全文获取类型
收费全文 | 3126篇 |
免费 | 354篇 |
国内免费 | 3篇 |
出版年
2022年 | 25篇 |
2021年 | 57篇 |
2020年 | 34篇 |
2019年 | 32篇 |
2018年 | 40篇 |
2017年 | 57篇 |
2016年 | 69篇 |
2015年 | 108篇 |
2014年 | 141篇 |
2013年 | 190篇 |
2012年 | 222篇 |
2011年 | 235篇 |
2010年 | 150篇 |
2009年 | 127篇 |
2008年 | 182篇 |
2007年 | 211篇 |
2006年 | 188篇 |
2005年 | 198篇 |
2004年 | 169篇 |
2003年 | 192篇 |
2002年 | 178篇 |
2001年 | 48篇 |
2000年 | 32篇 |
1999年 | 45篇 |
1998年 | 45篇 |
1997年 | 42篇 |
1996年 | 34篇 |
1995年 | 37篇 |
1994年 | 36篇 |
1993年 | 21篇 |
1992年 | 26篇 |
1991年 | 20篇 |
1990年 | 18篇 |
1989年 | 25篇 |
1988年 | 19篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 12篇 |
1984年 | 18篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 15篇 |
1978年 | 14篇 |
1976年 | 13篇 |
1974年 | 10篇 |
1973年 | 8篇 |
1972年 | 9篇 |
1970年 | 10篇 |
1969年 | 9篇 |
排序方式: 共有3483条查询结果,搜索用时 15 毫秒
131.
132.
Alberto Robador Albert L Müller Joanna E Sawicka David Berry Casey R J Hubert Alexander Loy Bo Barker J?rgensen Volker Brüchert 《The ISME journal》2016,10(4):796-809
Temperature has a fundamental impact on the metabolic rates of microorganisms and strongly influences microbial ecology and biogeochemical cycling in the environment. In this study, we examined the catabolic temperature response of natural communities of sulfate-reducing microorganisms (SRM) in polar, temperate and tropical marine sediments. In short-term sediment incubation experiments with 35S-sulfate, we demonstrated how the cardinal temperatures for sulfate reduction correlate with mean annual sediment temperatures, indicating specific thermal adaptations of the dominant SRM in each of the investigated ecosystems. The community structure of putative SRM in the sediments, as revealed by pyrosequencing of bacterial 16S rRNA gene amplicons and phylogenetic assignment to known SRM taxa, consistently correlated with in situ temperatures, but not with sediment organic carbon concentrations or C:N ratios of organic matter. Additionally, several species-level SRM phylotypes of the class Deltaproteobacteria tended to co-occur at sites with similar mean annual temperatures, regardless of geographic distance. The observed temperature adaptations of SRM imply that environmental temperature is a major controlling variable for physiological selection and ecological and evolutionary differentiation of microbial communities. 相似文献
133.
IntroductionRecently it has been shown that acute sleep loss has a direct impact on emotional processing in healthy individuals. Here we studied the effect of chronically disturbed sleep on emotional processing by investigating two samples of patients with sleep disorders.Methods25 patients with psychophysiologic insomnia (23 women and 2 men, mean age: 51.6 SD; 10.9 years), 19 patients with sleep apnea syndrome (4 women and 15 men, mean age: 51.9; SD 11.1) and a control sample of 24 subjects with normal sleep (15women and 9 men, mean age 45.3; SD 8.8) completed a Facial Expressed Emotion Labelling (FEEL) task, requiring participants to categorize and rate the intensity of six emotional expression categories: anger, anxiety, fear, happiness, disgust and sadness. Differences in FEEL score and its subscales among the three samples were analysed using ANOVA with gender as a covariate.ResultsBoth patients with psychophysiologic insomnia and patients with sleep apnea showed significantly lower performance in the FEEL test as compared to the control group. Differences were seen in the scales happiness and sadness. Patient groups did not differ from each other.ConclusionBy demonstrating that previously known effects of acute sleep deprivation on emotional processing can be extended to persons experiencing chronically disturbed sleep, our data contribute to a deeper understanding of the relationship between sleep loss and emotions. 相似文献
134.
Intraspecific trait variation and colonization sequence alter community assembly and disease epidemics 下载免费PDF全文
When individuals from multiple populations colonize a new habitat patch, intraspecific trait variation can make the arrival order of colonists an important factor for subsequent population and community dynamics. In particular, intraspecific priority effects (IPEs) allow early arrivers to limit the growth or establishment of later arrivers, even when competitively inferior on a per‐capita basis. Through their effects on genes and traits, IPEs can alter short‐term growth and long‐term evolutionary change in single species metapopulations. Given their importance for intraspecific interactions, IPEs in a dominant species have the potential to affect the composition of entire communities. We conducted an experiment to determine whether and how arrival order and IPEs in the zooplankter Daphnia pulex affected its interactions with both competitors (the cladoceran Simocephalus vetulus) and parasites (the virulent fungus Metschnikowia bicuspidata). We found strong evidence for IPEs in Daphnia, as early arrivers inhibited late arrivers even when competitively inferior. These IPEs in Daphnia altered both the establishment success of interspecific competitors and the size of disease epidemics: early colonization by fast‐growing D. pulex led to large Daphnia populations and low competitor establishment, but large disease epidemics. Early colonization by slow‐growing D. pulex, on the other hand, resulted in small Daphnia populations with high competitor establishment, but smaller disease epidemics. Overall, our results demonstrate the importance of intraspecific variation and arrival order for community dynamics, and highlight IPEs as a general mechanism driving variation in natural communities. 相似文献
135.
