全文获取类型
收费全文 | 3509篇 |
免费 | 340篇 |
国内免费 | 1篇 |
专业分类
3850篇 |
出版年
2024年 | 5篇 |
2023年 | 12篇 |
2022年 | 57篇 |
2021年 | 80篇 |
2020年 | 52篇 |
2019年 | 45篇 |
2018年 | 81篇 |
2017年 | 78篇 |
2016年 | 124篇 |
2015年 | 227篇 |
2014年 | 224篇 |
2013年 | 257篇 |
2012年 | 317篇 |
2011年 | 339篇 |
2010年 | 215篇 |
2009年 | 178篇 |
2008年 | 249篇 |
2007年 | 256篇 |
2006年 | 233篇 |
2005年 | 161篇 |
2004年 | 154篇 |
2003年 | 157篇 |
2002年 | 137篇 |
2001年 | 20篇 |
2000年 | 12篇 |
1999年 | 28篇 |
1998年 | 25篇 |
1997年 | 15篇 |
1996年 | 8篇 |
1995年 | 11篇 |
1994年 | 8篇 |
1993年 | 8篇 |
1992年 | 11篇 |
1991年 | 6篇 |
1990年 | 5篇 |
1989年 | 3篇 |
1988年 | 7篇 |
1987年 | 5篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 6篇 |
1981年 | 3篇 |
1980年 | 6篇 |
1972年 | 1篇 |
1965年 | 1篇 |
1940年 | 1篇 |
1938年 | 1篇 |
1937年 | 1篇 |
排序方式: 共有3850条查询结果,搜索用时 15 毫秒
91.
Melanie A. Zokoll Georg M. Klump Ulrike Langemann 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2008,194(5):457-467
This study evaluates auditory memory for variations in the rate of sinusoidal amplitude modulation (SAM) of noise bursts in
the European starling (Sturnus vulgaris). To estimate the extent of the starling’s auditory short-term memory store, a delayed non-matching-to-sample paradigm was
applied. The birds were trained to discriminate between a series of identical “sample stimuli” and a single “test stimulus”.
The birds classified SAM rates of sample and test stimuli as being either the same or different. Memory performance of the
birds was measured as the percentage of correct classifications. Auditory memory persistence time was estimated as a function
of the delay between sample and test stimuli. Memory performance was significantly affected by the delay between sample and
test and by the number of sample stimuli presented before the test stimulus, but was not affected by the difference in SAM
rate between sample and test stimuli. The individuals’ auditory memory persistence times varied between 2 and 13 s. The starlings’
auditory memory persistence in the present study for signals varying in the temporal domain was significantly shorter compared
to that of a previous study (Zokoll et al. in J Acoust Soc Am 121:2842, 2007) applying tonal stimuli varying in the spectral domain. 相似文献
92.
Most Malagasy primate communities harbor a diverse assemblage of omnivorous species. The mechanisms allowing the coexistence
of closely related species are poorly understood, partly because only preliminary data on the feeding ecology of most species
are available. We provide an exemplary feeding ecology data set to illuminate coexistence mechanisms between sympatric gray
and Madame Berthe’s mouse lemurs (Microcebus murinus, M. berthae). We studied their feeding ecology in Kirindy Forest/CFPF, a highly seasonal dry deciduous forest in western Madagascar.
Between August 2002 and December 2007, we regularly (re-)captured, marked, and radiotracked females of both species. A combination
of direct behavioral observations and fecal analyses revealed that both Microcebus species used fruit, arthropods, gum, insect secretions, and small vertebrates as food sources. However, Microcebus berthae and M. murinus differed in both composition and seasonal variation of their diets. Whereas the diet of Microcebus murinus varied seasonally and was generally more diverse, M. berthae relied mainly on insect secretions supplemented by animal matter. The differences were also reflected in a very narrow feeding
niche of Microcebus berthae and a comparatively broad feeding niche of M. murinus. Resource use patterns of Madame Berthe’s and more so of opportunistic gray mouse lemurs broadly followed resource availability
within the strongly seasonal dry forest. Feeding niche overlap between the 2 sympatric species was high, indicating that food
resource usage patterns did not reflect niche partitioning, but can instead be explained by constraints due to food availability. 相似文献
93.
