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   127篇
  免费   4篇
  国内免费   12篇
林业   6篇
农学   3篇
基础科学   15篇
  36篇
综合类   54篇
农作物   9篇
水产渔业   5篇
畜牧兽医   7篇
园艺   7篇
植物保护   1篇
  2024年   1篇
  2023年   1篇
  2022年   3篇
  2021年   4篇
  2020年   1篇
  2019年   3篇
  2018年   3篇
  2017年   2篇
  2016年   6篇
  2015年   7篇
  2014年   11篇
  2013年   9篇
  2012年   7篇
  2011年   10篇
  2010年   8篇
  2009年   13篇
  2008年   5篇
  2007年   14篇
  2006年   9篇
  2005年   3篇
  2004年   1篇
  2002年   2篇
  2001年   1篇
  2000年   2篇
  1999年   8篇
  1998年   2篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1993年   1篇
  1990年   1篇
  1988年   1篇
排序方式: 共有143条查询结果,搜索用时 515 毫秒
11.
栽培方式对马铃薯产量和品质的影响   总被引:5,自引:0,他引:5  
以马铃薯郑薯6号为材料,进行4种不同栽培方式的比较试验,探讨不同栽培方式对其生长、产量及品质的影响。结果表明,以垄栽覆盖地膜方式马铃薯的出苗率最高,成熟期最早,植株最高,分枝数最多;但茎粗、叶面积指数、匍匐茎长、产量和单株生物学产量则以浅旋耕覆盖稻草方式最高;商品薯率以传统垄栽方式最高。不同栽培方式下,除蛋白质含量外,马铃薯的干物质、淀粉、还原糖以及VC含量等品质指标均以浅旋耕覆盖稻草方式最高。因此,生产上采用浅旋耕覆盖稻草栽培方式,有利于提高马铃薯的产量和品质。  相似文献   
12.
The design of integrated weed management (IWM) systems is essential in order to reduce the use of herbicides for crop production. By combining different weed management practices, herbicides may be used at lower doses than normally recommended, while still maintaining acceptable weed population levels. The purpose of this study was to develop tillage strategies, with and without herbicides at reduced rates, appropriate for different weed populations. The influences of type and time of stubble cultivation, harrowing and mouldboard ploughing on the weed flora were followed during 1988–1994 in eight long-term field trials situated in southern Sweden. Spring-sown barley (Hordeum distichon L.) and oats (Avena sativa L.) dominated the crop rotations. Herbicides were either omitted or used at ca. 50% of a full dose. The perennial species Sonchus arvensis L. was favoured by omittance of ploughing but was better controlled by late ploughing not preceded by stubble cultivation; the reduction in the latter treatment being 74%. Stubble cultivation succeeded by ploughing reduced biomass of Elymus repens (L.) Gould. by 90% compared with ploughing solely. Early ploughing reduced the biomass of the species by 50% compared with late ploughing. The species Cirsium arvense (L.) Scop. was highly favoured by early ploughing followed by late autumn harrowing, the biomass of the species being six-fold higher than in other treatments. Compared with other treatments, stubble cultivation favoured four annuals but efficiently controlled three others, while omittance of ploughing favoured six annual and two perennial weed species. Late ploughing not preceded by stubble cultivation favoured four annual and one perennial species, while early ploughing was more efficient than late ploughing in controlling two of the annual species. Influences of treatments on weed species were frequently moderated by interspecific competition resulting in inconsistent response at different sites. Herbicides reduced the number of species by three, from 11 to eight species, averaged across sites and tillage systems. Influences of treatments on diversity were not consistent, since weed floras differed between sites and since some of the species responded inconsistently to tillage and herbicides. This study shows that by utilizing appropriate tillage strategies it is possible at many sites to maintain acceptable weed population levels, although herbicides are used at 50% lower doses than is normally recommended. The timing and type of tillage have to be chosen for being as efficient as possible to the most troublesome weed species at a site.  相似文献   
13.
