全文获取类型
收费全文 | 3232篇 |
免费 | 153篇 |
国内免费 | 107篇 |
出版年
2024年 | 2篇 |
2023年 | 31篇 |
2022年 | 42篇 |
2021年 | 47篇 |
2020年 | 63篇 |
2019年 | 80篇 |
2018年 | 77篇 |
2017年 | 65篇 |
2016年 | 65篇 |
2015年 | 80篇 |
2014年 | 129篇 |
2013年 | 224篇 |
2012年 | 91篇 |
2011年 | 107篇 |
2010年 | 69篇 |
2009年 | 97篇 |
2008年 | 129篇 |
2007年 | 173篇 |
2006年 | 152篇 |
2005年 | 129篇 |
2004年 | 158篇 |
2003年 | 153篇 |
2002年 | 124篇 |
2001年 | 75篇 |
2000年 | 80篇 |
1999年 | 84篇 |
1998年 | 83篇 |
1997年 | 93篇 |
1996年 | 83篇 |
1995年 | 79篇 |
1994年 | 103篇 |
1993年 | 69篇 |
1992年 | 66篇 |
1991年 | 69篇 |
1990年 | 55篇 |
1989年 | 52篇 |
1988年 | 49篇 |
1987年 | 45篇 |
1986年 | 31篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 15篇 |
1981年 | 14篇 |
1980年 | 3篇 |
1979年 | 4篇 |
1978年 | 2篇 |
1977年 | 4篇 |
1976年 | 2篇 |
排序方式: 共有3492条查询结果,搜索用时 15 毫秒
1.
Diego Sustaita Patty Finfrock Quickert Laura Patterson Laureen Barthman-Thompson Sarah Estrella 《The Journal of wildlife management》2011,75(6):1498-1507
We undertook a 2-year (2002–2004) mark–recapture study to investigate demographic performance and habitat use of salt marsh harvest mice (Reithrodontomys raviventris halicoetes) in the Suisun Marsh. We examined the effects of different wetland types and microhabitats on 3 demographic variables: density, reproductive potential, and persistence. Our results indicate that microhabitats dominated by mixed vegetation or pickleweed (Salicornia spp.) supported similar salt marsh harvest mouse densities, reproductive potential, and persistence throughout much of the year, whereas few salt marsh harvest mice inhabited upland grass-dominated microhabitats. We found that densities were higher in diked wetlands, whereas post-winter persistence was higher in tidal wetlands, and reproductive potential did not differ statistically between wetland types. Our results emphasize the importance of mixed vegetation for providing adequate salt marsh harvest mouse habitat and suggest that, despite their physiognomic and hydrological differences, both diked and tidal wetlands support salt marsh harvest mouse populations by promoting different demographic attributes. We recommend that habitat management, restoration, and enhancement efforts include areas containing mixed vegetation in addition to pickleweed in both diked and tidal wetlands. © 2011 The Wildlife Society. 相似文献
2.
3.
Inflammatory responses mediated by activated microglia play a pivotal role in the pathogenesis of human immunodeficiency virus type 1 (HIV-1)-associated neurocognitive disorders. Studies on identification of specific targets to control microglia activation and resultant neurotoxic activity are imperative. Increasing evidence indicate that voltage-gated K+ (Kv) channels are involved in the regulation of microglia functionality. In this study, we investigated Kv1.3 channels in the regulation of neurotoxic activity mediated by HIV-1 glycoprotein 120 (gp120)-stimulated rat microglia. Our results showed treatment of microglia with gp120 increased the expression levels of Kv1.3 mRNA and protein. In parallel, whole-cell patch-clamp studies revealed that gp120 enhanced microglia Kv1.3 current, which was blocked by margatoxin, a Kv1.3 blocker. The association of gp120 enhancement of Kv1.3 current with microglia neurotoxicity was demonstrated by experimental results that blocking microglia Kv1.3 attenuated gp120-associated microglia production of neurotoxins and neurotoxicity. Knockdown of Kv1.3 gene by transfection of microglia with Kv1.3-siRNA abrogated gp120-associated microglia neurotoxic activity. Further investigation unraveled an involvement of p38 MAPK in gp120 enhancement of microglia Kv1.3 expression and resultant neurotoxic activity. These results suggest not only a role Kv1.3 may have in gp120-associated microglia neurotoxic activity, but also a potential target for the development of therapeutic strategies. 相似文献
4.
