全文获取类型
收费全文 | 5763篇 |
免费 | 615篇 |
国内免费 | 6篇 |
专业分类
6384篇 |
出版年
2022年 | 44篇 |
2021年 | 81篇 |
2019年 | 40篇 |
2018年 | 75篇 |
2017年 | 56篇 |
2016年 | 95篇 |
2015年 | 172篇 |
2014年 | 206篇 |
2013年 | 260篇 |
2012年 | 282篇 |
2011年 | 298篇 |
2010年 | 189篇 |
2009年 | 198篇 |
2008年 | 260篇 |
2007年 | 283篇 |
2006年 | 246篇 |
2005年 | 222篇 |
2004年 | 219篇 |
2003年 | 235篇 |
2002年 | 208篇 |
2001年 | 166篇 |
2000年 | 141篇 |
1999年 | 137篇 |
1998年 | 96篇 |
1997年 | 69篇 |
1996年 | 64篇 |
1995年 | 75篇 |
1994年 | 61篇 |
1993年 | 71篇 |
1992年 | 108篇 |
1991年 | 86篇 |
1990年 | 123篇 |
1989年 | 78篇 |
1988年 | 73篇 |
1987年 | 81篇 |
1986年 | 67篇 |
1985年 | 65篇 |
1984年 | 50篇 |
1983年 | 58篇 |
1982年 | 59篇 |
1981年 | 53篇 |
1980年 | 52篇 |
1979年 | 56篇 |
1978年 | 34篇 |
1977年 | 49篇 |
1976年 | 54篇 |
1975年 | 39篇 |
1974年 | 42篇 |
1972年 | 38篇 |
1971年 | 46篇 |
排序方式: 共有6384条查询结果,搜索用时 15 毫秒
171.
Gerco den Hartog Ranajoy Chattopadhyay Amber Ablack Emily H. Hall Lindsay D. Butcher Asima Bhattacharyya Lars Eckmann Paul R. Harris Soumita Das Peter B. Ernst Sheila E. Crowe 《PLoS pathogens》2016,12(1)
Generation of reactive oxygen species (ROS) during infection is an immediate host defense leading to microbial killing. APE1 is a multifunctional protein induced by ROS and after induction, protects against ROS-mediated DNA damage. Rac1 and NAPDH oxidase (Nox1) are important contributors of ROS generation following infection and associated with gastrointestinal epithelial injury. The purpose of this study was to determine if APE1 regulates the function of Rac1 and Nox1 during oxidative stress. Gastric or colonic epithelial cells (wild-type or with suppressed APE1) were infected with Helicobacter pylori or Salmonella enterica and assessed for Rac1 and NADPH oxidase-dependent superoxide production. Rac1 and APE1 interactions were measured by co-immunoprecipitation, confocal microscopy and proximity ligation assay (PLA) in cell lines or in biopsy specimens. Significantly greater levels of ROS were produced by APE1-deficient human gastric and colonic cell lines and primary gastric epithelial cells compared to control cells after infection with either gastric or enteric pathogens. H. pylori activated Rac1 and Nox1 in all cell types, but activation was higher in APE1 suppressed cells. APE1 overexpression decreased H. pylori-induced ROS generation, Rac1 activation, and Nox1 expression. We determined that the effects of APE1 were mediated through its N-terminal lysine residues interacting with Rac1, leading to inhibition of Nox1 expression and ROS generation. APE1 is a negative regulator of oxidative stress in the gastrointestinal epithelium during bacterial infection by modulating Rac1 and Nox1. Our results implicate APE1 in novel molecular interactions that regulate early stress responses elicited by microbial infections. 相似文献
172.
173.
