全文获取类型
收费全文 | 786篇 |
免费 | 51篇 |
专业分类
837篇 |
出版年
2022年 | 10篇 |
2021年 | 12篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 13篇 |
2017年 | 12篇 |
2016年 | 10篇 |
2015年 | 30篇 |
2014年 | 30篇 |
2013年 | 33篇 |
2012年 | 45篇 |
2011年 | 35篇 |
2010年 | 23篇 |
2009年 | 17篇 |
2008年 | 30篇 |
2007年 | 23篇 |
2006年 | 22篇 |
2005年 | 27篇 |
2004年 | 24篇 |
2003年 | 26篇 |
2002年 | 44篇 |
1999年 | 9篇 |
1998年 | 6篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 9篇 |
1994年 | 7篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 11篇 |
1990年 | 17篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 21篇 |
1986年 | 12篇 |
1985年 | 7篇 |
1984年 | 15篇 |
1983年 | 7篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 10篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 5篇 |
1974年 | 5篇 |
1971年 | 6篇 |
1970年 | 5篇 |
1907年 | 8篇 |
1905年 | 8篇 |
1904年 | 6篇 |
排序方式: 共有837条查询结果,搜索用时 15 毫秒
151.
Dieter Blottner Najet Serradj Michele Salanova Chadi Touma Rupert Palme Mitchell Silva Jean Marie Aerts Daniel Berckmans Laurence Vico Yi Liu Alessandra Giuliani Franco Rustichelli Ranieri Cancedda Marc Jamon 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2009,179(4):519-533
Environmental conditions likely affect physiology and behaviour of mice used for life sciences research on Earth or in Space.
Here, we analysed the effects of cage confinement on the weightbearing musculoskeletal system, behaviour and stress of wild-type
mice (C57BL/6JRj, 30 g b.wt., total n = 24) housed for 25 days in a prototypical ground-based and fully automated life support habitat device called “Mice in Space”
(MIS). Compared with control housing (individually ventilated cages) the MIS mice revealed no significant changes in soleus
muscle size and myofiber distribution (type I vs. II) and quality of bone (3-D microarchitecture and mineralisation of calvaria,
spine and femur) determined by confocal and micro-computed tomography. Corticosterone metabolism measured non-invasively (faeces)
monitored elevated adrenocortical activity at only start of the MIS cage confinement (day 1). Behavioural tests (i.e., grip
strength, rotarod, L/D box, elevated plus-maze, open field, aggressiveness) performed subsequently revealed only minor changes
in motor performance (MIS vs. controls). The MIS habitat will not, on its own, produce major effects that could confound interpretation
of data induced by microgravity exposure during spaceflight. Our results may be even more helpful in developing multidisciplinary
protocols with adequate scenarios addressing molecular to systems levels using mice of various genetic phenotypes in many
laboratories.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
152.
Predation is a strong selective force with both direct and indirect effects on an animal’s fitness. In order to increase the chances of survival, animals have developed different antipredator strategies. However, these strategies have associated costs, so animals should assess their actual risk of predation and shape their antipredator effort accordingly. Under a stressful situation, such as the presence of predators, animals display a physiological stress response that might be proportional to the risk perceived. We tested this hypothesis in wild European rabbits (Oryctolagus cuniculus), subjected to different predator pressures, in Doñana National Park (Spain). We measured the concentrations of fecal corticosterone metabolites (FCM) in 20 rabbit populations. By means of track censuses we obtained indexes of mammalian predator presence for each rabbit population. Other factors that could modify the physiological stress response, such as breeding status, food availability and rabbit density, were also considered. Model selection based on information theory showed that predator pressure was the main factor triggering the glucocorticoid release and that the physiological stress response was positively correlated with the indexes of the presence of mammalian carnivore predators. Other factors, such as food availability and density of rabbits, were considerably less important. We conclude that rabbits are able to assess their actual risk of predation and show a threat-sensitive physiological response. 相似文献
153.
Michaela Aschan Oleg V. Karamushko Ingvar Byrkjedal Rupert Wienerroither Igor V. Borkin Jørgen S. Christiansen 《Polar Biology》2009,32(7):963-970
The Arctogadus glacialis is endemic to the Arctic Ocean and its apparently disjunct circumpolar distribution range from the Siberian coast through
the Chukchi Sea and the Canadian Arctic to the shelf off NE Greenland. Records of A. glacialis are scarce in the European Arctic and here we present all available and reliable records of the species in the area. Altogether,
296 specimens of A. glacialis are reported from 53 positions in the European Arctic during the period 1976–2008. The specimens were registered off Iceland
and the Jan Mayen Island, northwest and northeast of Svalbard, northeast in the Barents Sea, and south and east off Franz
Josef Land. The additional records show that A. glacialis display a circumpolar and more continuous distribution than described before. In the European Arctic, A. glacialis has been caught at 155–741 m depth with the highest abundance at 300–400 m. We therefore suggest that A. glacialis is more associated to the continental shelves surrounding the Arctic Ocean than previously thought. The length–weight relation
of A. glacialis is similar across the European Arctic. 相似文献
154.
