全文获取类型
收费全文 | 1909篇 |
免费 | 167篇 |
国内免费 | 2篇 |
出版年
2023年 | 16篇 |
2022年 | 28篇 |
2021年 | 65篇 |
2020年 | 45篇 |
2019年 | 49篇 |
2018年 | 35篇 |
2017年 | 44篇 |
2016年 | 74篇 |
2015年 | 140篇 |
2014年 | 114篇 |
2013年 | 141篇 |
2012年 | 208篇 |
2011年 | 162篇 |
2010年 | 105篇 |
2009年 | 76篇 |
2008年 | 95篇 |
2007年 | 120篇 |
2006年 | 95篇 |
2005年 | 81篇 |
2004年 | 48篇 |
2003年 | 53篇 |
2002年 | 38篇 |
2001年 | 20篇 |
2000年 | 17篇 |
1999年 | 18篇 |
1998年 | 14篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 6篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 9篇 |
1985年 | 10篇 |
1984年 | 3篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1977年 | 3篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1969年 | 9篇 |
1968年 | 4篇 |
1907年 | 4篇 |
排序方式: 共有2078条查询结果,搜索用时 15 毫秒
11.
Production of antibacterial compounds by phylloplane-inhabiting yeasts and yeastlike fungi. 总被引:3,自引:2,他引:1 下载免费PDF全文
The production of antibacterial compounds by yeasts and yeastlike fungi isolated from the phylloplane is reported. Aureobasidium pullulans, Citeromyces matritensis, Cryptococcus laurentii, Rhodotorula glutinis, and Sporobolomyces roseus produced antibacterial compounds inhibitory to both Pseudomonas fluorescens and Staphylococcus aureus in an overlay bioassay. In contrast, isolates of Candida albicans, Filobasidium uniguttulatum, Saccharomyces cerevisiae, Torulaspora delbruckii, Tremella foliacea, Trichosporon beigelii, and Trichosporon dulcitum obtained from soil or from culture collections did not produce inhibitory compounds when screened by the same procedure. The production of antibacterial compounds was examined in more detail, using several isolates of A. pullulans distinguished by cluster analysis on the basis of biochemical and physiological tests. They were found to produce a range of antibacterial compounds with different activities. Two distinct antibiotics were produced by an isolate of A. pullulans in liquid culture during both the logarithmic and the stationary phases of growth. 相似文献
12.
13.
Adam L. Crane Reid Bryshun Megan McCormack Gabrielle H. Achtymichuk Ita A. E. Rivera-Hernández Maud C. O. Ferrari 《Journal of evolutionary biology》2023,36(1):57-66
Many species possess damage-released chemical alarm cues that function in alerting nearby individuals to a predator attack. One hypothesis for the evolution and/or maintenance of such cues is the Predator Attraction Hypothesis, where predators, rather than prey, are the “intended” recipients of these cues. If a predator attack attracts additional predators, these secondary predators might interfere with the predation event, providing the prey with a better chance to escape. In this study, we conducted two experiments to explore this hypothesis in an amphibian predator/prey system. In Experiment 1, we found that tiger salamanders (Ambystoma mavortium) showed a foraging attraction to chemical cues from wood frog (Lithobates sylvaticus) tadpoles. Salamanders that were experienced with tadpole prey, in particular, were strongly attracted to tadpole alarm cues. In Experiment 2, we observed experimental encounters between a tadpole and either one or two salamanders. The presence of the second predator caused salamanders to increase attack speed at the cost of decreased attack accuracy (i.e., increasing the probability that the tadpole would escape attacks). We also found that the mere presence of visual and chemical cues from a second predator did not affect this speed/accuracy trade-off but did cause enough of a distraction to increase tadpole survival. Thus, our findings are consistent with the Predator Attraction Hypothesis for the evolution and/or maintenance of alarm cues. 相似文献
14.
Taiye Winful Katie McCormack Elsa Mueller Lijuan Chen La Corporación Piñones Se Integra Maricruz Rivera Clemente Jada Benn Torres 《American journal of physical anthropology》2023,182(2):194-209
Objectives
From an anthropological genetic perspective, little is known about the ethnogenesis of African descendants in Puerto Rico. Furthermore, historical interactions between Indigenous Caribbean and African descendant peoples that may be reflected in the ancestry of contemporary populations are understudied. Given this dearth of genetic research and the precedence for Afro-Indigenous interactions documented by historical, archeological, and other lines of evidence, we sought to assess the biogeographic origins of African descendant Puerto Ricans and to query the potential for Indigenous ancestry within this community.Materials and Methods
Saliva samples were collected from 58 self-identified African descendant Puerto Ricans residing in Puerto Rico. We sequenced whole mitochondrial genomes and genotyped Y chromosome haplogroups for each male individual (n = 25). Summary statistics, comparative analyses, and network analysis were used to assess diversity and variation in haplogroup distribution between the sample and comparative populations.Results
As indicated by mitochondrial haplogroups, 66% had African, 5% had European, and 29% had Indigenous American matrilines. Along the Y chromosome, 52% had African, 28% had Western European, 16% had Eurasian, and, notably, 4% had Indigenous American patrilines. Both mitochondrial and Y chromosome haplogroup frequencies were significantly different from several comparative populations.Discussion
Biogeographic origins are consistent with historical accounts of African, Indigenous American, and European ancestry. However, this first report of Indigenous American paternal ancestry in Puerto Rico suggests distinctive features within African descendant communities on the island. Future studies expanding sampling and incorporating higher resolution genetic markers are necessary to more fully understand African descendant history in Puerto Rico. 相似文献15.
