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71.
Butterfield DA Howard B Yatin S Koppal T Drake J Hensley K Aksenov M Aksenova M Subramaniam R Varadarajan S Harris-White ME Pedigo NW Carney JM 《Life sciences》1999,65(18-19):1883-1892
Age-associated neurodegenerative disorders are becoming more prevalent as the mean age of the population increases in the United States over the next few decades. Both normal brain aging and Alzheimer's disease (AD) are associated with oxidative stress. Our laboratory has used a wide variety of physical and biochemical methods to investigate free radical oxidative stress in several models of aging and AD. Beta-amyloid (A beta), the peptide that constitutes the central core of senile plaques in AD brain, is associated with free radical oxidative stress and is toxic to neurons. This review summarizes some of our studies in aging and A beta-associated free radical oxidative stress and on the modulating effects of free radical scavengers on neocortical synaptosomal membrane damage found in aging and A beta-treated systems. 相似文献
72.
Short‐term carbon cycling responses of a mature eucalypt woodland to gradual stepwise enrichment of atmospheric CO2 concentration 下载免费PDF全文
John E. Drake Catriona A. Macdonald Mark G. Tjoelker Kristine Y. Crous Teresa E. Gimeno Brajesh K. Singh Peter B. Reich Ian C. Anderson David S. Ellsworth 《Global Change Biology》2016,22(1):380-390
Projections of future climate are highly sensitive to uncertainties regarding carbon (C) uptake and storage by terrestrial ecosystems. The Eucalyptus Free‐Air CO2 Enrichment (EucFACE) experiment was established to study the effects of elevated atmospheric CO2 concentrations (eCO2) on a native mature eucalypt woodland with low fertility soils in southeast Australia. In contrast to other FACE experiments, the concentration of CO2 at EucFACE was increased gradually in steps above ambient (+0, 30, 60, 90, 120, and 150 ppm CO2 above ambient of ~400 ppm), with each step lasting approximately 5 weeks. This provided a unique opportunity to study the short‐term (weeks to months) response of C cycle flux components to eCO2 across a range of CO2 concentrations in an intact ecosystem. Soil CO2 efflux (i.e., soil respiration or Rsoil) increased in response to initial enrichment (e.g., +30 and +60 ppm CO2) but did not continue to increase as the CO2 enrichment was stepped up to higher concentrations. Light‐saturated photosynthesis of canopy leaves (Asat) also showed similar stimulation by elevated CO2 at +60 ppm as at +150 ppm CO2. The lack of significant effects of eCO2 on soil moisture, microbial biomass, or activity suggests that the increase in Rsoil likely reflected increased root and rhizosphere respiration rather than increased microbial decomposition of soil organic matter. This rapid increase in Rsoil suggests that under eCO2, additional photosynthate was produced, transported belowground, and respired. The consequences of this increased belowground activity and whether it is sustained through time in mature ecosystems under eCO2 are a priority for future research. 相似文献
73.
The nucleotide and deduced amino acid sequences of the encephalomyocarditis viral polyprotein coding region. 总被引:42,自引:11,他引:42 下载免费PDF全文
A C Palmenberg E M Kirby M R Janda N L Drake G M Duke K F Potratz M S Collett 《Nucleic acids research》1984,12(6):2969-2985
The nucleotide sequence of 7200 bases of encephalomyocarditis (EMC) viral RNA, including the complete polyprotein-coding region, was determined. The polyprotein is encoded within a unique translational reading frame, 6870 bases in length. Protein synthesis begins with the sequence Met-Ala-Thr, and ends with the sequence Leu-Phe-Trp, 126 bases from the 3' end of the RNA. Viral capsid and noncapsid proteins were aligned with the deduced amino acid sequence of the polyprotein. The proteolytic processing map follows the standard 4-3-4 picornaviral pattern except for a short leader peptide (8 kd), which precedes the capsid proteins. Identification of the proteolytic cleavage sites showed that EMC viral protease, p22, has cleavage specificity for gln-gly or gln-ser sequences with adjacent proline residues. The cleavage specificity of the host-coded protease(s) includes both tyr-pro and gln-gly sequences. 相似文献
74.
Lapierre LA Ducharme NA Drake KR Goldenring JR Kenworthy AK 《Experimental cell research》2012,318(2):103-113
Recent studies have identified caveolin-1, a protein best known for its functions in caveolae, in apical endocytic recycling compartments in polarized epithelial cells. However, very little is known about the regulation of caveolin-1 in the endocytic recycling pathway. To address this question, in the current study we compared the relationship between compartments enriched in sub-apical caveolin-1 and Rab11a, a well-defined marker of apical recycling endosomes, using polarized MDCK cells as a model. We show that caveolin-1-containing vesicles define a compartment that partially overlaps with Rab11a, and that the distribution of subapical caveolin-1 and Rab11a shows a similar dependence on microtubule disruption. Mutants of the Rab11a effector, Rab11-FIP2 also altered the localization of caveolin-1. These findings indicate that caveolin-1 is coordinately regulated with Rab11a within the apical recycling system of polarized epithelial cells, suggesting that the two proteins are components of the same pathway. 相似文献
75.
