全文获取类型
收费全文 | 4495篇 |
免费 | 385篇 |
国内免费 | 2篇 |
出版年
2024年 | 4篇 |
2023年 | 43篇 |
2022年 | 32篇 |
2021年 | 167篇 |
2020年 | 92篇 |
2019年 | 138篇 |
2018年 | 154篇 |
2017年 | 103篇 |
2016年 | 210篇 |
2015年 | 313篇 |
2014年 | 340篇 |
2013年 | 341篇 |
2012年 | 452篇 |
2011年 | 458篇 |
2010年 | 241篇 |
2009年 | 210篇 |
2008年 | 280篇 |
2007年 | 293篇 |
2006年 | 213篇 |
2005年 | 190篇 |
2004年 | 149篇 |
2003年 | 125篇 |
2002年 | 116篇 |
2001年 | 24篇 |
2000年 | 22篇 |
1999年 | 26篇 |
1998年 | 16篇 |
1997年 | 9篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1990年 | 6篇 |
1989年 | 5篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1983年 | 4篇 |
1982年 | 7篇 |
1981年 | 4篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1962年 | 2篇 |
1961年 | 3篇 |
1960年 | 3篇 |
1955年 | 4篇 |
1911年 | 2篇 |
排序方式: 共有4882条查询结果,搜索用时 19 毫秒
61.
EcoHealth - West Nile virus (WNV) is the most significant mosquito-borne disease affecting humans in the United States. Eastern redcedar (ERC) is a native encroaching plant in the southern Great... 相似文献
62.
63.
Tra-My N. Duong Thanh-Van Le Khanh-Linh H. Tran Phuong-Tuyen Nguyen Bich-Phuong T. Nguyen Thu-Anh Nguyen Huong-Lan P. Nguyen Bich-Ngoc T. Nguyen Matthew C. Fisher Johanna Rhodes Guy Marks Greg J. Fox Sharon C.-A. Chen Michael G. Walsh Vanessa R. Barrs Jessica Talbot Catriona L. Halliday Tania C. Sorrell Jeremy N. Day Justin Beardsley 《Environmental microbiology》2021,23(12):7632-7642
Azole-resistant environmental Aspergillus fumigatus presents a threat to public health but the extent of this threat in Southeast Asia is poorly described. We conducted environmental surveillance in the Mekong Delta region of Vietnam, collecting air and ground samples across key land-use types, and determined antifungal susceptibilities of Aspergillus section Fumigati (ASF) isolates and azole concentrations in soils. Of 119 ASF isolates, 55% were resistant (or non-wild type) to itraconazole, 65% to posaconazole and 50% to voriconazole. Azole resistance was more frequent in A. fumigatus sensu stricto isolates (95%) than other ASF species (32%). Resistant isolates and agricultural azole residues were overrepresented in samples from cultivated land. cyp51A gene sequence analysis showed 38/56 resistant A. fumigatus sensu stricto isolates carried known resistance mutations, with TR34/L98H most frequent (34/38). 相似文献
64.
65.
66.
Lantana (Lantana camara) poses a serious threat to the biodiversity of the dry rainforest vegetation at Forty Mile Scrub National Park, Queensland, Australia, by outcompeting native species and increasing vulnerability to fire. This pilot study tests the effectiveness of three weed control methods (hand pulling, a glyphosphate‐based foliar spray herbicide and a picloram‐ and triclopyr‐based basal bark herbicide) in removing lantana and their success in reducing lantana fuel loads. The foliar spray herbicide was the most effective in killing lantana, while manual pulling resulted in the largest decrease in fuel height. We suggest that foliar spraying will be most efficient for combating large infestations of lantana, while hand pulling techniques are recommended for creating firebreaks or when minimizing damage to native species is paramount. 相似文献
67.
Karen Z. Weinbaum Justin S. Brashares Christopher D. Golden Wayne M. Getz 《Ecology letters》2013,16(1):99-111
The unsustainable harvest of wildlife is a major threat to global biodiversity and to the millions of people who depend on wildlife for food and income. Past research has called attention to the fact that commonly used methods to evaluate the sustainability of wildlife hunting perform poorly, yet these methods remain in popular use today. Here, we conduct a systematic review of empirical sustainability assessments to quantify the use of sustainability indicators in the scientific literature and highlight associations between analytical methods and their outcomes. We find that indicator type, continent of study, species body mass, taxonomic group and socio‐economic status of study site are important predictors of the probability of reported sustainability. The most common measures of sustainability include population growth models, the Robinson & Redford (1991) model and population trends through time. Indicators relying on population‐specific biological data are most often used in North America and Europe, while cruder estimates are more often used in Africa, Latin America and Oceania. Our results highlight both the uncertainty and lack of uniformity in sustainability science. Given our urgent need to conserve both wildlife and the food security of rural peoples around the world, improvements in sustainability indicators are of utmost importance. 相似文献
68.
