全文获取类型
收费全文 | 6254篇 |
免费 | 528篇 |
国内免费 | 5篇 |
专业分类
6787篇 |
出版年
2023年 | 39篇 |
2022年 | 95篇 |
2021年 | 174篇 |
2020年 | 90篇 |
2019年 | 96篇 |
2018年 | 138篇 |
2017年 | 128篇 |
2016年 | 220篇 |
2015年 | 400篇 |
2014年 | 439篇 |
2013年 | 429篇 |
2012年 | 623篇 |
2011年 | 566篇 |
2010年 | 334篇 |
2009年 | 290篇 |
2008年 | 400篇 |
2007年 | 398篇 |
2006年 | 385篇 |
2005年 | 292篇 |
2004年 | 311篇 |
2003年 | 211篇 |
2002年 | 217篇 |
2001年 | 42篇 |
2000年 | 27篇 |
1999年 | 46篇 |
1998年 | 42篇 |
1997年 | 45篇 |
1996年 | 29篇 |
1995年 | 20篇 |
1994年 | 35篇 |
1993年 | 19篇 |
1992年 | 22篇 |
1991年 | 20篇 |
1990年 | 12篇 |
1989年 | 15篇 |
1988年 | 6篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 10篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1978年 | 6篇 |
1977年 | 13篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1970年 | 4篇 |
1960年 | 3篇 |
排序方式: 共有6787条查询结果,搜索用时 0 毫秒
91.
Ammonia-oxidising archaea (AOA) are a ubiquitous component of microbial communities and dominate the first stage of nitrification in some soils. While we are beginning to understand soil virus dynamics, we have no knowledge of the composition or activity of those infecting nitrifiers or their potential to influence processes. This study aimed to characterise viruses having infected autotrophic AOA in two nitrifying soils of contrasting pH by following transfer of assimilated CO2-derived 13C from host to virus via DNA stable-isotope probing and metagenomic analysis. Incorporation of 13C into low GC mol% AOA and virus genomes increased DNA buoyant density in CsCl gradients but resulted in co-migration with dominant non-enriched high GC mol% genomes, reducing sequencing depth and contig assembly. We therefore developed a hybrid approach where AOA and virus genomes were assembled from low buoyant density DNA with subsequent mapping of 13C isotopically enriched high buoyant density DNA reads to identify activity of AOA. Metagenome-assembled genomes were different between the two soils and represented a broad diversity of active populations. Sixty-four AOA-infecting viral operational taxonomic units (vOTUs) were identified with no clear relatedness to previously characterised prokaryote viruses. These vOTUs were also distinct between soils, with 42% enriched in 13C derived from hosts. The majority were predicted as capable of lysogeny and auxiliary metabolic genes included an AOA-specific multicopper oxidase suggesting infection may augment copper uptake essential for central metabolic functioning. These findings indicate virus infection of AOA may be a frequent process during nitrification with potential to influence host physiology and activity.Subject terms: Microbial ecology, Stable isotope analysisMicrobially mediated oxidation of ammonia to nitrate during nitrification is a central component of the global nitrogen (N) cycle. It is also responsible for major losses of applied fertiliser N in soil, generating atmospheric pollution via direct and indirect production of nitrous oxide (N2O) as well as nitrate (NO3-) pollution of groundwater [1]. Autotrophic ammonia-oxidising archaea (AOA) of the class Nitrososphaeria are a ubiquitous component of soil microbial communities and often dominate ammonia oxidation and nitrification-associated N2O emissions when ammonia is supplied at low rates via organic matter mineralisation [2], slow-release fertilisers [3] or in acidic soils [4]. Integrated temperate viruses (proviruses) and other virus-associated protein-encoding genes are found in most AOA genomes suggesting frequent interaction (see Supplementary Text). While viruses infecting marine AOA have been characterised through metagenomic approaches [5] and cultivation [6], those infecting soil AOA or other nitrifier groups are currently uncharacterised.Virus infection can influence biogeochemical cycling by augmenting host activity or causing cell mortality and subsequent release of nutrients [7]. Recent advances have demonstrated that soil virus communities are dynamic in a wide range of soils [e.g. 8, 9] and augmenting virus loads modulate C and N fluxes [10, 11]. Nevertheless, identifying active interactions with specific populations or functional groups in soil remains challenging due to structural complexity and the vast diversity of hosts and viruses. Recent use of stable-isotope approaches has investigated whole community host-virus dynamics [12, 13] or interactions between individual host-virus populations specific to a functional process and substrate [14]. The aim of this study was to utilise the latter approach with 13CO2-based DNA-SIP to focus on nitrification-associated interactions and to test the hypothesis that viruses are a dynamic component of soil AOA activity. 相似文献
92.
93.
94.
95.
96.
97.
Laura Noël-Romas Michelle Perner Refilwe Molatlhegi Christina Farr Zuend Amanda Mabhula Sarah Hoger Alana Lamont Kenzie Birse Alicia Berard Stuart McCorrister Garett Westmacott Al Leslie Vanessa Poliquin Renee Heffron Lyle R. McKinnon Adam D. Burgener 《PLoS pathogens》2020,16(12)
Alterations to the mucosal environment of the female genital tract, such as genital inflammation, have been associated with increased HIV acquisition in women. As the microbiome and hormonal contraceptives can affect vaginal mucosal immunity, we hypothesized these components may interact in the context of HIV susceptibility. Using previously published microbiome data from 685 women in the CAPRISA-004 trial, we compared relative risk of HIV acquisition in this cohort who were using injectable depot medroxyprogesterone acetate (DMPA), norethisterone enanthate (NET-EN), and combined oral contraceptives (COC). In women who were Lactobacillus-dominant, HIV acquisition was 3-fold higher in women using DMPA relative to women using NET-EN or COC (OR: 3.27; 95% CI: 1.24–11.24, P = 0.0305). This was not observed in non-Lactobacillus-dominant women (OR: 0.95, 95% CI: 0.44–2.15, P = 0.895) (interaction P = 0.0686). Higher serum MPA levels associated with increased molecular pathways of inflammation in the vaginal mucosal fluid of Lactobacillus-dominant women, but no differences were seen in non-Lactobacillus dominant women. This study provides data suggesting an interaction between the microbiome, hormonal contraceptives, and HIV susceptibility. 相似文献
98.
99.
100.