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101.
Janice A. Williams Simon Y. Long Xiankun Zeng Kathleen Kuehl April M. Babka Neil M. Davis Jun Liu John C. Trefry Sharon Daye Paul R. Facemire Patrick L. Iversen Sina Bavari Margaret L. Pitt Farooq Nasar 《PLoS neglected tropical diseases》2022,16(5)
Eastern equine encephalitis virus (EEEV) is mosquito-borne virus that produces fatal encephalitis in humans. We recently conducted a first of its kind study to investigate EEEV clinical disease course following aerosol challenge in a cynomolgus macaque model utilizing the state-of-the-art telemetry to measure critical physiological parameters. Here, we report the results of a comprehensive pathology study of NHP tissues collected at euthanasia to gain insights into EEEV pathogenesis. Viral RNA and proteins as well as microscopic lesions were absent in the visceral organs. In contrast, viral RNA and proteins were readily detected throughout the brain including autonomic nervous system (ANS) control centers and spinal cord. However, despite presence of viral RNA and proteins, majority of the brain and spinal cord tissues exhibited minimal or no microscopic lesions. The virus tropism was restricted primarily to neurons, and virus particles (~61–68 nm) were present within axons of neurons and throughout the extracellular spaces. However, active virus replication was absent or minimal in majority of the brain and was limited to regions proximal to the olfactory tract. These data suggest that EEEV initially replicates in/near the olfactory bulb following aerosol challenge and is rapidly transported to distal regions of the brain by exploiting the neuronal axonal transport system to facilitate neuron-to-neuron spread. Once within the brain, the virus gains access to the ANS control centers likely leading to disruption and/or dysregulation of critical physiological parameters to produce severe disease. Moreover, the absence of microscopic lesions strongly suggests that the underlying mechanism of EEEV pathogenesis is due to neuronal dysfunction rather than neuronal death. This study is the first comprehensive investigation into EEEV pathology in a NHP model and will provide significant insights into the evaluation of countermeasure. 相似文献
102.
The composition and ecological role of ciliates and dinoflagellates were investigated at one station in Kongsfjorden, Svalbard,
during six consecutive field campaigns between March and December 2006. Total ciliate and dinoflagellate abundance mirrored
the seasonal progression of phytoplankton, peaking with 5.8 × 104 cells l−1 in April at an average chlorophyll a concentration of 10 μg l−1. Dinoflagellates were more abundant than ciliates, dominated by small athecates. Among ciliates, aloricate oligotrichs dominated
the assemblage. A large fraction (>60%) of ciliates and dinoflagellates contained chloroplasts in spring and summer. The biomass
of the purely heterotrophic fraction of the ciliate and dinoflagellate community (protozooplankton) was with 14 μg C l−1 highest in conjunction with the phytoplankton spring bloom in April. Growth experiments revealed similar specific growth
rates for heterotrophic ciliates and dinoflagellates (<0–0.8 d−1). Food availability may have controlled the protozooplankton assemblage in winter, while copepods may have exerted a strong
control during the post-bloom period. Calculations of the potential grazing rates of the protozooplankton indicated its ability
to control or heavily impact the phytoplankton stocks at most times. The results show that ciliates and dinoflagellates were
an important component of the pelagic food web in Kongsfjorden and need to be taken into account when discussing the fate
of phytoplankton and biogeochemical cycling in Arctic marine ecosystems. 相似文献
103.
Stan D. Wullschleger Amy L. Breen Colleen M. Iversen Matthew S. Olson Torgny Näsholm Ulrika Ganeteg Matthew D. Wallenstein David J. Weston 《Molecular ecology》2015,24(10):2301-2309
Molecular ecology is poised to tackle a host of interesting questions in the coming years. The Arctic provides a unique and rapidly changing environment with a suite of emerging research needs that can be addressed through genetics and genomics. Here we highlight recent research on boreal and tundra ecosystems and put forth a series of questions related to plant and microbial responses to climate change that can benefit from technologies and analytical approaches contained within the molecular ecologist's toolbox. These questions include understanding (i) the mechanisms of plant acquisition and uptake of N in cold soils, (ii) how these processes are mediated by root traits, (iii) the role played by the plant microbiome in cycling C and nutrients within high‐latitude ecosystems and (iv) plant adaptation to extreme Arctic climates. We highlight how contributions can be made in these areas through studies that target model and nonmodel organisms and emphasize that the sequencing of the Populus and Salix genomes provides a valuable resource for scientific discoveries related to the plant microbiome and plant adaptation in the Arctic. Moreover, there exists an exciting role to play in model development, including incorporating genetic and evolutionary knowledge into ecosystem and Earth System Models. In this regard, the molecular ecologist provides a valuable perspective on plant genetics as a driver for community biodiversity, and how ecological and evolutionary forces govern community dynamics in a rapidly changing climate. 相似文献
104.
