全文获取类型
| 收费全文 | 1164篇 |
| 免费 | 659篇 |
| 国内免费 | 2篇 |
专业分类
| 林业 | 50篇 |
| 农学 | 79篇 |
| 基础科学 | 323篇 |
| 532篇 | |
| 综合类 | 683篇 |
| 农作物 | 39篇 |
| 水产渔业 | 4篇 |
| 畜牧兽医 | 48篇 |
| 园艺 | 38篇 |
| 植物保护 | 29篇 |
出版年
| 2025年 | 18篇 |
| 2024年 | 30篇 |
| 2023年 | 45篇 |
| 2022年 | 47篇 |
| 2021年 | 45篇 |
| 2020年 | 69篇 |
| 2019年 | 83篇 |
| 2018年 | 62篇 |
| 2017年 | 67篇 |
| 2016年 | 93篇 |
| 2015年 | 69篇 |
| 2014年 | 108篇 |
| 2013年 | 119篇 |
| 2012年 | 197篇 |
| 2011年 | 176篇 |
| 2010年 | 103篇 |
| 2009年 | 83篇 |
| 2008年 | 65篇 |
| 2007年 | 100篇 |
| 2006年 | 65篇 |
| 2005年 | 24篇 |
| 2004年 | 20篇 |
| 2003年 | 33篇 |
| 2002年 | 14篇 |
| 2001年 | 16篇 |
| 2000年 | 12篇 |
| 1999年 | 9篇 |
| 1998年 | 11篇 |
| 1997年 | 9篇 |
| 1996年 | 3篇 |
| 1995年 | 7篇 |
| 1994年 | 3篇 |
| 1993年 | 11篇 |
| 1992年 | 2篇 |
| 1991年 | 3篇 |
| 1990年 | 1篇 |
| 1989年 | 2篇 |
| 1987年 | 1篇 |
排序方式： 共有1825条查询结果，搜索用时 0 毫秒
1.
Due to energy crises and stricter environmental regulations, renewable energy sources like bio‐methane produced by anaerobic digestion (biogas) become increasingly important. However, the application of slurries produced by biogas fermentation to agricultural land and subsequent ammonia emission may also create environmental risks to the atmosphere and to N‐limited ecosystems. Evaluating ammonia loss from agricultural land by model simulation is an important tool of agricultural‐systems analysis. The objective of this study was the systematical comparison of ammonia volatilization after application of two types of biogas slurries containing high amounts of energy crops in comparison with conventional animal slurries and to investigate the relative importance of factors affecting the emission process through an empirical model. A high number of ammonia‐loss field measurements were carried out in the years 2007/08 in biogas cropping systems in N Germany. The study consisted of simultaneous measurement of NH3 losses from animal and biogas slurries in multiple‐plot field experiments with different N‐fertilization levels. The derived empirical model for the calculation of NH3 losses based on explanatory variables gave good predictions of ammonia emission for both biogas and pig slurries. The root mean square error (RMSE) and mean bias error (MBE) of the empirical model for validation data were 2.19 kg N ha–1 (rRMSE 29%) and –1.19 kg N ha–1, respectively. Biogas slurries produced highest NH3 emissions compared to the two animal slurries. In view of the explanatory variables included in the model, total NH$ _4^+ $ application rate, slurry type, temperature, precipitation, crop type, and leaf‐area index were important for ammonia‐volatilization losses. 相似文献
2.
作者依据实例,对使用粉煤灰泡沫隔墙板与普通材料隔墙的经济效益做了综合比较,提出应大力推广使用粉煤灰泡沫墙板这一新型建筑材料。 相似文献
3.