Donald S. McLusky 《Aquatic Ecology》1993,27(2-4):489-493
The Proceedings of the ECSA 21 symposium on Marine and Estuarine Gradients are reviewed. It is emphasised that this is probably
the first time that a full set of papers on the tidal freshwater sections of estuaries has appeared. There is however some
ambiguity in the terminology applied to such waters, and a more consistent terminology is proposed. In particular the estuary
is defined as reaching upstream as far as the tidal limit, irrespective of salinity.
A wide variety of gradients within estuaries and coastal waters are considered, but it is apparent that the crucial spatial
gradients are based on salinity, oxygen and turbidity, and that many other gradients are co-variables with these parameters.
Temperature is also important for temporal gradients. 相似文献
5.
《Bioorganic & medicinal chemistry》2014,22(6):1797-1803
Neuropathic pain is a serious physical disabling condition resulting from lesion or dysfunction of the peripheral sensory nervous system. Despite the fact that the mechanisms underlying neuropathic pain are poorly understood, the involvement of voltage-gated calcium (CaV) channels in its pathophysiology has justified the use of drugs that bind the CaV channel α2δ auxiliary subunit, such as gabapentin (GBP), to attain analgesic and anti-allodynic effects in models involving neuronal sensitization and nerve injury. GBP binding to α2δ inhibits nerve injury-induced trafficking of the α1 pore forming subunits of CaV channels, particularly of the N-type, from the cytoplasm to the plasma membrane of pre-synaptic terminals in dorsal root ganglion neurons and dorsal horn spinal neurons. In the search for alternative forms of treatment, in this study we describe the synthesis and pharmacological profile of a GABA derivative, 2-aminoadamantane-1-carboxylic acid (GZ4), which displays a close structure–activity relationship with GBP. Behavioral assessment using von Frey filament stimuli showed that GZ4 treatment reverted mechanical allodynia/hyperalgesia in an animal model of spinal nerve ligation-induced neuropathic pain. In addition, using the patch clamp technique we show that GZ4 treatment significantly decreased whole-cell currents through N-type CaV channels heterologously expressed in HEK-293 cells. Interestingly, the behavioral and electrophysiological time course of GZ4 actions reflects that its mechanism of action is similar but not identical to that of GBP. While GBP actions require at least 24 h and imply uptake of the drug, which suggests that the drug acts mainly intracellularly affecting channels trafficking to the plasma membrane, the faster time course (1–3 h) of GZ4 effects suggests also a direct inhibition of Ca2+ currents acting on cell surface channels. 相似文献
6.
《Somatosensory & motor research》2013,30(4):345-357
Thresholds for detecting vibrotactile signals of variable frequency applied to the thenar eminence of the hand by small and large contactors were measured in subjects ranging in age from 10 to 89 years. Thresholds were found to increase as a function of age, but the rate of increase was greater after than before the age of 65 years. The rate of loss of vibrotactile sensitivity was substantially greater in the P channel (mediated by Pacinian corpuscles) than in the NP I channel (mediated by rapidly adapting fibers), the NP II channel (mediated by slowly adapting type II fibers), or the NP HI channel (mediated by slowly adapting type I fibers). Women were frequently found to have greater sensitivity than men. 相似文献
7.