105.
Seven male subjects ran at 3.0 m/s on a motorized treadmill including a force platform under the tread. The subjects ran at each of five treadmill inclinations: +0.17, +0.077, 0, -0.077, and -0.17 radians. The position of the subjects' legs were read from ciné films (100 frames/s). Results of the film and force plate analysis generally corroborated the "hanging triangle" hypothesis, which postulates that the angle between the leg and the vertical upon foot strike does not change as the treadmill is tipped up or down. A mathematical model of running, in which the leg is represented as a nonlinear spring, made satisfactory predictions of the way many parameters of running change with the treadmill angle, including the length of the leg at touchdown and liftoff and the peak leg force in the middle of a step. The peak leg force reaches a maximum at a treadmill angle near -0.12 radians, close to the downhill angle where other authors have found a minimum in the rate of oxygen consumption. 相似文献
106.
David A. Schaer Richard P. Beckmann Jack A. Dempsey Lysiane Huber Amelie Forest Nelusha Amaladas Yanxia Li Ying Cindy Wang Erik R. Rasmussen Darin Chin Andrew Capen Carmine Carpenito Kirk A. Staschke Linda A. Chung Lacey M. Litchfield Farhana F. Merzoug Xueqian Gong Philip W. Iversen Michael Kalos 《Cell reports》2018,22(11):2978-2994
107.
Three-year study of benthic algal spring bloom development in a small, Danish lowland stream 总被引:1,自引:1,他引:0
Seasonal development of benthic algae was studied over a three-year period in a small, nutrient-rich lowland stream to investigate inter-annual variation in the algal spring bloom and differences in algal biomass regulation on two different substrata: fine-grained sediments and stones. The algal spring bloom was initiated when irradiance at the sediment surface exceeded 7 mol photons m-2 d-1 and mean water velocity was concomitantly below the threshold for bed load transport in the stream. Large inter-annual and substratum-dependent differences in peak algal biomass were observed, thus suggesting that different parameters regulate algal biomass development on the two substrata. On fine-grained sediments algal biomass development was predominantly coupled to light availability, while on stony substrata algal composition and peak biomass might be affected by invertebrate grazing. 相似文献
108.
Magne Refsnes Olav F. Dajani Dagny Sandnes G. Hege Thoresen John-Arne Rttingen Jens-Gustav Iversen Thoralf Christoffersen 《Journal of cellular physiology》1995,164(3):465-473
While many observations indicate that prostaglandins may act as positive regulators of hepatocyte proliferation, the underlying mechanisms are not known. We have examined some of the signal pathways in the growth response induced by prostaglandins in hepatocytes, with particular focus on adenylyl cyclase and phosphoinositide-specific phospholipase C. Adult rat hepatocytes were cultured as primary monolayers in serum-free medium in the presence of EGF and insulin. PGE2 or PGF2α (added 0-3 h after plating) enhanced the incorporation of [3H]-thymidine into DNA (measured at 50 h); at 100 γM the stimulation was about threefold. PGI2 and PGD2 also showed significant but smaller stimulatory effects. No significant increase in the level of cyclic AMP (cAMP) was detected in response to any of the prostaglandins. Low concentrations of glucagon (0.1-10 nM), a potent activator of hepatic adenylyl cyclase, or 8-bromo-cAMP (0.1-10 γM) enhanced the DNA synthesis. When 8-bromo-cAMP was used in maximally effective concentrations, no further stimulation was obtained by combining it with glucagon, whereas the effects of PGE2 and 8-bromo-cAMP were completely additive. All the prostaglandins also showed additivity with the effect of glucagon on the DNA synthesis. PGE2, PGF2α, PGI2, and PGD2 increased intracellular inositol-1,4,5-trisphosphate (InsP3), with a relative order of efficacy roughly corresponding to their activity as stimulators of DNA synthesis. Increases in cytosolic free Ca2+, as measured in single cells, were elicited in a majority of the hepatocytes by all these prostaglandins at 1 γM. Supramaximal concentrations of vasopressin, a strong activator of phospholipase C in hepatocytes, acted additively with PGE2 on the DNA synthesis. Pretreatment of the hepatocytes with a concentration of pertussis toxin that prevented the inhibitory effect of PGE2 on glucagon-induced cAMP accumulation did not abolish the ability of PGE2 to stimulate the DNA synthesis. The results do not support a role for adenylyl cyclase activation in the stimulatory effect of prostaglandins on hepatocyte growth. While the data are compatible with an involvement of phosphoinositide-specific phospholipase C in the growth-promoting effect of prostaglandins in cultured rat hepatocytes, they suggest this may not be the sole mechanism. © 1995 Wiley-Liss, Inc. 相似文献
109.
