全文获取类型
收费全文 | 18214篇 |
免费 | 1199篇 |
国内免费 | 635篇 |
专业分类
林业 | 4144篇 |
农学 | 615篇 |
基础科学 | 1450篇 |
2319篇 | |
综合类 | 6835篇 |
农作物 | 688篇 |
水产渔业 | 1055篇 |
畜牧兽医 | 1326篇 |
园艺 | 354篇 |
植物保护 | 1262篇 |
出版年
2024年 | 37篇 |
2023年 | 287篇 |
2022年 | 327篇 |
2021年 | 501篇 |
2020年 | 561篇 |
2019年 | 628篇 |
2018年 | 429篇 |
2017年 | 527篇 |
2016年 | 673篇 |
2015年 | 591篇 |
2014年 | 1000篇 |
2013年 | 1181篇 |
2012年 | 1516篇 |
2011年 | 1512篇 |
2010年 | 1135篇 |
2009年 | 1246篇 |
2008年 | 1109篇 |
2007年 | 1151篇 |
2006年 | 951篇 |
2005年 | 916篇 |
2004年 | 712篇 |
2003年 | 617篇 |
2002年 | 454篇 |
2001年 | 414篇 |
2000年 | 344篇 |
1999年 | 241篇 |
1998年 | 175篇 |
1997年 | 157篇 |
1996年 | 135篇 |
1995年 | 107篇 |
1994年 | 81篇 |
1993年 | 63篇 |
1992年 | 68篇 |
1991年 | 64篇 |
1990年 | 35篇 |
1989年 | 46篇 |
1988年 | 33篇 |
1987年 | 13篇 |
1986年 | 6篇 |
1985年 | 4篇 |
1980年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Responses of Australian sea lions,Neophoca cinerea,to anthropogenic activities in the Perth metropolitan area,Western Australia 下载免费PDF全文
- Tourist‐based activities, partly due to their rapid increase, have raised concerns regarding the impacts of anthropogenic activity on marine fauna. Documented effects on pinnipeds in proximity to humans include changes in behaviour, site use and potentially higher aggression levels towards people. Effects vary considerably between populations and sites, thus requiring separate assessment of human impacts on activity and energy budgets.
- Responses of the endangered Australian sea lion, Neophoca cinerea, to human visitation were recorded from November 2013 through April 2014. Exposure levels and response types to anthropogenic activities were assessed at two easily accessible locations with different management schemes, Seal (landing prohibited) and Carnac (landing permitted) islands, Western Australia. Exposure levels were measured as both stimulus type (i.e. ‘People’, ‘Paddlers’, ‘Small’, ‘Medium’, and ‘Large vessels’, ‘Tour vessels’, and ‘Jet skies’), and people (‘Direct’, ‘Attract’, ‘Interact’, ‘View’, ‘Incidental’, ‘Water’, ‘Low‐level’), and vessel activities (‘Interact’, ‘Approach/Follow’, ‘Anchor noise’, ‘Engine noise’, ‘Close to beach’, ‘Moderate/Fast travel’, ‘Slow travel’, ‘Transit’, ‘Drift/At anchor’, ‘Aircraft noise’).
- Exposure levels varied significantly between the islands in numbers, stimuli type, duration and minimum approach distances. The instantaneous behaviours of ‘Lift head’, ‘Interact’ and ‘Sit’ were the most frequent responses. ‘Aggressive’ and ‘Retreat’ responses, the highest disturbance levels measured, occurred on Carnac approximately once per day, but rarely on Seal Island. ‘Aggressive’ behaviour towards ‘People’ was observed only on Carnac Island and elicited only by ‘People’. ‘People’, ‘Tour vessels’, and scenic ‘Aircrafts’ on both islands as well as ‘Jet skis’ on Carnac Island had the highest probability of triggering responses. Owing to their relatively high visitation at Seal Island, ‘Paddle powered vessels’, followed by ‘Tour vessels’ elicited the highest number of responses, compared with ‘People’, ‘Small’, and ‘Medium vessels’ at Carnac Island. The majority of responses occurred when any stimulus type was at short‐range (≤10 m), and ‘People’ ‘Viewing’ N. cinerea elicited most. Vessels triggered more responses at larger ranges than ‘People’.