The excised patch clamp configuration provides a unique technique for some types of single channel analyses, but maintenance of stable, long-lasting preparations may be confounded by rundown and/or rapid loss of seal. Studies were performed on the amiloride-sensitive Na+ channel, located on the apical surface of A6 cells, to determine whether the nystatininduced open cell-attached patch could serve as an alternative configuration.Compared to excised inside-out patches, stable preparations were achieved more readily with the open cell-attached patch (9% vs. 56% of attempts). In both preparations, the current voltage (I-V) relation was linear, current amplitudes were equal at opposite equivalent clamped voltages, and E
rev was zero in symmetrical Na+ solutions, indicating similar Na+ activities on the cytosolic and external surfaces of the patch. Moreover, there was no evidence that nystatin altered channel activity in the patch because slope conductance (3–4pS) and E
rev (75 mV), when the bath was perfused with a high K:low Na solution (E
Na=80 mV), were nearly equal in both patch configurations.Our results therefore indicate that the nystatininduced open cell-attached patch can serve as an alternative approach to the excised inside-out patch when experiments require modulation of univalent ions in the cytosol.We thank Dr. Olaf S. Andersen for his suggestions in the development of the open cell-attached recording technique. This work was supported by a National Institutes of Health grant (DK-18061) 相似文献
8.
The assembly of high voltage-activated Ca2+ channels with different β subunits influences channel properties and possibly subcellular targeting. We studied β subunit expression in the somata and axon terminals of the magnocellular neurosecretory cells, which are located in the supraoptic nucleus (SON) and neurohypophysis, respectively. Antibodies directed against the 4 CaVβ subunits (CaVβ1-CaVβ4) were used for immunoblots and for immunostaining of slices of these two tissues. We found that all 4 β subunits are expressed in both locations, but that CaVβ2 had the highest relative expression in the neurohypophysis. These data suggest that the CaVβ2 subunit is selectively targeted to axon terminals and may play a role in targeting and/or regulating the properties of Ca2+ channels. 相似文献
9.
Summary The voltage-dependent sodium channel from the eel electroplax was purified and reconstituted into vesicles of varying lipid composition. Isotopic sodium uptake experiments were conducted with vesicles at zero membrane potential, using veratridine to activate channels and tetrodotoxin to block them. Under these conditions, channel-dependent uptake of isotopic sodium by the vesicles was observed, demonstrating that a certain fraction of the reconstituted protein was capable of mediating ion fluxes. In addition, vesicles untreated with veratridine showed significant background uptake of sodium; a considerable proportion of this flux was blocked by tetrodotoxin. Thus these measurements showed that a significant subpopulation of channels was present that could mediate ionic fluxes in the absence of activating toxins. The proportion of channels exhibiting this behavior was dependent on the lipid composition of the vesicles and the temperature at which the uptake was measured; furthermore, the effect of temperature was reversible. However, the phenomenon was not affected by the degree of purification of the protein used for reconstitution, and channels in resealed electroplax membrane fragments or reconstituted, solely into native eel lipids did not show this behavior. The kinetics of vesicular uptake through these spontaneously-opening channels was slow, and we attribute this behavior to a modification of sodium channel inactivation. 相似文献
10.
R. L. Robbins 《Journal of fish biology》2007,70(5):1350-1364
The seasonal temporal sexual segregation of white sharks Carcharodon carcharias , at the Neptune Islands, South Australia, is described in relation to environmental variables. A significant sexual segregation was found at this site with sex ratios strongly favouring males overall. Males were more prevalent than females in all months in a 3 year sampling period, aside from April and May. There was a significant difference between the sexes in terms of mean daily numbers over the months of the study. It was also observed that sexual segregation fluctuated for unknown reasons on a temporal scale. Predictive models for estimating male and female numbers based on a series of abiotic factors were generated. Sea surface temperature, tidal height, tidal range, moon phase, cloud cover, underwater visibility and swell height were related to daily sightings of male and female white sharks to determine the influence of these variables on sexual segregation. Visibility and sea surface temperature affected male numbers, however, visibility did not affect sexual segregation. Tidal height was significantly different between males and females. Sea surface temperature also appeared to be related to sexual segregation in this species. Females were present when temperatures ranged from 15·7 to 18·1° C whereas males were observed at temperatures ranging from 14·3 to 17·8° C, with a peak in sightings in September, when sea surface temperatures were at their lowest. Since parturition is thought to occur in spring or summer, it is suggested that females are absent at this time and only return during prime feeding periods or times at which temperatures are elevated in order to increase developmental growth rates of their young. The significantly lower temperatures in 2003 may explain the absence of females in this year. Hypotheses related to temperature regulation in this species are put forward to explain the sexual segregation observed. 相似文献