全文获取类型
收费全文 | 149篇 |
免费 | 24篇 |
出版年
2022年 | 2篇 |
2021年 | 2篇 |
2020年 | 4篇 |
2018年 | 7篇 |
2017年 | 6篇 |
2016年 | 4篇 |
2015年 | 5篇 |
2014年 | 11篇 |
2013年 | 12篇 |
2012年 | 15篇 |
2011年 | 10篇 |
2010年 | 3篇 |
2009年 | 6篇 |
2008年 | 3篇 |
2007年 | 11篇 |
2006年 | 9篇 |
2005年 | 6篇 |
2004年 | 6篇 |
2003年 | 2篇 |
2002年 | 5篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 2篇 |
1996年 | 3篇 |
1994年 | 1篇 |
1990年 | 3篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1985年 | 1篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 2篇 |
1973年 | 2篇 |
1970年 | 2篇 |
1966年 | 2篇 |
排序方式: 共有173条查询结果,搜索用时 31 毫秒
101.
Global predictions of increasing mean temperature and its variance result in concerns about the fate of biodiversity under future climatic conditions. On the local scale of interacting species, the response of diversity to warming will depend much on the change in interspecific interactions such as competition or predation. Using a phytoplankton model community, we conducted a 2 × 2 × 2 factorial long‐term microcosm experiment (16 months) with an underlying seasonal temperature profile. We manipulated the mean temperature (Tmean), the temperature variance (Tvar), and the presence of consumers (ciliates) and monitored treatment effects on algal biomass, species composition and species richness. Temperature effects on algal biomass depended on the seasonal development and consumer presence. Algal biomass decreased with increasing Tmean at consumer absence, but increased at consumer presence. Overall, algal biomass decreased with increasing Tvar. Consumer presence reduced algal biomass from summer to winter, but then ciliates and the consumer effect disappeared. Almost all treatment combinations collapsed to monocultures after 16 months, but extinction occurred faster at higher Tmean (especially at consumer absence) and slower at consumer presence (especially at higher Tmean). Contrasting our predictions, increasing Tvar reduced richness and increased extinction rate. The treatment effects on biomass and richness were not independent, as algal species richness and biomass were positively correlated. Moreover, accelerated loss of species was consistently correlated to higher temporal variability in biomass. In conclusion, altered temperature regimes strongly affected algal biomass and diversity by interdependently altering competitive and consumer interactions. 相似文献
102.
Presence of habitat-forming macroalgae is supposed to mitigate effects of altered resources on benthic microalgae and their consumers. In a field experiment in a microtidal area of the Western Baltic Sea, we tested the interactive effects of nutrient enrichment, artificial shading, and habitat complexity on microalgal biomass and diversity as well as invertebrate abundance and richness. Habitat complexity comprised three levels, the presence of macroalgal canopy of Fucus vesiculosus, the presence of macroalgal propagules, and the absence of both (=control). Microalgal biomass (and richness) was significantly reduced by canopy presence (−88%, compared to control) and shading (−42%), with the highest biomass in the absence of both canopy and macroalgal propagules at ambient light. Within the microalgal assemblage, higher biomass was related to lower evenness (higher dominance). Density of two main invertebrate groups (snails and amphipods) strongly increased with canopy presence (on average from 53 to 154 individuals m−2 stone area for snails, and from 234 to 1203 individuals m−2 for amphipods) and so did invertebrate richness (from 4.3 to 10.3). Additionally, snail density doubled with increasing light availability. The snail responses to light and canopy were independent, the former relating to higher availability of microalgal prey, the latter to more structure. Microalgal taxon richness and biomass decreased with increasing invertebrate richness and with density of snails and amphipods. Our experiment thus showed that the presence of habitat-forming macroalgae alters biomass and diversity across trophic levels in benthic coastal communities as well as their response to resource manipulations. 相似文献
103.
Helmut Hillebrand 《Ecological Research》2011,26(3):533-539
The dependence of competitive interactions on abiotic conditions is attracting increasing interest in the face of globally
rising temperatures and altered biogeochemical cycles of major nutrients. In a microcosm experiment involving a natural inoculum
of benthic microalgae, temperature and nutrient supply ratios were manipulated in order to test three main hypotheses: (1)
temperature and nutrient supply ratios determine species composition and diversity of the assemblage, (2) the identity of
the dominating species depends on nutrient supply and temperature, and (3) higher temperature leads to faster competitive
exclusion and thus more rapid decline in species richness. Over a period of 7 weeks, algal biomass reached an equilibrium
carrying capacity, with was higher at colder temperatures and intermediate N:P supply ratios (N:P = 16). Initial growth rate
increased with temperature and under high P-supply. Species richness in the stationary phase of the experiment decreased with
increasing temperature, reflecting a higher extinction rate in the warmer treatments, which were also characterized by higher
dominance of single species. Thus, increasing temperature both altered the identity of the dominating species and accelerated
competitive displacement. This experiment thus indicates that warming might influence outcome and temporal dynamics in species
interactions, and thereby eventually local diversity. 相似文献
104.
