全文获取类型
收费全文 | 1112篇 |
免费 | 106篇 |
国内免费 | 2篇 |
出版年
2022年 | 7篇 |
2021年 | 16篇 |
2020年 | 7篇 |
2019年 | 11篇 |
2018年 | 15篇 |
2017年 | 23篇 |
2016年 | 22篇 |
2015年 | 39篇 |
2014年 | 55篇 |
2013年 | 69篇 |
2012年 | 76篇 |
2011年 | 93篇 |
2010年 | 47篇 |
2009年 | 43篇 |
2008年 | 67篇 |
2007年 | 76篇 |
2006年 | 82篇 |
2005年 | 83篇 |
2004年 | 34篇 |
2003年 | 25篇 |
2002年 | 37篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 13篇 |
1996年 | 7篇 |
1995年 | 8篇 |
1994年 | 5篇 |
1993年 | 8篇 |
1992年 | 7篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 21篇 |
1988年 | 16篇 |
1987年 | 12篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 13篇 |
1983年 | 6篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1968年 | 7篇 |
排序方式: 共有1220条查询结果,搜索用时 687 毫秒
901.
A role for IL-10-mediated HLA-DR7-restricted T cell-dependent events in development of the modified Th2 response to cat allergen 总被引:8,自引:0,他引:8
Reefer AJ Carneiro RM Custis NJ Platts-Mills TA Sung SS Hammer J Woodfolk JA 《Journal of immunology (Baltimore, Md. : 1950)》2004,172(5):2763-2772
Although high dose exposure to inhaled cat allergen (Fel d 1) can cause a form of tolerance (modified Th2 response), the T cell mechanism for this phenomenon has not been studied. T cell responses to Fel d 1 were characterized in both allergic (IgE(pos)) and modified Th2 (IgE(neg)IgG(pos)) responders as well as serum Ab-negative controls (IgE(neg)IgG(neg)). Fel d 1 stimulated high levels of IL-10 in PBMC cultures from all individuals, with evidence of Th2 and Th1 cytokine skewing in allergic and control subjects, respectively. Using overlapping peptides, epitopes at the N terminus of Fel d 1 chain 2 were shown to stimulate strong T cell proliferation and to preferentially induce IL-10 (peptide 2:1 (P2:1)) or IFN-gamma (P2:2) regardless of the allergic status of the donor. Injection of cat extract during conventional immunotherapy stimulated expansion of IL-10- and IFN-gamma-producing chain 2 epitope-specific T cells along with increased Fel d 1-specific serum IgG and IgG4 Ab. Six of 12 modified responders expressed the major HLA-DRB1 allele, *0701, and both P2:1 and P2:2 were predicted ligands for this allele. Cultures from DR7-positive modified responders produced the highest levels of IL-10 to P2:1 in addition to other major and minor epitopes within chains 1 and 2. In the presence of anti-IL-10 mAb, both T cell proliferation and IFN-gamma production were enhanced in a Fel d 1- and epitope-specific manner. We conclude that IL-10-producing T cells specific for chain 2 epitopes are relevant to tolerance induction, and that DR7-restricted recognition of these epitopes favors a modified Th2 response. 相似文献
902.
903.
Species richness effects on grassland recovery from drought depend on community productivity in a multisite experiment
下载免费PDF全文
![点击此处可从《Ecology letters》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Juergen Kreyling Jürgen Dengler Julia Walter Nikolay Velev Emin Ugurlu Desislava Sopotlieva Johannes Ransijn Catherine Picon‐Cochard Ivan Nijs Pauline Hernandez Behlül Güler Philipp von Gillhaussen Hans J. De Boeck Juliette M.G. Bloor Sigi Berwaers Carl Beierkuhnlein Mohammed A.S. Arfin Khan Iva Apostolova Yasin Altan Michaela Zeiter Camilla Wellstein Marcelo Sternberg Andreas Stampfli Giandiego Campetella Sándor Bartha Michael Bahn Anke Jentsch 《Ecology letters》2017,20(11):1405-1413
Biodiversity can buffer ecosystem functioning against extreme climatic events, but few experiments have explicitly tested this. Here, we present the first multisite biodiversity × drought manipulation experiment to examine drought resistance and recovery at five temperate and Mediterranean grassland sites. Aboveground biomass production declined by 30% due to experimental drought (standardised local extremity by rainfall exclusion for 72–98 consecutive days). Species richness did not affect resistance but promoted recovery. Recovery was only positively affected by species richness in low‐productive communities, with most diverse communities even showing overcompensation. This positive diversity effect could be linked to asynchrony of species responses. Our results suggest that a more context‐dependent view considering the nature of the climatic disturbance as well as the productivity of the studied system will help identify under which circumstances biodiversity promotes drought resistance or recovery. Stability of biomass production can generally be expected to decrease with biodiversity loss and climate change. 相似文献
904.