Sheila N. Balinda Pascale Ondoa Ekwaro A. Obuku Aletta Kliphuis Isaac Egau Michelle Bronze Lordwin Kasambula Rob Schuurman Nicole Spieker Tobias F. Rinke de Wit Cissy Kityo ART–A consortium 《PloS one》2016,11(1)
Background
WHO recommends regular viral load (VL) monitoring of patients on antiretroviral therapy (ART) for timely detection of virological failure, prevention of acquired HIV drug resistance (HIVDR) and avoiding unnecessary switching to second-line ART. However, the cost and complexity of routine VL testing remains prohibitive in most resource limited settings (RLS). We evaluated a simple, low–cost, qualitative viral–failure assay (VFA) on dried blood spots (DBS) in three clinical settings in Uganda.Methods
We conducted a cross–sectional diagnostic accuracy study in three HIV/AIDS treatment centres at the Joint Clinical Research Centre in Uganda. The VFA employs semi-quantitative detection of HIV–1 RNA amplified from the LTR gene. We used paired dry blood spot (DBS) and plasma with the COBASAmpliPrep/COBASTaqMan, Roche version 2 (VLref) as the reference assay. We used the VFA at two thresholds of viral load, (>5,000 or >1,000 copies/ml).Results
496 paired VFA and VLref results were available for comparative analysis. Overall, VFA demonstrated 78.4% sensitivity, (95% CI: 69.7%–87.1%), 93% specificity (95% CI: 89.7%–96.4%), 89.3% accuracy (95% CI: 85%–92%) and an agreement kappa = 0.72 as compared to the VLref. The predictive values of positivity and negativity among patients on ART for >12 months were 72.7% and 99.3%, respectively.Conclusions
VFA allowed 89% of correct classification of VF. Only 11% of the patients were misclassified with the potential of unnecessary or late switch to second–line ART. Our findings present an opportunity to roll out simple and affordable VL monitoring for HIV–1 treatment in RLS. 相似文献174.
Kirsty E. Russell Kian Fan Chung Colin J. Clarke Andrew L. Durham Patrick Mallia Joseph Footitt Sebastian L. Johnston Peter J. Barnes Simon R. Hall Karen D. Simpson Malcolm R. Starkey Philip M. Hansbro Ian M. Adcock Coen H. Wiegman 《PloS one》2016,11(1)
Introduction
Macrophage migration inhibitory factor (MIF) is an inflammatory cytokine associated with acute and chronic inflammatory disorders and corticosteroid insensitivity. Its expression in the airways of patients with chronic obstructive pulmonary disease (COPD), a relatively steroid insensitive inflammatory disease is unclear, however.Methods
Sputum, bronchoalveolar lavage (BAL) macrophages and serum were obtained from non-smokers, smokers and COPD patients. To mimic oxidative stress-induced COPD, mice were exposed to ozone for six-weeks and treated with ISO-1, a MIF inhibitor, and/or dexamethasone before each exposure. BAL fluid and lung tissue were collected after the final exposure. Airway hyperresponsiveness (AHR) and lung function were measured using whole body plethysmography. HIF-1α binding to the Mif promoter was determined by Chromatin Immunoprecipitation assays.Results
MIF levels in sputum and BAL macrophages from COPD patients were higher than those from non-smokers, with healthy smokers having intermediate levels. MIF expression correlated with that of HIF-1α in all patients groups and in ozone-exposed mice. BAL cell counts, cytokine mRNA and protein expression in lungs and BAL, including MIF, were elevated in ozone-exposed mice and had increased AHR. Dexamethasone had no effect on these parameters in the mouse but ISO-1 attenuated cell recruitment, cytokine release and AHR.Conclusion
MIF and HIF-1α levels are elevated in COPD BAL macrophages and inhibition of MIF function blocks corticosteroid-insensitive lung inflammation and AHR. Inhibition of MIF may provide a novel anti-inflammatory approach in COPD. 相似文献175.
Ellen Clarke 《Biology & philosophy》2016,31(6):893-911
What changes when an evolutionary transition in individuality takes place? Many different answers have been given, in respect of different cases of actual transition, but some have suggested a general answer: that a major transition is a change in the extent to which selection acts at one hierarchical level rather than another. The current paper evaluates some different ways to develop this general answer as a way to characterise the property ‘evolutionary individuality’; and offers a justification of the option taken in Clarke (J Philos 110(8):413–435, 2013)—to define evolutionary individuality in terms of an object’s capacity to undergo selection at its own level. In addition, I suggest a method by which the property can be measured and argue that a problem which is often considered to be fatal to that method—the problem of ‘cross-level by-products’—can be avoided. 相似文献
176.
