全文获取类型
收费全文 | 745篇 |
免费 | 65篇 |
专业分类
810篇 |
出版年
2022年 | 4篇 |
2021年 | 9篇 |
2020年 | 6篇 |
2019年 | 10篇 |
2018年 | 9篇 |
2017年 | 8篇 |
2016年 | 11篇 |
2015年 | 23篇 |
2014年 | 24篇 |
2013年 | 35篇 |
2012年 | 37篇 |
2011年 | 50篇 |
2010年 | 29篇 |
2009年 | 29篇 |
2008年 | 36篇 |
2007年 | 38篇 |
2006年 | 33篇 |
2005年 | 24篇 |
2004年 | 35篇 |
2003年 | 24篇 |
2002年 | 23篇 |
2001年 | 32篇 |
2000年 | 31篇 |
1999年 | 32篇 |
1998年 | 14篇 |
1997年 | 11篇 |
1996年 | 15篇 |
1995年 | 5篇 |
1994年 | 10篇 |
1993年 | 6篇 |
1992年 | 21篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 10篇 |
1987年 | 8篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 5篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 2篇 |
1972年 | 2篇 |
1970年 | 3篇 |
1964年 | 2篇 |
排序方式: 共有810条查询结果,搜索用时 15 毫秒
731.
Microbial eukaryotes that are morphologically indistinguishable (i.e. 'morphospecies') tend to be genetically diverse. While most protist morphospecies have cosmopolitan distribution, it has been suggested that ribotypes (unique rRNA gene sequences) or rRNA sequence clusters do have biogeography and such clusters may correlate with particular (non-morphological) adaptations. We have studied this in the ciliated protozoan morphospecies Cyclidium glaucoma. Fifty-four isolates collected worldwide represented 31 distinct ribotypes. There was no evidence of biogeographic distribution patterns. For example, identical ribotypes occurred in samples from Argentina, Peru, Morocco, Russia and Ukraine; in samples from Denmark and Australia; and in samples from Great Salt Lake and hyperhaline ponds in Spain. The morphospecies Cyclidium glaucoma is euryhaline and occurs in freshwater, brackish water, seawater, and hyperhaline waters. Evidence suggests that one ribotype cluster occurs only in marine or brackish habitats, and another one has so far been found only in hyperhaline habitats. Two clades seem to occur only in freshwater, but one clade includes ribotypes that were found in freshwater as well as in brackish water. 相似文献
732.
Cary A. Kuliasha John A. Finlay Sofia C. Franco Anthony S. Clare Shane J. Stafslien 《Biofouling》2017,33(3):252-267
There is currently strong motivation due to ecological concerns to develop effective anti-biofouling coatings that are environmentally benign, durable, and stable for use by the maritime industry. The antifouling (AF) and fouling-release (FR) efficacy of amphiphilic, charged copolymers composed of ~52% acrylamide, ~34% acrylic acid, and ~14% methyl acrylate grafted to poly(dimethyl siloxane) (PDMSe) surfaces were tested against zoospores of the green alga Ulva linza and the diatom Navicula incerta. The biofouling response to molecular weight variation was analyzed for grafts ranging from ~100 to 1,400 kg mol?1, The amphiphilic coatings showed a marked improvement in the FR response, with a 55% increase in the percentage removal of diatoms and increased AF efficacy, with 92% reduction in initial attachment density of zoospores, compared to PDMSe controls. However, graft molecular weight, in the range tested, was statistically insignificant. Grafting copolymers to PDMSe embossed with the Sharklet? microtopography did not produce enhanced AF efficacy. 相似文献
733.
