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   455篇
  免费   25篇
  国内免费   36篇
林业   81篇
农学   28篇
基础科学   26篇
  42篇
综合类   195篇
农作物   13篇
水产渔业   14篇
畜牧兽医   38篇
园艺   1篇
植物保护   78篇
  2023年   12篇
  2022年   16篇
  2021年   18篇
  2020年   21篇
  2019年   31篇
  2018年   7篇
  2017年   13篇
  2016年   41篇
  2015年   17篇
  2014年   28篇
  2013年   23篇
  2012年   34篇
  2011年   28篇
  2010年   38篇
  2009年   27篇
  2008年   15篇
  2007年   19篇
  2006年   26篇
  2005年   12篇
  2004年   11篇
  2003年   8篇
  2002年   14篇
  2001年   7篇
  2000年   7篇
  1999年   9篇
  1998年   5篇
  1997年   7篇
  1996年   1篇
  1995年   8篇
  1994年   1篇
  1993年   1篇
  1992年   2篇
  1991年   2篇
  1990年   2篇
  1989年   4篇
  1986年   1篇
排序方式: 共有516条查询结果,搜索用时 15 毫秒
71.
以学生自评学习任务表单为构架,在高校《信息资源检索与利用》课程中运用翻转课堂的教学模式,提升学生的学习兴趣,强化知识学习与内化吸收过程。设计“学生自评学习任务表单”,重构教学内容结构为单个具体可执行的任务,师生围绕着学习任务表单进行课上课下的教学协调。  相似文献   
72.
A Nowak  S Nowak  M Nobis  A Nobis 《Weed Research》2014,54(6):635-648
Intensification of agriculture has significantly diminished the populations of segetal weeds worldwide in recent decades. Remarkable changes to the entire flora and vegetation of man‐made habitats are being observed in agroecosystems. The present study analyses, for the first time, the threat status of segetal weeds in Tajikistan. A group of 871 weed species were evaluated against IUCN criteria. The assessment of threat status revealed that 214 weed taxa have to be regarded as threatened in Tajikistan, including 18 endemic and four subendemic plants. Five species have been classified as extinct, 27 as critically endangered, 27 as endangered, 39 as vulnerable, 34 as near threatened and 44 as in the ‘least concern’ category. For 38 species, the threat level was not possible, due to lack of data. The most threatened group of taxa is related to rice paddy fields. Numerous losses and disappearances were also observed in cereal communities. Percentages of threatened species in different chorological groups amounted to 58% in the Irano–Turanian, 17% in the Pluriregional, 11% in the Mediterranean, 9.5% in the Cosmopolitan and 4% in the Euro–Siberian species group. Assessment of the threatened status of the rich segetal flora of Tajikistan affords the opportunity to raise awareness of the value of this group of species in the country and may be useful in the conservation management of arable habitats. The results show that even though agriculture in Tajikistan is still based on traditional management and manual work, weed control causes a serious threat to its segetal flora.  相似文献   
73.
Common voles (Microtus arvalis) are common small mammals in some European landscapes. They can be a major rodent pest in European agriculture and they are also a representative generic focal small herbivorous mammal species used in risk assessment for plant protection products. In this paper, common vole population dynamics, habitat and food preferences, pest potential and use of the common vole as a model small wild mammal species in the risk assessment process are reviewed. Common voles are a component of agroecosystems in many parts of Europe, inhabiting agricultural areas (secondary habitats) when the carrying capacity of primary grassland habitats is exceeded. Colonisation of secondary habitats occurs during multiannual outbreaks, when population sizes can exceed 1000 individuals ha?1. In such cases, in‐crop common vole population control management has been practised to avoid significant crop damage. The species' status as a crop pest, high fecundity, resilience to disturbance and intermittent colonisation of crop habitats are important characteristics that should be reflected in risk assessment. Based on the information provided in the scientific literature, it seems justified to modify elements of the current risk assessment scheme for plant protection products, including the use of realistic food intake rates, reduced assessment factors or the use of alternativee focal rodent species in particular European regions. Some of these adjustments are already being applied in some EU member states. Therefore, it seems reasonable consistently to apply such pragmatic and realistic approaches in risk assessments for plant protection products across the EU. © 2013 Society of Chemical Industry  相似文献   
74.