Multiple stressors: using the honeybee model BEEHAVE to explore how spatial and temporal forage stress affects colony resilience 下载免费PDF全文
Juliane Horn Matthias A. Becher Peter J. Kennedy Juliet L. Osborne Volker Grimm 《Oikos》2016,125(7):1001-1016
The causes underlying the increased mortality of honeybee Apis mellifera colonies observed over the past decade remain unclear. Since so far the evidence for monocausal explanations is equivocal, involvement of multiple stressors is generally assumed. We here focus on various aspects of forage availability, which have received less attention than other stressors because it is virtually impossible to explore them empirically. We applied the colony model BEEHAVE, which links within‐hive dynamics and foraging, to stylized landscape settings to explore how foraging distance, forage supply, and “forage gaps”, i.e. periods in which honeybees cannot find any nectar and pollen, affect colony resilience and the mechanisms behind. We found that colony extinction was mainly driven by foraging distance, but the timing of forage gaps had strongest effects on time to extinction. Sensitivity to forage gaps of 15 days was highest in June or July even if otherwise forage availability was sufficient to survive. Forage availability affected colonies via cascading effects on queen's egg‐laying rate, reduction of new‐emerging brood stages developing into adult workers, pollen debt, lack of workforce for nursing, and reduced foraging activity. Forage gaps in July led to reduction in egg‐laying and increased mortality of brood stages at a time when the queen's seasonal egg‐laying rate is at its maximum, leading to colony failure over time. Our results demonstrate that badly timed forage gaps interacting with poor overall forage supply reduce honeybee colony resilience. Existing regulation mechanisms which in principle enable colonies to cope with varying forage supply in a given landscape and year, such as a reduction in egg‐laying, have only a certain capacity. Our results are hypothetical, as they are obtained from simplified landscape settings, but they are consistent with existing empirical knowledge. They offer ample opportunities for testing the predicted effects of forage stress in controlled experiments. 相似文献
136.
137.
Juan L. Fuentes Volker A. R. Huss Zaida Montero Rafael Torronteras María Cuaresma Inés Garbayo Carlos Vílchez 《Journal of applied phycology》2016,28(6):3269-3279
The genus Coccomyxa comprises green microalgae, which can be found worldwide in remarkably versatile aquatic and terrestrial ecosystems including symbiotic associations with a number of different hosts. In this study, we describe a new species, Coccomyxa onubensis, based on 18S and ITS ribosomal DNA (rDNA) sequence data. Coccomyxa onubensis was isolated from acidic water, and its ability to adapt to a wide range of acidic and alkaline pH values and to high salinity was analyzed. The long-term adaptation capacity of the microalga to such extreme conditions was evaluated by performing continuous repeated batches at selected salt concentrations and pH values. Adapted cultures of C. onubensis were found to yield high biomass productivities from pH 2.5 to 9, with maximum yields at acidic pH between 2.5 and 4.5. Moreover, C. onubensis was also found to adapt to salinities as high as 0.5 M NaCl, reaching biomass productivities that were similar to those of control cultures. Ultrastructural analysis by transmission electron microscopy of C. onubensis cells adapted to high salinity showed a robust response to hyperosmotic shock. Thus, C. onubensis was found to be acidotolerant and halotolerant. High biomass productivity over a wide range of pH and salinities denotes C. onubensis as an interesting candidate for various biotechnological applications including outdoor biomass production. 相似文献
138.
139.
Gajewski Konrad Kriesche Björn Chaput Michelle A. Kulik Rafal Schmidt Volker 《Vegetation History and Archaeobotany》2019,28(6):635-647
Vegetation History and Archaeobotany - Between the initial colonization of North America and the European settlement period, Indigenous American land use practices shaped North American landscapes... 相似文献
140.
Zishu Liu Nicolas Cichocki Thomas Hübschmann Christine Süring Irina Dana Ofiţeru William T. Sloan Volker Grimm Susann Müller 《Environmental microbiology》2019,21(1):164-181
In completely insular microbial communities, evolution of community structure cannot be shaped by the immigration of new members. In addition, when those communities are run in steady state, the influence of environmental factors on their assembly is reduced. Therefore, one would expect similar community structures under steady-state conditions. Yet, in parallel setups, variability does occur. To reveal ecological mechanisms behind this phenomenon, five parallel reactors were studied at the single-cell level for about 100 generations and community structure variations were quantified by ecological measures. Whether community variability can be controlled was tested by implementing soft temperature stressors as potential synchronizers. The low slope of the lognormal rank-order abundance curves indicated a predominance of neutral mechanisms, i.e., where species identity plays no role. Variations in abundance ranks of subcommunities and increase in inter-community pairwise β-diversity over time support this. Niche differentiation was also observed, as indicated by steeper geometric-like rank-order abundance curves and increased numbers of correlations between abiotic and biotic parameters during initial adaptation and after disturbances. Still, neutral forces dominated community assembly. Our findings suggest that complex microbial communities in insular steady-state environments can be difficult to synchronize and maintained in their original or desired structure, as they are non-equilibrium systems. 相似文献