Finlay A. McAlister Erik Youngson Jeffrey A. Bakal Padma Kaul Justin Ezekowitz Carl van Walraven 《CMAJ》2013,185(14):E681-E689
Background:
Early physician follow-up after discharge is associated with lower rates of death and readmission among patients with heart failure. We explored whether physician continuity further influences outcomes after discharge.Methods:
We used data from linked administrative databases for all adults aged 20 years or more in the province of Alberta who were discharged alive from hospital between January 1999 and June 2009 with a first-time diagnosis of heart failure. We used Cox proportional hazard models with time-dependent covariates to analyze the effect of follow-up with a familiar physician within the first month after discharge on the primary outcome of death or urgent all-cause readmission over 6 months. A familiar physician was defined as one who had seen the patient at least twice in the year before the index admission or once during the index admission.Results:
In the first month after discharge, 5336 (21.9%) of the 24 373 identified patients had no follow-up visits, 16 855 (69.2%) saw a familiar physician, and 2182 (9.0%) saw unfamiliar physician(s) exclusively. The risk of death or unplanned readmission during the 6-month observation period was lower among patients who saw a familiar physician (43.6%; adjusted hazard ratio [HR] 0.87, 95% confidence interval [CI] 0.83–0.91) or an unfamiliar physician (43.6%; adjusted HR 0.90, 95% CI 0.83–0.97) for early follow-up visits, as compared with patients who had no follow-up visits (62.9%). Taking into account all follow-up visits over the 6-month period, we found that the risk of death or urgent readmission was lower among patients who had all of their visits with a familiar physician than among those followed by unfamiliar physicians (adjusted HR 0.91, 95% CI 0.85–0.98).Interpretation:
Early physician follow-up after discharge and physician continuity were both associated with better outcomes among patients with heart failure. Research is needed to explore whether physician continuity is important for other conditions and in settings other than recent hospital discharge.Hospital care accounts for almost one-third of health care spending, and unplanned readmissions within 30 days after discharge cost more than $20 billion each year in the United States and Canada.1 Heart failure is one of the most common reasons for admission to hospital and is associated with a high risk of readmission.1 Although the prognosis for patients with heart failure has improved over the past decade, the risk of early death or readmission after discharge is still high and is increasing.2 Prompt follow-up of patients with heart failure has been associated with lower rates of death and readmission,3,4 and 30-day follow-up has been included as a quality-of-care indicator in Canada.5It is unclear, however, whether the postdischarge visits should be with the physician who previously saw the patient or with any physician. Results of studies exploring the association between provider continuity and postdischarge outcomes have been inconclusive and the studies have included few patients with heart failure.6–9 Intuitively, one might consider physician continuity important for patients with heart failure discharged from hospital, given their age, high comorbidity burdens and complex treatment regimens. However, a robust evidence base and multiple guidelines with consistent messaging on key management principles have made physician continuity potentially less important.We designed this study to determine whether physician continuity influenced postdischarge outcomes among patients with heart failure beyond the influence of early physician follow-up. 相似文献734.
Stephanie M. Bennett John A. Finlay Nikhil Gunari David D. Wells Anne E. Meyer Gilbert C. Walker 《Biofouling》2013,29(2):235-246
Xerogel films with uniform surface topogrophy, as determined by scanning electron microscopy, atomic force microscopy (AFM), and time-of-flight secondary ion mass spectrometry, were prepared from aminopropylsilyl-, fluorocarbonsilyl-, and hydrocarbonsilyl- containing precursors. Young's modulus was determined from AFM indentation measurements. The xerogel coatings gave reduced settlement of zoospores of the marine fouling alga Ulva compared to a poly(dimethylsiloxane) elastomer (PDMSE) standard. Increased settlement correlated with decreased water wettability as measured by the static water contact angle, θWs, or with decreased polar contribution (γP) to the surface free energy (γS) as measured by comprehensive contact angle analysis. The strength of attachment of 7-day sporelings (young plants) of Ulva on several of the xerogels was similar to that on PDMSE although no overall correlation was observed with either θWs or γS. For sporelings attached to the fluorocarbon/hydrocarbon-modified xerogels, the strength of attachment increased with increased water wettability. The aminopropyl-modified xerogels did not follow this trend. 相似文献
735.
Laura M. Cunningham Chris D. Nugent George Moore Dewar D. Finlay David Craig 《Computer methods in biomechanics and biomedical engineering》2013,16(10):1081-1092
The prevalence of Parkinson's disease (PD) is increasing due to an ageing population. It is an unpredictable disease which requires regular assessment and monitoring. Current techniques used to assess PD are subjective. Clinicians observe movements made by a patient and subsequently rate the level of severity of, for example tremor or slowness of movement. Within this work, we have developed and evaluated a prototype computer-based assessment tool capable of collecting information on the movement difficulties present in PD. Twenty participants took part in an assessment of the tool, 10 of whom were diagnosed with PD and 10 were without the disease. Following the usage of the tool, it was found that there was a significant difference (p = 0.038) in the speed of movement between the two groups. We envisage that this tool could have the potential to enable more objective clinical conclusions to be made. 相似文献
736.
