全文获取类型
收费全文 | 3875篇 |
免费 | 218篇 |
国内免费 | 421篇 |
专业分类
林业 | 300篇 |
农学 | 281篇 |
基础科学 | 228篇 |
1221篇 | |
综合类 | 1201篇 |
农作物 | 241篇 |
水产渔业 | 272篇 |
畜牧兽医 | 403篇 |
园艺 | 240篇 |
植物保护 | 127篇 |
出版年
2024年 | 33篇 |
2023年 | 88篇 |
2022年 | 116篇 |
2021年 | 155篇 |
2020年 | 144篇 |
2019年 | 130篇 |
2018年 | 96篇 |
2017年 | 160篇 |
2016年 | 171篇 |
2015年 | 130篇 |
2014年 | 189篇 |
2013年 | 267篇 |
2012年 | 229篇 |
2011年 | 238篇 |
2010年 | 207篇 |
2009年 | 248篇 |
2008年 | 218篇 |
2007年 | 255篇 |
2006年 | 205篇 |
2005年 | 187篇 |
2004年 | 136篇 |
2003年 | 124篇 |
2002年 | 103篇 |
2001年 | 106篇 |
2000年 | 88篇 |
1999年 | 76篇 |
1998年 | 57篇 |
1997年 | 54篇 |
1996年 | 59篇 |
1995年 | 45篇 |
1994年 | 41篇 |
1993年 | 45篇 |
1992年 | 26篇 |
1991年 | 21篇 |
1990年 | 19篇 |
1989年 | 21篇 |
1988年 | 10篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1984年 | 1篇 |
1980年 | 1篇 |
排序方式: 共有4514条查询结果,搜索用时 15 毫秒
41.
基于GIS的农田养分管理与推荐施肥系统设计与开发 总被引:3,自引:0,他引:3
针对我国南方农业过于分散的农田经营管理体系和施肥现状,以浙江绍兴东湖镇独树村为研究区域,应用信息技术、系统养分研究法和推荐施肥模型,研制和开发出适于南方土壤及作物体系的土壤养分管理和决策信息系统平台,实施田块或田畈为基本单元的村级信息化农田养分全程管理,进行推荐施肥,初步应用结果表明,推荐施肥示范方各农户水稻产量大部分达到每亩450~500公斤以上. 相似文献
42.
43.
44.
45.
46.
An aquaponics system (AS) is an integrated system that combines a recirculating aquaculture system and a hydroponics system (HS). It is designed to recover nutrients released from fish and transfer them to plants to provide a system more environmentally-friendly than the two systems working separately. As a result, several AS are under development, but little information is available about their overall performances. The aim of this study was to assess nutrient-use efficiency and environmental impacts of an AS, specifically a common carp-lettuce AS located in a greenhouse. Nutrient budgets of nitrogen (N) and phosphorus (P) were calculated and Life Cycle Assessment (LCA) was performed for the AS and for a lettuce Individual Hydroponics System (IHS), similar to the HS of the AS, operating in the greenhouse at the same time. The experiment was performed over a 52-day cycle, which corresponds to the growing time required to harvest marketable lettuce. The nutrient budgets were well balanced, with 24.6% of the N unaccounted-for, most likely due to N2 gas emission, and 6.6% of the P unaccounted-for, most likely due to having underestimated the quantity of sediment. At the beginning of the experiment, N represented 55.9%, 37.1% and 0.1% of the total N input in the formulated feed, stocked fish and lettuce seedlings, respectively. At the end of the experiment, N represented 47.6% and 0.4% of the total N input in the harvested fish and lettuce, respectively. At the beginning of the experiment, P represented 56.94%, 40.20% and 0.03% of the total P input in the formulated feed, stocked fish and lettuce seedlings, respectively. At the end of the experiment, P represented 51.52% and 0.42% of the total P input in the harvested fish and lettuce, respectively. LCA clearly indicated two environmental impact hotspots: the origin of nutrients and energy use. One kg of lettuce growth in the AS clearly had lower environmental impacts than that in the IHS for climate change, acidification, eutrophication, land competition and cumulative energy demand; however, a decrease in water dependence was not observed. The indicator for net primary production use highlighted the dependence of the AS on natural resources, especially fish meal and fish oil. Compared to the use of chemical nutrients in the IHS, the use of nutrients from formulated feed in the AS decreased climate change impact but increased the use of natural resources. 相似文献
47.