During reinforcement learning, dopamine release shifts from the moment of reward consumption to the time point when the reward can be predicted. Previous studies provide consistent evidence that reward-predicting cues enhance long-term memory (LTM) formation of these items via dopaminergic projections to the ventral striatum. However, it is less clear whether memory for items that do not precede a reward but are directly associated with reward consumption is also facilitated. Here, we investigated this question in an fMRI paradigm in which LTM for reward-predicting and neutral cues was compared to LTM for items presented during consumption of reliably predictable as compared to less predictable rewards. We observed activation of the ventral striatum and enhanced memory formation during reward anticipation. During processing of less predictable as compared to reliably predictable rewards, the ventral striatum was activated as well, but items associated with less predictable outcomes were remembered worse than items associated with reliably predictable outcomes. Processing of reliably predictable rewards activated the ventromedial prefrontal cortex (vmPFC), and vmPFC BOLD responses were associated with successful memory formation of these items. Taken together, these findings show that consumption of reliably predictable rewards facilitates LTM formation and is associated with activation of the vmPFC. 相似文献
905.
Stephanie O. M. Dyke Anthony A. Philippakis Jordi Rambla De Argila Dina N. Paltoo Erin S. Luetkemeier Bartha M. Knoppers Anthony J. Brookes J. Dylan Spalding Mark Thompson Marco Roos Kym M. Boycott Michael Brudno Matthew Hurles Heidi L. Rehm Andreas Matern Marc Fiume Stephen T. Sherry 《PLoS genetics》2016,12(1)
906.
907.
908.
Zusammenfassung Beim Abbau von Tetradecanol durch Pseudomonas aeruginosa wird Tetradecanal als Semicarbazon angereichert und als 2,4-Dinitrophenylhydrazon nachgewiesen.Die Gewinnung eines Aldehyds wird durch Anreicherung aus einer wachsenden Kultur möglich.
Accumulation of aldehyd intermediate by Pseudomonas aeruginosa in growing culture on tetradecanol
Summary In the oxidation of tetradecanol by Pseudomonas aeruginosa tetradecanal was accumulated as semicarbazon and was identified as 2,4-Dinitrophenylhydrazon.This confirms the possibility of production of an intermediate aldehyde out of the growing culture.相似文献
909.
Juergen Dukart Robert Perneczky Stefan F?rster Henryk Barthel Janine Diehl-Schmid Bogdan Draganski Hellmuth Obrig Emiliano Santarnecchi Alexander Drzezga Andreas Fellgiebel Richard Frackowiak Alexander Kurz Karsten Müller Osama Sabri Matthias L. Schroeter Igor Yakushev 《PloS one》2013,8(2)
Positron emission tomography with [18F] fluorodeoxyglucose (FDG-PET) plays a well-established role in assisting early detection of frontotemporal lobar degeneration (FTLD). Here, we examined the impact of intensity normalization to different reference areas on accuracy of FDG-PET to discriminate between patients with mild FTLD and healthy elderly subjects. FDG-PET was conducted at two centers using different acquisition protocols: 41 FTLD patients and 42 controls were studied at center 1, 11 FTLD patients and 13 controls were studied at center 2. All PET images were intensity normalized to the cerebellum, primary sensorimotor cortex (SMC), cerebral global mean (CGM), and a reference cluster with most preserved FDG uptake in the aforementioned patients group of center 1. Metabolic deficits in the patient group at center 1 appeared 1.5, 3.6, and 4.6 times greater in spatial extent, when tracer uptake was normalized to the reference cluster rather than to the cerebellum, SMC, and CGM, respectively. Logistic regression analyses based on normalized values from FTLD-typical regions showed that at center 1, cerebellar, SMC, CGM, and cluster normalizations differentiated patients from controls with accuracies of 86%, 76%, 75% and 90%, respectively. A similar order of effects was found at center 2. Cluster normalization leads to a significant increase of statistical power in detecting early FTLD-associated metabolic deficits. The established FTLD-specific cluster can be used to improve detection of FTLD on a single case basis at independent centers – a decisive step towards early diagnosis and prediction of FTLD syndromes enabling specific therapies in the future. 相似文献
910.
The effects of guanine nucleotides on arachidonic acid (AA) release were studied in intact and saponin-permeabilized human platelets. While GTP[S] itself caused a stimulation of AA release in permeabilized cells, GTP[S], GDP[S], GTP, ATP and other nucleotides inhibited AA release in response to thrombin and other agonists in intact, as well as permeabilized platelets. Inhibition of agonist-stimulated AA release by nucleotides was partially attenuated by addition of ADP, and was abolished by prior stimulation of platelets to discharge the ADP-containing dense granules. These results suggest: (i) that released ADP plays an important contributory role in agonist-stimulated platelet AA release, and (ii) that guanine nucleotides can modulate platelet activation through an extracellular action which is distinct from their effects on G-proteins. 相似文献