Julio J. Amaral Luis Caetano M. Antunes Cristiana S. de Macedo Katherine A. Mattos Jun Han Jingxi Pan André L. P. Candéa Maria das Gra?as M. O. Henriques Marcelo Ribeiro-Alves Christoph H. Borchers Euzenir N. Sarno Patrícia T. Bozza B. Brett Finlay Maria Cristina V. Pessolani 《PLoS neglected tropical diseases》2013,7(8)
Despite considerable efforts over the last decades, our understanding of leprosy pathogenesis remains limited. The complex interplay between pathogens and hosts has profound effects on host metabolism. To explore the metabolic perturbations associated with leprosy, we analyzed the serum metabolome of leprosy patients. Samples collected from lepromatous and tuberculoid patients before and immediately after the conclusion of multidrug therapy (MDT) were subjected to high-throughput metabolic profiling. Our results show marked metabolic alterations during leprosy that subside at the conclusion of MDT. Pathways showing the highest modulation were related to polyunsaturated fatty acid (PUFA) metabolism, with emphasis on anti-inflammatory, pro-resolving omega-3 fatty acids. These results were confirmed by eicosanoid measurements through enzyme-linked immunoassays. Corroborating the repertoire of metabolites altered in sera, metabonomic analysis of skin specimens revealed alterations in the levels of lipids derived from lipase activity, including PUFAs, suggesting a high lipid turnover in highly-infected lesions. Our data suggest that omega-6 and omega-3, PUFA-derived, pro-resolving lipid mediators contribute to reduced tissue damage irrespectively of pathogen burden during leprosy disease. Our results demonstrate the utility of a comprehensive metabonomic approach for identifying potential contributors to disease pathology that may facilitate the development of more targeted treatments for leprosy and other inflammatory diseases. 相似文献
737.
Alteration of epithelial structure and function associated with PtdIns(4,5)P2 degradation by a bacterial phosphatase 下载免费PDF全文
Mason D Mallo GV Terebiznik MR Payrastre B Finlay BB Brumell JH Rameh L Grinstein S 《The Journal of general physiology》2007,129(4):267-283
Elucidation of the role of PtdIns(4,5)P(2) in epithelial function has been hampered by the inability to selectively manipulate the cellular content of this phosphoinositide. Here we report that SigD, a phosphatase derived from Salmonella, can effectively hydrolyze PtdIns(4,5)P(2), generating PtdIns(5)P. When expressed by microinjecting cDNA into epithelial cells forming confluent monolayers, wild-type SigD induced striking morphological and functional changes that were not mimicked by a phosphatase-deficient SigD mutant (C462S). Depletion of PtdIns(4,5)P(2) in intact SigD-injected cells was verified by detachment from the membrane of the pleckstrin homology domain of phospholipase Cdelta, used as a probe for the phosphoinositide by conjugation to green fluorescent protein. Single-cell measurements of cytosolic pH indicated that the Na(+)/H(+) exchange activity of epithelia was markedly inhibited by depletion of PtdIns(4,5)P(2). Similarly, anion permeability, measured using two different halide-sensitive probes, was depressed in cells expressing SigD. Depletion of PtdIns(4,5)P(2) was associated with marked alterations in the actin cytoskeleton and its association with the plasma membrane. The junctional complexes surrounding the injected cells gradually opened and the PtdIns(4,5)P(2)-depleted cells eventually detached from the monolayer, which underwent rapid restitution. Similar observations were made in intestinal and renal epithelial cultures. In addition to its effects on phosphoinositides, SigD has been shown to convert inositol 1,3,4,5,6-pentakisphosphate (IP(5)) into inositol 1,4,5,6-tetrakisphosphate (IP(4)), and the latter has been postulated to mediate the diarrhea caused by Salmonella. However, the effects of SigD on epithelial cells were not mimicked by microinjection of IP(4). In contrast, the cytoskeletal and ion transport effects were replicated by hydrolyzing PtdIns(4,5)P(2) with a membrane-targeted 5-phosphatase or by occluding the inositide using high-avidity tandem PH domain constructs. We therefore suggest that opening of the tight junctions and inhibition of Na(+)/H(+) exchange caused by PtdIns(4,5)P(2) hydrolysis combine to account, at least in part, for the fluid loss observed during Salmonella-induced diarrhea. 相似文献
738.
