全文获取类型
收费全文 | 7384篇 |
免费 | 687篇 |
国内免费 | 6篇 |
专业分类
8077篇 |
出版年
2023年 | 51篇 |
2022年 | 116篇 |
2021年 | 233篇 |
2020年 | 154篇 |
2019年 | 183篇 |
2018年 | 180篇 |
2017年 | 157篇 |
2016年 | 210篇 |
2015年 | 357篇 |
2014年 | 380篇 |
2013年 | 463篇 |
2012年 | 548篇 |
2011年 | 543篇 |
2010年 | 321篇 |
2009年 | 288篇 |
2008年 | 380篇 |
2007年 | 392篇 |
2006年 | 328篇 |
2005年 | 337篇 |
2004年 | 316篇 |
2003年 | 280篇 |
2002年 | 273篇 |
2001年 | 67篇 |
2000年 | 44篇 |
1999年 | 65篇 |
1998年 | 83篇 |
1997年 | 39篇 |
1996年 | 32篇 |
1995年 | 36篇 |
1994年 | 30篇 |
1993年 | 42篇 |
1992年 | 44篇 |
1991年 | 30篇 |
1990年 | 32篇 |
1989年 | 40篇 |
1988年 | 29篇 |
1987年 | 38篇 |
1986年 | 33篇 |
1985年 | 28篇 |
1984年 | 37篇 |
1982年 | 43篇 |
1981年 | 47篇 |
1980年 | 42篇 |
1979年 | 23篇 |
1978年 | 40篇 |
1977年 | 30篇 |
1976年 | 24篇 |
1975年 | 34篇 |
1974年 | 31篇 |
1973年 | 29篇 |
排序方式: 共有8077条查询结果,搜索用时 15 毫秒
81.
Bonny Breckinridge DiNovo Richard Doan Roy B. Dyer Samuel Baron Norbert K. Herzog David W. Niesel 《FEMS immunology and medical microbiology》1996,15(2-3):149-158
Abstract Pathogenesis mediated by Shigella flexneri requires invasion of the gastrointestinal epithelium. It has been previously shown that HeLa cells challenged with S. flexneri show alterations in their phosphotyrosine-containing protein profile. In this report, we demonstrated that bacterial water extracts (WE) abrogated the invasion of HeLa cells by S. flexneri in a dose-dependent manner. A proteinaceous component of S. flexneri was shown to be responsible for this inhibitory activity. Proteins encoded on the 140-MDa plasmid were not responsible for the observed inhibition. WE from other Gram-negative bacteria also inhibited Shigella invasion of HeLa cells. HeLa cells pretreated with WE showed changes in the profile and the intensity of phosphotyrosine-containing protein bands. These data were consistent with a surface protein component in WE which initiated aberrant host cell signaling at the membrane which may account for the inhibition of bacterial entry. 相似文献
82.
Cervical cancer stem‐like cells: systematic review and identification of reference genes for gene expression 下载免费PDF全文
83.
Kenefick RW Cheuvront SN Elliott LD Ely BR Sawka MN 《American journal of physiology. Regulatory, integrative and comparative physiology》2012,302(2):R252-R258
Appropriate quantification of analytical and biological variation of thermoregulatory sweating has important practical utility for research design and statistical analysis. We sought to examine contributors to variability in local forearm sweating rate (SR) and sweating onset (SO) and to evaluate the potential for using bilateral measurements. Two women and eight men (26 ± 9 yr; 79 ± 12 kg) completed 5 days of heat acclimation and walked (1.8 l/min VO(2)) on three occasions for 30 min in 40°C, 20% RH, while local SR and SO were measured. Local SR measures among days were not different (2.14 ± 0.72 vs. 2.02 ± 0.79 vs. 2.31 ± 0.72 mg·cm(2)·min(-1), P = 0.19) nor was SO (10.47 ± 2.54 vs. 10.04 ± 2.97 vs. 9.87 ± 3.44 min P = 0.82). Bilateral SR (2.14 ± 0.72 vs. 2.16 ± 0.71 mg·cm(2)·min(-1), P = 0.56) and SO (10.47 ± 2.54 vs. 10.83 ± 2.48 min, P = 0.09) were similar and differences were ≤ 1 SD of day-to-day differences for a single forearm. Analytical imprecision (CV(a)), within (CV(i))-, and between (CV(g))-subjects' coefficient of variation for local SR were 2.4%, 22.3%, and 56.4%, respectively, and were 0%, 9.6%, and 41%, respectively, for SO. We conclude: 1) technologically, sweat capsules contribute negligibly to sweat measurement variation; 2) bilateral measures of SR and SO appear interchangeable; 3) when studying potential factors affecting sweating, changes in SO afford a more favorable signal-to-noise ratio vs. changes in SR. These findings provide a quantitative basis for study design and optimization of power/sample size analysis in the evaluation of thermoregulatory sweating. 相似文献
84.
