全文获取类型
收费全文 | 3209篇 |
免费 | 260篇 |
出版年
2024年 | 4篇 |
2023年 | 36篇 |
2022年 | 82篇 |
2021年 | 148篇 |
2020年 | 114篇 |
2019年 | 110篇 |
2018年 | 96篇 |
2017年 | 85篇 |
2016年 | 148篇 |
2015年 | 295篇 |
2014年 | 283篇 |
2013年 | 254篇 |
2012年 | 333篇 |
2011年 | 342篇 |
2010年 | 177篇 |
2009年 | 108篇 |
2008年 | 155篇 |
2007年 | 134篇 |
2006年 | 132篇 |
2005年 | 115篇 |
2004年 | 67篇 |
2003年 | 52篇 |
2002年 | 61篇 |
2001年 | 14篇 |
2000年 | 8篇 |
1999年 | 14篇 |
1998年 | 12篇 |
1997年 | 14篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 6篇 |
1992年 | 4篇 |
1991年 | 10篇 |
1990年 | 6篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 4篇 |
1986年 | 8篇 |
1985年 | 3篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1976年 | 1篇 |
1975年 | 2篇 |
1940年 | 1篇 |
排序方式: 共有3469条查询结果,搜索用时 513 毫秒
991.
Anna Riba Peschel Emma Lauren Boehm Ruth Geyer Shaw 《Evolution; international journal of organic evolution》2021,75(1):73-85
Adaptation through natural selection may be the only means by which small and fragmented plant populations will persist through present day environmental change. A population's additive genetic variance for fitness (VA(W)) represents its immediate capacity to adapt to the environment in which it exists. We evaluated this property for a population of the annual legume Chamaecrista fasciculata through a quantitative genetic experiment in the tallgrass prairie region of the Midwestern United States, where changing climate is predicted to include more variability in rainfall. To reduce incident rainfall, relative to controls receiving ambient rain, we deployed rain exclusion shelters. We found significant VA(W) in both treatments. We also detected a significant genotype‐by‐treatment interaction for fitness, which suggests that the genetic basis of the response to natural selection will differ depending on precipitation. For the trait‐specific leaf area, we detected maladaptive phenotypic plasticity and an interaction between genotype and environment. Selection for thicker leaves was detected with increased precipitation. These results indicate capacity of this population of C. fasciculata to adapt in situ to environmental change. 相似文献
992.
993.
Elizabeth T. Borer Lale Asik Rebecca A. Everett Thijs Frenken Angelica L. Gonzalez Rachel E. Paseka Angela Peace Eric W. Seabloom Alexander T. Strauss Dedmer B. Van de Waal Lauren A. White 《Ecology letters》2021,24(1):6-19
An overlooked effect of ecosystem eutrophication is the potential to alter disease dynamics in primary producers, inducing disease‐mediated feedbacks that alter net primary productivity and elemental recycling. Models in disease ecology rarely track organisms past death, yet death from infection can alter important ecosystem processes including elemental recycling rates and nutrient supply to living hosts. In contrast, models in ecosystem ecology rarely track disease dynamics, yet elemental nutrient pools (e.g. nitrogen, phosphorus) can regulate important disease processes including pathogen reproduction and transmission. Thus, both disease and ecosystem ecology stand to grow as fields by exploring questions that arise at their intersection. However, we currently lack a framework explicitly linking these disciplines. We developed a stoichiometric model using elemental currencies to track primary producer biomass (carbon) in vegetation and soil pools, and to track prevalence and the basic reproduction number (R0) of a directly transmitted pathogen. This model, parameterised for a deciduous forest, demonstrates that anthropogenic nutrient supply can interact with disease to qualitatively alter both ecosystem and disease dynamics. Using this element‐focused approach, we identify knowledge gaps and generate predictions about the impact of anthropogenic nutrient supply rates on infectious disease and feedbacks to ecosystem carbon and nutrient cycling. 相似文献
994.