Melanie Calvert Derek Kyte Helen Duffy Adrian Gheorghe Rebecca Mercieca-Bebber Jonathan Ives Heather Draper Michael Brundage Jane Blazeby Madeleine King 《PloS one》2014,9(10)
Background
Evidence suggests there are inconsistencies in patient-reported outcome (PRO) assessment and reporting in clinical trials, which may limit the use of these data to inform patient care. For trials with a PRO endpoint, routine inclusion of key PRO information in the protocol may help improve trial conduct and the reporting and appraisal of PRO results; however, it is currently unclear exactly what PRO-specific information should be included. The aim of this review was to summarize the current PRO-specific guidance for clinical trial protocol developers.Methods and Findings
We searched the MEDLINE, EMBASE, CINHAL and Cochrane Library databases (inception to February 2013) for PRO-specific guidance regarding trial protocol development. Further guidance documents were identified via Google, Google scholar, requests to members of the UK Clinical Research Collaboration registered clinical trials units and international experts. Two independent investigators undertook title/abstract screening, full text review and data extraction, with a third involved in the event of disagreement. 21,175 citations were screened and 54 met the inclusion criteria. Guidance documents were difficult to access: electronic database searches identified just 8 documents, with the remaining 46 sourced elsewhere (5 from citation tracking, 27 from hand searching, 7 from the grey literature review and 7 from experts). 162 unique PRO-specific protocol recommendations were extracted from included documents. A further 10 PRO recommendations were identified relating to supporting trial documentation. Only 5/162 (3%) recommendations appeared in ≥50% of guidance documents reviewed, indicating a lack of consistency.Conclusions
PRO-specific protocol guidelines were difficult to access, lacked consistency and may be challenging to implement in practice. There is a need to develop easily accessible consensus-driven PRO protocol guidance. Guidance should be aimed at ensuring key PRO information is routinely included in appropriate trial protocols, in order to facilitate rigorous collection/reporting of PRO data, to effectively inform patient care. 相似文献94.
95.
Styers ML O'Connor AK Grabski R Cormet-Boyaka E Sztul E 《American journal of physiology. Cell physiology》2008,294(6):C1485-C1498
We have utilized small interfering RNA (siRNA)-mediated depletion of the beta-COP subunit of COP-I to explore COP-I function in organellar compartmentalization and protein traffic. Reduction in beta-COP levels causes the colocalization of markers for the endoplasmic reticulum (ER)-Golgi intermediate compartment (ERGIC), Golgi, trans-Golgi network (TGN), and recycling endosomes in large, globular compartments. The lack of spatial differentiation of these compartments is not due to a general collapse of all cellular organelles since markers for the early endosomes and lysosomes do not redistribute to the common structures. Anterograde trafficking of the transmembrane cargo vesicular stomatitis virus membrane glycoprotein and of a subset of soluble cargoes is arrested within the common globular compartments. Similarly, recycling traffic of transferrin through the common compartment is perturbed. Furthermore, the trafficking of caveolin-1 (Cav1), a structural protein of caveolae, is arrested within the globular structures. Importantly, Cav1 coprecipitates with the gamma-subunit of COP-I, suggesting that Cav1 is a COP-I cargo. Our findings suggest that COP-I is required for the compartmentalization of the ERGIC, Golgi, TGN, and recycling endosomes and that COP-I plays a novel role in the biosynthetic transport of Cav1. 相似文献
96.
Sze Chern Lim Katherine R. Smith David A. Stroud Alison G. Compton Elena J. Tucker Ayan Dasvarma Luke C. Gandolfo Justine E. Marum Matthew McKenzie Heidi L. Peters David Mowat Peter G. Procopis Bridget Wilcken John Christodoulou Garry K. Brown Michael T. Ryan Melanie Bahlo David R. Thorburn 《American journal of human genetics》2014
97.
Mark Williams Melanie J. Leng Michael H. Stephenson Julian E. Andrews Ian P. Wilkinson David J. Siveter David J. Horne Jean M.C. Vannier 《Palaeogeography, Palaeoclimatology, Palaeoecology》2006,230(3-4):299-318
A study of the stable isotope composition (δ18O, δ13C) of biogenic (ostracod, mollusc) and authigenic carbonates in the Ballagan Formation, Lower Carboniferous of Scotland, coupled with evidence from sedimentology and associated fossil fauna and flora, supports the argument that this formation was deposited in a coastal flood plain setting, in brackish (0.5 < 30‰ NaCl) and hypersaline (> 40‰ NaCl) waters, but in the absence of persistent normal marine conditions. The oxygen isotope data from the Ballagan Formation divide into three clusters: a diagenetic field defined by low δ18O (< − 11‰ VPDB); an intermediary field (δ18O − 11‰ to − 9‰) composed of a mixture of known primary and secondary (diagenetic) carbonates; and samples within the range of − 9‰ to − 4‰ which, as far as we can ascertain, are largely unaltered. No samples give typical Early Carboniferous δ18O marine values. Average marine carbonates from Europe have δ18O between − 4‰ to − 3‰. The Ballagan Formation carbonates were probably deposited in evaporated freshwater and/or brackish water. This conclusion is supported by the presence of evaporites (gypsum, anhydrite, halite pseudomorphs) and common desiccation-cracked mudstone surfaces throughout the Ballagan Formation, suggesting conditions of fluctuating salinity in ephemeral bodies of water. The stable isotope data support the notion that the ostracod assemblages of the Ballagan Formation were colonising brackish water and hypersaline ecologies on a coastal flood plain during the Early Carboniferous, a stage of development that may have encouraged their colonisation of fully non-marine (limnetic) environments during the later Carboniferous. The ostracods include cytherellacean and kloedenellacean species known from marginal marine sites elsewhere, but probably tolerant of brackish water, podocopid species such as ‘Bythocypris’ aequalis that may have been adapted for brackish water settings on coastal flood plains (ephemeral lakes and lagoons), and paraparchitacean-dominated assemblages that may signal harsh (hypersaline or desiccating) environments. 相似文献
98.