Roxane M Barthélémy Anne Chenuil Samuel Blanquart Jean-Paul Casanova Eric Faure 《BMC evolutionary biology》2007,7(1):146
Background
Chaetognaths, or arrow worms, are small marine, bilaterally symmetrical metazoans. The objective of this study was to analyse ribosomal protein (RP) coding sequences from a published collection of expressed sequence tags (ESTs) from a chaetognath (Spadella cephaloptera) and to use them in phylogenetic studies. 相似文献85.
86.
Jean-Luc Montillet Nathalie Leonhardt Samuel Mondy Sylvain Tranchimand Dominique Rumeau Marie Boudsocq Ana Victoria Garcia Thierry Douki Jean Bigeard Christiane Laurière Anne Chevalier Carmen Castresana Heribert Hirt 《PLoS biology》2013,11(3)
Plant stomata function in innate immunity against bacterial invasion and abscisic acid (ABA) has been suggested to regulate this process. Using genetic, biochemical, and pharmacological approaches, we demonstrate that (i) the Arabidopsis thaliana nine-specific-lipoxygenase encoding gene, LOX1, which is expressed in guard cells, is required to trigger stomatal closure in response to both bacteria and the pathogen-associated molecular pattern flagellin peptide flg22; (ii) LOX1 participates in stomatal defense; (iii) polyunsaturated fatty acids, the LOX substrates, trigger stomatal closure; (iv) the LOX products, fatty acid hydroperoxides, or reactive electrophile oxylipins induce stomatal closure; and (v) the flg22-mediated stomatal closure is conveyed by both LOX1 and the mitogen-activated protein kinases MPK3 and MPK6 and involves salicylic acid whereas the ABA-induced process depends on the protein kinases OST1, MPK9, or MPK12. Finally, we show that the oxylipin and the ABA pathways converge at the level of the anion channel SLAC1 to regulate stomatal closure. Collectively, our results demonstrate that early biotic signaling in guard cells is an ABA-independent process revealing a novel function of LOX1-dependent stomatal pathway in plant immunity. 相似文献
87.
Jessica K. Calland Ben Pascoe Sion C. Bayliss Evangelos Mourkas Elvire Berthenet Harry A. Thorpe Matthew D. Hitchings Edward J. Feil Jukka Corander Martin J. Blaser Daniel Falush Samuel K. Sheppard 《PLoS genetics》2021,17(9)
Measuring molecular evolution in bacteria typically requires estimation of the rate at which nucleotide changes accumulate in strains sampled at different times that share a common ancestor. This approach has been useful for dating ecological and evolutionary events that coincide with the emergence of important lineages, such as outbreak strains and obligate human pathogens. However, in multi-host (niche) transmission scenarios, where the pathogen is essentially an opportunistic environmental organism, sampling is often sporadic and rarely reflects the overall population, particularly when concentrated on clinical isolates. This means that approaches that assume recent common ancestry are not applicable. Here we present a new approach to estimate the molecular clock rate in Campylobacter that draws on the popular probability conundrum known as the ‘birthday problem’. Using large genomic datasets and comparative genomic approaches, we use isolate pairs that share recent common ancestry to estimate the rate of nucleotide change for the population. Identifying synonymous and non-synonymous nucleotide changes, both within and outside of recombined regions of the genome, we quantify clock-like diversification to estimate synonymous rates of nucleotide change for the common pathogenic bacteria Campylobacter coli (2.4 x 10−6 s/s/y) and Campylobacter jejuni (3.4 x 10−6 s/s/y). Finally, using estimated total rates of nucleotide change, we infer the number of effective lineages within the sample time frame–analogous to a shared birthday–and assess the rate of turnover of lineages in our sample set over short evolutionary timescales. This provides a generalizable approach to calibrating rates in populations of environmental bacteria and shows that multiple lineages are maintained, implying that large-scale clonal sweeps may take hundreds of years or more in these species. 相似文献
88.