ALEXANDRA C. LEY REGINE CLAßEN‐BOCKHOFF 《Botanical journal of the Linnean Society. Linnean Society of London》2012,168(3):300-322
The flowers of Marantaceae (~ 550 species) exhibit a highly derived pollination mechanism within Zingiberales, with a rapid and irreversible style movement based on a close synorganization of different floral parts. Given the complexity of the structure, we assume that little variation is possible if functionality is to be maintained. To test this, we investigated how much floral diversity exists in the clade and whether this diversity potentially influences the breeding system and placement of pollen on the pollinator. Flowers of 66 species covering the five major phylogenetic clades of the family were analysed. All species are similar in their basic flower construction: the fleshy staminode forms the tunnel‐shaped roof of the flower and narrows the tube with stiff swellings, and the hooded staminode holds the style under tension and narrows the flower entrance with its trigger appendage. Despite morphological diversity of the pollination apparatus, functionality is maintained by coordinated variation of the fleshy and hooded staminodes. Autogamy is usually avoided by herkogamy. However, in a few exceptions, subtle morphological changes alter the breeding system from allogamy to autogamy. Variable floral proportions allow for differential pollen deposition potentially causing mechanical isolation between sister taxa. This study clearly illustrates that structural variation is not only present in the highly synorganized flowers of Marantaceae, but that it also creates potentially new options for evolutionary diversification. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 300–322. 相似文献
76.
Sensitive probes are required for studying the biochemistry of Gd(III) contrast agents used in magnetic resonance imaging. We show that complexation of Gd(III) by diethylenetriamine-N,N,N',N',N"-pentaacetic acid (DTPA) in aqueous solution can be readily determined from the sharp 4f-4f bands for free and bound Gd(III) in the range 270-282 nm, and, with greater sensitivity, from the associated magnetic-circular-dichroic spectra. 相似文献
77.
Justin A. G. Hubbard D. Andrew R. Drake Nicholas E. Mandrak 《Diversity & distributions》2023,29(8):986-996
Aim
We employed a climate-matching method to evaluate potential source regions of freshwater invasive species to an introduced region and their potential secondary spread under historical and future climates.Location
Global source regions, with primary introductions to the Laurentian Great Lakes and secondary introductions throughout North America.Methods
We conducted a climate-match analysis using the CLIMATE algorithm to estimate global source freshwater ecoregions under historical and future climates with an ensemble of global climate models for climate-change scenario SSP5-8.5. Given existing research, we use a climate match of ≥71.7% between ecoregions to indicate climatic conditions that will not inhibit the survival of introduced freshwater organisms. Further, we estimate the secondary spread of freshwater invaders to the ecoregions of North America under historical and future climates.Results
We identified 54 global freshwater ecoregions with a climate match ≥71.7% to the recipient Laurentian Great Lakes under historical climatic conditions, and 11 additional ecoregions were predicted to exceed the threshold under climate change. Three of the 11 ecoregions were located in South America, a continent where no matches existed under historical climates and eight were located in the southern United States, southern Europe, Japan and New Zealand. Further, we identify 34 North American ecoregions of potential secondary spread of freshwater invasions from the Great Lakes under historical climatic conditions, and five ecoregions were predicted to exceed the threshold under climate change.Main Conclusion
We provide a climate-match method that can be employed to assess the sources and spread of freshwater invasions under historical and future climate scenarios. Our climate-match method predicted increases in climate match between the recipient region and several potential source regions, and changes in areas of potential spread under climate change. The identified ecoregions are candidates for detailed biosecurity risk assessments and related management actions. 相似文献78.