Sandra E. Branham Amnon Levi Melanie Katawczik Zhangjun Fei W. Patrick Wechter 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》2018,131(4):829-837
Key message
Four QTLs and an epistatic interaction were associated with disease severity in response to inoculation with Fusarium oxysporum f. sp. melonis race 1 in a recombinant inbred line population of melon.Abstract
The USDA Cucumis melo inbred line, MR-1, harbors a wealth of alleles associated with resistance to several major diseases of melon, including powdery mildew, downy mildew, Alternaria leaf blight, and Fusarium wilt. MR-1 was crossed to an Israeli cultivar, Ananas Yok’neam, which is susceptible to all of these diseases, to generate a recombinant inbred line (RIL) population of 172 lines. In this study, the RIL population was genotyped to construct an ultra-dense genetic linkage map with 5663 binned SNPs anchored to the C. melo genome and exhibits the overall high quality of the assembly. The utility of the densely genotyped population was demonstrated through QTL mapping of a well-studied trait, resistance to Fusarium wilt caused by Fusarium oxysporum f. sp. melonis (Fom) race 1. A major QTL co-located with the previously validated resistance gene Fom-2. In addition, three minor QTLs and an epistatic interaction contributing to Fom race 1 resistance were identified. The MR-1 × AY RIL population provides a valuable resource for future QTL mapping studies and marker-assisted selection of disease resistance in melon.99.
Spatial distribution and functional structure of intertidal benthic macrofauna in relation to environmental variables in the Jade Bay (southern North Sea) were studied and compared with other intertidal areas of the Wadden Sea. A total of 128 stations covering the whole Jade Bay were sampled in summer 2009. A total of 114 taxa were found. Highest species numbers occurred in the subtidal areas, whereas highest mean abundances were found in the upper intertidal areas. Based on species abundance data, six significantly distinct macrofauna communities in the Jade Bay were identified and evaluated with multivariate statistics, univariate correlations and canonical correspondence analysis. Differences in these community patterns were caused by the response of the dominant species (Hydrobia ulvae, Tubificoides benedii, Pygospio elegans, Caulleriella killariensis, Scoloplos armiger, Urothoe poseidonis, Microprotopus maculatus) to prevailing environmental conditions along the gradient from the lower and exposed sandy intertidal areas via intermediate mixed sediments to the upper mudflat areas. Distribution patterns in relation to tidal zonation were best explained by variability in submergence time, Chlorophyll a (chl a) content and sediment composition (mud content), which are proxies for hydrodynamic conditions and food availability. Species inventory and species richness were comparable with other intertidal areas of the Wadden Sea, but the Jade Bay differs from these areas regarding dominant species. Differences in sediment composition and morphological characteristics (macrotidal versus mesotidal Wadden Sea areas) are discussed for comparison of regional differences. 相似文献
100.
Abstract. The contribution of resprouts and seedling recruitment to post-fire regeneration of the South African fynbos conifer Widdringtonia nodiflora was compared eight months after wildfires in 1990. Stems on all trees were killed by fire but resprouting success was > 90 % at all but one site. A demographic study of burned skeletons revealed that prior to these fires, nearly all plants were multi-stemmed (4–9 stems/plant) and multi-aged, indicating continuous sprout production between fires. All stems were killed by these 1990 fires and at most sites > 90 % of the stems were burned to ground level. All diameter stems were susceptible to such incineration as, at most sites, there was no difference in average diameter of stems burned to ground level and those left standing. Individual genets usually had all ramets incinerated to ground level or all ramets charred, but intact, suggesting certain micro-sites burned hotter, whereas other sites were somewhat protected. Although not true of the 1990 fires, there was evidence that occasionally Widdring-tonia stems may survive fire. At one site, four of the 16 plants sampled had a burned stem twice as old as the oldest burned stem on the other 12 plants at the site, suggesting some stems had survived the previous fire (ca. 1970) and this conclusion was supported by fire-scars on these four stems that dated to ca. 1970. Based on the highly significant correlation between stem diameter and cone density left standing after the 1990 fires, we calculated that for most sites > 80 % of the initial cone crop was incinerated by fire. This is important because we observed a strong relationship between size of the canopy cone crop surviving fire and post-fire seedling recruitment. Under these conditions we hypothesize that sprouting confers a selective advantage to genets when fires cause heavy losses of seed. The infrequent occurrence of sprouting in the Cupressaceae suggests the hypothesis that resprouting is an apomorphic or derived trait in Widdringtonia. Data from this study suggests resprouting provides a selective advantage under severe fynbos fires, which are not only 'stand-replacing fires,’but also are intense enough to incinerate cone-bearing stems. 相似文献