首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   105篇
  免费   14篇
林业   8篇
农学   7篇
  23篇
综合类   6篇
农作物   5篇
水产渔业   8篇
畜牧兽医   50篇
园艺   5篇
植物保护   7篇
  2023年   3篇
  2022年   1篇
  2021年   1篇
  2020年   4篇
  2019年   6篇
  2018年   6篇
  2017年   3篇
  2016年   4篇
  2015年   7篇
  2014年   6篇
  2013年   7篇
  2012年   7篇
  2011年   11篇
  2010年   7篇
  2009年   4篇
  2008年   10篇
  2007年   3篇
  2006年   4篇
  2005年   5篇
  2004年   7篇
  2003年   6篇
  2002年   5篇
  2000年   1篇
  1997年   1篇
排序方式: 共有119条查询结果,搜索用时 296 毫秒
81.
In 2002, the Food and Agriculture Organization of the United Nations (FAO) published its FAO Country Profiles, an innovative information retrieval system which allows access to FAO's thematic, country-based information from a single entry point. This ontology uses some of the country profiles’ underlying data to provide a reusable resource for the international community, with a more streamlined means of accessing country data. Aimed at improving information management, the ontology facilitates standardized data sharing and interoperability, delivering the most updated geopolitical information. This ontology organizes coding systems and multilingual representations and tracks historical changes to geopolitical data as determined by trustworthy data holders like the United Nations. This article will show how the FAO Country Profiles has defined a new standard in geopolitical ontology and how and why the ontology became a reference for country-based information, as well as discuss future challenges.  相似文献   
82.
Previous lymphangiographic studies have investigated the use of computed tomography (CT) for characterizing the thoracic duct and its tributaries in dogs. However, there is limited published information on the appearance of the canine cisterna chyli using CT. The objective of this retrospective study was to describe the features of the canine cisterna chyli in pre‐ and post‐contrast abdominal CT studies. The presence, location, shape, maximum width, size compared with the aortic diameter (Ao:cisterna chyli ratio) and mean attenuation of the cisterna chyli were recorded from archived abdominal CT scans of 30 dogs. Breed, age, sex and neutering status were also noted. A cisterna chyli was identified in 26 of the dogs (87%). In 22 cases a cisterna chyli could be reliably identified prior to intravenous contrast administration and in all 26 cases in postcontrast images. The cisterna chyli was most commonly located right dorsolateral to the abdominal aorta between L1 and L4. Shape varied on transverse images from crescent‐like to globular and maximum diameters ranged from 5 to 9 mm. The Ao:cisterna chyli ratio varied between 0.29 and 0.71 (mean value—males: 0.32; females: 0.38). On pre‐contrast images the mean Hounsfield units were 21.3HU (range: –3.8 to 64.25). Mild enhancement of the cisterna chyli post‐contrast was observed in 24 dogs (80%). Findings supported the use of pre‐ and post‐contrast abdominal CT as a non‐invasive method for assessing qualitative and quantitative characteristics of the canine cisterna chyli.  相似文献   
83.
Schmallenberg virus (SBV) is a novel orthobunyavirus, discovered in Germany in late 2011. It mainly infects cattle, sheep and goats and could lead to congenital infection, causing abortion and fetal abnormalities. SBV is transmitted by biting midges from the Culicoides genus and there is no evidence that natural infection occurs directly between ruminants. Here, we could detect SBV RNA in infected bull semen using qRT-PCR (three bulls out of seven tested positive; 29 positive semen batches out of 136). We also found that highly positive semen batches from SBV infected bulls can provoke an acute infection in IFNAR-/- mice, suggesting the potential presence of infectious virus in the semen of SBV infected bulls.  相似文献   
84.
Truffles, i.e. tree root-associated fungal fruiting bodies, clearly range among the world’s most exclusive delicacies. Despite the quite restricted natural geographic occurrence of one of the most renowned fungal species, namely Tuber melanosporum, the development of inoculation procedures in the late 1960s made it possible to enlarge its production area in different countries. This was achieved by planting orchards with host tree seedlings colonized by the fungus. In the present work, we investigate the behavior of one of the earliest T. melanosporum orchards planted in Burgundy (France) over a long-term scale (more than 30 years). A picture of the orchard evolution was obtained by recording truffle yields and fungal morphotypes over the seasons and relating them to host-tree development and climate data. The most relevant results include the time-delayed, but rather fast replacement of inoculated T. melanosporum by naturally occurring T. aestivum and the key role of climate in the inter-annual variability of truffle production.  相似文献   
85.
