全文获取类型
收费全文 | 7166篇 |
免费 | 663篇 |
国内免费 | 3篇 |
专业分类
7832篇 |
出版年
2024年 | 10篇 |
2023年 | 51篇 |
2022年 | 136篇 |
2021年 | 258篇 |
2020年 | 141篇 |
2019年 | 158篇 |
2018年 | 201篇 |
2017年 | 158篇 |
2016年 | 247篇 |
2015年 | 469篇 |
2014年 | 467篇 |
2013年 | 559篇 |
2012年 | 734篇 |
2011年 | 656篇 |
2010年 | 376篇 |
2009年 | 331篇 |
2008年 | 471篇 |
2007年 | 451篇 |
2006年 | 415篇 |
2005年 | 342篇 |
2004年 | 307篇 |
2003年 | 271篇 |
2002年 | 217篇 |
2001年 | 47篇 |
2000年 | 22篇 |
1999年 | 35篇 |
1998年 | 57篇 |
1997年 | 31篇 |
1996年 | 21篇 |
1995年 | 19篇 |
1994年 | 21篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 11篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 6篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 9篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 10篇 |
1979年 | 5篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1971年 | 2篇 |
排序方式: 共有7832条查询结果,搜索用时 0 毫秒
71.
Karin Strijbis ?mer H. Yilmaz Stephanie K. Dougan Alexandre Esteban Andrea Gr?ne Carol A. Kumamoto Hidde L. Ploegh 《PloS one》2014,9(11)
The commensal yeast Candida albicans is part of the human intestinal microflora and is considered a “pathobiont”, a resident microbe with pathogenic potential yet harmless under normal conditions. The aim of this study was to investigate the effect of C. albicans on inflammation of the intestinal tract and the role of Bruton''s tyrosine kinase (Btk). Btk is an enzyme that modulates downstream signaling of multiple receptors involved in innate and adaptive immunity, including the major anti-fungal receptor Dectin-1. Colitis was induced in wild type and Btk-/- mice by treatment with dextran sodium sulfate (DSS) and the gastrointestinal tract of selected treatment groups were then colonized with C. albicans. Colonization by C. albicans neither dampened nor exacerbated inflammation in wild type mice, but colon length and spleen weight were improved in Btk-deficient mice colonized with C. albicans. Neutrophil infiltration was comparable between wild type and Btk-/- mice, but the knockout mice displayed severely reduced numbers of macrophages in the colon during both DSS and DSS/Candida treatment. Smaller numbers and reduced responsiveness of Btk-/- macrophages might partially explain the improved colon length of Btk-/- mice as a result of Candida colonization. Surprisingly, DSS/Candida-treated Btk-/- animals had higher levels of certain pro-inflammatory cytokines and levels of the anti-inflammatory cytokine TGF-β were reduced compared to wild type. A clustering and correlation analysis showed that for wild type animals, spleen TGF-β and colon IL-10 and for Btk-/- spleen and colon levels of IL-17A best correlated with the inflammatory parameters. We conclude that in Btk-/- immunocompromised animals, colonization of the gastrointestinal tract by the commensal yeast C. albicans alters inflammatory symptoms associated with colitis. 相似文献
72.
73.
Community structure and dynamics in aquatic ecosystems are influenced by a variety of abiotic and biotic factors including productivity, species composition, and temperature. These factors may also affect local-scale community resilience to nonnative species invasions. We used habitat characteristics, zooplankton concentrations, fish abundances, and species composition and richness data collected by two fish population monitoring programs to define relationships that influence stress and nutrition in invasive silver carp (Hypophthalmichthys molitrix). We collected blood samples and quantified nutritional (alkaline phosphatase, cholesterol, protein, and triglycerides) and stress metrics (cortisol and glucose) from individuals across three distinct time periods. Nutritional patterns in silver carp were explained by temperature and food resources, indicating elevated feeding in warmer months. Patterns in blood-based stress parameters were most strongly driven by environmental characteristics, elevating with high water temperatures and increased turbidity. Nutrient levels and community richness parameters did not influence the stress or condition of silver carp, likely due to the absence of limiting resources or competition for this species. Together, our results provide insights into the factors that may influence the spread and distribution of silver carp, as well as the characteristics of habitats that could be vulnerable to future silver carp invasion. 相似文献
74.
Anastasia Chasapi Paulina Wachowicz Anne Niknejad Philippe Collin Andrea Krapp Elena Cano Viesturs Simanis Ioannis Xenarios 《PloS one》2015,10(8)
Cytokinesis in fission yeast is controlled by the Septation Initiation Network (SIN), a protein kinase signaling network using the spindle pole body as scaffold. In order to describe the qualitative behavior of the system and predict unknown mutant behaviors we decided to adopt a Boolean modeling approach. In this paper, we report the construction of an extended, Boolean model of the SIN, comprising most SIN components and regulators as individual, experimentally testable nodes. The model uses CDK activity levels as control nodes for the simulation of SIN related events in different stages of the cell cycle. The model was optimized using single knock-out experiments of known phenotypic effect as a training set, and was able to correctly predict a double knock-out test set. Moreover, the model has made in silico predictions that have been validated in vivo, providing new insights into the regulation and hierarchical organization of the SIN. 相似文献
75.