Background
Sorghum is a tropical C4 cereal that recently adapted to temperate latitudes and mechanized grain harvest through selection for dwarfism and photoperiod-insensitivity. Quantitative trait loci for these traits have been introgressed from a dwarf temperate donor into hundreds of diverse sorghum landraces to yield the Sorghum Conversion lines. Here, we report the first comprehensive genomic analysis of the molecular changes underlying this adaptation.Results
We apply genotyping-by-sequencing to 1,160 Sorghum Conversion lines and their exotic progenitors, and map donor introgressions in each Sorghum Conversion line. Many Sorghum Conversion lines carry unexpected haplotypes not found in either presumed parent. Genome-wide mapping of introgression frequencies reveals three genomic regions necessary for temperate adaptation across all Sorghum Conversion lines, containing the Dw1, Dw2, and Dw3 loci on chromosomes 9, 6, and 7 respectively. Association mapping of plant height and flowering time in Sorghum Conversion lines detects significant associations in the Dw1 but not the Dw2 or Dw3 regions. Subpopulation-specific introgression mapping suggests that chromosome 6 contains at least four loci required for temperate adaptation in different sorghum genetic backgrounds. The Dw1 region fractionates into separate quantitative trait loci for plant height and flowering time.Conclusions
Generating Sorghum Conversion lines has been accompanied by substantial unintended gene flow. Sorghum adaptation to temperate-zone grain production involves a small number of genomic regions, each containing multiple linked loci for plant height and flowering time. Further characterization of these loci will accelerate the adaptation of sorghum and related grasses to new production systems for food and fuel. 相似文献69.
Karen Page David S. Guttery Nathalie Zahra Lindsay Primrose Shona R. Elshaw J. Howard Pringle Kevin Blighe Stephanie D. Marchese Allison Hills Laura Woodley Justin Stebbing R. Charles Coombes Jacqueline A. Shaw 《PloS one》2013,8(10)
Circulating nucleic acids (CNAs) are under investigation as a liquid biopsy in cancer. However there is wide variation in blood processing and methods for isolation of circulating free DNA (cfDNA) and microRNAs (miRNAs). Here we compare the extraction efficiency and reproducibility of 4 commercially available kits for cfDNA and 3 for miRNA using spike-in of reference templates. We also compare the effects of increasing time between venepuncture and centrifugation and differential centrifugation force on recovery of CNAs. cfDNA was quantified by TaqMan qPCR and targeted deep sequencing. miRNA profiles were assessed with TaqMan low-density arrays and assays. The QIAamp® DNA Blood Mini and Circulating nucleic acid kits gave the highest recovery of cfDNA and efficient recovery (>90%) of a 564bp spike-in. Moreover, targeted sequencing revealed overlapping cfDNA profiles and variant depth, including detection of HER2 gene amplification, using the Ion AmpliSeq™Cancer Hotspot Panel v2. Highest yields of miRNA and the synthetic Arabidopsis thaliana miR-159a spike-in were obtained using the miRNeasy Serum/Plasma kit, with saturation above 200 µl of plasma. miRNA profiles showed significant variation with increasing time before centrifugation (p<0.001) and increasing centrifugation force, with depletion of platelet associated miRNAs, whereas cfDNA was unaffected. However, sample replicates showed excellent reproducibility on TaqMan low density arrays (ρ = 0.96, p<0.0001). We also successfully generated miRNA profiles for plasma samples stored > 12 years, highlighting the potential for analysis of stored sample biobanks. In the era of the liquid biopsy, standardisation of methods is required to minimise variation, particularly for miRNA. 相似文献
70.
Mathieu E. Wimmer Justin Rising Raymond J. Galante Abraham Wyner Allan I. Pack Ted Abel 《PloS one》2013,8(12)
One of the most significant problems facing older individuals is difficulty staying asleep at night and awake during the day. Understanding the mechanisms by which the regulation of sleep/wake goes awry with age is a critical step in identifying novel therapeutic strategies to improve quality of life for the elderly. We measured wake, non-rapid eye movement (NREM) and rapid-eye movement (REM) sleep in young (2–4 months-old) and aged (22–24 months-old) C57BL6/NIA mice. We used both conventional measures (i.e., bout number and bout duration) and an innovative spike-and-slab statistical approach to characterize age-related fragmentation of sleep/wake. The short (spike) and long (slab) components of the spike-and-slab mixture model capture the distribution of bouts for each behavioral state in mice. Using this novel analytical approach, we found that aged animals are less able to sustain long episodes of wakefulness or NREM sleep. Additionally, spectral analysis of EEG recordings revealed that aging slows theta peak frequency, a correlate of arousal. These combined analyses provide a window into the mechanisms underlying the destabilization of long periods of sleep and wake and reduced vigilance that develop with aging. 相似文献