全文获取类型
收费全文 | 1334篇 |
免费 | 105篇 |
国内免费 | 2篇 |
出版年
2021年 | 17篇 |
2020年 | 15篇 |
2019年 | 22篇 |
2018年 | 28篇 |
2017年 | 16篇 |
2016年 | 35篇 |
2015年 | 57篇 |
2014年 | 34篇 |
2013年 | 68篇 |
2012年 | 79篇 |
2011年 | 87篇 |
2010年 | 53篇 |
2009年 | 52篇 |
2008年 | 79篇 |
2007年 | 69篇 |
2006年 | 57篇 |
2005年 | 55篇 |
2004年 | 43篇 |
2003年 | 60篇 |
2002年 | 56篇 |
2001年 | 37篇 |
2000年 | 32篇 |
1999年 | 27篇 |
1998年 | 23篇 |
1997年 | 9篇 |
1996年 | 14篇 |
1995年 | 17篇 |
1994年 | 7篇 |
1993年 | 14篇 |
1992年 | 25篇 |
1991年 | 22篇 |
1990年 | 12篇 |
1989年 | 16篇 |
1988年 | 15篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 6篇 |
1979年 | 12篇 |
1978年 | 15篇 |
1976年 | 8篇 |
1975年 | 6篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1972年 | 8篇 |
1971年 | 10篇 |
1970年 | 6篇 |
1969年 | 8篇 |
排序方式: 共有1441条查询结果,搜索用时 31 毫秒
51.
Christine Wittmann Markus Reischl Asmi H. Shah Eva Kronfuss Ralf Mikut Urban Liebel Clemens Grabher 《PloS one》2015,10(10)
Tissue injury and infection trigger innate immune responses. However, dysregulation may result in chronic inflammation and is commonly treated with corticosteroids and non-steroidal anti-inflammatory drugs. Unfortunately, long-term administration of both therapeutic classes can cause unwanted side effects. To identify alternative immune-modulatory compounds we have previously established a novel screening method using zebrafish larvae. Using this method we here present results of an in vivo high-content drug-repurposing screen, identifying 63 potent anti-inflammatory drugs that are in clinical use for other indications. Our approach reveals a novel pro-inflammatory role of nitric oxide. Nitric oxide affects leukocyte recruitment upon peripheral sensory nervous system or epithelial injury in zebrafish larvae both via soluble guanylate cyclase and in a soluble guanylate cyclase -independent manner through protein S-nitrosylation. Together, we show that our screening method can help to identify novel immune-modulatory activities and provide new mechanistic insights into the regulation of inflammatory processes. 相似文献
52.
53.
Ladislav ?igut Petra Holi?ová Karel Klem Mirka ?prtová Carlo Calfapietra Michal V. Marek Vladimír ?punda Otmar Urban 《Annals of botany》2015,116(6):929-939
Background and Aims Plants growing under elevated atmospheric CO2 concentrations often have reduced stomatal conductance and subsequently increased leaf temperature. This study therefore tested the hypothesis that under long-term elevated CO2 the temperature optima of photosynthetic processes will shift towards higher temperatures and the thermostability of the photosynthetic apparatus will increase.Methods The hypothesis was tested for saplings of broadleaved Fagus sylvatica and coniferous Picea abies exposed for 4–5 years to either ambient (AC; 385 µmol mol−1) or elevated (EC; 700 µmol mol−1) CO2 concentrations. Temperature response curves of photosynthetic processes were determined by gas-exchange and chlorophyll fluorescence techniques.Key Results Initial assumptions of reduced light-saturated stomatal conductance and increased leaf temperatures for EC plants were confirmed. Temperature response curves revealed stimulation of light-saturated rates of CO2 assimilation (Amax) and a decline in photorespiration (RL) as a result of EC within a wide temperature range. However, these effects were negligible or reduced at low and high temperatures. Higher temperature optima (Topt) of Amax, Rubisco carboxylation rates (VCmax) and RL were found for EC saplings compared with AC saplings. However, the shifts in Topt of Amax were instantaneous, and disappeared when measured at identical CO2 concentrations. Higher values of Topt at elevated CO2 were attributed particularly to reduced photorespiration and prevailing limitation of photosynthesis by ribulose-1,5-bisphosphate (RuBP) regeneration. Temperature response curves of fluorescence parameters suggested a negligible effect of EC on enhancement of thermostability of photosystem II photochemistry.Conclusions Elevated CO2 instantaneously increases temperature optima of Amax due to reduced photorespiration and limitation of photosynthesis by RuBP regeneration. However, this increase disappears when plants are exposed to identical CO2 concentrations. In addition, increased heat-stress tolerance of primary photochemistry in plants grown at elevated CO2 is unlikely. The hypothesis that long-term cultivation at elevated CO2 leads to acclimation of photosynthesis to higher temperatures is therefore rejected. Nevertheless, incorporating acclimation mechanisms into models simulating carbon flux between the atmosphere and vegetation is necessary. 相似文献
54.