系统调查了武汉市解放公园、月湖公园以及南湖等城市园林湿地植物上的昆虫群落组成,已鉴定出12目,52科,86种昆虫.调查结果为进一步研究园林湿地植物的昆虫群落更替以及湿地植物害虫综合治理奠定了基础.  相似文献   
75.
夫妻关系期间所获得的财产属法定共同财产,夫妻作为共有人对其共同共有财产享有共同处分权。对夫妻共同财产的保护,既要从道德层面来约束自身,体恤他人,又要从制度、法律层面加以完善、强化。  相似文献   
76.
盾水螨总科是水螨的一大类群,其下阶元间分类系统和系统发育存在争议,目前世界各国包括中国对该类群分类学和生物学的研究尚欠深入.对盾水螨总科生物学和分类学研究的发展、现状及我国研究情况进行了综述,简要分析了中国区系,展望了盾水螨总科的发展趋势.  相似文献   
77.
中国草品种审定登记工作进展   总被引:2,自引:2,他引:0  
介绍了中国草品种审定登记机构的发展与变革、草品种审定标准体系建设、国家草品种区域试验网建设、草品种审定登记情况等。截至2010年,全国草品种审定委员会已审定登记草品种434个,其中引进品种138个,育成品种161个,野生栽培品种86个,地方品种49个。在审定标准制定、国家草品种区域试验网络建设和品种审定数量等方面均有所突破。同时,对当前中国草品种审定工作中存在的问题进行了讨论,并提出了改进和完善的建议。  相似文献   
78.
This paper describes a computer vision based model for object detection that can serve as a preliminary step in fruit prognosis, which involves the estimation of the number, diameter and yield of apple fruits. In order to overcome the recognition unreliability in uncontrolled environments caused by uneven illumination conditions, partly occluded surfaces, and similar background features, we rely on a combination of the object's colour, texture and 3D shape properties. In our research, we apply colour segmentation to multiple scene snapshots to separate potential regions from the background and verify them first with texture analysis and second by reconstructing them to 3D space. By analysing all three distinct features (colour, texture and 3D shape) of possible areas, we can safely conclude if they represent fruits we are looking for. Once we detect and verify all areas representing fruits, we can measure their size and model estimated fruit yield.  相似文献   
79.
This paper establishes a system to support the dose evaluation part of the pesticide registration process so that growers can make more efficient use of different spraying products across a broad range of European orchards and vineyards. The system comprises: a dose adjustment model and a small database of standard target structures (i.e., regional exemplars where efficient and efficacious use of pesticide is obtained at the label dose rate). The model includes a generalised scaling group relationship between the parameters that describe: sprayer output, target row structure and spray volume deposit. The upper limit for dose adjustment is based on the environmental fate of pesticide and this is represented in the model by the ratio of maximum ground area dose rate to minimum efficacious deposit which is normalised for alignment with target structure measurements. The model is used to examine the leaf-wall-area dose rate recently proposed by the European agrochemical manufacturing industry for harmonising pesticide registration. Good agreement is demonstrated between published measurements and model predictions of ground area and leaf-wall-area dose rate variation at constant deposit for a wide range of target structures (i.e., English pome- and stone-fruit orchards and Italian vineyards). The results are used to establish standard target structures for spraying products with different uses. These standards are needed by regulators to: translate between the different methods of expressing dose rate and improve the accuracy of label dose recommendations. The standards are also needed by growers to enable: more accurate calibration of spraying equipment and prediction of the optimum adjustment of label dose rate for different orchards and vineyards.  相似文献   
80.
江苏省天蛾科昆虫(鳞翅目:天蛾总科)   总被引:1,自引:0,他引:1  
通过对文献资料的查找与汇总,总结出江苏省天蛾科昆虫32种18亚种,分属于5个亚科、27个属。记述了每个种类的寄主、异名、别名及分布。  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