Pejcic-Karapetrovic B Gurnani K Russell MS Finlay BB Sad S Krishnan L 《Journal of immunology (Baltimore, Md. : 1950)》2007,179(9):6088-6096
Typhoid fever and gastroenteritis caused by Salmonella enterica species are increasing globally. Pregnancy poses a high risk, but it is unclear how maternal immunity to infection is altered. In mice, susceptible strains die of S. enterica serovar typhimurium (ST) infection within 7 days whereas resistant mice (129 x 1/SvJ) develop a chronic infection. We found that virulent ST infection during pregnancy, in normally resistant 129 x 1/SvJ mice, evoked approximately 100% fetal loss and surprisingly >60% host fatality, with a median survival of 6 days. Splenic bacterial load was 1000-fold higher in pregnant mice. This correlated to a diminished splenic recruitment/expansion of innate immune cells: dendritic cells, neutrophils, and NK cells. In particular, the splenic expansion and activation of NK cells postinfection seen in nonpregnant mice was lacking in pregnancy. Most notably, pregnant-infected mice had decreased production of serum IL-12 and increased IL-6 levels. Moreover, uteroplacental tissue of pregnant-infected mice exhibited an approximately 40-fold increase in IL-6 mRNA expression relative to noninfected placenta, whereas IL-12p40 was not increased. In vivo blocking of IL-6 significantly reduced the splenic bacterial burden in pregnant mice yet failed to prevent fetal loss. Fetal demise correlated to the rapidity of infection; by 14 h, ST expanded to >10(5) in the placenta and had reached the fetus. Therefore, the preferential placental expansion of ST plausibly altered the inflammatory response toward IL-6 and away from IL-12, reducing the recruitment/activation of splenic innate immune cells. Thus, highly virulent pathogens may use placental invasion to alter systemic host resistance to infection. 相似文献
739.
Seasonal Dynamics of Arbuscular Mycorrhizal Fungal Communities in Roots in a Seminatural Grassland 总被引:1,自引:1,他引:0 下载免费PDF全文
Symbiotic arbuscular mycorrhizal fungi (AMF) have been shown to influence both the diversity and productivity of grassland plant communities. These effects have been postulated to depend on the differential effects of individual mycorrhizal taxa on different plant species; however, so far there are few detailed studies of the dynamics of AMF colonization of different plant species. In this study, we characterized the communities of AMF colonizing the roots of two plant species, Prunella vulgaris and Antennaria dioica, in a Swedish seminatural grassland at different times of the year. The AMF small subunit rRNA genes were subjected to PCR, cloning, sequencing, and phylogenetic analysis. Nineteen discrete sequence types belonging to Glomus groups A and B and to the genus Acaulospora were distinguished. No significant seasonal changes in the species compositions of the AMF communities as a whole were observed. However, the two plant species hosted significantly different AMF communities. P. vulgaris hosted a rich AMF community throughout the entire growing season. The presence of AMF in A. dioica decreased dramatically in autumn, while an increased presence of Ascomycetes species was detected. 相似文献
740.
Motohiro Wakakuwa Finlay Stewart Yukiko Matsumoto Shigeru Matsunaga Kentaro Arikawa 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2014,200(6):527-536
In a previous study of the phototaxis of green rice leafhoppers, Nephotettix cincticeps (Hemiptera, Cicadellidae), we found positive responses to 735 nm light. Here, we investigated the mechanism underlying this sensitivity to near-infrared light. We first measured the action spectrum using a Y-maze with monochromatic lights from 480 to 740 nm. We thus found that the action spectrum peaks at 520 nm in the tested wavelength range, but that a significant effect is still observed at 740 nm, albeit with a sensitivity 5 log units lower than the peak. Second, we measured the spectral sensitivity of the eye, and found that the sensitivity in the long-wavelength region parallels the behaviorally determined action spectrum. We further identified mRNAs encoding opsins of ultraviolet, blue, and green-absorbing visual pigments, and localized the mRNAs in the ommatidia by in situ hybridization. The electrophysiology, molecular biology and the anatomy of the eye together indicate that the eyes of N. cincticeps do not contain true “red” receptors, but rather that the behavioral response to near-infrared light is mediated by the tail sensitivity of the green receptors in the long-wavelength region of the spectrum. 相似文献