全文获取类型
| 收费全文 | 201篇 |
| 免费 | 33篇 |
专业分类
| 林业 | 4篇 |
| 农学 | 2篇 |
| 35篇 | |
| 综合类 | 23篇 |
| 农作物 | 6篇 |
| 畜牧兽医 | 134篇 |
| 园艺 | 3篇 |
| 植物保护 | 27篇 |
出版年
| 2024年 | 2篇 |
| 2023年 | 2篇 |
| 2022年 | 1篇 |
| 2021年 | 1篇 |
| 2020年 | 6篇 |
| 2019年 | 22篇 |
| 2018年 | 30篇 |
| 2017年 | 7篇 |
| 2016年 | 12篇 |
| 2015年 | 10篇 |
| 2014年 | 10篇 |
| 2013年 | 15篇 |
| 2012年 | 11篇 |
| 2011年 | 8篇 |
| 2010年 | 9篇 |
| 2009年 | 5篇 |
| 2008年 | 10篇 |
| 2007年 | 16篇 |
| 2006年 | 7篇 |
| 2005年 | 11篇 |
| 2004年 | 7篇 |
| 2003年 | 2篇 |
| 2002年 | 7篇 |
| 2001年 | 4篇 |
| 2000年 | 3篇 |
| 1999年 | 3篇 |
| 1998年 | 1篇 |
| 1997年 | 4篇 |
| 1995年 | 3篇 |
| 1994年 | 3篇 |
| 1991年 | 1篇 |
| 1989年 | 1篇 |
排序方式： 共有234条查询结果，搜索用时 15 毫秒
41.
《Land Degradation u0026amp; Development》2017,28(7):2030-2038
Rangelands are vital for wildlife conservation and socio‐economic well‐being, but many face widespread degradation because in part of poor grazing management practices. Planned grazing management, typically involving time‐controlled rotational livestock grazing, is widely touted as a tool for promoting sustainable rangelands. However, real‐world assessments of its efficacy have been lacking in communal pastoral landscapes globally, and especially in Africa. We performed landscape‐scale assessment of the effects of planned grazing on selected vegetation, wildlife, and cattle attributes across wide‐ranging communally managed pastoral rangelands in northern Kenya. We found that planned grazing enhanced vegetation condition through a 17% increase in normalized difference vegetation index, 45–234% increases in herbaceous vegetation foliar cover, species richness and diversity, and a 70% reduction in plant basal gap. In addition, planned grazing increased the presence (44%) and species richness (53%) of wild ungulates and improved cattle weight gain (>71%) during dry periods when cattle were in relatively poor condition. These changes occurred relatively rapidly (within 5 years) and despite grazing incursion incidents and higher livestock stocking rates in planned grazing areas. These results demonstrate, for the first time in Africa, the positive effects of planned grazing implementation in communal pastoral rangelands. These improvements can have broad implications for biodiversity conservation and pastoral livelihoods. Copyright © 2017 John Wiley & Sons, Ltd. 相似文献
42.
Larry Larson Douglas E. Johnson Marie Wilson Kerry Wilson Mounir Louhaichi John Williams 《Animal Science Journal》2017,88(3):553-558
The spatial occupancy patterns and activity of cattle grazing three riparian pastures was investigated in northeastern Oregon using Global Positioning System (GPS) collars logging at 1‐sec intervals. Cattle consistently selected plant communities as grazing areas that had forage in sufficient volume to meet their requirements and favored communities as resting areas that were dry and open. Cattle were stationary for more than 50% of the time in each pasture and consistently rested between dark and 04:00 hours. Interaction with stream channels was found to be 1‐2% of total occupancy time and occurred on less than 10% of channel length. Cattle were indifferent or avoided channel areas relative to their area and, when in this zone, they spent most of their time moving not resting. Cattle did not prefer the stream bank zone and spent only 2% of their time in that zone. When occupied, the stream bank zone was used as a travel corridor to gain access to water or cross the channel to access other pasture areas. These results are in contrast with the general belief that cattle are a primary occupant of the stream bank/channel area; additional research is needed to define factors influencing cattle occupancy. 相似文献
43.