Bjømstad, O. N., Iversen, A. & Hansen, M. 1995. The spatial structure of the gene pool of a viviparous population of Poa alpina — environmental controls and spatial constraints. — Nord. J. Bot. 15: 347–354. Copenhagen. ISSN 0107–055X.
Because both the genetic make-up and the environmental conditions of a population are spatially autocorrelated, it is difficult to infer processes of selection or drift for population genetic mappings. We propose a methodology based on partial Mantel techniques and partial autocorrelation techniques to separate the action of these processes. The method is applied to data on Poa alpina to indicate that isolation-by-distance (drift) is the main process inducing positive autocorrelation at the scale of diaspore dispersal (< 100m). The pattern at larger distances is more consistent with selection. 相似文献
Because both the genetic make-up and the environmental conditions of a population are spatially autocorrelated, it is difficult to infer processes of selection or drift for population genetic mappings. We propose a methodology based on partial Mantel techniques and partial autocorrelation techniques to separate the action of these processes. The method is applied to data on Poa alpina to indicate that isolation-by-distance (drift) is the main process inducing positive autocorrelation at the scale of diaspore dispersal (< 100m). The pattern at larger distances is more consistent with selection. 相似文献
110.
Andrea Hidalgo Kaveh Barami Kristin Iversen Steven A. Goldman 《Developmental neurobiology》1995,27(4):470-487
The higher vocal center (HVC) of the songbird forebrain exhibits persistent neurogenesis in adulthood, particularly in a region of the mediocaudal neostriatum that is associated with a subventricular layer of estrogen receptive cells. We asked whether estrogens might influence adult neurogenesis, by assessing the effect of ovariectomy on HVC neuronal production in the adult female canary. Fifteen 1-year-old females were separated into groups of ovariectomized, estradiol-replaced ovariectomized, and gonadally intact birds. To label dividing cells and their progency, the birds were given [3H]thymidine for 8 days, killed 32 days later, and their brains autoradiographed. A significant rise was noted in the number of HVC neurons per section in estradiol-treated birds relative to the untreated control birds. The number of [3H]-thymidine-labeled HVC neurons was also higher in the estrogen-treated birds; however, the neuronal labeling index (LI) did not vary as a function of estradiol replacement, as the total number of HVC neurons rose in parallel with the added new neurons. In contrast, the neuronal LI did rise as a result of ovariectomy, and this ovariectomy-associated increase in the LI was not reversed by estradiol. Among non-neuronal cell types, the endothelial LI was higher in estrogen-treated birds than in their untreated counterparts, suggesting estrogen-associated angiogenesis. Radioimmunoassay confirmed that serum estradiol was reduced in the castrated birds. Since estrogen appeared to promote the survival of [3H]thymidine+ neurons, we next sought to determine whether estrogen acted directly on the newly generated neurons, or rather indirectly through an intermediary cell population. To this end, we asked whether the new neurons or their precursors expressed estrogen receptor immunoreactivity (ER-IR). Five adult male canaries were given [3H]thymidine for periods ranging from 2 to 28 days, killed at varying times up to 3 weeks therafter, then probed for ER-IR and autoradiographed. [3H]thymidine+ cells displayed no detectable ER-IR within their first 4 weeks of postmitotic life. Rather, during migration from the ventricular zone (VZ), the new neurons traversed a layer of mitotically quiescent, ER+ subventricular cells. Double labeling for ER-IR and cell-type selective antigens confirmed that these ER+ cells were neurons. These results indicate that the early survival of new neurons in the adult songbird HVC is promoted by estrogen, and may be mediated by the estrogen-stimulated paracrine release of neurotrophic agents by ER-IR subventricular neurons. Our data suggest that estrogen's promotion of neuronal survival may operate concurrently with an estrogen-independent ovarian suppression of neuronal mitogenesis. 相似文献