全文获取类型
收费全文 | 2244篇 |
免费 | 137篇 |
国内免费 | 91篇 |
专业分类
林业 | 359篇 |
农学 | 98篇 |
基础科学 | 115篇 |
241篇 | |
综合类 | 894篇 |
农作物 | 68篇 |
水产渔业 | 171篇 |
畜牧兽医 | 366篇 |
园艺 | 39篇 |
植物保护 | 121篇 |
出版年
2024年 | 20篇 |
2023年 | 42篇 |
2022年 | 61篇 |
2021年 | 81篇 |
2020年 | 77篇 |
2019年 | 117篇 |
2018年 | 42篇 |
2017年 | 74篇 |
2016年 | 86篇 |
2015年 | 73篇 |
2014年 | 149篇 |
2013年 | 164篇 |
2012年 | 211篇 |
2011年 | 200篇 |
2010年 | 161篇 |
2009年 | 124篇 |
2008年 | 108篇 |
2007年 | 121篇 |
2006年 | 83篇 |
2005年 | 77篇 |
2004年 | 78篇 |
2003年 | 51篇 |
2002年 | 30篇 |
2001年 | 48篇 |
2000年 | 19篇 |
1999年 | 25篇 |
1998年 | 19篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 22篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 7篇 |
1991年 | 8篇 |
1990年 | 8篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 6篇 |
1986年 | 1篇 |
1984年 | 3篇 |
1962年 | 1篇 |
排序方式: 共有2472条查询结果,搜索用时 31 毫秒
161.
Sea lice treatments, management practices and sea lice sampling methods on Atlantic salmon farms in the Bay of Fundy, New Brunswick, Canada 总被引:4,自引:0,他引:4
Proper monitoring of all stages of sea lice is imperative to ensure the strategic timing of treatments. Although sea lice receive close attention and management for production purposes, there are no regulations for the reporting of lice burdens on salmon farms in Atlantic Canada, nor are there officially standardized protocols for conducting sea lice counts in the field. The purpose of this study was to complete a survey of Atlantic salmon farms in the Bay of Fundy, NB, Canada. The survey addressed many aspects of sea lice monitoring and control, including methods for sea lice sampling at the site, types of treatments administered for control of sea lice and management practices and decisions regarding the control of sea lice. A total of 83 surveys were completed from July to December 2002. Twelve of the 60 respondents owned and/or operated more than one site and completed a survey for each of their sites at the time of the interview. The position of individuals surveyed included 48 site managers (representing 63 sites), three site owners (representing 11 sites), eight individuals who were both owner and manager (representing nine sites) and one site veterinarian (representing one site). Surveys were completed on 30 sites from the Limekiln Bay and surrounding areas, 23 sites from Grand Manan Island, 18 sites from Deer Island, six sites from Campobello Island and six sites from Passamaquoddy Bay. Fish farmers, in concert with their veterinarians, generally perform intensive monitoring and control practices. However, there is a continued reliance on emamectin benzoate (SLICE®) for sea lice control on Atlantic salmon farms in the Bay of Fundy, which raises concerns regarding the potential for sea lice to develop resistance to the drug. 相似文献
162.
Andrew S. Brierley Paul G. Fernandes Mark A. Brandon Frederick Armstrong Nicholas W. Millard Steven D. McPhail Peter Stevenson Miles Pebody James Perrett Mark Squires Douglas G. Bone Gwyn Griffiths 《Fisheries Research》2003,60(2-3):569-576
The autonomous underwater vehicle (AUV) Autosub-2 was deployed on eight missions ahead of RRS James Clark Ross in the northern Weddell Sea and in the Bransfield Strait, Southern Ocean, to assess avoidance of the research vessel by Antarctic krill Euphausia superba. The AUV was equipped with the same type of scientific echosounder as the research vessel (Simrad EK500 operating at 38 and 120 kHz) and measured the density of krill along transect acoustically (g m−2 wet mass) prior to the ship’s arrival. We hypothesised that if krill avoided the ship, perhaps in response to radiated noise, then the ship should detect less krill than the AUV which is known to have much lower noise levels than the ship. We were unable to detect any significant difference between the density of krill detected by the ship or the AUV, either at the transect level or at finer scales within transects. We conclude, therefore, that avoidance by krill of RRS James Clark Ross will not significantly bias acoustic estimates of krill abundance by this vessel. 相似文献
163.
