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   738篇
  免费   59篇
  国内免费   2篇
林业   77篇
农学   12篇
基础科学   6篇
  113篇
综合类   116篇
农作物   32篇
水产渔业   70篇
畜牧兽医   299篇
园艺   31篇
植物保护   43篇
  2023年   10篇
  2022年   8篇
  2021年   28篇
  2020年   42篇
  2019年   49篇
  2018年   33篇
  2017年   43篇
  2016年   28篇
  2015年   18篇
  2014年   29篇
  2013年   44篇
  2012年   63篇
  2011年   55篇
  2010年   31篇
  2009年   26篇
  2008年   49篇
  2007年   45篇
  2006年   30篇
  2005年   24篇
  2004年   23篇
  2003年   15篇
  2002年   24篇
  2001年   4篇
  2000年   3篇
  1999年   2篇
  1997年   2篇
  1994年   2篇
  1993年   2篇
  1992年   3篇
  1991年   2篇
  1990年   3篇
  1989年   2篇
  1985年   2篇
  1984年   5篇
  1983年   5篇
  1982年   1篇
  1981年   2篇
  1980年   1篇
  1979年   3篇
  1978年   3篇
  1977年   7篇
  1976年   3篇
  1975年   2篇
  1974年   5篇
  1973年   5篇
  1969年   1篇
  1967年   2篇
  1966年   2篇
  1965年   2篇
  1924年   1篇
排序方式: 共有799条查询结果,搜索用时 15 毫秒
1.
A bottleneck of crustacean larval culture concerns nutrition and associated cannibalism in communal rearing systems, which impact on larval survival, development and growth. For early‐stage European lobster, Homarus gammarus larvae, feeding ecology and body composition are largely unknown. We initiated four progressive feeding experiments (novel feed types, feeding regime and feed size and cannibalism effects) on growth and survival, to inform and update husbandry protocols. Performance of larvae offered a dry commercial feed was not significantly different compared with a conventional wet plankton feed of the same ration and size grade (both within 600–1,000 μm). Further experiments found that the same ration of dry feed offered six times daily improved development and growth, over the conventional regime of three times daily. Small‐grade dry feed (particles: 250–360 μm) improved larval performance compared with a larger feed (360–650 μm). Larvae were also fed different proportions of dry feed and/or conspecifics in both communal and individual rearing systems (the latter preventing cannibalism via segregation). Individually reared larvae, fed only dead conspecifics, displayed the greatest survival (80%) to postlarvae. This underlines the impact of cannibalism on survival and nutrition in H. gammarus larviculture. A final experiment analysed H. gammarus zoea 1 composition, identifying deficiencies in ash and carbohydrate in lobster feeds. This suggests a need for a species‐specific, formulated dry feed for H. gammarus larviculture. Our research represents the first investigation of H. gammarus larval composition and dietary requirements and highlights decreased growth potential associated with providing nutrition solely from generic commercial feed.  相似文献   
2.
  1. Spread of the crayfish plague pathogen, Aphanomyces astaci, by North American crayfish species is considered one of the main reasons for substantial declines and local extinctions of native European crayfish populations. Owing to human introductions, several American crayfish species have become established throughout the world, and thus pose a potential threat to indigenous crayfish populations susceptible to crayfish plague.
  2. In Japan, two such widespread alien species, Procambarus clarkii and Pacifastacus leniusculus, were introduced for aquaculture purposes in the late 1920s and since then successfully expanded their ranges.
  3. Aggressive interactions with alien crayfish along with habitat modifications have been considered primarily responsible for drastic declines in populations of the Japanese endemic crayfish, Cambaroides japonicus, observed in the last few decades. However, the presence of the crayfish plague pathogen, to which Japanese crayfish are susceptible, may be expected, and could contribute to these declines.
  4. Only recently, A. astaci has been reported from Taiwan, and to our knowledge no study focusing on its presence outside of the Western Palearctic has been conducted.
  5. To fill this gap, 54 P. clarkii and 47 P. leniusculus individuals from five different Japanese locations were screened using molecular methods recommended by the World Organization for Animal Health. Aphanomyces astaci DNA was detected in all studied populations, altogether in 61% and 21% of examined individuals of P. clarkii and P. leniusculus, respectively.
