全文获取类型
| 收费全文 | 115篇 |
| 免费 | 34篇 |
| 国内免费 | 2篇 |
专业分类
| 林业 | 7篇 |
| 农学 | 5篇 |
| 基础科学 | 24篇 |
| 24篇 | |
| 综合类 | 73篇 |
| 农作物 | 5篇 |
| 水产渔业 | 2篇 |
| 畜牧兽医 | 2篇 |
| 园艺 | 5篇 |
| 植物保护 | 4篇 |
出版年
| 2024年 | 6篇 |
| 2023年 | 1篇 |
| 2022年 | 2篇 |
| 2021年 | 4篇 |
| 2020年 | 1篇 |
| 2019年 | 1篇 |
| 2017年 | 3篇 |
| 2016年 | 6篇 |
| 2015年 | 5篇 |
| 2014年 | 4篇 |
| 2013年 | 6篇 |
| 2012年 | 13篇 |
| 2011年 | 15篇 |
| 2010年 | 9篇 |
| 2009年 | 7篇 |
| 2008年 | 11篇 |
| 2007年 | 9篇 |
| 2006年 | 10篇 |
| 2005年 | 5篇 |
| 2004年 | 5篇 |
| 2003年 | 2篇 |
| 2002年 | 1篇 |
| 2000年 | 3篇 |
| 1999年 | 3篇 |
| 1998年 | 3篇 |
| 1997年 | 4篇 |
| 1995年 | 2篇 |
| 1994年 | 1篇 |
| 1993年 | 1篇 |
| 1992年 | 2篇 |
| 1991年 | 3篇 |
| 1990年 | 1篇 |
| 1989年 | 1篇 |
| 1988年 | 1篇 |
排序方式： 共有151条查询结果，搜索用时 15 毫秒
1.
Crop models are widely used in agricultural impact studies. However, many studies have reported large uncertainties from single-model-based simulation analyses, suggesting the need for multi-model simulation capabilities. In this study, the APSIM-Nwheat model was integrated into the Decision Support System for Agro-technology (DSSAT), which already includes two wheat models, to create multi-model simulation capabilities for wheat cropping systems analysis. The new model in DSSAT (DSSAT-Nwheat) was evaluated using more than 1000 observations from field experiments of 65 treatments, which included a wide range of nitrogen fertilizer applications, water supply (irrigation and rainout shelter), planting dates, elevated atmospheric CO2 concentrations, temperature variations, cultivars, and soil types in diverse climatic regions that represented the main wheat growing areas of the world.DSSAT-Nwheat reproduced the observed grain yields well with an overall root mean square deviation (RMSD) of 0.89 t/ha (13%). Nitrogen applications, water supply, and planting dates had large effects on observed biomass and grain yields, and the model reproduced these crop responses well. Crop total biomass and nitrogen uptake were reproduced well despite relatively poor simulations of observed leaf area measurements during the growing season. The low sensitivity of biomass simulations to poor simulations of leaf area index (LAI) were due to little changes in intercepted solar radiation at LAI >3 and water and nitrogen stress often limiting photosynthesis and growth rather than light interception at low LAI.The responses of DSSAT-Nwheat to temperature variations and elevated atmospheric CO2 concentrations were close to observed responses. When compared with the two other DSSAT-wheat models (CERES and CROPSIM), these responses were similar, except for the responses to hot environments, due to different approaches in modeling heat stress effects.The comprehensive evaluation of the DSSAT-Nwheat model with field measurements, including a comparison with two other DSSAT-wheat models, created a multi-model simulation platform that allows the quantification of model uncertainties in wheat impact assessments. 相似文献
2.
The effects of three set-sizes (12.5, 17.5 and 22.5 mm in diameter) and seven storage temperatures (0, 5, 10, 15, 20, 25 and 30 °C) on bolting, bulbing and seed yield in two onion (Allium cepa L.) cultivars ‘Hygro’ and ‘Delta’ were investigated. The incidence of bolting increased linearly with set-size and curvi-linearly with decreasing storage temperature. Time to inflorescence emergence and floret opening showed a curvi-linear response to storage temperature with the earliest inflorescence emergence and floret opening occurring at 5 °C and the latest at 30 °C for ‘Hygro’ and at 25 °C for ‘Delta’. Seed yield per umbel also showed a curvi-linear response to storage temperature with the lowest seed yield occurring at 30 °C for ‘Hygro’ and at 25 °C for ‘Delta’ and the highest seed yield at 5 °C. For a seed crop, storage of large sets (22.5 mm) of these cultivars at 5 °C for 120 days appeared to be optimum with 5–12% higher seed yield per umbel than that of 90 days storage. Bulb yield showed a curvi-linear response to storage temperature with the highest bulb yield occurring at 25 °C and the lowest at 5 °C. 相似文献
3.
Shigeya Maeda Toshihiko Kawachi Koichi Unami Junichiro Takeuchi Tomoki Izumi Syunsuke Chono 《Paddy and Water Environment》2009,7(3):163-175
A fuzzy optimization model is developed to allocate allowable total nitrogen (T-N) loads to distributed nonpoint sources (NPSs)
and point sources (PSs) in a watershed for river water quality management using the linear programing technique. The watershed
is divided into uniform grid cells on which T-N loads issuing from NPSs such as paddy fields, upland crop fields and cities
are controlled. A geographic information system integrated with the digital elevation model facilitates computation of route
lengths of surface and subsurface flows from cells to a river running through the watershed. The T-N loads discharged from
their sources are assumed to decay, subject to distance-related first-order kinetics. As management goals, maximizations of
total allowable NPS loads, total allowable PS loads and total yield of rice are considered from environmental and economic
viewpoints. A prime constraint is an effluent limitation standard for the aggregate amount of loads that arrive at the downstream
end of the river. The fuzzy sets theory helps appropriately describe vague attitudes of decision-makers (i.e., stakeholders
and management authorities) in terms of constraints and conflicting goals. An application of the fuzzy optimization model,
developed as an improvement over our last nonfuzzy model, to a real watershed in Shiga prefecture, Japan, demonstrates that
the fuzzy model embodies our last model, and is capable of creating management alternatives for T-N load allocation in a more
practical and flexible manner. 相似文献
4.