Feeding habits of the Pacific bearded brotula Brotula clarkae Hubbs, 1944 (Ophidiidae) along the Pacific coast of Costa Rica,Central America 下载免费PDF全文
B. Naranjo‐Elizondo M. Espinoza M. Herrera T. M. Clarke I. S. Wehrtmann 《Zeitschrift fur angewandte Ichthyologie》2016,32(3):439-447
The present study analyzed the diet composition, ontogenetic shifts and dietary overlap of Brotula clarkae in relation to stage of maturity and sex. Samples were collected from the trawling fishery along the Pacific coast of Costa Rica (2011–2012) at depths ranging from 41.4 to 168.3 m; however, over 80% of the sampled fish were obtained at depths between 50 and 75 m. Size ranged from 14.4 to 98.4 cm total length. Of the 323 analyzed stomachs, 44.3% were from males, 86% were from immature individuals, and 49.8% had at least one prey item. According to the prey‐specific index of relative importance (PSIRI), decapod shrimps were the most important prey (57.6% PSIRIi) followed by teleosts (28.2% PSIRIi), stomatopods (10.8% PSIRIi), and crabs (3.3% PSIRIi). Male and female B. clarkae exhibited a high dietary overlap (CH = 0.94). Immature B. clarkae consumed primarily shrimps and crabs (71.5% of stomachs from immature specimens contained shrimps, which accounted for over 66.0% PSIRIi); mature individuals consumed a large proportion of teleosts and stomatopods, which together contributed to over 91.0% PSIRIi. Both immature and mature B. clarkae overlapped spatially with the commercial trawling fishery grounds along the Pacific coast of Costa Rica. However, juveniles feed predominantly on shrimps, suggesting that immature B. clarkae may be subjected to high fishing pressure as by‐catch, making them particularly vulnerable to overexploitation. 相似文献
177.
Sheila Ommeh Wei Zhang Ali Zohaib Jing Chen Huajun Zhang Ben Hu Xing-Yi Ge Xing-Lou Yang Moses Masika Vincent Obanda Yun Luo Shan Li Cecilia Waruhiu Bei Li Yan Zhu Desterio Ouma Vincent Odendo Lin-Fa Wang Danielle E. Anderson Jacqueline Lichoti Erick Mungube Francis Gakuya Peng Zhou Kisa-Juma Ngeiywa Bing Yan Bernard Agwanda Zheng-Li Shi 《中国病毒学》2019,34(1):115-115
178.
Badr Benjelloun Frdric Boyer Ian Streeter Wahid Zamani Stefan Engelen Adriana Alberti Florian J. Alberto Mohamed BenBati Mustapha Ibnelbachyr Mouad Chentouf Abdelmajid Bechchari Hamid R. Rezaei Saeid Naderi Alessandra Stella Abdelkader Chikhi Laura Clarke James Kijas Paul Flicek Pierre Taberlet Franois Pompanon 《Molecular ecology resources》2019,19(6):1497-1515
Whole genome sequences (WGS) greatly increase our ability to precisely infer population genetic parameters, demographic processes, and selection signatures. However, WGS may still be not affordable for a representative number of individuals/populations. In this context, our goal was to assess the efficiency of several SNP genotyping strategies by testing their ability to accurately estimate parameters describing neutral diversity and to detect signatures of selection. We analysed 110 WGS at 12× coverage for four different species, i.e., sheep, goats and their wild counterparts. From these data we generated 946 data sets corresponding to random panels of 1K to 5M variants, commercial SNP chips and exome capture, for sample sizes of five to 48 individuals. We also extracted low‐coverage genome resequencing of 1×, 2× and 5× by randomly subsampling reads from the 12× resequencing data. Globally, 5K to 10K random variants were enough for an accurate estimation of genome diversity. Conversely, commercial panels and exome capture displayed strong ascertainment biases. Besides the characterization of neutral diversity, the detection of the signature of selection and the accurate estimation of linkage disequilibrium (LD) required high‐density panels of at least 1M variants. Finally, genotype likelihoods increased the quality of variant calling from low coverage resequencing but proportions of incorrect genotypes remained substantial, especially for heterozygote sites. Whole genome resequencing coverage of at least 5× appeared to be necessary for accurate assessment of genomic variations. These results have implications for studies seeking to deploy low‐density SNP collections or genome scans across genetically diverse populations/species showing similar genetic characteristics and patterns of LD decay for a wide variety of purposes. 相似文献
179.
