全文获取类型
收费全文 | 1760篇 |
免费 | 142篇 |
国内免费 | 1篇 |
出版年
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 24篇 |
2020年 | 16篇 |
2019年 | 19篇 |
2018年 | 31篇 |
2017年 | 16篇 |
2016年 | 49篇 |
2015年 | 88篇 |
2014年 | 79篇 |
2013年 | 135篇 |
2012年 | 127篇 |
2011年 | 120篇 |
2010年 | 83篇 |
2009年 | 81篇 |
2008年 | 103篇 |
2007年 | 95篇 |
2006年 | 98篇 |
2005年 | 84篇 |
2004年 | 81篇 |
2003年 | 73篇 |
2002年 | 76篇 |
2001年 | 22篇 |
2000年 | 30篇 |
1999年 | 35篇 |
1998年 | 24篇 |
1997年 | 19篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 9篇 |
1992年 | 13篇 |
1991年 | 8篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 11篇 |
1987年 | 6篇 |
1986年 | 11篇 |
1985年 | 11篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 15篇 |
1976年 | 5篇 |
1969年 | 4篇 |
1967年 | 6篇 |
1966年 | 5篇 |
1911年 | 5篇 |
排序方式: 共有1903条查询结果,搜索用时 125 毫秒
71.
Ausana Mapook Hiran A. Ariyawansa Saowaluck Tibpromma Erio Campesori E. B. Gareth Jones Ali H. Bahkali K. D. Hyde 《Mycological Progress》2016,15(4):34
Nodulosphaeria is a ubiquitous genus that comprises saprobic, endophytic and pathogenic species associated with a wide variety of substrates and has 64 species epithets listed in Index Fungorum. The classification of species in the genus has been a major challenge due to a lack of understanding of the importance of characters used to distinguish taxa, as well as the lack of reference strains. The present study clarifies the phylogenetic placement of the genus and related species, using fresh collections from Italy. Four Nodulosphaeria species are characterized based on multi-loci analyses of ITS, LSU, SSU, TEF and RPB2 sequence datasets. Phylogenetic analyses indicate that Nodulosphaeria species group within the family Phaeosphaeriaceae as a distinct genus. The sexual morphs of Nodulosphaeria hirta and N. spectabilis are described and illustrated using modern concepts. Two new Nodulosphaeria species are introduced. The phylogenetic relationships and taxonomy of the genus Nodulosphaeria are discussed, but further sampling with fresh collections, reference or ex-type strains and molecular data are needed to obtain a better and natural classification for the genus. 相似文献
72.
73.
We used a before-after-control-impact paired design to examine the effects of a switch from low-pressure sodium (LPS) to light emitting diode (LED) street lights on bat activity at twelve sites across southern England. LED lights produce broad spectrum ‘white’ light compared to LPS street lights that emit narrow spectrum, orange light. These spectral differences could influence the abundance of insects at street lights and thereby the activity of the bats that prey on them. Most of the bats flying around the LPS lights were aerial-hawking species, and the species composition of bats remained the same after the switch-over to LED. We found that the switch-over from LPS to LED street lights did not affect the activity (number of bat passes), or the proportion of passes containing feeding buzzes, of those bat species typically found in close proximity to street lights in suburban environments in Britain. This is encouraging from a conservation perspective as many existing street lights are being, or have been, switched to LED before the ecological consequences have been assessed. However, lighting of all spectra studied to date generally has a negative impact on several slow-flying bat species, and LED lights are rarely frequented by these ‘light-intolerant’ bat species. 相似文献
74.
Capsule: Urban Black Sparrowhawk males hunt mostly within 2.27?km of their nest during the breeding season (‘home range’ of 16.15?km2) and increased the distance slightly to 2.43?km outside of the breeding season (18.56?km2). We found high individual variation within and between six global positioning systems tagged breeding males, but no significant seasonal differences in the urban environment of Cape Town, South Africa. 相似文献
75.
76.
Differential foraging success across a light level spectrum explains the maintenance and spatial structure of colour morphs in a polymorphic bird 下载免费PDF全文
Detectability of different colour morphs under varying light conditions has been proposed as an important driver in the maintenance of colour polymorphism via disruptive selection. To date, no studies have tested whether different morphs have selective advantages under differing light conditions. We tested this hypothesis in the black sparrowhawk, a polymorphic raptor exhibiting a discrete white and dark morph, and found that prey provisioning rates differ between the morphs depending on light condition. Dark morphs delivered more prey in lower light conditions, while white morphs provided more prey in brighter conditions. We found support for the role of breeding season light level in explaining the clinal pattern of variation in morph ratio across the species range throughout South Africa. Our results provide the first empirical evidence supporting the hypothesis that polymorphism in a species, and the spatial structuring of morphs across its distribution, may be driven by differential selective advantage via improved crypsis, under varying light conditions. 相似文献
77.
78.