本文以不同于常规的方法定义了二维随机集,及其联合分布、联合落影测度、联合落影函数,给出了成为二维随机集的充要条件。讨论了二维模糊集与随机集落影的关系。 相似文献
5.
M. Haapalainen S. Latvala E. Kuivainen Y. Qiu M. Segerstedt A. O. Hannukkala 《Plant pathology》2016,65(8):1310-1320
In recent years in Finland, Fusarium infections in onions have increased, both in the field and in storage, and Fusarium species have taken the place of Botrytis as the worst pathogens causing post‐harvest rot of onion. To study Fusarium occurrence, samples were taken from onion sets, harvested onions and also from other plants grown in the onion fields. Isolates of five Fusarium species found in the survey were tested for pathogenicity on onion. Fusarium oxysporum was frequently found in onions and other plants, and, of the isolates tested, 31% caused disease symptoms and 15% caused growth stunting in onion seedlings. Fusarium proliferatum, a species previously not reported in Finland, was also identified. Over 50% of the diseased onion crop samples were infected with F. proliferatum, and all the F. proliferatum isolates tested were pathogenic to onion. Thus, compared to F. oxysporum, F. proliferatum seems to be more aggressive on onion. Also some of the F. redolens isolates were highly virulent, killing onion seedlings. Comparison of the translation elongation factor 1α gene sequences revealed that the majority of the aggressive isolates of F. oxysporum f. sp. cepae group together and are distinct from the other isolates. Incidence and relative proportions of the different Fusarium species differed between the sets and the mature bulbs. More research is required to determine to what extent Fusarium infections spoiling onions originate from infected onion sets rather than the field soil. 相似文献
6.
《河北农业大学学报(农林教育版)》2024,26(4):33-43
电子商务成为实现数字经济与乡村振兴的重要发展引擎,探究电子商务对乡村振兴的影响与提升路径具有重大的现实意义。以中国31个省级政府作为研究样本,运用模糊集定性比较分析方法(fsQCA),探究电子商务对乡村振兴水平的影响。研究发现:电子商务各条件变量均不是提升乡村振兴水平的必要条件,而是通过组态的方式来提升乡村振兴水平。电子商务提升乡村振兴水平高组态存在4条推动路径,即“组织推动型”“环境推动型”“技术—组织—环境推动型”和“技术—环境推动型”。据此,各地区应当根据自身实际发展情况,因地制宜,从自身所具有的优势和资源禀赋出发,制定符合本地区实际情况的电子商务助推乡村振兴水平提升策略,不断加强基础设施、人力资源、发展规模、政府支持和市场环境各要素之间的协调作用。 相似文献
7.
城乡结合带是流域复杂多样污染物的主要源汇区。科学识别该类区域的污染物入河湖特征,并根据河湖水功能区划等环境保护目标要求,优化区域城乡发展规模与种养结构,对河湖保护和综合治理具有重要意义。以四湖流域中下区这一典型城乡结合带为研究对象,采用改进输出系数法与浓度法,分别计算2008-2018年各市县的非点源与点源污染物入河量,得到污染物入河时空分布规律与特征,探明洪湖市农业种养是主要贡献源区之一。通过建立区间模糊多目标规划模型,对低、高两种节水控污水平下2030年种养结构及城乡规模进行了优化。结果表明：①2008-2018年研究区TP、COD入河量呈增高趋势,分别增加3.86%、11.11%,而NH3-N减少14.91%,TN减少0.4%,各类污染物入河总量最大值来源由监利市转移至洪湖市,研究区污染主控来源由城市污染逐渐转为农村污染,应加强农村面源污染的治理;②2030年研究区优化后节水减排效果显著,在高节水控污水平下荆州区域和潜江区域的万元GDP用水量比2018年最多下降42.2%和61.7%,TN、TP、COD、NH3-N比2018年最多分别削减47.9%、50.5%、56.2%、57.3%;③2030年研究区内水田种植应转变为旱作或虾稻种养模式,畜禽养殖量缩减20.9%,水产养殖量增加8.9%,农村人口缩减48.5%~49.4%,城镇人口增加76.2%~77.7%,工业增加值提高183.4%~183.9%。研究结果为洪湖水环境治理和四湖流域污染物入河总量控制提供了科学依据。 相似文献
8.
在经典粗糙集模型的基础上引入了参数β(0≤β0.5),得到变精度粗糙集模型。讨论变精度粗糙集模型上、下近似算子的一些性质,即随着分类误差β的增大,X的正域与负域均扩大,边界缩小。同时通过经典的例子,说明变精度粗糙集模型相对于经典粗糙集模型其精确性提高了。 相似文献
9.
10.
针对KDY型输油泵运行中存在的润滑油泄漏、轴窜动量大、泵腰部拆卸不便、易损坏轴承和轴瓦等缺陷进行了原因分析,对泵的原设计提出了相应的改进措施。应用效果表明,改进后的KDY型输油泵的泵效已由原来的65%上升至80%,月润滑油泄漏量降至4kg,延长了止推轴承和轴瓦的使用寿命。 相似文献