Emily J. Mockford Rupert C. Marshall 《Proceedings. Biological sciences / The Royal Society》2009,276(1669):2979-2985
Acoustic communication is fundamental in avian territory defence and mate attraction. In urban environments where sound transmissions are more likely to be masked by low-frequency anthropogenic noise, acoustic adaptations may be advantageous. However, minor modifications to a signal could affect its efficacy. While recent research has shown that there is divergence between songs from noisy and quiet areas, it is unknown whether these differences affect the response to the signal by its receivers. Here, we show that there is a difference in spectral aspects of rural and urban song in a common passerine, the great tit Parus major, at 20 sites across the UK. We also provide, to our knowledge, the first demonstration that such environmentally induced differences in song influence the response of male territory holders. Males from quiet territories exhibited a significantly stronger response when hearing song from another territory holder with low background noise than from those with high background noise. The opposite distinction in response intensity to homotypic versus heterotypic song was observed in males from noisy territories. This behavioural difference may intensify further signal divergence between urban and rural populations and raises important questions concerning signal evolution. 相似文献
155.
Chadi Touma Thomas Fenzl J?rg Ruschel Rupert Palme Florian Holsboer Mayumi Kimura Rainer Landgraf 《PloS one》2009,4(1)
Background
Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, including hyper- or hypo-activity of the stress hormone system, plays a critical role in the pathophysiology of mood disorders such as major depression (MD). Further biological hallmarks of MD are disturbances in circadian rhythms and sleep architecture. Applying a translational approach, an animal model has recently been developed, focusing on the deviation in sensitivity to stressful encounters. This so-called ‘stress reactivity’ (SR) mouse model consists of three separate breeding lines selected for either high (HR), intermediate (IR), or low (LR) corticosterone increase in response to stressors.Methodology/Principle Findings
In order to contribute to the validation of the SR mouse model, our study combined the analysis of behavioural and HPA axis rhythmicity with sleep-EEG recordings in the HR/IR/LR mouse lines. We found that hyper-responsiveness to stressors was associated with psychomotor alterations (increased locomotor activity and exploration towards the end of the resting period), resembling symptoms like restlessness, sleep continuity disturbances and early awakenings that are commonly observed in melancholic depression. Additionally, HR mice also showed neuroendocrine abnormalities similar to symptoms of MD patients such as reduced amplitude of the circadian glucocorticoid rhythm and elevated trough levels. The sleep-EEG analyses, furthermore, revealed changes in rapid eye movement (REM) and non-REM sleep as well as slow wave activity, indicative of reduced sleep efficacy and REM sleep disinhibition in HR mice.Conclusion/Significance
Thus, we could show that by selectively breeding mice for extremes in stress reactivity, clinically relevant endophenotypes of MD can be modelled. Given the importance of rhythmicity and sleep disturbances as biomarkers of MD, both animal and clinical studies on the interaction of behavioural, neuroendocrine and sleep parameters may reveal molecular pathways that ultimately lead to the discovery of new targets for antidepressant drugs tailored to match specific pathologies within MD. 相似文献156.
Low physiologic oxygen tensions reduce proliferation and differentiation of human multipotent mesenchymal stromal cells 总被引:1,自引:0,他引:1
Christina Holzwarth Martin Vaegler Friederike Gieseke Stefan M Pfister Rupert Handgretinger Gunter Kerst Ingo Müller 《BMC cell biology》2010,11(1):1-11
Background
Human multipotent mesenchymal stromal cells (MSC) can be isolated from various tissues including bone marrow. Here, MSC participate as bone lining cells in the formation of the hematopoietic stem cell niche. In this compartment, the oxygen tension is low and oxygen partial pressure is estimated to range from 1% to 7%. We analyzed the effect of low oxygen tensions on human MSC cultured with platelet-lysate supplemented media and assessed proliferation, morphology, chromosomal stability, immunophenotype and plasticity.Results
After transferring MSC from atmospheric oxygen levels of 21% to 1%, HIF-1α expression was induced, indicating efficient oxygen reduction. Simultaneously, MSC exhibited a significantly different morphology with shorter extensions and broader cell bodies. MSC did not proliferate as rapidly as under 21% oxygen and accumulated in G1 phase. The immunophenotype, however, was unaffected. Hypoxic stress as well as free oxygen radicals may affect chromosomal stability. However, no chromosomal abnormalities in human MSC under either culture condition were detected using high-resolution matrix-based comparative genomic hybridization. Reduced oxygen tension severely impaired adipogenic and osteogenic differentiation of human MSC. Elevation of oxygen from 1% to 3% restored osteogenic differentiation.Conclusion
Physiologic oxygen tension during in vitro culture of human MSC slows down cell cycle progression and differentiation. Under physiological conditions this may keep a proportion of MSC in a resting state. Further studies are needed to analyze these aspects of MSC in tissue regeneration. 相似文献157.