Robert B. Lochhead David Ordoez Sheila L. Arvikar John M. Aversa Luke S. Oh Benton Heyworth Ruslan Sadreyev Allen C. Steere Klemen Strle 《Cellular microbiology》2019,21(2)
Lyme arthritis (LA), a late disease manifestation of Borrelia burgdorferi infection, usually resolves with antibiotic therapy. However, some patients develop proliferative synovitis lasting months to several years after spirochetal killing, called postinfectious LA. In this study, we phenotyped haematopoietic and stromal cell populations in the synovial lesion ex vivo and used these findings to generate an in vitro model of LA using patient‐derived fibroblast‐like synoviocytes (FLS). Ex vivo analysis of synovial tissue revealed high abundance of IFNγ‐producing T cells and NK cells. Similar to marked IFNγ responses in tissue, postinfectious LA synovial fluid also had high levels of IFNγ. HLA‐DR‐positive FLS were present throughout the synovial lesion, particularly in areas of inflammation. FLS stimulated in vitro with B. burgdorferi, which were similar to conditions during infection, expressed 68 genes associated primarily with innate immune activation and neutrophil recruitment. In contrast, FLS stimulated with IFNγ, which were similar to conditions in the postinfectious phase, expressed >2,000 genes associated with pathogen sensing, inflammation, and MHC Class II antigen presentation, similar to the expression profile in postinfectious synovial tissue. Furthermore, costimulation of FLS with B. burgdorferi and IFNγ induced greater expression of IL‐6 and other innate immune response proteins and genes than with IFNγ stimulation alone. These results suggest that B. burgdorferi infection, in combination with IFNγ, initiates the differentiation of FLS into a highly inflammatory phenotype. We hypothesise that overexpression of IFNγ by lymphocytes within synovia perpetuates these responses in the postinfectious period, causing proliferative synovitis and stalling appropriate repair of damaged tissue. 相似文献
180.
Heena Dhiman Matthias P. Gerstl David Ruckerbauer Michael Hanscho Heinz Himmelbauer Colin Clarke Niall Barron Jürgen Zanghellini Nicole Borth 《Biotechnology journal》2019,14(7)
The increasingdemandfor biopharmaceutical products drives the search for efficient cell factories that are able to sustainably support rapid growth, high productivity, and product quality. As these depend on energy generation, here the genomic variation in nuclear genes associated with mitochondria and energy metabolism and the mitochondrial genome of 14 cell lines is investigated. The variants called enable reliable tracing of lineages. Unique sequence variations are observed in cell lines adapted to grow in protein‐free media, enriched in signaling pathways or mitogen‐activated protein kinase 3. High‐producing cell lines bear unique mutations in nicotinamide adenine dinucleotide (NADH) dehydrogenase (ND2 and ND4) and in peroxisomal acyl‐CoA synthetase (ACSL4), involved in lipid metabolism. As phenotypes are determined not only by functional mutations, but also by the exquisite regulation of expression patterns, it is not surprising that ≈50% of the genes investigated here are found to be differentially methylated and thus epigenetically controlled, enabling a clear distinction of high producers, and cells adapted to a minimal, glutamine (Gln)‐free medium. Similar pathways are enriched as those identified by genome variation. This strengthens the hypothesis that these phenomena act together to define cell behavior. 相似文献