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   1037篇
  免费   168篇
  国内免费   96篇
林业   19篇
农学   16篇
基础科学   23篇
  51篇
综合类   305篇
农作物   10篇
水产渔业   838篇
畜牧兽医   32篇
园艺   2篇
植物保护   5篇
  2024年   10篇
  2023年   31篇
  2022年   33篇
  2021年   56篇
  2020年   67篇
  2019年   72篇
  2018年   51篇
  2017年   69篇
  2016年   66篇
  2015年   46篇
  2014年   58篇
  2013年   69篇
  2012年   56篇
  2011年   64篇
  2010年   54篇
  2009年   48篇
  2008年   46篇
  2007年   44篇
  2006年   46篇
  2005年   60篇
  2004年   46篇
  2003年   36篇
  2002年   24篇
  2001年   21篇
  2000年   29篇
  1999年   21篇
  1998年   14篇
  1997年   15篇
  1996年   10篇
  1995年   13篇
  1994年   9篇
  1993年   1篇
  1992年   4篇
  1991年   3篇
  1990年   2篇
  1988年   4篇
  1987年   1篇
  1984年   1篇
  1982年   1篇
排序方式: 共有1301条查询结果,搜索用时 62 毫秒
41.
42.
近几年来,随着人们生活水平的提高,钓鱼爱好者不断增加,休闲渔业这一垂钓业正在悄然兴起。本文就我国休闲渔业的发展作一简要介绍。  相似文献   
43.
Abstract Weekly exploitation rates of Atlantic salmon, Salmo salar L., in the River Utsjoki, Finland, were estimated from catch reports during the 2003, 2004, 2006 and 2007 seasons, and recordings of all Atlantic salmon ascending the river using a submerged video camera array. In all years, mean weekly fishing mortality rates were significantly higher in June than July to August, with a falling trend throughout the fishing season. Owing to overlap in size between one‐sea‐winter (1SW) and multi‐sea‐winter (MSW) salmon, the estimated fishing mortality rates were based on all sea‐age categories combined. By the second week in June, 18.3–34.7% of large salmon (only MSW) had ascended, compared with 2.2–6.4% of small salmon (1SW and some MSW). Indirectly, the earlier start of ascent of large salmon to River Utsjoki indicated that in‐river fishing mortality of MSW salmon is higher than for 1SW salmon. A later opening of the fishing season may be used to reduce the in‐river fishing mortality, especially for the MSW component.  相似文献   
44.
45.
依据中国渔政指挥系统江苏省渔业船舶水上安全事故的统计资料,对2010—2019年事故的发生时间、事故起数、死亡人数、事故类型和事故等级等方面进行了统计分析。结果表明,江苏省渔业船舶水上安全事故以一般等级事故居多,事故发生时间呈现一定规律性,渔船自身安全隐患突出,从业人员岗位技能不足,渔船安全管理责任不到位。基于分析结果,提出压降一般等级事故,遏制较大等级以上事故,提高风险管控和事故防范能力的对策建议。  相似文献   
46.
This study evaluated the status of native and stocked fish species in 13 prairie lakes in central Canada over eight years (2007–14) using three metrics: resource-use (benthic versus pelagic carbon via stable isotopes); body condition (relative weight index Wr); and parasite load (cestode gut enumerations). Analyses included game and non-game fishes, like naturally occurring northern pike, Esox lucius L., and yellow perch, Perca flavescens Mitchill, but focused on stocked walleye, Sander vitreus (Mitchill) because it supports a robust recreational fishery. Walleye and northern pike were significantly more reliant on benthic carbon than yellow perch or forage fishes (p < 0.05), but this reliance was not associated with any measured environmental variables for any species. In lakes with game fishes, forage fishes exhibited higher reliance on benthic energy, possibly due to predator avoidance strategy, particularly yellow perch. Walleye body condition index was consistently lower (<95–105) than values exhibited by the other two game fishes (81–139), and parasites were only common in walleye and associated with lake-water salinity (r2 = 0.93, p < 0.05) and sex (p < 0.05). Based on the results, the most desirable game fish, walleye, appears less resilient to environmental variability than northern pike and yellow perch, making this species more susceptible to impacts of future climate change.  相似文献   
47.
Growth of Eurasian perch Perca fluviatilis L. and fish community structure between sites within a marine‐protected area (MPA) and unprotected sites in the Baltic Sea were examined. Von Bertalanffy, logistic and Gompertz growth models were fitted to P. fluviatilis length at age data, and the logistic model was the most parsimonious for growth between locations. A larger mean maximum size (L) and a smaller instantaneous growth rate (g) were found within the MPA. All three models also predicted that after age seven, fish inside the MPA would be larger. Community structure differed with more P. fluviatilis collected outside of the MPA, and more roach Rutilus rutilus (L.) and bleak Alburnus alburnus (L.) collected inside the MPA. These growth differences may be indicative of recreational fishing effects on P. fluviatilis outside of the MPA, a result of complex interspecific and intraspecific species interactions, or other undetected environmental variation between locations.  相似文献   
48.
Advocates, practitioners and policy-makers continue to use and advocate for marine protected areas (MPAs) to meet global ocean protection targets. Yet many of the worlds MPAs, and especially no-take MPAs, are plagued by poaching and ineffective governance. Using a global dataset on coral reefs as an example, we quantify the potential ecological gains of governing MPAs to increase compliance, which we call the ‘compliance gap’. Using ecological simulations based on model posteriors of joint Bayesian hierarchical models, we demonstrate how increased compliance in no-take MPAs could nearly double target fish biomass (91% increases in median fish biomass), and result in a 292% higher likelihood of encountering top predators. Achieving these gains and closing the compliance gap necessitates a substantial shift in approach and practice to go beyond optimizing enforcement, and towards governing for compliance. This will require engaging and integrating a broad suite of actors, principles, and practices across three key domains: (i)) harnessing social influence, (ii) integrating equity principles, and (iii) aligning incentives through market-based instruments. Empowering and shaping communication between actor groups (e.g., between fishers, practitioners, and policy-makers) using theoretically underpinned approaches from the behavioural sciences is one of the most essential, but often underserved aspects of governing MPAs. We therefore close by highlighting how this cross-cutting tool could be further integrated in governance to bolster high levels of compliance in MPAs.  相似文献   
49.
七十年代中期以来,中国沿海机动渔船迅速增加,其中250马力以下小型渔船占极大比例。随着海洋捕捞产量增加,海洋鱼类资源状况也在不断恶化,渔获物中优质鱼的比例持续降低。单位马力产量和网次产量下降。因此,必须在国家大力发展远洋渔业的同时,尽快地大幅度减轻对近海渔场的捕捞压  相似文献   
50.
Ecosystem‐based management is an emerging paradigm influencing the management of commercial fisheries. Increasingly, developed nations are adopting explicit legislation and policy governing the assessment and management of their fisheries against criteria of ecological sustainability. Yet the ability to evaluate ecosystem impacts of fisheries is compromised by a general lack of understanding of marine ecosystem function (beyond the population level) and a lack of robust and practical indicators for ecosystem health and management. Recent technological advances can assist in developing criteria, including structural analyses of seafloor communities potentially impacted by fishing gears (e.g. demersal trawling). Similarly, advances in fishing gear technology, including improved selectivity and the development of gears which have a more benign environmental impact, can mitigate some of the ecological impacts of fishing. Such technological advances are summarized in the context of contemporary fisheries management.  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