A. Andersen   《Crop Protection》1999,18(10):407-657
In five field experiments run for four years the infestation of pests and the activity of carabids and staphylinids were compared in autumn ploughed and reduced tillage (no-tillage or spring harrowing) plots. Differences were generally most evident in experiments with no-tillage. Weed cover was denser in reduced tillage, and could explain much of the differences. The agromyzid Chromatomyia fuscula was most common in autumn ploughed plots, probably due to healthier plants. Thrips numbers were correlated with grain quality in no-tillage plots. Field slugs were most common in reduced tillage, and were positively correlated with weed cover. Generally, more carabids and staphylinids were caught in reduced tillage. This was especially true for Amara-species and Loricera pilicornis, Philonthus cognatus and Tachinus signatus, which also were positively correlated with weed cover. Aloconota gregaria, Bembidion quadrimaculatum, B. lampros, Harpalus rufipes and Trechus quadristriatus were more common in autumn ploughed plots, several of them preferring open soil.  相似文献   
14.
The hydrologic and water quality impacts of subsurface drainage design and management practices are being investigated through field and simulation studies throughout the northern Corn-belt. Six years of data from an ongoing field study in south central Minnesota (Sands et al., 2008) were used to support a modeling effort with DRAINMOD-NII to investigate: (1) the performance of the model in a region where soils are subject to seasonal freeze-thaw and (2) the long-term hydrologic and water quality characteristics of conventional and alternative subsurface drainage practices. Post-calibration model prediction and efficiency were deemed satisfactory using standard model performance criteria. Prediction errors were primarily associated with early spring snowmelt hydrology and were attributed to the methods used for simulating snow accumulation and melting processes, in addition to potential sublimation effects on ET estimates. Long-term simulations with DRAINMOD-NII indicated that drainage design and/or management practices proposed as alternatives to conventional design may offer opportunities to reduce nitrate (NO3)-nitrogen losses without significantly decreasing (and in some cases, increasing) crop yields for a Webster silty clay loam soil at Waseca, Minnesota. The simulation study indicated that both shallow drainage and controlled drainage may reduce annual drainage discharge and NO3-nitrogen losses by 20-30%, while impacting crop yields from −3% (yield decrease) to 2%, depending on lateral drain spacing. The practice of increasing drainage intensity (decreasing drain spacing) beyond recommended values appears to not significantly affect crop yield but may substantially increase drainage discharge and nitrate-nitrogen losses to surface waters.  相似文献   
15.
In the irrigated western U.S. disposal of drainage water has become a significant economic and environmental liability. Development of irrigation water management practices that reduce drainage water volumes is essential. One strategy combines restricted drainage outflow (by plugging the drains) with deficit irrigation to maximize shallow groundwater consumption by crops, thus reducing drainage that needs disposal. This approach is not without potential pitfalls; upward movement of groundwater in response to crop water uptake may increase salt and sodium concentrations in the root zone. The purposes for this study were: to observe changes in the spatial and temporal distributions of SAR (sodium adsorption ratio) and salt in a field managed to minimize drainage discharge; to determine if in situ drainage reduction strategy affects SAR distribution in the soil profile; and to identify soil or management factors that can help explain field wide variability. We measured SAR, soil salinity (EC1:1) and soil texture over 3 years in a 60-ha irrigated field on the west side of the San Joaquin Valley, California. At the time we started our measurements, the field was beginning to be managed according to a shallow groundwater/drainage reduction strategy. Soil salinity and SAR were found to be highly correlated in the field. The observed spatial and temporal variability in SAR was largely a product of soil textural variations within the field and their associated variations in apparent leaching fraction. During the 3-year study period, the percentage of the field in which the lower profile (90-180 cm) depth averaged SAR was above 10, increased from 20 to 40%. Since salinity was increasing concomitantly with SAR, and because the soil contained gypsum, sodium hazard was not expected to become a limiting factor for long term shallow groundwater management by drain control. It is anticipated that the technology will be viable for future seasons.  相似文献   
16.
通过对贵阳市城郊区浅层地下水的调查及采样分析,探讨土地利用方式对地下水硝态氮含量的影响。研究结果表明:不同土地利用方式下浅层地下水中NO3--N含量出现较大差异,与林地相比,城市生活用地、耕地和工业用地的地下水硝态氮平均含量分别增加2.47倍、3.88倍和2.25倍。丰水期地下水硝酸盐含量普遍高于枯水期。以NO3--N为评价指标,耕地、城市生活用地、工业用地地下水质在枯水期均为Ⅳ类,而丰水期地下水质均为Ⅴ类;林地地下水的NO3--N浓度在枯水期和丰水期均小于10 mg/L,水质达到Ⅲ类。  相似文献   
17.