Prejaas Tewarie Menno M. Schoonheim Cornelis J. Stam Marieke L. van der Meer Bob W. van Dijk Frederik Barkhof Chris H. Polman Arjan Hillebrand 《PloS one》2013,8(7)
The relation between pathological findings and clinical and cognitive decline in Multiple Sclerosis remains unclear. Here, we tested the hypothesis that altered functional connectivity could provide a missing link between structural findings, such as thalamic atrophy and white matter lesion load, and clinical and cognitive dysfunction. Resting-state magnetoencephalography recordings from 21 MS patients and 17 gender- and age matched controls were projected onto atlas-based regions-of–interest using beamforming. Average functional connectivity was computed for each ROI and literature-based resting-state networks using the phase-lag index. Structural measures of whole brain and thalamic atrophy and lesion load were estimated from MRI scans. Global analyses showed lower functional connectivity in the alpha2 band and higher functional connectivity in the beta band in patients with Multiple Sclerosis. Additionally, alpha2 band functional connectivity was lower for the patients in two resting-state networks, namely the default mode network and the visual network. Higher beta band functional connectivity was found in the default mode network and in the temporo-parietal network. Lower alpha2 band functional connectivity in the visual network was related to lower thalamic volumes. Beta band functional connectivity correlated positively with disability scores, most prominently in the default mode network, and correlated negatively with cognitive performance in this network. These findings illustrate the relationship between thalamic atrophy, altered functional connectivity and clinical and cognitive dysfunction in MS, which could serve as a bridge to understand how neurodegeneration is associated with altered functional connectivity and subsequently clinical and cognitive decline. 相似文献
105.
Anne Ebeling Sebastian T. Meyer Maike Abbas Nico Eisenhauer Helmut Hillebrand Markus Lange Christoph Scherber Anja Vogel Alexandra Weigelt Wolfgang W. Weisser 《PloS one》2014,9(9)
Loss of plant diversity influences essential ecosystem processes as aboveground productivity, and can have cascading effects on the arthropod communities in adjacent trophic levels. However, few studies have examined how those changes in arthropod communities can have additional impacts on ecosystem processes caused by them (e.g. pollination, bioturbation, predation, decomposition, herbivory). Therefore, including arthropod effects in predictions of the impact of plant diversity loss on such ecosystem processes is an important but little studied piece of information. In a grassland biodiversity experiment, we addressed this gap by assessing aboveground decomposer and herbivore communities and linking their abundance and diversity to rates of decomposition and herbivory. Path analyses showed that increasing plant diversity led to higher abundance and diversity of decomposing arthropods through higher plant biomass. Higher species richness of decomposers, in turn, enhanced decomposition. Similarly, species-rich plant communities hosted a higher abundance and diversity of herbivores through elevated plant biomass and C:N ratio, leading to higher herbivory rates. Integrating trophic interactions into the study of biodiversity effects is required to understand the multiple pathways by which biodiversity affects ecosystem functioning. 相似文献
106.
Elizabeth T. Borer Matthew E. S. Bracken Eric W. Seabloom Jennifer E. Smith Just Cebrian Elsa E. Cleland James J. Elser William F. Fagan Daniel S. Gruner W. Stanley Harpole Helmut Hillebrand Andrew J. Kerkhoff Jacqueline T. Ngai 《Oikos》2013,122(8):1121-1130
Synthesis The tissue chemistry of plants can influence ecosystem processes including growth, herbivory, and decomposition. Our comparison of nitrogen and phosphorus in over 1700 autotroph taxa demonstrates that latitudinal trends in tissue chemistry are consistent across non‐vascular and vascular species in freshwater, terrestrial, and marine ecosystems. Tissue chemistry varies most within species and taxonomic lineages, yet the nitrogen to phosphorus ratio within individuals is strikingly similar among species in different ecosystems. These results shed new light on existing hypotheses, suggesting that light (e.g. photon flux) and growing season duration are primary drivers of latitudinal gradients in tissue chemistry, but providing little support for temperature, nutrient supply, or soil substrate age. Photoautotroph nitrogen (N) and phosphorus (P) tissue concentrations can influence ecosystem function via processes including growth, decomposition, and consumption, and may reflect traits maintaining coexistence. Studies in terrestrial systems have led to hypotheses that latitudinal trends in the N and P content of leaves may be driven by soil substrate age, environmental temperature, or season length; however, terrestrial patterns alone cannot differentiate these mechanisms. Here, we demonstrate that broad geographical patterns of N and P in freshwater and marine multicellular photoautotrophs are concordant with those in terrestrial ecosystems. Our > 6800 record database reveals that mean tissue N and P increase with latitude in all ecosystems, but P increases more rapidly, causing N:P to decline; mean N:P scaling within individuals also is identical among systems, despite very different evolutionary environments. A partitioning of the variance in these data suggests that species composition and local environmental context likely lead to the variation observed within a latitudinal band. However, the consistency of trends in photosynthetic tissue chemistry across Earth’s ecosystems suggests that biogeographical gradients in insolation and growing season length may constrain tissue N and P, whereas global trends in temperature, nutrient supply, and soil substrate age are unlikely to generate the consistent latitudinal trends among ecosystems. Thus, this cross‐ecosystem comparison suggests a new hypothesis, global patterns of insolation, while also providing a new perspective on other mechanisms that have been hypothesized to underlie latitudinal trends in photosynthetic tissue chemistry. 相似文献
107.