E.?Tapia-VenegasEmail author L.?Cabrol B.?Brandhoff J.?Hamelin E.?Trably JP?Steyer G.?Ruiz-Filippi 《Applied microbiology and biotechnology》2015,99(19):8295-8308
Hydrogen is a promising alternative as an energetic carrier and its production by dark fermentation from wastewater has been recently proposed, with special attention to crude glycerol as potential substrate. In this study, two different feeding strategies were evaluated for replacing the glucose substrate by glycerol substrate: a one-step strategy (glucose was replaced abruptly by glycerol) and a step-by-step strategy (progressive decrease of glucose concentration and increase of glycerol concentration from 0 to 5 g L?1), in a continuous stirred tank reactor (12 h of hydraulic retention time (HRT), pH 5.5, 35 °C). While the one-step strategy led to biomass washout and unsuccessful H2 production, the step-by-step strategy was efficient for biomass adaptation, reaching acceptable hydrogen yields (0.4?±?0.1 molH2?mol?1 glycerol consumed) around 33 % of the theoretical yield independently of the glycerol concentration. Microbial community structure was investigated by single-strand conformation polymorphism (SSCP) and denaturing gradient gel electrophoresis (DGGE) fingerprinting techniques, targeting either the total community (16S ribosomal RNA (rRNA) gene) or the functional Clostridium population involved in H2 production (hydA gene), as well as by 454 pyrosequencing of the total community. Multivariate analysis of fingerprinting and pyrosequencing results revealed the influence of the feeding strategy on the bacterial community structure and suggested the progressive structural adaptation of the community to increasing glycerol concentrations, through the emergence and selection of specific species, highly correlated to environmental parameters. Particularly, this work highlighted an interesting shift of dominant community members (putatively responsible of hydrogen production in the continuous stirred tank reactor (CSTR)) according to the gradient of glycerol proportion in the feed, from the family Veillonellaceae to the genera Prevotella and Clostridium sp., putatively responsible of hydrogen production in the CSTR. 相似文献
55.
56.
57.
Joanna Furmankiewicz Ireneusz Ruczyński Radosław Urban Gareth Jones 《Ethology : formerly Zeitschrift fur Tierpsychologie》2011,117(6):480-489
Animals can use signals emitted by other animals as sources of information. Auditory signals are important in communication networks, as they can potentially convey information about the location and state of conspecifics and other species over long distances. Signalling is important in fission–fusion societies, in which animals from the same social group temporarily split into subgroups and frequently change roost sites. We used playbacks of social calls of the noctule Nyctalus noctula produced in roosts, to show how bats might maintain group cohesion and to test the hypothesis that noctules can locate conspecifics when returning from foraging trips by eavesdropping on or communicating with roosting individuals. Noctules responded strongly to broadcasted social calls. Their reactions included inspections and landing on a loudspeaker broadcasting social calls and occasional social vocalisation. Responses by other bat species to the noctule social calls were negligible. The high amplitude, low‐frequency vocalisations emitted by noctules in roosts can propagate over long distances and allow group members to announce their position. Bats can extract information about the location of roosts containing conspecifics by eavesdropping or by communication. Social calls may thus be sufficient to locate conspecifics in roosts and maintain spatial associations of groups in mammals. 相似文献
58.
Non-monophyly of the avian genus Seicercus (Aves: Sylviidae) revealed by mitochondrial DNA 总被引:1,自引:0,他引:1
The phylogeny of all species and nearly all subspecies of Seicercus and representatives of all subgenera in Phylloscopus was estimated based on two mitochondrial genes. According to the gene tree, and supported by non-molecular data, Seicercus belongs in three separate clades. Two of these include only taxa currently classified as Seicercus , while the third comprises S. xanthoschistos and P. occipitalis . These results suggest that both Seicercus and Phylloscopus are paraphyletic. The gene tree suggests two more cases of non-monophyly: (1) the ' S. burkii complex' is separated into two different clades, one of which also includes S. affinis and S. poliogenys ; (2) two populations of S. affinis intermedius are more closely related to S. affinis ocularis than to a third population of intermedius . A recent proposal to split the ' S. burkii complex' into six species is corroborated, as is the recognition of the taxon cognitus as a colour morph of S. affinis intermedius . Our study also revealed unexpectedly large genetic divergences between three different populations of the monotypic S. poliogenys , indicating the presence of cryptic species. Our results underscore the importance of dense sampling at the specific and infraspecific levels in intrageneric phylogenetic studies. 相似文献
59.
60.
Close and distant: Contrasting the metabolism of two closely related subspecies of Scots pine under the effects of folivory and summer drought 下载免费PDF全文
Albert Rivas‐Ubach Jordi Sardans José Antonio Hódar Joan Garcia‐Porta Alex Guenther Ljiljana Paša‐Tolić Michal Oravec Otmar Urban Josep Peñuelas 《Ecology and evolution》2017,7(21):8976-8988
Metabolomes, as chemical phenotypes of organisms, are likely not only shaped by the environment but also by common ancestry. If this is the case, we expect that closely related species of pines will tend to reach similar metabolomic solutions to the same environmental stressors. We examined the metabolomes of two sympatric subspecies of Pinus sylvestris in Sierra Nevada (southern Iberian Peninsula), in summer and winter and exposed to folivory by the pine processionary moth. The overall metabolomes differed between the subspecies but both tended to respond more similarly to folivory. The metabolomes of the subspecies were more dissimilar in summer than in winter, and iberica trees had higher concentrations of metabolites directly related to drought stress. Our results are consistent with the notion that certain plant metabolic responses associated with folivory have been phylogenetically conserved. The larger divergence between subspecies metabolomes in summer is likely due to the warmer and drier conditions that the northern iberica subspecies experience in Sierra Nevada. Our results provide crucial insights into how iberica populations would respond to the predicted conditions of climate change under an increased defoliation in the Mediterranean Basin. 相似文献