- To limit close‐range access to N. cinerea, one possibility is to close the beach at Carnac Island to human visitation and increase the minimum approach distance by vessels and ‘People’ by installing marker buoys at least 15 m from the shore.
72.
Recreational fisheries in Portofino Marine Protected Area,Italy: Some implications for the management 下载免费PDF全文
S. Venturini P. Campodonico V. Cappanera G. Fanciulli R. Cattaneo Vietti 《Fisheries Management and Ecology》2017,24(5):382-391
Since the 1970s, recreational fishing has become a mass hobby in Italy, reaching a large number of people, who, using modern equipment, increased their harvesting capacity, provoking serious conflicts with the professional fisheries. Recreational fishing is strictly regulated inside Italian Marine Protected Areas (MPAs) and is generally allocated to local residents, mainly to reduce the tensions caused by limitations of access to the resources. The aim of this study was to provide an analysis of recreational fishing activities within the Portofino MPA (Mediterranean Sea), to assess the possible impact on the local fish stocks and to plan potential management actions. Furthermore, some serious inconsistencies on the minimum lengths of fish caught as defined by law relative to the minimum size of first reproduction are discussed. Since 2014, all anglers exploiting the Portofino MPA have been obliged to fill out a logbook. The compilation of these was not completely satisfactory, when compared with a group of reliable anglers whose catches were accurately monitored, but allowed for estimated yields of about 24 kg/angler/yr. After 15 years of protection, the fish biomass has increased within the Portofino MPA, generating a positive spillover effect. At the same time, it has attracted many anglers whose gross harvesting was estimated at about 8 t/year, representing about the 8% of the total yield of the local small‐scale fishery. 相似文献
73.
74.
Biodegradable plastic films are desirable alternatives to traditional black polyethylene plastic for use as mulches in agroecosystems. Efforts are ongoing to engineer biodegradable plastic mulches that could be incorporated into the soil at the end of the crop season, and decomposed by microorganisms, ultimately to CO2, H2O, and biomass. Whether changes in soil quality occur during or following biodegradation is unknown. An 18-month study evaluated the effects on soil quality following burial of four potentially biodegradable mulches and a no mulch control in high tunnel and open field tomato production systems across three geographically distinct locations (Knoxville, TN; Lubbock, TX; Mount Vernon, WA). The mulch treatments included: two starch-based mulches (BioAgri® Ag-Film and BioTelo Agri); one experimental 100% polylactic acid mulch (Spunbond-PLA-10); one cellulose-based mulch (WeedGuardPlus; positive control); and a negative control (no mulch). The soil management assessment framework (SMAF) was used to calculate a soil quality index (SQI) according to five dynamic soil properties: microbial biomass carbon, β-glucosidase, electrical conductivity, total organic carbon (TOC), and pH. Within the 18-month evaluation period, the effects of the biodegradable mulches on the SQI were minor, and dependent upon production system and time of incubation at all locations. In general, the SQI was higher in the high tunnel systems for some of the mulch treatments at Knoxville and Lubbock but the opposite was true at Mount Vernon. By the final sampling at 18 months, the SQI was lowest for WeedGuardPlus at Lubbock and Mount Vernon but at Knoxville, the WeedGuardPlus SQI was not significantly different from the no mulch control. Of the five SMAF indicators evaluated, soil microbial biomass and β-glucosidase activity were the most responsive to mulch and production systems, supporting the use of these variables as soil quality indicators for short-term changes due to this agricultural management practice. 相似文献
75.