Rajanna G. Adireddy;Suman Manna;Neeraj Patanjali;Anupama Singh;Anchal Dass;Dibakar Mahanta;Vinod Kumar Singh; 《Journal of Agronomy and Crop Science》2024,210(4):e12730
The sustainability of global agriculture at higher productivity level is a concern owing to climate change, serious environmental footprints, dipping factor productivity and shrinking availability of natural resources, especially. The situation is worsening in the ‘Food Bowl of India’—Indo-Gangetic plains (IGP) by several amalgamated factors, such as declining groundwater, unpredictable precipitation owing to climate change and cultivation of heavy water duty crops. To neutralise these issues, a field experiment was executed for the period 2019–2021 to assess the efficacy of indigenous hydrogels (P-hydrogel and Superabsorbent polymer hydrogel-1118) and their application methods viz., seed treatment, slurry application and soil application on crop yield and water productivity, soil moisture dynamics and profitability in a soybean–wheat cropping system under irrigation and rainfed conditions. In both study years (2019–2020 and 2020–2021), due to higher seed germination percentage, irrigation application together with seed treatment and slurry application of superabsorbent polymer hydrogel-1118 improved system productivity by 8.1%–26.7% and system water productivity by 17.6%–33.8% over control. Wheat grain yield was enhanced by 8.0% (2019–2020) to 32.2% (2020–2021) due to superabsorbent polymer hydrogel-1118 hydrogel with 10 cm lesser use of irrigation water compared with control (no-hydrogel). Soil moisture content in 0–15 cm soil layer was also found higher by 1.8%–2.4% in superabsorbent polymer hydrogel-1118 and P-hydrogel slurry-applied plots. Therefore, higher gross profitability (31.8%), net profitability (89.8%) and B:C (26.9%) in wheat could be attributed to increased crop yields when seeds were treated with superabsorbent polymer hydrogel-1118. Therefore, the utilisation of modified hydrogel application, in the form of seed treatment (seed coating) and slurry application has demonstrated improvement in seed germination, crop yield and water productivity and made soybean–wheat cultivation more economical. This approach presents a feasible solution to achieving a viable production system of soybean and wheat crops by reducing irrigation amounts in the IGP of India, as well as other comparable ecological places worldwide. 相似文献
4.
The use of semi-natural grasslands for the production of renewable energy through conventional conversion techniques faces major limitations because of chemical and physical properties of the biomass. A new conversion procedure was developed which separates the biomass, as silage, into a liquid phase for biogas production and into a solid fraction to be used as fuel. Separation (mechanical dehydration) is carried out with a screw press after mashing with water (hydrothermal conditioning). The effect of hydrothermal conditioning at different temperatures (5, 60 and 80°C) and mechanical dehydration on mass flows of plant compounds into the press fluid was investigated for five grassland pastures typical of mountain areas of Germany. Results show that 0·18 of the crude fibre was transferred into the fluid, whereas more digestible organic compounds, such as crude protein and nitrogen-free extract, showed mass flows of 0·40 and 0·31 respectively. While 0·52–0·89 of potassium (K), magnesium (Mg) and chloride (Cl), which are detrimental for the combustion of the press cake, were transferred into the press fluid, more than 0·50 of calcium, which has positive combustion properties, remained in the press cake. Significantly ( P < 0·05) higher mass flows were detected at conditioning temperatures of 60°C (K and Mg) and 80°C (crude fibre and nitrogen-free extract) compared with the 5°C treatment. Because of the separation of solids and liquids, high proportions of P (0·61–0·74) and K (0·64–0·85) but only 0·32–0·45 of nitrogen exported from the grassland would be recycled with an application of the digestates from the anaerobic digestion of the press liquid. 相似文献
5.
6.
