Z)-9-hexadecenal (III). No other olfactory stimulants could be found, although hexadecenal (IV) and 1-hexadecan-1-ol (V) were detected by gas chromatography. In field tests in Malawi, (Z)-11-hexadecenal (I) attracted a few male H. armigera moths to traps but was very much less attractive than the virgin female moth. The attractiveness of (I) was not consistently affected by addition of alcohol (II), aldehydes (III) and (IV), or (E)-11-hexadecenal. Significant numbers of male Earias biplaga moths were found to be attracted to (Z)-11-hexadecenal (I). 相似文献
45.
SVEN-BÖR JE SVENSSON 《Physiologia plantarum》1972,27(1):13-24
Effects of coumarin on fresh weight, dry matter, protein and nucleic acid content per cell in attached roots of maize and wheat and in whole excised elongation zones of maize were determined. The inhibition in cell length exerted by coumarin did not correspond to an inhibition of the net synthetic capacity. Coumarin treatment increased the cell surface, the production of dry matter and the protein content per cell. The dry matter and the protein content per unit surface was slightly increased or unaffected. The effect of coumann on cell shape seemed to be independent of that on dry matter production and net protein synthesis. The same was found in excised elongation zones. —The net DNA-synthesis per cell was slightly increased in attached roots by coumann treatment, but this effect was probably not correlated with the morphogenetic changes. Inhibition of DNA-synthesis with hydroxyurea did not alter the coumarin induced changes in cell shape. —The net RNA-synthesis per cell was slightly decreased after coumarin treatment, but the net RNA-synthesis per cell and the morphogenetic effects exerted by coumarin were not related with each other. Inhibition of m-RNA-synthesis with actinomycin D did not prevent the effects of coumarin on cell division, cell expansion, dry matter production and net protein synthesis. The same was true for inhibitors of protein synthesis, puromycin and p-fluorophenyl-alanine. The findings are in support of the view that coumarin affects already existing structures or enzymes. —Comparisons between coumarin and the uncouplers, DNP and dicoumarol, showed that the effects of coumarin were not, solely, due to uncoupling. SH-protecting agents, BAL, DTE and glutathione, did, with few exceptions, not reduce the morphogenetic effects of coumarin. 相似文献
46.
47.
Phosphorus nutrition of rice in relation to flooding and temporary loss of soil-water saturation in two lowland soils of Cambodia 总被引:1,自引:1,他引:0
In the rainfed lowlands, temporary loss of soil-water saturation during crop growth is a common factor limiting rice (Oryza
sativa L.) yield but its effects on phosphorus (P) availability are poorly understood. Rice plants were transplanted into
pots containing soils that were either continuously flooded, maintained at field capacity or flooded and then dried to field
capacity for 3 weeks during the vegetative stage. A black clay soil (Kandic Plinthaquult) and a sandy soil (Plinthustalf)
from south-east Cambodia were compared with or without amendments by rice straw and P fertilizer.
Under continuously flooded conditions, the growth of rice was vigorous without straw addition and there was a strong response
of rice growth to the addition of P fertilizer. The soil underwent reduction, which increased pH from 4.2 to 5.5 or 6.0, in
the black clay or sandy soil, respectively. By contrast, a loss of soil-water saturation 3 weeks before panicle initiation
(PI) markedly impaired the growth of rice. This was not through any effect of water stress, and the growth reductions were
not as strong as with continued loss of soil-water saturation from transplanting to PI. Fluctuations in soil pH and Eh corresponded
closely to changes in soil-water regimes. Growth reductions were attributed to reduced shoot P levels resulting from the decline
in P availability during the loss of soil-water saturation. The addition of rice straw stimulated soil reduction and lessened
changes in soil pH and Eh during the loss of soil-water saturation in both soils. Straw addition enhanced P uptake by the
rice plants during loss of soil-water saturation, but its beneficial effects could not be attributed to the direct addition
of P, N or K to the soils. Thus the application of rice straw may be effective in lessening the effects of temporary loss
of soil-water saturation on rice growth in lowland rice soils by minimising the decline in P availability.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
48.
David L. Kimbro Edwin D. Grosholz Adam J. Baukus Nicholas J. Nesbitt Nicole M. Travis Sarikka Attoe Caitlin Coleman-Hulbert 《Oecologia》2009,160(3):563-575
Although invasive species often resemble their native counterparts, differences in their foraging and anti-predator strategies
may disrupt native food webs. In a California estuary, we showed that regions dominated by native crabs and native whelks
have low mortality of native oysters (the basal prey), while regions dominated by invasive crabs and invasive whelks have
high oyster mortality and are consequently losing a biologically diverse habitat. Using field experiments, we demonstrated
that the invasive whelk’s distribution is causally related to a large-scale pattern of oyster mortality. To determine whether
predator–prey interactions between crabs (top predators) and whelks (intermediate consumers) indirectly control the pattern
of oyster mortality, we manipulated the presence and invasion status of the intermediate and top trophic levels in laboratory
mesocosms. Our results show that native crabs indirectly maintain a portion of the estuary’s oyster habitat by both consuming
native whelks (density-mediated trophic cascade) and altering their foraging behavior (trait-mediated trophic cascade). In
contrast, invasive whelks are naive to crab predators and fail to avoid them, thereby inhibiting trait-mediated cascades and
their invasion into areas with native crabs. Similarly, when native crabs are replaced with invasive crabs, the naive foraging
strategy and smaller size of invasive crabs prevents them from efficiently consuming adult whelks, thereby inhibiting strong
density-mediated cascades. Thus, while trophic cascades allow native crabs, whelks, and oysters to locally co-exist, the replacement
of native crabs and whelks by functionally similar invasive species results in severe depletion of native oysters. As coastal
systems become increasingly invaded, the mismatch of evolutionarily based strategies among predators and prey may lead to
further losses of critical habitat that support marine biodiversity and ecosystem function.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
49.
Kitty F Verzijlbergen Alex W Faber Iris JE Stulemeijer Fred van Leeuwen 《BMC molecular biology》2009,10(1):76
Background
Methylation of lysine 79 on histone H3 by Dot1 is required for maintenance of heterochromatin structure in yeast and humans. However, this histone modification occurs predominantly in euchromatin. Thus, Dot1 affects silencing by indirect mechanisms and does not act by the recruitment model commonly proposed for histone modifications. To better understand the role of H3K79 methylation gene silencing, we investigated the silencing function of Dot1 by genetic suppressor and enhancer analysis and examined the relationship between Dot1 and other global euchromatic histone modifiers. 相似文献50.
Eoghan M Cunnane John JE Mulvihill Hilary E Barrett Michael T Walsh 《Biomedical engineering online》2015,14(Z1):S7