Competition for soil resources plays a key role in the crop yield of intercropping systems. There is a lack of knowledge on the main factors involved in competitive interactions between crops and weeds for nutrients uptake. Hence, the purpose of this work was to compare the effects of arbuscular mycorrhial fungi (Funneliformis mosseae) colonization in interspecific competitive relations and its effect on nutrients uptake and weed control in dill and common bean intercropping. Two field experiments were carried out with factorial arrangements based on randomized complete block design with three replications during 2013–2014. The factors were cropping systems including a) common bean (Phaseolus vulgaris L.) sole cropping (40 plants m−2), b) dill (Anethum graveolens L.) sole cropping at different densities (25, 50 and 75 plants m−2) and c) the additive intercropping of dill + common bean (25 + 40, 50 + 40 and 75 + 40 plants m−2). All these treatments were applied with (+AM) or without (-AM) arbuscular mycorrhiza colonization. In both cropping systems, inoculation with F. mosseae increased the P, K, Fe and Zn concentrations of dill plants by 40, 524, 57 and 1.0 μg kg−1 DW, respectively. Intercropping increased Mn concentration in common bean (4.0 μg kg−1 DW) and dill (3.0 μg kg−1 DW), and also seed yields of both crops (198 g m−2 and161 g m−2, respectively). AM colonization improved seed yields of dill and common bean by 169 and 177 g m−2 in 2013 and 2014, respectively. Moreover, AM application enhanced competitive ability of dill + common bean intercrops against weeds at different intercropping systems. Intercropping significantly changed weed density compared to sole cropping, as weed density was decreased in the dill + common bean intercropping. Diversity (H), Evenness (E) and richness of weed species of weeds for intercrops were higher than those for sole crops. 相似文献
48.
The effect of phosphorus (P) and carbon (C) on methanogenesis was investigated in a low-P (130 mg P kg−1 soil) wetland within Everglades National Park. Soil was amended with C substrates (acetate, formate, butyrate, and glucose) with or without P, and CO2 and CH4 production was monitored. Production of CH4 increased with P addition although no effect on CO2 was observed. Methane production was stimulated by all C substrates except for butyrate. No effect of C on CO2 production was observed except for stimulation following glucose addition. Production of CH4 following formate addition was not affected by P, suggesting hydrogenotrophic methanogens may be substrate, not P, limited. Addition of P to all other C substrates heightened CH4 production and lowered the CO2–C:CH4–C ratio relative to the corresponding C only treatment, suggesting that P may have limited acetoclastic methanogens and fermentation. 相似文献
49.
In Hungary, maize is grown on 1 million ha and occupies more than 20% of the arable land. The rich assortment of maize cultivars of different vegetation periods and different responses to nutritional effects, water supply etc. gives the growers the possibility to choose the cultivars suiting best the site characteristics (Jolânkai et al. 1999). Among the cereals maize has the highest genetical potential. To utilize its yield and quality potential, soil types of high nutrient content and regular nutrient supply are required (Gyõrffy, 1979). Both over‐ and under‐fertilization have an unfavourable effect on the yield and quality of maize (Debreczeni, 1985). Crops can be supplied with the appropriate nutrient amounts only with the knowledge of soil characteristics in the different agro‐ecological regions (nutrient content, water supply, soil compactness, pH, nutrient supplying capacity etc.). In Hungary, a network of long‐term field fertilization trials with uniform fertilizer treatments has been maintained at nine experimental sites representing different agro‐ecological regions of the country. This experimental network gives a basis to test the nutrient responses of our main crops and calibrate their optimal nutrient supply (Kismányoky, 1991). 相似文献
50.
本试验旨在研究改造运输车对缓解驴运输应激的效果。选取28头健康德州公驴,随机分为2组,从北京密云县运输至聊城市东阿县东阿黑毛驴研究所,路程约500 km,历时18 h。试验使用9.6 m长单层货车为运输车,对试验组(T)运输车进行改造,即加装顶层和双侧篷布、底部加装草帘和中部加装隔栏,对照组(C)不作处理。运输前后测定驴血液生化和激素指标,统计体重变化和发病驴数量。结果表明,与运输前相比,普通车组驴在落地当天检测到血清皮质醇(COR)、白蛋白(ALB)水平均显著升高(P<0.05),总蛋白(TP)、谷草转氨酶(AST)、热休克蛋白-90(HSP90)和肌酸激酶(CK)指标极显著升高(P<0.01),钙(Ca)浓度显著降低(P<0.05)。改造车组驴血液指标TP、AST和CK的变化范围低于普通车组。两组驴落地后血糖(GLU)水平均比运输前升高,但差异均不显著(P<0.05)。与运输前相比,改造车组驴落地后的体重减少低于普通车组;改造车组驴在落地后第10天平均体重接近运输前,而普通车组驴的平均体重在落地后第20天才基本恢复至运输前水平,即使用改造运输车辆可以尽早恢复体重。普通车组驴发病率为21.4%,改造车组为7.1%;两组均无死亡。综合上述结果,改造运输车可有效降低驴的运输应激,有利于提高动物运输福利,减少经济损失;本试验结果可为动物运输应激提供参考。 相似文献