Hillebrand M Gersting SW Lotz-Havla AS Schäfer A Rosewich H Valerius O Muntau AC Gärtner J 《The Journal of biological chemistry》2012,287(1):210-221
The neurodegenerative disease X-linked adrenoleukodystrophy (X-ALD) is characterized by the abnormal accumulation of very long chain fatty acids. Mutations in the gene encoding the peroxisomal ATP-binding cassette half-transporter, adrenoleukodystrophy protein (ALDP), are the primary cause of X-ALD. To gain a better understanding of ALDP dysfunction, we searched for interaction partners of ALDP and identified binary interactions to proteins with functions in fatty acid synthesis (ACLY, FASN, and ACC) and activation (FATP4), constituting a thus far unknown fatty acid synthesis-transport machinery at the cytoplasmic side of the peroxisomal membrane. This machinery adds to the knowledge of the complex mechanisms of peroxisomal fatty acid metabolism at a molecular level and elucidates potential epigenetic mechanisms as regulatory processes in the pathogenesis and thus the clinical course of X-ALD. 相似文献
108.
Herbivore metabolism and stoichiometry each constrain herbivory at different organizational scales across ecosystems 总被引:1,自引:0,他引:1
Helmut Hillebrand Elizabeth T. Borer Matthew E. S. Bracken Bradley J. Cardinale Just Cebrian Elsa E. Cleland James J. Elser Daniel S. Gruner W. Stanley Harpole Jacqueline T. Ngai Stuart Sandin Eric W. Seabloom Jonathan B. Shurin Jennifer E. Smith Melinda D. Smith 《Ecology letters》2009,12(6):516-527
Plant-herbivore interactions mediate the trophic structure of ecosystems. We use a comprehensive data set extracted from the literature to test the relative explanatory power of two contrasting bodies of ecological theory, the metabolic theory of ecology (MTE) and ecological stoichiometry (ES), for per-capita and population-level rates of herbivory across ecosystems. We found that ambient temperature and herbivore body size (MTE) as well as stoichiometric mismatch (ES) both constrained herbivory, but at different scales of biological organization. Herbivore body size, which varied over 11 orders of magnitude, was the primary factor explaining variation in per-capita rates of herbivory. Stoichiometric mismatch explained more variation in population-level herbivory rates and also in per-capita rates when we examined data from within functionally similar trophic groups (e.g. zooplankton). Thus, predictions from metabolic and stoichiometric theories offer complementary explanations for patterns of herbivory that operate at different scales of biological organization. 相似文献
109.
The evidence for species diversity effects on ecosystem functions is mainly based on studies not explicitly addressing local
or regional processes regulating coexistence or the importance of community structure in terms of species evenness. In experimental
communities of marine benthic microalgae, we altered the successional stages and thus the strength of local species interactions
by manipulating rates of dispersal and disturbance. The treatments altered realized species richness, evenness and community
biomass. For species richness, dispersal mattered only at high disturbance rates; when opening new space, dispersal led to
maximized richness at intermediate dispersal rates. Evenness, in contrast, decreased with dispersal at low or no disturbance,
i.e. at late successional stages. Community biomass showed a non-linear hump-shaped response to increasing dispersal at all
disturbance levels. We found a positive correlation between richness and biomass at early succession, and a strong negative
correlation between evenness and biomass at late succession. In early succession both community biomass and richness depend
directly on dispersal from the regional pool, whereas the late successional pattern shows that if interactions allow the most
productive species to become dominant, diverting resources from this species (i.e. higher evenness) reduces production. Our
study emphasizes the difference in biodiversity–function relationships over time, as different mechanisms contribute to the
regulation of richness and evenness in early and late successional stages. 相似文献
110.
Dorlo TP Hillebrand MJ Rosing H Eggelte TA de Vries PJ Beijnen JH 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2008,865(1-2):55-62
A sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the quantification of miltefosine is presented. A 250 microL human EDTA plasma aliquot was spiked with miltefosine and extracted by a solid-phase extraction method. Separation was performed on a Gemini C18 column (150 mm x 2.0 mm I.D., 5 microm) using an alkaline eluent. Detection was performed by positive ion electrospray ionization followed by triple-quadrupole mass spectrometry. The assay has been validated for miltefosine from 4 to 2000 ng/mL using 250 microL human EDTA plasma samples. Results from the validation demonstrate that miltefosine can be accurately and precisely quantified in human plasma. At the lowest level, the intra-assay precision was lower than 10.7%, the inter-assay precision was 10.6% and accuracies were between 95.1 and 109%. This assay is successfully used in a clinical pharmacokinetic study with miltefosine. 相似文献