Cody F. CREECH Blair L. WALDRON Corey V. RAMSOM Dale R. ZOBELL Joseph Earl CREECH 《农业科学与工程前沿(英文版)》2018,5(1):71
Forage kochia (Bassia prostrata) is used for rangeland reclamation and livestock and wildlife forage, but limited research has been conducted on its seed production. Therefore, this research evaluated the effect of harvest date on seed weight, germination, and seed yield of forage kochia subspecies virescens and grisea. Seed was harvested from individual plants for 3 years during October, November, and December. October harvest had the lightest 100-seed weights, with the November harvest slightly heavier than December, for most accessions. Cultivar Snowstorm and breeding line Sahsel, both subsp. grisea, had the greatest 100-seed weights in November, 155 and 143 mg, respectively, whereas, cv. Immigrant (subsp. virescens), the standard for forage kochia, ranked among the least for 100-seed weight. For most accessions, germination was lowest from the October harvest (11%–43%), with greater germination with November and December harvested seeds (43%–64%). Viable seed yields were greatest in November with the exception of two accessions, which peaked in October, indicating earlier maturity. Results indicate that forage kochia usually reaches optimum seed maturity by early November, after plants are exposed to freezing temperatures; however, earlier maturing accessions exist in both subspecies virescens and grisea. 相似文献
44.
Dawn M. BROWNING Sheri SPIEGAL Richard E. ESTELL Andres F. CIBILS Raul H. PEINETTI 《农业科学与工程前沿(英文版)》2018,5(1):44
In water-limited landscapes, patterns in primary production are highly variable across space and time. Livestock grazing is a common agricultural practice worldwide and a concern is localized overuse of specific pasture resources that can exacerbate grass losses and soil erosion. On a research ranch in New Mexico with average annual rainfall of 217 mm, we demonstrate with a quantitative approach that annual seasons vary greatly and examine foraging patterns in Angus-Hereford (Bos taurus) cows. We define five seasonal stages based on MODIS NDVI: pre-greenup, greenup, peak green, drydown and dormant, and examine livestock movements in 2008. Daily distance traveled by cows was greater and foraging area expanded during periods with higher precipitation. A regression model including minimum NDVI, rainfall and their interaction explained 81% of the seasonal variation in distance traveled by cows (P<0.01). Cows explored about 81 ha·d−1 while foraging, but tended to explore smaller areas as the pasture became greener (greenup and peak green stages). Cows foraged an average of 9.7 h daily and spent more time foraging with more concentrated search patterns as pastures became greener. Our findings suggest that phenological context can expand the capacity to compare and integrate findings, and facilitate meta-analyses of grazing studies conducted at different locations and times of year. 相似文献
45.
J. Ibaez J. M. Valderrama V. Papanastasis C. Evangelou J. Puigdefabregas 《Land Degradation u0026amp; Development》2014,25(5):468-482
This paper presents an annual multidisciplinary, non‐spatial model which formalizes the relationships linking the dynamics of shrubs, herbs, soil, livestock and farmers' behaviour with possible exogenous drivers of degradation, such as weather and prices. The model does not represent a pasture–livestock system but a shrub–soil one and is applied to a rangeland in Lagadas County (Northern Greece). A sensitivity analysis of the model is also presented. It shows that livestock, in general, and factors increasing farmers' profits, in particular, are currently helping to combat shrub invasion in Lagadas while having low impacts on erosion rates. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
46.
R. Setia M. Lewis P. Marschner R. Raja Segaran D. Summers D. Chittleborough 《Land Degradation u0026amp; Development》2013,24(4):375-384
We hypothesised that digital mapping of various forms of salt‐affected soils using high resolution satellite imagery, supported by field studies, would be an efficient method to classify and map salinity, sodicity or both at paddock level, particularly in areas where salt‐affected patches are small and the effort to map these by field‐based soil survey methods alone would be inordinately time consuming. To test this hypothesis, QuickBird satellite data (pan‐sharpened four band multispectral imagery) was used to map various forms of surface‐expressed salinity in an agricultural area of South Australia. Ground‐truthing was performed by collecting 160 soil samples over the study area of 159 km2. Unsupervised classification of the imagery covering the study area allowed differentiation of severity levels of salt‐affected soils, but these levels did not match those based on measured electrical conductivity (EC) and sodium adsorption ratio (SAR) of the soil samples, primarily because the expression of salinity was strongly influenced by paddock‐level variations in crop type, growth and prior land management. Segmentation of the whole image into 450 paddocks and unsupervised classification using a paddock‐by‐paddock approach resulted in a more accurate discrimination of salinity and sodicity levels that was correlated with EC and SAR. Image‐based classes discriminating severity levels of salt‐affected soils were significantly related with EC but not with SAR. Of the spectral bands, bands 2 (green, 520–600 nm) and 4 (near‐infrared, 760–900 nm) explained the majority of the variation (99 per cent) in the spectral values. Thus, paddock‐by‐paddock classification of QuickBird imagery has the potential to accurately delineate salinity at farm level, which will allow more informed decisions about sustainable agricultural management of soils. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
47.