Nitrous oxide, methane and ammonia emissions following slurry spreading on grassland 总被引：1，自引：0，他引：1
In Sweden, 90% of ammonia (NH3) emissions to the atmosphere originate from agriculture, predominantly from animal manure handling. It is well known that incorporation of manure into soil can reduce NH3 emissions after spreading. However, there is a risk of increased nitrous oxide (N2O) and methane (CH4) emissions caused by bacterial activity and limited oxygen availability under these conditions. A full‐scale injector was developed and evaluated in a field experiment on grassland. Cattle slurry was either injected in closed slots 5 cm below ground or band spread on the soil surface above the crop canopy at a rate of 25 t ha?1. In a control treatment, no slurry was applied. During a 5‐day period after application, NH3 emissions were measured using an equilibrium concentration method. Gas samples for estimating CH4 and N2O emissions were also collected during 7 weeks following slurry application. Injection in closed slots resulted in no detectable NH3 emissions. After band spreading, however, NH3 emissions corresponded to nearly 40% of the total ammoniacal nitrogen in the applied slurry. The injection of slurry gave rise to a broad peak of N2O emissions during the first 3 weeks after application. In total, for the measuring period, N2O emissions corresponded to 0.75 kg N ha?1. Band spreading resulted in only a very small N2O release of about 0.2 kg N ha?1 during the same period. Except for the first sampling occasion, the soil was predominantly a sink for CH4 in all the treatments. The use of the injector without slurry application reduced grass yield during unfavourable growing conditions. In conclusion, shallow injection in closed slots seems to be a promising technique to reduce negative environmental impacts from NH3 emissions with a limited release of N2O and CH4. 相似文献
7.
龙海市农村户用沼气池蓬勃发展,总结了在沼气池建设、厨房沼气管路配件安装、沼气灶台改造、沼气池使用管理方面的具体要求。 相似文献
8.
在高寒地区农户仅将沼气作为炊事用能,冬季采暖方式主要还以直接燃烧秸秆、薪柴等生物质为主。为了实现冬季取暖和炊事都利用沼气,设计小型户用沼气锅炉,并参照大中型锅炉的设计方法,提出适用于小型户用沼气锅炉的热力计算方法。通过理论计算和选取相应参数,利用炉膛出口温度和排烟温度先假设与后校核的方法,对沼气锅炉辐射换热面和对流换热面进行理论设计计算,并设计出沼气锅炉的整体结构。通过试验对锅炉性能进行测试,平均热效率为92.76%,完全符合锅炉的设计要求。 相似文献
9.
10.
Anaerobic digestion of organic materials generates residues of differing chemical composition compared to undigested animal manures, which may affect the soil microbial ecosystem differently when used as fertilizers. This study investigated the effects of two biogas residues (BR-A and BR-B) and cattle slurry (CS) applied at rates corresponding to 70 kg NH4+-N ha−1 on bacterial community structure and microbial activity in three soils of different texture (a sandy, a clay and an organic clay soil). 16S rRNA genes were targeted in PCR reactions and bacterial community profiles visualized using terminal restriction fragment length polymorphism. General microbial activity was measured as basal respiration (B-resp), substrate-induced respiration (SIR), specific growth rate (μSIR), metabolic quotient (qCO2) and nitrogen mineralization capacity (NMC). Non-metric multidimensional scaling analysis visualized shifts in bacterial community structure related to microbial functions. There were significant differences in bacterial community structure after 120 days of incubation (+20 °C at 70% of WHC) between non-amended (control) and amended soils, especially in the sandy soil, where CS caused a more pronounced shift than biogas residues. Terminal-restriction fragment (TRF) 307, the predominant peak in CS-amended sandy soil, was identified as possibly Bacillus or Streptococcus. TRF 226, the dominant peak in organic soil amended with BR-B, was classified as Rhodopseudomonas. B-resp significantly increased and SIR decreased in all amendments to organic soil compared with the control, potentially indicating decreased efficiency of heterotrophic microorganisms to convert organic carbon into microbial biomass. This was also reflected in an elevated qCO2 in the organic soil. The μSIR level was higher in the sandy soil amended with BR-A than with BR-B or CS, indicating a shift toward species capable of rapidly utilizing glucose. NMC was significantly elevated in the clay and organic soils amended with BR-A and BR-B and in the sandy soil amended with BR-B and CS. Thus, biogas residues and cattle slurry had different effects on the bacterial community structure and microbial activity in the three soils. However, the effects of biogas residues on microbial activities were comparable in magnitude to those of cattle slurry and the bacterial community structure was less affected. Therefore, we do not see any reason not to recommend using biogas residues as fertilizers based on the results presented. 相似文献