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   9851篇
  免费   318篇
  国内免费   1776篇
林业   371篇
农学   480篇
基础科学   3763篇
  2634篇
综合类   3039篇
农作物   350篇
水产渔业   21篇
畜牧兽医   197篇
园艺   221篇
植物保护   869篇
  2024年   79篇
  2023年   203篇
  2022年   317篇
  2021年   363篇
  2020年   335篇
  2019年   459篇
  2018年   352篇
  2017年   500篇
  2016年   706篇
  2015年   481篇
  2014年   501篇
  2013年   603篇
  2012年   863篇
  2011年   782篇
  2010年   722篇
  2009年   625篇
  2008年   525篇
  2007年   566篇
  2006年   470篇
  2005年   475篇
  2004年   320篇
  2003年   307篇
  2002年   196篇
  2001年   190篇
  2000年   175篇
  1999年   148篇
  1998年   107篇
  1997年   101篇
  1996年   76篇
  1995年   65篇
  1994年   56篇
  1993年   74篇
  1992年   51篇
  1991年   46篇
  1990年   36篇
  1989年   25篇
  1988年   16篇
  1987年   18篇
  1986年   4篇
  1985年   4篇
  1983年   2篇
  1981年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
集雨灌溉工程是对降雨进行收集、汇流,存储和进行节水灌溉的微型水利工程,主要解决农业生产缺水性问题.通过国内外集雨灌溉利用的研究和实践,较详细地阐述了集雨灌溉工程的主要研究内容:集水工程集雨面防渗材料的研究、蓄水工程中蓄水设施的防渗,水分蒸发处理,喷灌、滴灌、渗灌等灌溉技术.文章分析了目前集雨灌溉工程研究存在的问题并提出了发展研究方向.  相似文献   
52.
在大田条件下,探讨了不同降水年型不同水分处理条件下大穗型小麦品种籽粒灌浆及产量的变化。结果表明:通过用不同方程对籽粒生长动态进行拟合,Cubic方程最精确。2000~2001干早年型W和Ws与两个灌浆持续期参数(Se、S)相关性显著.2001~2002丰雨年型W和Ws与3个灌浆速率参数(V、Vs、Vmax)间相关性达显著水平。两年度相比,2000~2001年度籽粒灌浆持续期短,灌浆速率小,导致粒重降低。灌水对灌浆参数的效应年际间存在差异,2000~2001年度随灌水次数增多,S和Se延长,灌浆速率降低;而2001~2002年度随灌水次数增多,S和Se缩短,灌浆速率以灌—水处理最小.灌两水处理最高。灌水对产量的影响,2000~2001年度显著增产,2001~2002年度处理间无显著差异,灌三水处理较灌两水处理反而减产。  相似文献   
53.
枣树是宁夏山地造林的必选树种之一,文章从苗木质量、苗木出圃起运、苗木栽植等方面综述了山地栽植枣树的技术措施。  相似文献   
54.
Although ‘sewage farming’ or wastewater irrigation started in Australia in the latter parts of the 19th century, it was in the late 1960s that a considerable interest was revived in arid and semi-arid parts of the world due to scarcity of alternative water sources and the urgency to increase local food production. The practice has manifold benefits in the form of water conservation, nutrient recycling, surface and ground water pollution prevention. But for arid and semi-arid regions like many parts of Australia, while wastewater irrigation can be an attractive solution to irrigation water problems, it might not be the ideal solution for the common soil types encountered in these regions. Due to characteristic low rainfall, high evaporation and low leaching, these soils tend to have higher salt accumulations. This paper examines the soil salinity and sodicity effects of wastewater irrigation in soil types typical to South Eastern Australia and takes the soils of Western Treatment Plant (WTP) as a case study to highlight these issues.  相似文献   
55.
This paper presents a case study of Goulburn-Murray Water's approach to the development and implementation of its asset management program for irrigation infrastructure. The success and effectiveness of asset management is not a matter of technical aspects only, rather it depends on an integrated package of institutional, organisational, technical and financial aspects.  相似文献   
56.
Over-watering cotton wastes a valuable and scarce resource; it can also lead to rank growth, nutrient leaching, and contaminated groundwater. Since under-watering can decrease yields, the question becomes one of finding the optimum application regime. An irrigation experiment was set up to apply water at six different application rates, ranging from 33% to 144% of normal, with hopes of identifying the regime that produces maximum yield. Two cultivars, Acala Maxxa and Acala PhytoGen-72 (Gossypium hirsutum L.), were planted on sandy soil and irrigated daily with a highly efficient subsurface drip irrigation system for four seasons. The results showed that on the average there was no significant difference in the yield of the two cultivars and there was no significant difference in the yield for the three wettest treatments. The driest of the three wettest treatments, treatment 4, was a critical point on the water production function curve. It represented the least amount of water applied that still produced essentially maximum yield, and it had the highest water use efficiency. This critical level of water application during mid-season was found to be, on the average, 95% of Class A pan evaporation; it corresponded to a total seasonal application of 654 mm of water. Any application less than this critical level decreased yields. Reducing the water application by 5% below the critical level caused about a 4.6% reduction in yield. The critical level produced a soil moisture level that remained nearly constant throughout the season. The final plant height was closely related to the depth of water applied, with the wettest treatment producing plant heights of 2.0 m, and the driest treatment producing plant heights of 0.6 m. At the extremes of the water application rates there were some small differences in the early-season growth rate of the plants, but the main cause of differences in final plant height was the date of cutout (cessation of main stem node production). The length of season for the driest treatment was about 4 weeks shorter than for the wettest treatment on both cultivars. Results showed that deficit irrigation of cotton on sandy soil can greatly reduce yield, and the practice should probably be avoided.  相似文献   
57.