Henipaviruses and lyssaviruses target nucleolar treacle protein and regulate ribosomal RNA synthesis
Stephen M. Rawlinson Tianyue Zhao Katie Ardipradja Yilin Zhang Patrick F. Veugelers Jennifer A. Harper Cassandra T. David Vinod Sundaramoorthy Gregory W. Moseley 《Traffic (Copenhagen, Denmark)》2023,24(3):146-157
The nucleolus is a common target of viruses and viral proteins, but for many viruses the functional outcomes and significance of this targeting remains unresolved. Recently, the first intranucleolar function of a protein of a cytoplasmically-replicating negative-sense RNA virus (NSV) was identified, with the finding that the matrix (M) protein of Hendra virus (HeV) (genus Henipavirus, family Paramyxoviridae) interacts with Treacle protein within nucleolar subcompartments and mimics a cellular mechanism of the nucleolar DNA-damage response (DDR) to suppress ribosomal RNA (rRNA) synthesis. Whether other viruses utilise this mechanism has not been examined. We report that sub-nucleolar Treacle targeting and modulation is conserved between M proteins of multiple Henipaviruses, including Nipah virus and other potentially zoonotic viruses. Furthermore, this function is also evident for P3 protein of rabies virus, the prototype virus of a different RNA virus family (Rhabdoviridae), with Treacle depletion in cells also found to impact virus production. These data indicate that unrelated proteins of viruses from different families have independently developed nucleolar/Treacle targeting function, but that modulation of Treacle has distinct effects on infection. Thus, subversion of Treacle may be an important process in infection by diverse NSVs, and so could provide novel targets for antiviral approaches with broad specificity. 相似文献
16.
Gerardo A. Cordero Katie Birk Sara Ruane Stephen A. Dinkelacker Fredric J. Janzen 《Evolution & development》2023,25(2):153-169
Developing organisms are often exposed to fluctuating environments that destabilize tissue-scale processes and induce abnormal phenotypes. This might be common in species that lay eggs in the external environment and with little parental care, such as many reptiles. In turtles, morphological development has provided striking examples of abnormal phenotypic patterns, though the influence of the environment remains unclear. To this end, we compared fluctuating asymmetry, as a proxy for developmental instability, in turtle hatchlings incubated in controlled laboratory and unstable natural conditions. Wild and laboratory hatchlings featured similar proportions of supernumerary scales (scutes) on the dorsal shell (carapace). Such abnormal scutes likely elevated shape asymmetry, which was highest in natural nests. Moreover, we tested the hypothesis that hot and dry environments cause abnormal scute formation by subjecting eggs to a range of hydric and thermal laboratory incubation regimes. Shape asymmetry was similar in hatchlings incubated at five constant temperatures (26–30°C). A hot (30°C) and severely Dry substrate yielded smaller hatchlings but scutes were not overtly affected. Our study suggests that changing nest environments contribute to fluctuating asymmetry in egg-laying reptiles, while clarifying the conditions at which turtle shell development remains buffered from the external environment. 相似文献
17.
Samantha G. Robinson Katie M. Walker Henrietta A. Bellman Daniel Gibson Daniel H. Catlin Sarah M. Karpanty Shannon J. Ritter James D. Fraser 《The Journal of wildlife management》2023,87(1):e22325
Population declines of disturbance-dependent species due to suppression of natural disturbances are realized across ecosystems. The piping plover (Charadrius melodus; plover), a disturbance-dependent and conservation-reliant shorebird that nests on sandy beaches and barrier islands on the Atlantic Coast, was listed under the United States Endangered Species Act in 1986. In 2012, Hurricane Sandy landed on Fire and Westhampton islands, barrier island nesting sites for plovers in New York, USA. Hurricane Sandy was a natural disturbance in this system, creating abundant nesting habitat. The number of chicks produced by a pair, or a population, is a direct measure of reproductive output, and gaining a better understanding of productivity and chick behavior following large-scale habitat creation may improve plover habitat management and potentially species persistence. We evaluated the effects of landscape features on habitat selection, behavior, and survival of plover broods using logistic regression, generalized linear mixed effects models, and survival models. Plover broods selected flatter sites with less dense vegetation than available at random. Chick foraging rates were highest in moist substrates and were lower in areas of higher nesting plover density. Chick survival was greater for broods that hatched earlier in the breeding season and increased as chicks aged. Generally, providing access to sites with flatter, moist substrates will likely result in higher quality brood rearing habitat on the landscape. Ultimately, vegetation removal and habitat management may be needed to reduce plover nesting density and ensure sufficient habitat, which may in turn improve plover chick survival. Moreover, sustaining natural landscape disturbances such as those resulting from storms, and not taking actions to prevent hurricane-created overwash, will allow these landscape features to persist. 相似文献
18.
19.
20.
Bruce Aylward Katie Allen Jaime Echeverría Joseph Tosi 《Biodiversity and Conservation》1996,5(3):315-343
The paper discusses the sustainability of the Monteverde Cloud Forest Preserve in the context of Costa Rican ecotourism. While the history of the Preserve is somewhat unique, the analysis of visitation, financial, ecological and economic factors provides a convincing case that tourism at the Preserve is sustainable. The experience of the Preserve is also put in the context of Costa Rican ecotourism, particularly to the national parks. The paper concludes that the Preserve has played a very important role in the development of Costa Rica as an ecotourism destination. Nonetheless, the failure of experience at the Preserve to inform recent changes in national park pricing policy reveal that Costa Rica has yet to fully capitalize on the experience gained and lessons learned at the Preserve. 相似文献