James Kennedy Ásgeir Gunnarsson Christophe Pampoulie Rupert Wienerroither 《Journal of fish biology》2024,104(4):1247-1250
The stomach of a spotted wolffish (Anarhichas minor) caught in Icelandic waters was found to contain ~727 greater eelpout larvae (Lycodes esmarkii). All the larvae were of similar size and at a similar state of digestion, indicating they were all consumed together. The likely explanation for this observation is that greater eelpout lay their eggs in a nest, with the larvae remaining in the nest for a short period after hatching. The larvae were then predated upon by the spotted wolffish while still in the nest. This study sheds new light on greater eelpout in Icelandic waters, with recently hatched larvae being present in March, breeding at a depth of ~200–250 m, and likely exhibiting nesting behavior, which has not previously been documented. 相似文献
158.
Lochlainn SO Fray RG Hammond JP King GJ White PJ Young SD Broadley MR 《The New phytologist》2011,189(2):409-414
Noccaea caerulescens (formerly Thlaspi caerulescens) is a widely studied metal hyperaccumulator. However, molecular genetic studies are challenging in this species because of its vernal-obligate biennial life cycle of 7-9months. Here, we describe the development of genetically stable, faster cycling lines of N. caerulescens which are nonvernal-obligate. A total of 5500 M(0) seeds from Saint Laurent Le Minier (France) were subjected to fast neutron mutagenesis. Following vernalization of young plants, 79% of plants survived to maturity. In all, 80,000 M(2) lines were screened for flowering in the absence of vernalization. Floral initials were observed in 35 lines, with nine flowering in <12wk. Two lines (A2 and A7) were selfed to the M(4) generation. Floral initials were observed 66 and 87d after sowing (DAS) in A2 and A7, respectively. Silicle development occurred for all A2 and for most A7 at 92 and 123 DAS, respectively. Floral or silicle development was not observed in wild-type (WT) plants. Leaf zinc (Zn) concentration was similar in WT, A2 and A7 lines. These lines should facilitate future genetic studies of this remarkable species. Seed is publicly available through the European Arabidopsis Stock Centre (NASC). 相似文献
159.
Stress responses play a key role in allowing animals to cope with change and challenge in the face of both environmental certainty
and uncertainty. Measurement of glucocorticoid levels, key elements in the neuroendocrine stress axis, can give insight into
an animal’s well-being and can aid understanding ecological and evolutionary processes as well as conservation and management
issues. We give an overview of the four main biological samples that have been utilized [blood, saliva, excreta (feces and
urine), and integumentary structures (hair and feathers)], their advantages and disadvantages for use with wildlife, and some
of the background and pitfalls that users must consider in interpreting their results. The matrix of choice will depend on
the nature of the study and of the species, on whether one is examining the impact of acute versus chronic stressors, and
on the degree of invasiveness that is possible or desirable. In some cases, more than one matrix can be measured to achieve
the same ends. All require a significant degree of expertise, sometimes in obtaining the sample and always in extracting and
analyzing the glucocorticoid or its metabolites. Glucocorticoid measurement is proving to be a powerful integrator of environmental
stressors and of an animal’s condition. 相似文献
160.
The adaptive immune system plays an essential role in protecting vertebrates against a broad range of pathogens and cancer. The MHC class I-dependent pathway of antigen presentation represents a sophisticated cellular machinery to recognize and eliminate infected or malignantly transformed cells, taking advantage of the proteasomal turnover of the cell's proteome. TAP (transporter associated with antigen processing) 1/2 (ABCB2/3, where ABC is ATP-binding cassette) is the principal component in the recognition, translocation, chaperoning, editing and final loading of antigenic peptides on to MHC I complexes in the ER (endoplasmic reticulum) lumen. These different tasks are co-ordinated within a dynamic macromolecular peptide-loading complex consisting of TAP1/2 and various auxiliary factors, such as the adapter protein tapasin, the oxidoreductase ERp57, the lectin chaperone calreticulin, and the final peptide acceptor the MHC I heavy chain associated with β2-microglobulin. In this chapter, we summarize the structural organization and molecular mechanism of the antigen-translocation machinery as well as various modes of regulation by viral factors and in genetic diseases and tumour development. 相似文献