89.
Paced QRS morphology predicts incident left ventricular systolic dysfunction and atrial fibrillation
Martin van Zyl Chance M. Witt Subir Bhatia Majd Khasawneh Prakriti Gaba Charles J. Lenz Andrew N. Rosenbaum Htin Aung David O. Hodge Christopher J. McLeod Samuel J. Asirvatham 《Indian pacing and electrophysiology journal》2019,19(2):40-46
Background
The prognostic significance of paced QRS complex morphology on surface ECG remains unclear. This study aimed to assess long-term outcomes associated with variations in the paced QRS complex.Methods
Adult patients who underwent dual-chamber pacemaker implantation with 20% or more ventricular pacing and a 12-lead ECG showing a paced complex were included. The paced QRS was analyzed in leads I and aVL. Long-term clinical and echocardiographic outcomes were compared at 5 years.Results
The study included 844 patients (43.1% female; age 75.0?±?12.1). Patients with a longer paced QRS (pQRS) duration in lead I had a lower rate of atrial fibrillation (HR 0.80; p?=?0.03) and higher rate of systolic dysfunction (HR 1.17; p?<?0.001). Total pacing complex (TPC) duration was linked to higher rates of ICD implantation (HR 1.18; p?=?0.04) and systolic dysfunction (HR 1.22, p?<?0.001). Longer paced intrinsicoid deflection (pID) was associated with less atrial fibrillation (HR 0.75; p?=?0.01), more systolic dysfunction (HR 1.17; p?<?0.001), ICD implantation (HR 1.23; p?=?0.04), and CRT upgrade (HR 1.23; p?=?0.03). Exceeding thresholds for TPC, pQRS, and pID of 170, 146, and 112?ms in lead I, respectively, was associated with a substantial increase in systolic dysfunction over 5 years (p?<?0.001).Conclusions
Longer durations of all tested parameters in lead I were associated with increased rates of left ventricular systolic dysfunction. ICD implantation and CRT upgrade were also linked to increased TPC and pID durations. Paradoxically, patients with longer pID and pQRS had less incident atrial fibrillation. 相似文献90.
Charles Rocabert Guillaume Beslon Carole Knibbe Samuel Bernard 《Evolution; international journal of organic evolution》2020,74(10):2221-2237
Experimental studies demonstrate the existence of phenotypic diversity despite constant genotype and environment. Theoretical models based on a single phenotypic character predict that during an adaptation event, phenotypic noise should be positively selected far from the fitness optimum because it increases the fitness of the genotype, and then be selected against when the population reaches the optimum. It is suggested that because of this fitness gain, phenotypic noise should promote adaptive evolution. However, it is unclear how the selective advantage of phenotypic noise is linked to the rate of evolution, and whether any advantage would hold for more realistic, multidimensional phenotypes. Indeed, complex organisms suffer a cost of complexity, where beneficial mutations become rarer as the number of phenotypic characters increases. Using a quantitative genetics approach, we first show that for a one-dimensional phenotype, phenotypic noise promotes adaptive evolution on plateaus of positive fitness, independently from the direct selective advantage on fitness. Second, we show that for multidimensional phenotypes, phenotypic noise evolves to a low-dimensional configuration, with elevated noise in the direction of the fitness optimum. Such a dimensionality reduction of the phenotypic noise promotes adaptive evolution and numerical simulations show that it reduces the cost of complexity. 相似文献