以像元二分法模型为基础,构建了基于改进归一化植被指数(NDVI)的植被覆盖度定量估算模型,并利用MODIS卫星遥感数据,基于3S技术(GIS,RS,GPS)空间分析功能,分级计算得到了甘南2002,2004,2006,2008年的草地植被覆盖度,分析了甘南2002-2008年植被覆盖度变化的空间动态演变过程和趋势。结果表明,2002-2008年,甘南植被覆盖度质量总体呈下降趋势,一级盖度植被的退化比较严重,草地植被的演变情况主要由优等植被覆盖(一、二级)向低等植被覆盖(四、五级)演变。研究结果揭示了甘南州草地退化状况日趋严重的事实,为相关研究和政府草地管理提供了有效依据。 相似文献
48.
植物病害是草地生产力和可持续发展的关键限制因素之一,目前国内外多关注以紫花苜蓿Medicago sativa为代表的栽培草地植物病害,而天然草原病害的相关研究非常薄弱,严重限制了草原植物病害防控技术的研发和生产实践。该文系统综述了天然草原植物病害的种类及其主要寄主植物,继而梳理了病害发生、发展的规律以及生物因素和非生物因素对病害的影响,在此基础上分析了植物病害对天然草原生态系统演替的作用,着重讨论了植物病害对草地生产力和植物群落结构的影响,并对未来研究的重点和方向进行了展望,提出了应综合生态学思想并着重研发绿色调控技术的建议。 相似文献
49.
对青南地区玉树县境内2牧场的草地植被及成年母牦牛的采食行为和选择性采食习性及其关系进行了探讨,结果表明：B牧场禁牧区的生物量显著高于A牧场的禁牧区及A,B牧场的放牧区（P〈0.05）,B牧场的可食植物量显著高于A牧场（P〈0.05）,A牧场的可食植物量只占地上生物量的一半以下;B牧场分别以小嵩草,矮嵩草,披碱草,针茅,蒲公英等优良牧草为优势种,次优势种,而A牧场以线叶嵩草为优势种,凤毛菊,狼毒,黄帚橐吾等毒杂草及早熟禾等为次优势种;B牧场以小嵩草、矮嵩草等莎草科和为主要采食植物,而在A牧场除以莎草科植物为主要采食植物外,由于可食牧草量的不足,还采食一些本不喜食的植物。矮嵩草和小嵩草是牦牛最喜食,选择性最高的植物;斑块内采食口数A牧场为50.6 bite/patch显著少于B牧场的81.1 bite/patch（P〈0.01）;斑块内采食站数A牧场为8.4 FS/patch显著多于B牧场的5.2 FS/patch（P〈0.001）;采食站内采食口数A牧场为6.6 bite/FS显著少于B牧场的17.4 bite/FS（P〈0.001）;采食速度A牧场为1.32 bites/sec显著慢于B牧场的1.46 bites/sec（P〈0.01）。放牧草地的食物资源的匮乏,使放牧牦牛的食物选择性降低,采食行为的内容变劣,A牧场草地处于严重退化状态;牦牛处于缺营养状态,草地的退化对牦牛的生产性能有很大的影响。 相似文献
50.
为明确蝗虫微孢子对蝗虫的持续控制,2015年在青海省开展了蝗虫微孢子防治草原蝗虫的试验和连续跟踪调查。结果表明,施用蝗虫微孢子前后温性和高寒草原蝗区天敌种类无明显变化,但部分天敌类群所占比例发生了变化,施用蝗虫微孢子2、3、4周后,温性草原中寄生蝇所占比例分别显著增加了330.6%、752.8%、752.8%,高寒草原中寄生蝇所占比例分别显著增加了108.1%、309.9%、310.8%,温性草原中芫菁所占比例分别显著下降了43.5%、45.5%、75.5%,高寒草原中芫菁所占比例分别显著下降了54.2%、77.2%、76.3%。施用蝗虫微孢子2、3和4周后,温性草原的Shannon指数比防治前分别显著增加了5.7%、7.0%、3.8%,Pielou指数比防治前分别显著增加了6.2%、6.2%、3.7%,Simpson指数比防治前分别显著增加了5.4%、6.8%、4.1%;施用蝗虫微孢子2周后,高寒草原的Shannon指数、Pielou指数和Simpson指数比防治前分别显著升高了4.8%、5.4%、3.8%,施用3周后,3个天敌群落多样性指数比防治前分别增加了1.8%、1.3%、2.2%,但Shannon指数和Simpson指数与防治前无显著差异,而Pielou指数比防治前显著增加,施用4周后,3个指数均与防治前无显著差异。施用蝗虫微孢子2、3和4周后,天敌群落布雷柯蒂斯距离与防治前差异显著,而重复样区间的布雷柯蒂斯距离在整个调查期无显著变化。表明蝗虫微孢子施用后对不同生态类型草原天敌群落多样性有一定的保护作用。 相似文献