The market for marine ornamentals encompasses all live marine species (fish and invertebrates) destined for the aquarium trade. In 1998, U.S. imports and exports were valued at approximately US $1.5 billion at the border (all dollar values cited in this paper are $US). In Florida, cultured freshwater and collected saltwater species accounted for $70 million and $4 million, respectively, in annual dockside revenue. To help explain Florida's marine landings and provide suggestions for future resource management and market campaigns that reflect the perceptions of the industry, a survey of wholesalers was initiated in 1999. Preliminary results indicate that there are several intermediate wholesale markets. Florida firms are closer to the supply as many also collect. Wholesalers in other states handle more freshwater product, are larger, and tend to import a larger share of their inventory. Consolidation is expected to continue, but niche markets for eco-friendly firms are expected to grow. In Florida, marketing strategies should focus on the observed higher survival rates and increasing supply of the popular invertebrate species. Many wholesalers are concerned about additional regulations that could reduce the number of collectors and thereby increase supply variability, a noted weakness of the Florida industry. 相似文献
164.
P. A. SMITH 《Fisheries Management and Ecology》2002,9(5):261-266
Abstract Twelve anglers fishing in a UK navigation canal for a total of 42 h caught 567 fish, mainly gudgeon, Gobio gobio (L.) ( n =306) and roach, Rutilus rutilus (L.) ( n =253) at an average catch rate of 13.4 fish angler-h−1 or 128.5 g angler-h−1 . The species and size of fish caught were compared with the numbers determined by depletion estimates at six sections of canal using micromesh seine netting. Fifty four percent of fish caught in the net were < 60 mm FL. Gudgeon (60–99 mm) were over-represented in the anglers' catches whilst roach (60–99 mm) were under-represented. The size distribution of roach and gudgeon caught by anglers using two types of bait (small maggots and chironomid larvae) was examined and smaller fish were found to be caught using the latter. 相似文献
165.
166.
彰武县是林业产业结构极其特殊的县区,近年来其林业产业在国家政策带动下快速发展。概述彰武县的自然条件与林业资源、林业产业及基础设施情况,分析彰武县林业产业产值现状,指出其发展中的不合理因素,并提出对策建议。 相似文献
167.
从剖析实践教学过程中存在的现实问题出发,结合学校及专业实际情况,以重庆三峡职业学院园林技术专业为例,提出了一套完整、专业特色鲜明,可操作性强的实践教学体系,并取得了一定的教学成果,也为我国部分地方本科院校相关专业由学术型教育转向应用型教育提供了一定的借鉴意义。 相似文献
168.
为了使野生资源得到合理的开发与利用,对黑龙江省仙翁山国家森林公园大型菌类资源进行调研,并对采集的菌株进行分类分析。在仙翁山森林公园,共采集食用菌类18科48种、药用菌类10科15种、毒菌10科15种。该地区有丰富、珍贵的菌类资源,应通过科学的规划和管理,合理开发利用,使得生态环境可持续平衡发展。 相似文献
169.
主要是对河南省河流普查成果进行简要分析和评价,主要内容包括河流普查成果概述及山地河流特征分析.对河南省境内普查河流的河流长度和流域面积的关系、河流比降的区域分布进行了简要分析,并在河流长度、流域面积和河流数量等方面与以往的资料内容进行了对比分析.总之,该次河湖普查成果取得了很大成就,但仍然存在一些问题. 相似文献
170.
基于在江西省东乡县农村土地调查外业调查的工作实践,对农村土地调查外业调查重要环节和关键技术进行总结和分析,在外业调查中调查底图、调查工具、地类判读和地物补测4个方面提出改进措施.结果表明,通过以上4个方面的改进,对加快外业调查进度和提高外业调查成果质量起到了积极作用. 相似文献