分析了国土资源管理对高分辨率影像的迫切需求,探讨了高分辨率影像处理和分析及应用环节从数据到服务的发展趋势,设计并实现了高分辨率影像服务,并以泰州市国土资源管理为例,验证了影像服务的可行性,最后,展望了高分辨率遥感影像服务的应用前景。 相似文献
76.
van Zyl, J.G., Sieverding, E.G., Viljoen, D.J., Fourie, P.H., 2014. Evaluation of two organosilicone adjuvants at reduced foliar spray volumes in South African citrus orchards of different canopy densities Crop Protection 00:0000–0000.Citrus producers in South Africa generally use high spray volumes (6000 to 16,000 l ha−1) to control pests and diseases adequately for the fresh fruit market. In order to study the benefit of organosilicone adjuvants at reduced spray volumes, trials were conducted with two organo tri-siloxane adjuvants. Two separate spray trials were conducted in the Western and Eastern Cape provinces of South Africa in uniform navel orange orchards. Break-Thru S240 (super-spreader) and Break-Thru Union (spreader-sticker), at recommended dosages per hectare (300 ml ha−1, respectively), were sprayed separately in combination with a yellow fluorescent pigment (1 ml l−1) at a high (20 l tree−1 ≈ 9600 to 12,100 l ha−1, depending on tree and inter-row spacing), medium (14 l tree−1 ≈ 6500 to 8500 l ha−1) and low (8 l tree−1 ≈ 3700 to 4800 l ha−1) spray application volumes. Sprays consisting of the fluorescent pigment in water alone were used as control treatments. Trees were sprayed from both sides with a commercial multi-fan tower sprayer (BSF-Multiwing) at a constant tractor speed (2.4 km h−1) and spray pressure (1500 kPa). The different spray volumes were achieved by using different spray nozzles (TeeJet Disc-Core type; full and hollow cone nozzles D3-DC56/46, D4-DC56/46, D5-DC56/46). Leaves were sampled from six canopy positions (inner and outer canopy position at bottom, middle and top of the tree). Deposition quantity and quality of fluorescent pigment were determined on upper and lower leaf surfaces using fluorometry, digital photomacrography and image analyses. Spray uniformity and efficiency were also compared among treatments. Deposition quantity generally increased with increasing spray volume, but normalised values showed better spray efficiency at lower volumes. In pruned and less dense canopies, a beneficial effect of adjuvants was observed in terms of deposition quantity, efficiency and uniformity, especially at reduced volume applications (14 l tree−1) on the inside and outside of the canopy. Little improvement in deposition quality was generally observed with the use of adjuvants. These benefits were not as evident in very dense canopies, illustrating the importance of canopy management when spraying at reduced volumes. Data obtained from the study is valuable for future improvement in spray application methodology in South Africa and other developing countries. 相似文献
77.
乡镇污水处理厂运行管理相关问题探讨 总被引:1,自引:0,他引:1
乡镇污水处理厂作为环保基础设施建设的重点,普遍存在重建设轻运营的问题。笔者结合重庆市实际情况,重点分析了乡镇污水处理厂运行管理中存在的问题,并有针对性地提出了建议,包括提高收集率、完善末端工艺、专业化运营、改变考核体系、优化污泥处置、加强再生利用和远程在线监控等。 相似文献
78.
农业生产基地项目具有影响范围大、产品服务多元化等特点,涉及行业类别较多,其环境影响评价文件也相对复杂。环境影响评价报告编制单位应充分与建设方进行沟通,熟悉项目建设内容,挖掘项目可能的产生污染的环节和设施,明确环境影响范围和环境敏感点,并对项目损益进行两方面的分析。 相似文献
79.
通过查阅生态公益林的相关文献,总结了生态公益林在宏观和微观方面管理存在的问题,并从健全体系、普及知识、补偿机制等方面提出了加强生态公益林管护对策。 相似文献
80.
外事管理工作对于农业科研单位而言,既是加强国际交流与合作的桥梁,又是吸收国外先进农业技术、管理经验的重要渠道之一。文章阐述了丹东农业科学院外事管理工作取得的成效,分析了农业科研单位外事管理工作存在的问题,并针对问题提出了解决对策,在此基础上,进一步提出了建立并完善外事管理规章制度、积极开展多领域的对外交往活动、促进面向国际市场的科研成果转化等促进农业科研单位外事管理水平提升的建议。 相似文献