全文获取类型
收费全文 | 634篇 |
免费 | 75篇 |
专业分类
709篇 |
出版年
2022年 | 13篇 |
2021年 | 15篇 |
2020年 | 9篇 |
2019年 | 7篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 29篇 |
2015年 | 34篇 |
2014年 | 37篇 |
2013年 | 37篇 |
2012年 | 52篇 |
2011年 | 42篇 |
2010年 | 27篇 |
2009年 | 29篇 |
2008年 | 34篇 |
2007年 | 28篇 |
2006年 | 23篇 |
2005年 | 27篇 |
2004年 | 19篇 |
2003年 | 21篇 |
2002年 | 21篇 |
2001年 | 9篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1992年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1987年 | 5篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 7篇 |
1978年 | 8篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 8篇 |
1972年 | 3篇 |
1971年 | 5篇 |
1970年 | 3篇 |
1969年 | 5篇 |
1968年 | 3篇 |
1966年 | 3篇 |
1961年 | 3篇 |
1960年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有709条查询结果,搜索用时 15 毫秒
61.
62.
Effects of physioball and conventional floor exercises on early phase adaptations in back and abdominal core stability and balance in women 总被引:1,自引:0,他引:1
Cosio-Lima LM Reynolds KL Winter C Paolone V Jones MT 《Journal of strength and conditioning research / National Strength & Conditioning Association》2003,17(4):721-725
The purpose of this study was to compare the effects of 5 weeks of physioball core stability and balance exercises with conventional floor exercises in women. The experimental group (n = 15) performed curl-ups and back extensions on the physioball while the control group (n = 15) performed the same exercises on the floor. Baseline and post-training tests included electromyography (EMG) recordings of the rectus abdominus and erector spinae muscles; abdominal, back, and knee strength measurements with the Cybex Norm System; and 2 unilateral stance balance tests. The physioball group was found to have significantly greater mean change in EMG flexion and extension activity (p = 0.04 and p = 0.01, respectively) and greater balance scores (p < 0.01) than the floor exercise group. No significant changes (p > 0.05) were observed for heart rate or Cybex strength measurements. Early adaptations in a short-term core exercise program using the physioball resulted in greater gains in torso balance and EMG neuronal activity in previously untrained women when compared to performing exercises on the floor. 相似文献
63.
Background
n-Butanol is a promising emerging biofuel, and recent metabolic engineering efforts have demonstrated the use of several microbial hosts for its production. However, most organisms have very low tolerance to n-butanol (up to 2% (v/v)), limiting the economic viability of this biofuel. The rational engineering of more robust n-butanol production hosts relies upon understanding the mechanisms involved in tolerance. However, the existing knowledge of genes involved in n-butanol tolerance is limited. The goal of this study is therefore to identify E. coli genes that are involved in n-butanol tolerance.Methodology/Principal Findings
Using a genomic library enrichment strategy, we identified approximately 270 genes that were enriched or depleted in n-butanol challenge. The effects of these candidate genes on n-butanol tolerance were experimentally determined using overexpression or deletion libraries. Among the 55 enriched genes tested, 11 were experimentally shown to confer enhanced tolerance to n-butanol when overexpressed compared to the wild-type. Among the 84 depleted genes tested, three conferred increased n-butanol resistance when deleted. The overexpressed genes that conferred the largest increase in n-butanol tolerance were related to iron transport and metabolism, entC and feoA, which increased the n-butanol tolerance by 32.8±4.0% and 49.1±3.3%, respectively. The deleted gene that resulted in the largest increase in resistance to n-butanol was astE, which enhanced n-butanol tolerance by 48.7±6.3%.Conclusions/Significance
We identified and experimentally verified 14 genes that decreased the inhibitory effect of n-butanol tolerance on E. coli. From the data, we were able to expand the current knowledge on the genes involved in n-butanol tolerance; the results suggest that an increased iron transport and metabolism and decreased acid resistance may enhance n-butanol tolerance. The genes and mechanisms identified in this study will be helpful in the rational engineering of more robust biofuel producers. 相似文献64.