Aishwarya Devaraj Juan F. Gonzlez Bradley Eichar Gatan Thilliez Robert A. Kingsley Stephen Baker Marc W. Allard Lauren O. Bakaletz John S. Gunn Steven D. Goodman 《PLoS pathogens》2021,17(1)
Salmonella Typhi is the primary causative agent of typhoid fever; an acute systemic infection that leads to chronic carriage in 3–5% of individuals. Chronic carriers are asymptomatic, difficult to treat and serve as reservoirs for typhoid outbreaks. Understanding the factors that contribute to chronic carriage is key to development of novel therapies to effectively resolve typhoid fever. Herein, although we observed no distinct clustering of chronic carriage isolates via phylogenetic analysis, we demonstrated that chronic isolates were phenotypically distinct from acute infection isolates. Chronic carriage isolates formed significantly thicker biofilms with greater biomass that correlated with significantly higher relative levels of extracellular DNA (eDNA) and DNABII proteins than biofilms formed by acute infection isolates. Importantly, extracellular DNABII proteins include integration host factor (IHF) and histone-like protein (HU) that are critical to the structural integrity of bacterial biofilms. In this study, we demonstrated that the biofilm formed by a chronic carriage isolate in vitro, was susceptible to disruption by a specific antibody against DNABII proteins, a successful first step in the development of a therapeutic to resolve chronic carriage. 相似文献
995.
996.
997.
998.
Jillette N Cammack L Lowenstein M Henry RP 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》2011,158(2):189-193
The euryhaline green crab, Carcinus maenas, undergoes an annual cycle of salinity exposure, having to adapt to low salinity during its annual spring migration into estuaries, and then having to re-adapt to high salinity when it moves off-shore at the end of summer. Most studies have focused on low salinity acclimation, the activation of osmoregulatory mechanisms, and the induction of transport protein and transport-related enzyme activity and gene expression. In this study we followed the changes in hemolymph osmolality, carbonic anhydrase activity, and mRNA expression of three proteins through a complete cycle of low (15 ppt) and high (32 ppt) salinity acclimation. One week of low salinity acclimation resulted in hemolymph osmoregulation and a four-fold induction of branchial carbonic anhydrase activity. Relative mRNA expression increased for two CA isoforms (CAc 100-fold, and CAg 7-fold) and the α-subunit of the Na/K-ATPase (8-fold). Upon re-exposure to high salinity, hemolymph osmolality increased to 32 ppt acclimated levels by 6 h, and mRNA levels returned to high salinity, baseline levels within 1 week. However, CA activity remained unchanged in response to high salinity exposure for the first week and then gradually declined to baseline levels over 4 weeks. The relative timing of these changes suggests that while whole-organism physiological adaptations and regulation at the gene level can be very rapid, changes at the level of protein expression and turnover are much slower. It is possible that the high metabolic cost of protein synthesis and/or processing could be the underlying reason for long biological life spans of physiologically important proteins. 相似文献
999.
Puntel GO Carvalho NR Amaral GP Lobato LD Silveira SO Daubermann MF Barbosa NV Rocha JB Soares FA 《Free radical research》2011,45(2):125-138
Muscular contusions affect the function of the skeletal muscle system. This study investigated the oxidative damage as well as the main morphological changes related to a skeletal muscle contusion in the gastrocnemius muscle of rats and also the capacity of therapeutic cold to modulate these parameters. The therapeutic cold modulated the increase of oxidative stress markers and also modulated the reduction in the antioxidants levels in the injured muscle. In enzyme assays, therapeutic cold was also effective in normalizing the muscle Na(+)/K(+) and Ca(2+) ATPases, lactate dehydrogenase and myeloperoxidase activities. Similarly, the lesioned non-treated animals presented evident impairments in the mitochondrial functions and in the muscle morphology which were diminished by the cold treatment. The therapeutic cold was able to modulate the oxidative damage possibly by its capacity to limit the inflammatory response intensity, to attenuate the impairment of the mitochondrial function and also to preserve the skeletal muscle morphology. 相似文献
1000.
ROS-mediated p53 induction of Lpin1 regulates fatty acid oxidation in response to nutritional stress
Assaily W Rubinger DA Wheaton K Lin Y Ma W Xuan W Brown-Endres L Tsuchihara K Mak TW Benchimol S 《Molecular cell》2011,44(3):491-501
The p53 protein is activated by stress signals and exhibits both protective and death-promoting functions that are considered important for its tumor suppressor function. Emerging evidence points toward an additional role for p53 in metabolism. Here, we identify Lpin1 as a p53-responsive gene that is induced in response to DNA damage and glucose deprivation. Lpin1 is essential for adipocyte development and fat metabolism, and mutation in this gene is responsible for the lypodystrophy phenotype in fld mice. We show that p53 and Lpin1 regulate fatty acid oxidation in mouse C2C12 myoblasts. p53 phosphorylation on Ser18 in response to low glucose is ROS and ATM dependent. Lpin1 expression in response to nutritional stress is controlled through the ROS-ATM-p53 pathway and is conserved in human cells. Lpin1 provides a critical link between p53 and metabolism that may be an important component in mediating the tumor suppressor function of p53. 相似文献