  6. The results provide the first evidence of A. astaci presence in Japan and highlight the threat of pathogen transmission to C. japonicus populations.
Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
3.
Surface runoff, erosion, compaction and the leaching of potential pollutants from land can degrade the soil resource and damage the water environment, reducing crop yields, causing loss of valuable nutrients and organic matter, together with increasing flood risk. Increasingly, it is recognized that scientific information must be translated into practical tools to change practices and protect the soil and water resource. Working alongside agencies in Scotland, we applied a suite of simple, transparent, rule-based models to identify areas most at risk of exporting sediment and pollutants that may degrade water quality based on field-scale (1:25,000) soil maps. The maps have been used by Scottish Environment Protection Agency, Scottish Water and Scottish Government to assess soil risks to waters from field to regional scale. The work brought scientists together with policy makers, agencies and the water industry to pool their knowledge to apply these practical tools for decision-making. It highlights the need to apply existing knowledge to answer salient questions. All three examples described show that providing the right type of information, which is based on fundamental soils data, can directly influence the implementation of policies, investment and monitoring decisions and provide evidence in support of government. However, this requires both researchers and agency scientists to develop skills as knowledge brokers and to normalize the use of soil data in everyday agency settings.  相似文献   
4.
In a search for alternative, environmentally friendly and effective disinfecting agents, a commercially available protease—Neutrase®—was tested in this work for inactivation of koi herpesvirus (KHV) and of viral haemorrhagic septicaemia virus (VHSV). For comparison, the stability of these viral pathogens in similar configurations at various pH values and concentrations of peracetic acid or quicklime, typically used for disinfection, was tested. Therefore, virus suspensions were incubated with various concentrations of different agents for 24 hr and the titre of the remaining infectious particles was determined by virus titration. Furthermore, the treatment of both viruses, with the agents at concentrations that were previously appointed as effective, was also examined in the presence of solid material (quartz sand). All procedures investigated in this study, including the protease treatment, were able to reduce the titre of KHV and VHSV below the detection limit of the titration. Although further studies are necessary, this is the first report of the application of a protease for the inactivation of the selected fish pathogens, demonstrating the great potential of the latter for disinfection.  相似文献   
5.
Journal of Plant Diseases and Protection - Prior to the first occurrence of chestnut blight in 1976, leaf spot caused by Cylindrosporium castaneae was one of the most important diseases of European...  相似文献   
6.
Bovine tuberculosis is a contagious and zoonotic disease of animals and humans. In Europe, the number of reported cases of tuberculosis has decreased. Equidae are relatively rarely infected even in endemic areas. The presented report describes a case of chronic Mycobacterium bovis tuberculosis in a 30-year-old female donkey. The donkey initially presented with persistent lymphadenopathy; however, as the disease progressed, weight loss became apparent. To the authors' knowledge, this is the second confirmed case of tuberculosis in a donkey in Europe.  相似文献   
7.
8.
9.
10.
A 10-month-old female, neutered French Bulldog presented with a history of unilateral right-sided intermittent conjunctivitis and exophthalmos. The patient suffered blunt force trauma to the right eye after a tennis ball impact approximately five months prior to presentation. Examination identified the patient was visual with exophthalmos, lateral strabismus, conjunctival hyperaemia, episcleral congestion, and papilloedema. Magnetic resonance imaging and ultrasonography identified an approximately two centimeter diameter fluid-filled structure directly posterior to the globe leading to displacement of the optic nerve and distortion of the posterior globe wall. Centesis of the lesion demonstrated neutrophilic and macrophagic inflammation with evidence of prior hemorrhage. Within four weeks, the structure had re-filled to its original size and was subsequently excised in its entirety, via a lateral orbitotomy. Histopathologic findings indicated a non-keratinising orbital cyst, the lining of which was consistent with a respiratory epithelial cyst. Recurrence had not occurred seven months' post-surgery. To the author's knowledge, previous reports of retrobulbar respiratory epithelial cysts have not been documented in animals.  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