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The effects of luteinizing hormone-releasing hormone (LRH) and thyrotropin-releasing hormone (TRH) upon the lordotic response to repetitive coital stimlation were studied using ovariectomized (OVX) and ovariectomized-adrenalectomized (OVX-ADX) female rats. Both OVX and OVX-ADX rats, pretreated with estrone alone, exhibited a dual behavioral response to repeated coital stimulation. The initial response to short-term stimulation was facilitatory with peak sexual receptivity occurring approximately 120 min following the initial male contact. This initial phase was followed by a depression of sexual receptivity associated with continued coital stimulation. Subcutaneous injection of 500 ng of LRH prior to mating was found to significantly potentiate the initial increases in sexual receptivity and to delay the onset of behavioral depression. The injection of 500 ng of TRH was observed to significantly depress behavioral enhancement due to repetitive coital stimulation.The repetitive coital stimulation model was utilized to localize forebrain areas behaviorally responsive to LRH and TRH. Stainless steel cannulas were implanted into either the medial preoptic area (MPOA), arcuate area (ARC), lateral hypothalamic area (LHA), or cerebral cortex (CC). Cannulated animals, primed with estrone, were tested for sexual receptivity immediately prior to experimental treatment, i.e., the infusion of 0.5 μl of 50 ng of LRH or TRH in 0.9% saline, 0.5 μl of 0.9% saline, or sham infusion. A second mating (postinfusion) test was performed 1.75 hr following infusion. When infused into the MPOA or ARC, LRH significantly enhanced lordotic behavior as compared to values obtained for saline or sham infusions. The infusion of LRH into LHA or CC showed no enhancement beyond the levels observed in control infusions (saline and sham infusions). The infusion of TRH into the MPOA or ARC depressed lordotic enhancement to repeated mating, however, this depression was significant only in ARC. These findings were consistent with previously demonstrated actions of releasing hormones upon neural activity within the MPOA and ARC. 相似文献
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Mike A. Steer Jayson M. Semmens 《Journal of experimental marine biology and ecology》2003,290(2):165-178
The influence of both predator and prey size on the shift from a pulling to a drilling predatory response was examined in the intertidal octopus Octopus dierythraeus, using an experimental program. Additionally, selective drilling, where particular regions of the prey are targeted, was examined for a variety of bivalve and gastropod prey. O. dierythraeus always initially attempted to pull bivalves apart. Shells that were eventually drilled were always subjected to significantly more pulling attempts than those that could be pulled apart, indicating that octopus are willing to expend more energy to access the flesh quickly. There was no defined threshold where bivalve size caused an octopus to switch from a pulling to a drilling response. Instead, there was a broad size range where the octopus could adopt either handling method and it varied for each individual. Octopus may only able to pull open bivalves before the molecular ratchet or ‘catch’ mechanism that many bivalves possess is engaged. This might explain the lack of a relationship between either octopus or bivalve size and the success of pulling, as it is likely that when the bivalves were presented to individual octopus they were either setting the ‘catch’ mechanism, or had already engaged it. O. dierythraeus demonstrated selective drilling on a variety of molluscan prey, with penetration sites differing between prey species. O. dierythraeus targeted the valve periphery, which was the thinnest part of the shell, therefore minimizing handling time. O. dierythraeus always drilled gastropods, but did not target the thinnest regions of the shells, with drill site varying according to the morphology of the prey. Elongate species with pronounced aperture lips were drilled in the apical region, close to the columella on the side of the opercula whereas nonelongate species were drilled immediately above the aperture. The location of drilling sites may represent a trade-off between targeting the most effective places to inject paralyzing secretions and the mechanically simplest places to drill. 相似文献
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Purification and some properties of the methyl-CoM reductase of Methanothrix soehngenii 总被引:1,自引:0,他引:1
Mike S.M. Jetten Alfons J.M. Stams Alexander J.B. Zehnder 《FEMS microbiology letters》1990,66(1-3):183-186
Abstract The methyl-CoM reductase from Methanothrix soehngenii was purified 18-fold to apparent homogeneity with 50% recovery in three steps. The native molecular mass of the enzyme estimated by gel-fitration was 280 kDa. SDS-polyacrylamide gel electrophoresis revealed three protein bands corresponding to M r 63 900, 41 700 and 30 400 Da. The methyl-coenzyme M reductase constitutes up to 10% of the soluble cell protein. The enzyme has K m apparent values of 23 μM and 2 mM for N -7-mercaptoheptanoylthreonine phosphate (HS- HTP = component B ) and methyl-coenzyme M (CH3 CoM) respectively. At the optimum pH of 7.0 60 nmol of methane were formed per min per mg protein. 相似文献
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