In France, implementation of systematic screening programs in 2000, as a complement to the mandatory reporting of animals with clinical signs of BSE (passive surveillance), revealed certain limitations of the mandatory system. Indeed, systematic screening showed that some BSE cases were not detected by the clinical surveillance system, implying considerable BSE case under-reporting throughout the epidemic. As the most likely explanation for variant Creutzfeldt-Jakob disease (vCJD) is exposure to the aetiologic agent of BSE, it is essential to reconstruct the French BSE epidemic pattern accounting for this under-reporting. We estimated age- and year-specific incidence rates of BSE by using a back-calculation method. This approach relies on the principle that the number of clinical BSE cases is the consequence of the number of BSE-infected animals after a known incubation time, defined as the time between infection and clinical onset. We generalized this model to take into account epidemiological characteristics of BSE, such as French cattle mortality, BSE case reporting probability, and age-dependent susceptibility and/or exposure to the BSE agent. We confirmed that the average BSE incubation period is five years and that the peak risk of bovine infection occurs between 6 and 12 months of age. The results also showed that the proportion of underreporting is the most influential parameter in the model, and that BSE was substantially underreported until rapid tests were introduced. Indeed, only 103 BSE cases were detected by passive surveillance up to June 2000, while we estimated that there was 301 200 (95% confidence interval (CI) [27 600-837 600]) cattle infected by the BSE agent. Despite uncertainty over the beginning of the epidemic, we showed that the French BSE epidemic in the late 1980s was completely undetected, and only the second wave, after 1990, was observed.  相似文献   
86.
Synthetic agonists of TLR9 containing novel DNA structures and R'pG (wherein R=1-(2'-deoxy-beta-d-ribofuranosyl)-2-oxo-7-deaza-8-methyl-purine) motifs, referred to as immune modulatory oligonucleotides (IMOs), have been shown to stimulate T(H)-1-type-immune responses and potently reverse allergen-induced T(H)-2 responses to T(H)-1 responses in vitro and in vivo in mice. In order to investigate the immunomodulatory potential of IMOs in dogs, canine peripheral blood mononuclear cells (PBMC) from healthy dogs were stimulated with three different IMOs and a control IMO, alone or in combination with concanavalin A (ConA). Lipopolysaccharide (LPS) was used as a positive control for B lymphocyte activation. Carboxyfluorescein diacetate succinimidyl ester and phenotype staining was used to tag proliferating T and B lymphocytes (CD5(+) and CD21(+)) by flow cytometry. Real-time PCR and ELISA were processed to assay cytokine production of IFN-gamma, IL-10, TGF-beta, IL-6 and IL-10. Like LPS, IMOs alone induced neither proliferation of CD5(+) T cells nor CD21(+) B cells, but both LPS and IMO had the capacity to co-stimulate ConA and induced proliferation of B cells. In combination with ConA, one of the IMOs (IMO1) also induced proliferation of T cells. IMO1 also significantly enhanced the expression of IFN-gamma on the mRNA and protein level in canine PBMC, whereas expression of IL-10, TGF-beta and IL-4 mRNAs was not induced by any of the IMOs. These results indicate that in canine PBMC from healthy dogs, IMO1 was able to induce a T(H)-1 immune response including T- and B-cell proliferation.  相似文献   
87.
88.
89.
90.
Sunflower rooting depth is strongly related with soil structural behavior and gravimetric water availability. A few studies have been done on sunflower, only one within a kinetic aspect, and none involving fine root study. This work's aim was to study the impact of soil compaction and its interactions with soil water content on sunflower root and shoot growth and growth rate. A destructive experiment in controlled conditions was implemented to determine the consequences of soil compaction in interaction with water management on the growth of sunflower root and shoot system. Strong modifications on root exploration, architecture and growth were reported under low and high compactions depending on their water regime, the stage sampled and the time duration. This had a negative impact on resources uptake and efficiency. Modifications on the above ground part of the plant through plant water and nutrients uptake, plant growth indicators, biomass production and leaves growth kinetics were also observed.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号