Previous studies have demonstrated the effective control of cytomegalovirus (CMV) infections post haematopoietic stem cell transplant through the adoptive transfer of donor derived CMV-specific T cells (CMV-T). Strategies for manufacturing CMV immunotherapies has involved a second leukapheresis or blood draw from the donor, which in the unrelated donor setting is not always possible. We have investigated the feasibility of using an aliquot of the original G-CSF-mobilized graft as a starting material for manufacture of CMV-T and examined the activation marker CD25 as a targeted approach for identification and isolation following CMVpp65 peptide stimulation. CD25+ cells isolated from G-CSF-mobilized apheresis revealed a significant increase in the proportion of FoxP3 expression when compared with conventional non-mobilized CD25+ cells and showed a superior suppressive capacity in a T cell proliferation assay, demonstrating the emergence of a population of Tregs not present in non-mobilized apheresis collections. The expansion of CD25+ CMV-T in short-term culture resulted in a mixed population of CD4+ and CD8+ T cells with CMV-specificity that secreted cytotoxic effector molecules and lysed CMVpp65 peptide-loaded phytohaemagglutinin-stimulated blasts. Furthermore CD25 expanded cells retained their suppressive capacity but did not maintain FoxP3 expression or secrete IL-10. In summary our data indicates that CD25 enrichment post CMV stimulation in G-CSF-mobilized PBMCs results in the simultaneous generation of both a functional population of anti-viral T cells and Tregs thus illustrating a potential single therapeutic strategy for the treatment of both GvHD and CMV reactivation following allogeneic haematopoietic stem cell transplantation. The use of G-CSF-mobilized cells as a starting material for cell therapy manufacture represents a feasible approach to alleviating the many problems incurred with successive donations and procurement of cells from unrelated donors. This approach may therefore simplify the clinical application of adoptive immunotherapy and broaden the approach for manufacturing multi-functional T cells. 相似文献
65.
William Whittaker Laura Anselmi S?ren Rud Kristensen Yiu-Shing Lau Simon Bailey Peter Bower Katherine Checkland Rebecca Elvey Katy Rothwell Jonathan Stokes Damian Hodgson 《PLoS medicine》2016,13(9)
BackgroundHealth services across the world increasingly face pressures on the use of expensive hospital services. Better organisation and delivery of primary care has the potential to manage demand and reduce costs for hospital services, but routine primary care services are not open during evenings and weekends.Extended access (evening and weekend opening) is hypothesized to reduce pressure on hospital services from emergency department visits. However, the existing evidence-base is weak, largely focused on emergency out-of-hours services, and analysed using a before-and after-methodology without effective comparators.ConclusionsThe study found that extending access was associated with a reduction in emergency department visits in the first 12 months. The results of the research have already informed the decision by National Health Service England to extend primary care access across Greater Manchester from 2016. However, further evidence is needed to understand whether extending primary care access is cost-effective and sustainable. 相似文献
66.
67.
Sexton KE Barrett S Bridgwood K Carroll M Dettling D Du D Fakhoury S Fedij V Hu LY Kostlan C Pocalyko D Raheja N Smith Y Shanmugasundaram V Wade K 《Bioorganic & medicinal chemistry letters》2011,21(18):5230-5233
A series of pantolactam based compounds were identified as potent antagonists for the androgen receptor (AR). Those that possessed properties suitable for topical delivery were evaluated in the validated Hamster Ear Model. Several compounds were found to be efficacious in reducing wax esters, a major component of sebum, initiating further preclinical work on these compounds. 相似文献
68.
Christie R. Klinger Jennifer A. Lau Katy D. Heath 《Proceedings. Biological sciences / The Royal Society》2016,283(1826)
Anthropogenic changes can influence mutualism evolution; however, the genomic regions underpinning mutualism that are most affected by environmental change are generally unknown, even in well-studied model mutualisms like the interaction between legumes and their nitrogen (N)-fixing rhizobia. Such genomic information can shed light on the agents and targets of selection maintaining cooperation in nature. We recently demonstrated that N-fertilization has caused an evolutionary decline in mutualistic partner quality in the rhizobia that form symbiosis with clover. Here, population genomic analyses of N-fertilized versus control rhizobium populations indicate that evolutionary differentiation at a key symbiosis gene region on the symbiotic plasmid (pSym) contributes to partner quality decline. Moreover, patterns of genetic variation at selected loci were consistent with recent positive selection within N-fertilized environments, suggesting that N-rich environments might select for less beneficial rhizobia. By studying the molecular population genomics of a natural bacterial population within a long-term ecological field experiment, we find that: (i) the N environment is indeed a potent selective force mediating mutualism evolution in this symbiosis, (ii) natural variation in rhizobium partner quality is mediated in part by key symbiosis genes on the symbiotic plasmid, and (iii) differentiation at selected genes occurred in the context of otherwise recombining genomes, resembling eukaryotic models of adaptation. 相似文献
69.
70.
George L. Gabor Miklos Marion J. Healy P. Pain A. J. Howells Robyn J. Russell 《Chromosoma》1984,89(3):218-227
A recombinant Charon 4 bacteriophage has been isolated on the basis of RNAs which are enriched in the head of the adult Drosophila melanogaster and hence are likely to be of neural origin. The cloned insert maps to the near vicinity of the uncoordinated locus in polytene chromosome band 19E8. This band is within the transition zone between the euchromatic and heterochromatic regions of the X chromosome, a region which has been well characterized cytogenetically. The insert contains both repetitious and low copy number sequences, some of which vary extensively in both frequency and restriction fragment size between different laboratory strains. One particular family of moderately repeated sequences occurs predominantly in divisions 19 and 20 of the X chromosome and perhaps the distally located X heterochromatin. The molecular landscape surrounding the initial entry point contains many repeated sequences and is thus unlike those observed in most published chromosomal walks. The possible significance of the presence of repeated sequence families in the distinct properties of this region are discussed. 相似文献