在上海浦东东滩采用刈割、耕翻与淹水集成技术清除外来物种互花米草,以加快沿海滩涂开发垦复,增加耕地面积.研究表明:对互花米草刈割1次、耕翻4次(淹水前和淹水期间各2次),淹水1个月后互花米草的地下部分死亡并开始腐烂,互花米草得到有效控制.该技术从1月开始实施,于当年5月底结束,能够满足水稻种植的季节要求,是一种适于推广的...  相似文献   
18.
[目的]评价郑州市浅层地下水质量。[方法]以郑州市区为研究范围,对其浅层地下水质量进行评价。利用中原城市群地下水污染调查所取得的大量实测数据,采用检出法和超标法对郑州市浅层地下水质量进行初步评价,并运用改进的权重集对分析法对其进行综合评价。[结果]郑州市浅层地下水质量整体较好,大部分采样点水质达Ⅲ级,近污染源的2个采样点水质达Ⅳ级,不符合饮用水标准;改进的集对分析方法简单实用,结果合理,能够较好地对地下水水质进行评价。[结论]该研究对郑州市市辖区供需水以及城镇用水安全具有一定的指导意义。  相似文献   
19.
干旱地区农田浅耕对杂草控制及土壤水分、养分的影响   总被引:15,自引:1,他引:15  
【目的】在干旱农业区有效控制农田杂草,减少对土壤水分、养分的消耗,有效利用自然降水,为发展旱作农业,提高产量提供依据。【方法】连续3年浅耕、深耕配施除草剂,采样调查耕层杂草种子的消长及土壤水分、养分的变化。【结果】秋收后2 d浅耕,将落入地表85%~90%的杂草种子全部耙入0~10 cm耕层内,便于防除。5、10 d浅耕,随土壤裂缝进入10 cm以下种子依次占1.8%、4.1%;深耕,0~10 cm耕层杂草种子占19.8%,10~30 cm耕层种子占80.2%,10 cm以下土层种子很少萌发出苗,难以根除;浅耕配施除草剂,耕层杂草种子平均每年以75.4%的速度下降,深耕以27.3%速度下降;浅耕可节约50%机耕费,在蓄水灌溉地区可节约50%灌水量;浅耕耙松表土,防止土壤水分散失,对不同耕作层的水分、养分含量影响不大;浅耕耕种2~3年应深翻耕种或休闲一年。【结论】在干旱地区秋收深耕,对翻入土壤10 cm以下的杂草种子难以根除,且造成土壤风蚀严重,水分严重不足,影响播种或出苗,也是形成春旱的主要原因。而浅耕则有助于旱作农业的持续、稳定发展。  相似文献   
20.
为探明环渤海"池-田"蓄引水模式下棉田水盐运移规律对棉花生产的影响,2017和2018年4-10月对未改造棉田(CK)及模式中的台田(A)、浅层地下水抽提棉田(B)、抑盐排涝棉田(C)进行土壤水分、盐分和pH值、棉花光合指标、产量进行测定,结果表明,模式中棉田0~80cm土层盐分和pH值显著降低,A和B棉田盐分降至3.0g/kg左右,pH值低于8.0;C棉田盐分低于5.0 g/kg,7-8月pH值低于8.0。A棉田土壤水分、盐分和pH值最低,滴灌条件下棉花光合性能长期保持高值,光合物质积累的直线增长持续时间和活跃期最长,籽棉产量超过3 500 kg/hm~2。B棉田水分0~40 cm土层高于20%,光合性能高值较长,籽棉产量超过3 000 kg/hm~2。C棉花7-8月光合性能明显提高,籽棉产量超过2 500kg/hm~2。环渤海"池-田"蓄引水模式显著改善棉田水盐运移,有利于棉花生产,从而提高产量。研究可为高效开发利用滨海盐碱地提供科学模式和理论基础。  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