Satish K. Madala Ramakrishna Edukulla Mukta Phatak Stephanie Schmidt Cynthia Davidson Thomas H. Acciani Thomas R. Korfhagen Mario Medvedovic Timothy D. LeCras Kimberly Wagner William D. Hardie 《PloS one》2014,9(1)
Pulmonary fibrosis is often triggered by an epithelial injury resulting in the formation of fibrotic lesions in the lung, which progress to impair gas exchange and ultimately cause death. Recent clinical trials using drugs that target either inflammation or a specific molecule have failed, suggesting that multiple pathways and cellular processes need to be attenuated for effective reversal of established and progressive fibrosis. Although activation of MAPK and PI3K pathways have been detected in human fibrotic lung samples, the therapeutic benefits of in vivo modulation of the MAPK and PI3K pathways in combination are unknown. Overexpression of TGFα in the lung epithelium of transgenic mice results in the formation of fibrotic lesions similar to those found in human pulmonary fibrosis, and previous work from our group shows that inhibitors of either the MAPK or PI3K pathway can alter the progression of fibrosis. In this study, we sought to determine whether simultaneous inhibition of the MAPK and PI3K signaling pathways is a more effective therapeutic strategy for established and progressive pulmonary fibrosis. Our results showed that inhibiting both pathways had additive effects compared to inhibiting either pathway alone in reducing fibrotic burden, including reducing lung weight, pleural thickness, and total collagen in the lungs of TGFα mice. This study demonstrates that inhibiting MEK and PI3K in combination abolishes proliferative changes associated with fibrosis and myfibroblast accumulation and thus may serve as a therapeutic option in the treatment of human fibrotic lung disease where these pathways play a role. 相似文献
76.
77.
Stephanie J. Watts‐Williams Timothy R. Cavagnaro Stephen D. Tyerman 《Plant, cell & environment》2019,42(1):285-294
Association with arbuscular mycorrhizal fungi (AMF) can impact on plant water relations; mycorrhizal plants can exhibit increased stomatal conductance (gs) and root hydraulic conductance (normalized to root dry weight, Lo), and altered expression of aquaporins (AQP). Many factors regulate such responses; however, plant intraspecific diversity effects have yet to be explored. Twenty geographically diverse accessions of Medicago truncatula were inoculated with the AMF Funneliformis mosseae or mock‐inoculated, and grown under well‐watered conditions. Biomass, gs, shoot nutrient concentrations and mycorrhizal colonization were measured in all accessions, and Lo and gene expression in five accessions. The diverse accessions varied in physiology and gene expression; some accessions were also larger or had higher gs when colonized by F. mosseae. In the five accessions, Lo was higher in two accessions when colonized by AMF and also maintained within a much smaller range than the mock‐inoculated plants. Expression of MtPIP1 correlated with both gs and Lo, and when plants were more than 3% colonized, mycorrhizal colonization correlated with Lo. Accession and AMF treatments had profound effects on M. truncatula, including several measures of plant water relations. Correlations between response variables, especially between molecular and physiological variables, across genotypes, highlight the findings of this study. 相似文献
78.
Benny Borremans Jonas Reijniers Nelika K. Hughes Stephanie S. Godfrey Sophie Gryseels Rhodes H. Makundi Herwig Leirs 《Oikos》2017,126(6):792-800
Density‐dependent shifts in population processes like territoriality, reproduction, dispersal, and parasite transmission are driven by changes in contacts between individuals. Despite this, surprisingly little is known about how contacts change with density, and thus the mechanisms driving density‐dependent processes. A simple linear contact–density function is often assumed, but this is not based on a sound basis of empirical data. We addressed this question using a replicated, semi‐natural experiment in which we measured contacts at feeding stations between multimammate mice, Mastomys natalensis, across ten distinct, linearly increasing densities between 10 and 272 animals/ha. Unexpectedly, unique contacts increased not linearly but sigmoidally with density, which we attribute to the species’ scramble competition mating system, small‐scale dominance/avoidance and absence of territoriality. These results provide new insights into how species’ characteristics can relate to density‐dependent changes in contacts, and the unexpected shape of the contact–density function warrants that density‐dependence in ecological models, such as parasite transmission models, must be parameterized with care. 相似文献
79.
Meghan E. Hall Nima Khadem Mohtaram Stephanie M. Willerth 《Journal of biological engineering》2017,11(1):38
Background
Human induced pluripotent stem cells (hiPSCs) can form any tissue found in the body, making them attractive for regenerative medicine applications. Seeding hiPSC aggregates into biomaterial scaffolds can control their differentiation into specific tissue types. Here we develop and analyze a mathematical model of hiPSC aggregate behavior when seeded on melt electrospun scaffolds with defined topography.Results
We used ordinary differential equations to model the different cellular populations (stem, progenitor, differentiated) present in our scaffolds based on experimental results and published literature. Our model successfully captures qualitative features of the cellular dynamics observed experimentally. We determined the optimal parameter sets to maximize specific cellular populations experimentally, showing that a physiologic oxygen level (~?5%) increases the number of neural progenitors and differentiated neurons compared to atmospheric oxygen levels (~?21%) and a scaffold porosity of ~?63% maximizes aggregate size.Conclusions
Our mathematical model determined the key factors controlling hiPSC behavior on melt electrospun scaffolds, enabling optimization of experimental parameters.80.
Weingärtner O Lütjohann D Vanmierlo T Müller S Günther L Herrmann W Böhm M Laufs U Herrmann M 《Chemistry and physics of lipids》2011,(6):451-456