全文获取类型
收费全文 | 8418篇 |
免费 | 571篇 |
国内免费 | 718篇 |
专业分类
林业 | 199篇 |
农学 | 568篇 |
基础科学 | 1040篇 |
1488篇 | |
综合类 | 5530篇 |
农作物 | 252篇 |
水产渔业 | 83篇 |
畜牧兽医 | 172篇 |
园艺 | 102篇 |
植物保护 | 273篇 |
出版年
2024年 | 32篇 |
2023年 | 179篇 |
2022年 | 217篇 |
2021年 | 195篇 |
2020年 | 231篇 |
2019年 | 240篇 |
2018年 | 148篇 |
2017年 | 236篇 |
2016年 | 335篇 |
2015年 | 328篇 |
2014年 | 529篇 |
2013年 | 539篇 |
2012年 | 759篇 |
2011年 | 842篇 |
2010年 | 610篇 |
2009年 | 533篇 |
2008年 | 498篇 |
2007年 | 607篇 |
2006年 | 514篇 |
2005年 | 468篇 |
2004年 | 322篇 |
2003年 | 286篇 |
2002年 | 200篇 |
2001年 | 178篇 |
2000年 | 175篇 |
1999年 | 124篇 |
1998年 | 75篇 |
1997年 | 75篇 |
1996年 | 39篇 |
1995年 | 45篇 |
1994年 | 28篇 |
1993年 | 35篇 |
1992年 | 15篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 2篇 |
排序方式: 共有9707条查询结果,搜索用时 31 毫秒
41.
42.
43.
44.
景电灌区农田防护林网是景电灌区防护林体系的重要组成部分,通过调查景电灌区农田防护林衰败现状,分析退化原因,提出优化改造模式,为景电灌区农田防护林更新改造从而发挥可持续效益提供技术支撑。结果表明,1)以杨树为主要树种的景电灌区农田防护林网目前呈严重衰败状态,尤其在个人管护的区域,残缺断代现象严重,部分地方甚至基本消失;2)病虫危害,耗水、胁地严重而被砍伐,耕地次生盐渍化导致树木生长不良、枯死,树种单一、结构不合理,管理不到位等是造成农田防护林衰败的主要原因;3)三倍体毛白杨(Populus tomentosa)、廊坊(P.langfanggensis)、樟子松(Pinus sylvestris)、刺槐(Robinia pseucdoacacia)、白蜡(Fraxinus chinensis)、鸣山大枣(Jujube minshan)等树种为该地区农田防护林建设的适宜树种,可采用农田防护林杨树优势树种轮换、针叶常绿树种优化改造、生态经济型防护林网营造等模式对景电灌区农田防护林网进行更新改造。农田防护林网的改造,将对完善防护林体系,保障景泰绿洲的安全产生重要意义。 相似文献
45.
Clayton T Larue Michael Goley Lei Shi Artem G Evdokimov Oscar C Sparks Christine Ellis Andrew M Wollacott Timothy J Rydel Coralie E Halls Brook Van Scoyoc Xiaoran Fu Jeffrey R Nageotte Adewale M Adio Meiying Zheng Eric J Sturman Graeme S Garvey Marguerite J Varagona 《Pest management science》2019,75(8):2086-2094
46.
Margarita Menndez Meritxell Abril Miriam Colls Xavier D. Quintana 《水产资源保护:海洋与淡水生态系统》2019,29(3):450-460
- Aside from structural indicators, functional indicators have been suggested as a tool for assessing the health of transitional water ecosystems. The aim of this study was to assess the potential for the use of plant litter decomposition as a functional indicator of ecosystem health in coastal lagoons.
- A field experiment was conducted to assess the decomposition rate of Ruppia maritima enclosed in coarse and fine mesh litterbags and incubated in 10 Mediterranean coastal lagoons that conform to a gradient of ecological status produced by anthropogenic impacts as determined by a structural quality index.
- The microbial decomposition rate in fine mesh litterbags increased linearly along the ecological gradient. However, this relationship was not observed for the overall decomposition rate in coarse mesh bags.
- Decomposition rates in coarse mesh bags were negatively related to macroinvertebrate diversity, indicating that, in transitional habitats, such as coastal lagoons, high biodiversity is not a prerequisite for successful ecosystem functioning.
- The results suggest that functional indicators, such as the microbial litter decomposition process, should be used in addition to structural ones to detect anthropogenic‐derived environmental perturbations in coastal lagoons.
47.
- The African manatee has been poorly studied throughout its range and is heavily hunted. This study aimed at discerning patterns in manatee sightings and emerging conflicts with humans, as well as the local perception of manatees, outside the southern periphery of Korup National Park, Cameroon.
- The study investigated whether patterns in manatee sightings and manatee‐related conflicts differ between aquatic systems in southern Korup, and which demographic variables determine perceptions of the manatee in the study area. For this purpose, the study used a three‐stage stratified random sampling design with a structured questionnaire to survey 101 local fishers.
- The reported patterns of manatee sightings and manatee‐related conflicts were as follows: in the Nyangorobe River during the wet season only, where crop raiding and net destruction by manatees were reported; in the Ndian River and the mangrove estuary only during the dry season, where fish theft and net damage were reported; and in the Moko River during both seasons, where crop raiding, fish theft, and net destruction were reported. Reducing these conflicts is likely to increase local support for the conservation of manatees, because fishermen kill them in response to net destruction and fish loss.
- Most reported sightings were at waterway intersections and river bends, suggesting that waterway connectivity is important to manatees for dispersal, foraging, and escape from danger.
- The log‐odds probability of negative perception decreased significantly with awareness of manatee protected status but increased with age and primary or higher education level. These findings have implications for community outreach focused on raising awareness of the importance of manatee conservation by schoolchildren and the public.
48.
为了解重庆市涪陵区的酸雨变化特征及降水对酸雨pH值的影响,本研究采用2005—2014年涪陵区的酸雨和降水数据,应用统计学方法分析降水与酸雨pH值月、季、年变化的相关性。结果表明:涪陵区酸性降水频率为42.13%,以弱酸性降水为主,自2011年起几乎无强酸性降水发生;酸雨pH值秋季最小、冬季最大,6月最小,7月最大。降水总量、有效降水日数和大量级降水占比都会影响酸雨的月、季、年变化,并不能单独由一个指标来说明酸雨的变化规律;其中,大量级降水占比对酸雨pH值影响最大。上述结果表明,了解降水与酸雨pH值的变化规律为有效防治酸雨和减少酸雨的危害提供了一定的依据。 相似文献
49.
50.
以农业信息化推进山西特色农业发展 总被引:1,自引:0,他引:1
段亚利 《农业图书情报学刊》2011,23(3):5-7
叙述了山西特色农业在"十二五"经济转型时期的特殊地位和作用,并详细分析了现状,提出农业信息化在推进山西特色农业发展的重要性及采取的措施。 相似文献