随着我国农业科技的发展,滴灌施肥智能化控制技术越来越引起人们的关注,成为未来优质高效设施农业的发展趋势。为此,通过市场调研,采用PLC控制技术,进行了自动化灌溉施肥系统的设计开发;通过性能测试,实验取得了较好的效果,为将PLC技术引入到灌溉施肥控制系统的后续研究提供了借鉴。  相似文献   
58.
以南京老门东为例,构建游憩者个人涉入和地方依恋的结构方程模型,运用AMOS软件进行测量模型的验证性因子分析、结构模型的路径分析及南京居民和外来游客的多群组分析,结果表明:吸引力和中心性显著正向影响地方认同;地方依赖受到吸引力、自我表达和地方认同的显著正向影响;中心性对地方认同影响最大;对地方依赖影响最大的是地方认同;多群组分析显示,南京居民和外来游客在7个假设路径中的影响存在显著差异。  相似文献   
59.
水分和氮素管理对提高作物产量具有重要作用。笔者研究尿素类型与灌溉管理对玉米节水保肥的影响以达到玉米高氮肥利用效率和高产田的生产目标。本研究在2016—2017年开展2年完全随机区组设计试验,讨论了尿素类型(普通尿素和控释尿素)及灌溉对玉米土壤和氮素利用的影响。每种尿素类型设置2种氮素水平,分别为75、150 kg N/hm2,以不施氮肥为对照。水分设置2种灌溉水平,分别为全生育期不灌水和灌浆阶段灌水85 mm。结果表明:在灌溉与施氮水平相同下,0~40 cm土层应用控释尿素处理氮含量较高,但在更深的土壤层低于普通尿素处理;相对于不灌溉,灌溉增加了硝态氮的损失,但施用控释尿素的处理硝态氮损失低于施用普通尿素处理;灌溉条件下施用控释尿素可以提高玉米氮素吸收,并使更多的氮向籽粒中转移;与普通尿素相比,控释尿素提高了氮肥利用率,降低土壤对氮需求的依赖。控释尿素低氮的释放可以减少硝态氮在土壤中的存留时间而迅速被玉米吸收,从而降低硝态氮的损失风险,提高了土壤氮肥利用效率。综上,控释尿素与少量灌溉相结合适用于华北半湿润地区达到玉米高氮肥利用效率和高产田的生产目标。  相似文献   
60.
In Mexico, corn production, part of which is sweet corn, is mainly destined for human consumption. In the present work, the morphological quality of sweet corn ears was assessed in response to four levels of soil moisture tension indicating irrigation start (−5, −30, −55, and −80 kPa) and three levels of phosphate fertilization (60, 80 and 100 kg ha−1) in carstic soils in the south-east of Mexico. A factorial experimental design with three replicates was used. The following variables were determined: fresh weight (SCFWh), dry weight (SCDWh), diameter (SCDh), and length (SCLh) of sweet corn ears, all without husk, as well as number of kernels (NKxE), number of unfilled kernels (NUK), number of rows (NRxE), and dry kernel weight per ear (DKW). Yield of fresh (YFSCh) and dry (YDSCh) sweet corn ears, both without husk, and the harvest index (HI) were also determined. HI did not show significant statistical differences among irrigation or fertilization treatments. Regarding the other variables, the effect of the more humid treatments (−5 and −30 kPa) and the effect of the higher phosphorus doses (80 and 100 kg ha−1) were statistically equal (P ≤ 0.01) with the lowest NUK and the highest values of all other variables; therefore, irrigation start at soil moisture tension of −30 kPa and phosphate fertilization application of 80 kg ha−1 are recommended. At this level of soil moisture, the mean values over the three fertilization levels and all the replicates, obtained for SCFWh, SCDh, SCLh and NKxE were 198.5 g, 4.39 cm, 26.72 cm and 467 grains, respectively. According to the regression models, moisture tensions from −11.8 to −24.0 kPa, and phosphate fertilization doses from 87.7 to 102.2 kg ha−1 minimize NUK and maximize the values of the rest of the variables. The highest irrigation water use efficiency was found in the moisture tension treatment of −30 kPa with an increase of 27 kg ha−1 ears for each millimeter of applied irrigation water.  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