James R. Probert Catherine L. Parr Ricardo M. Holdo T. Michael Anderson Sally Archibald Colin J. Courtney Mustaphi Andrew P. Dobson Jason E. Donaldson Grant C. Hopcraft Gareth P. Hempson Thomas A. Morrison Colin M. Beale 《Global Change Biology》2019,25(10):3406-3423
Fire is a key driver in savannah systems and widely used as a land management tool. Intensifying human land uses are leading to rapid changes in the fire regimes, with consequences for ecosystem functioning and composition. We undertake a novel analysis describing spatial patterns in the fire regime of the Serengeti‐Mara ecosystem, document multidecadal temporal changes and investigate the factors underlying these patterns. We used MODIS active fire and burned area products from 2001 to 2014 to identify individual fires; summarizing four characteristics for each detected fire: size, ignition date, time since last fire and radiative power. Using satellite imagery, we estimated the rate of change in the density of livestock bomas as a proxy for livestock density. We used these metrics to model drivers of variation in the four fire characteristics, as well as total number of fires and total area burned. Fires in the Serengeti‐Mara show high spatial variability—with number of fires and ignition date mirroring mean annual precipitation. The short‐term effect of rainfall decreases fire size and intensity but cumulative rainfall over several years leads to increased standing grass biomass and fuel loads, and, therefore, in larger and hotter fires. Our study reveals dramatic changes over time, with a reduction in total number of fires and total area burned, to the point where some areas now experience virtually no fire. We suggest that increasing livestock numbers are driving this decline, presumably by inhibiting fire spread. These temporal patterns are part of a global decline in total area burned, especially in savannahs, and we caution that ecosystem functioning may have been compromised. Land managers and policy formulators need to factor in rapid fire regime modifications to achieve management objectives and maintain the ecological function of savannah ecosystems. 相似文献
79.
Kristine von Bargen Mirella Scraba Ina Krmer Maren Ketterer Christian Nehls Sina Krokowski Urska Repnik Michaela Wittlich Anna Maaser Pia Zapka Madeleine Bunge Martin Schlesinger Gitta Huth Annette Klees Philipp Hansen Andreas Jeschke Gerd Bendas Olaf Utermhlen Gareth Griffiths Thomas Gutsmann Jens Wohlmann Albert Haas 《Cellular microbiology》2019,21(1)
Professional phagocytic cells such as macrophages are a central part of innate immune defence. They ingest microorganisms into membrane‐bound compartments (phagosomes), which acidify and eventually fuse with lysosomes, exposing their contents to a microbicidal environment. Gram‐positive Rhodococcus equi can cause pneumonia in young foals and in immunocompromised humans. The possession of a virulence plasmid allows them to subvert host defence mechanisms and to multiply in macrophages. Here, we show that the plasmid‐encoded and secreted virulence‐associated protein A (VapA) participates in exclusion of the proton‐pumping vacuolar‐ATPase complex from phagosomes and causes membrane permeabilisation, thus contributing to a pH‐neutral phagosome lumen. Using fluorescence and electron microscopy, we show that VapA is also transferred from phagosomes to lysosomes where it permeabilises the limiting membranes for small ions such as protons. This permeabilisation process is different from that of known membrane pore formers as revealed by experiments with artificial lipid bilayers. We demonstrate that, at 24 hr of infection, virulent R. equi is contained in a vacuole, which is enriched in lysosome material, yet possesses a pH of 7.2 whereas phagosomes containing a vapA deletion mutant have a pH of 5.8 and those with virulence plasmid‐less sister strains have a pH of 5.2. Experimentally neutralising the macrophage endocytic system allows avirulent R. equi to multiply. This observation is mirrored in the fact that virulent and avirulent R. equi multiply well in extracts of purified lysosomes at pH 7.2 but not at pH 5.1. Together these data indicate that the major function of VapA is to generate a pH‐neutral and hence growth‐promoting intracellular niche. VapA represents a new type of Gram‐positive virulence factor by trafficking from one subcellular compartment to another, affecting membrane permeability, excluding proton‐pumping ATPase, and consequently disarming host defences. 相似文献
80.
Guy Balme Matt Rogan Lisa Thomas Ross Pitman Gareth Mann Gareth Whittington-Jones Neil Midlane Mark Broodryk Kerryn Broodryk Michelle Campbell Marc Alkema Dave Wright Luke Hunter 《Population Ecology》2019,61(3):256-267
Human impact is near pervasive across the planet and studies of wildlife populations free of anthropogenic mortality are increasingly scarce. This is particularly true for large carnivores that often compete with and, in turn, are killed by humans. Accordingly, the densities at which carnivore populations occur naturally, and their role in shaping and/or being shaped by natural processes, are frequently unknown. We undertook a camera-trap survey in the Sabi Sand Game Reserve (SSGR), South Africa, to examine the density, structure and spatio-temporal patterns of a leopard Panthera pardus population largely unaffected by anthropogenic mortality. Estimated population density based on spatial capture–recapture models was 11.8 ± 2.6 leopards/100 km2. This is likely close to the upper density limit attainable by leopards, and can be attributed to high levels of protection (particularly, an absence of detrimental edge effects) and optimal habitat (in terms of prey availability and cover for hunting) within the SSGR. Although our spatio-temporal analyses indicated that leopard space use was modulated primarily by “bottom-up” forces, the population appeared to be self-regulating and at a threshold that is unlikely to change, irrespective of increases in prey abundance. Our study provides unique insight into a naturally-functioning carnivore population at its ecological carrying capacity. Such insight can potentially be used to assess the health of other leopard populations, inform conservation targets, and anticipate the outcomes of population recovery attempts. 相似文献