Graham J. Hymus David P. Johnson Sabina Dore† Hans P. Anderson C. Ross Hinkle‡ Bert G. Drake 《Global Change Biology》2003,9(12):1802-1812
We report the results of a 2‐year study of effects of the elevated (current ambient plus 350 μmol CO2 mol?1) atmospheric CO2 concentration (Ca) on net ecosystem CO2 exchange (NEE) of a scrub–oak ecosystem. The measurements were made in open‐top chambers (OTCs) modified to function as open gas‐exchange systems. The OTCs enclosed samples of the ecosystem (ca. 10 m2 surface area) that had regenerated after a fire, 5 years before, in either current ambient or elevated Ca. Throughout the study, elevated Ca increased maximum NEE (NEEmax) and the apparent quantum yield of the NEE (φNEE) during the photoperiod. The magnitude of the stimulation of NEEmax, expressed per unit ground area, was seasonal, rising from 50% in the winter to 180% in the summer. The key to this stimulation was effects of elevated Ca, and their interaction with the seasonal changes in the environment, on ecosystem leaf area index, photosynthesis and respiration. The separation of these factors was difficult. When expressed per unit leaf area the stimulation of the NEEmax ranged from 7% to 60%, with the increase being dependent on increasing soil water content (Wsoil). At night, the CO2 effluxes from the ecosystem (NEEnight) were on an average 39% higher in elevated Ca. However, the increase varied between 6% and 64%, and had no clear seasonality. The partitioning of NEEnight into its belowground (Rbelow) and aboveground (Rabove) components was carried out in the winter only. A 35% and 27% stimulation of NEEnight in December 1999 and 2000, respectively, was largely due to a 26% and 28% stimulation of Rbelow in the respective periods, because Rbelow constituted ca. 87% of NEEnight. The 37% and 42% stimulation of Rabove in December 1999 and 2000, respectively, was less than the 65% and 80% stimulation of the aboveground biomass by elevated Ca at these times. An increase in the relative amount of the aboveground biomass in woody tissue, combined with a decrease in the specific rate of stem respiration of the dominant species Quercus myrtifolia in elevated Ca, was responsible for this effect. Throughout this study, elevated Ca had a greater effect on carbon uptake than on carbon loss, in terms of both the absolute flux and relative stimulation. Consequently, for this scrub–oak ecosystem carbon sequestration was greater in the elevated Ca during this 2‐year study period. 相似文献
79.
Marijn Bauters Sofie Meeus Matti Barthel Piet Stoffelen Hannes P. T. De Deurwaerder Flicien Meunier Travis W. Drake Quentin Ponette Jerme Ebuy Pieter Vermeir Hans Beeckman Francis wyffels Samuel Bod Hans Verbeeck Filip Vandelook Pascal Boeckx 《Global Change Biology》2020,26(8):4449-4461
Forests exhibit leaf‐ and ecosystem‐level responses to environmental changes. Specifically, rising carbon dioxide (CO2) levels over the past century are expected to have increased the intrinsic water‐use efficiency (iWUE) of tropical trees while the ecosystem is gradually pushed into progressive nutrient limitation. Due to the long‐term character of these changes, however, observational datasets to validate both paradigms are limited in space and time. In this study, we used a unique herbarium record to go back nearly a century and show that despite the rise in CO2 concentrations, iWUE has decreased in central African tropical trees in the Congo Basin. Although we find evidence that points to leaf‐level adaptation to increasing CO2—that is, increasing photosynthesis‐related nutrients and decreasing maximum stomatal conductance, a decrease in leaf δ13C clearly indicates a decreasing iWUE over time. Additionally, the stoichiometric carbon to nitrogen and nitrogen to phosphorus ratios in the leaves show no sign of progressive nutrient limitation as they have remained constant since 1938, which suggests that nutrients have not increasingly limited productivity in this biome. Altogether, the data suggest that other environmental factors, such as increasing temperature, might have negatively affected net photosynthesis and consequently downregulated the iWUE. Results from this study reveal that the second largest tropical forest on Earth has responded differently to recent environmental changes than expected, highlighting the need for further on‐ground monitoring in the Congo Basin. 相似文献
80.
竹叶眼子菜(Potamogeton malaianus)、微齿眼子菜(Potamogeton maackianus)、苦草(Vallisneria spiralis)、穗花狐尾藻(Myriophyllum spicatum)、黑藻(Hydrilla verticillata)是长江中下游湖泊主要的沉水植物。在栽培条件下,它们的无性繁殖速率(单位时间内新增个体数)大小顺序为黑藻>微齿眼子菜>竹叶眼子菜>苦草>穗花狐尾藻。同时采用抛掷实验的方法观察研究了这5种沉水植物及其无性繁殖体的存活和生根情况;完整植株存活率为黑藻>穗花狐尾藻>微齿眼子菜>竹叶眼子菜>苦草,无性繁殖体部分存活率为黑藻>苦草>穗花狐尾藻>微齿眼子菜>竹叶眼子菜。生根能力和其存活时间长短相关,而且生根能力与存活率大小基本一致。在实验中,只有穗花狐尾藻的断枝存活率和生根能力存在差异,故无性繁殖体生根能力为黑藻>苦草>微齿眼子菜>竹叶眼子菜>穗花狐尾藻。 相似文献