全文获取类型
收费全文 | 3473篇 |
免费 | 154篇 |
国内免费 | 454篇 |
专业分类
林业 | 280篇 |
农学 | 190篇 |
基础科学 | 185篇 |
1300篇 | |
综合类 | 1145篇 |
农作物 | 86篇 |
水产渔业 | 62篇 |
畜牧兽医 | 468篇 |
园艺 | 255篇 |
植物保护 | 110篇 |
出版年
2024年 | 35篇 |
2023年 | 110篇 |
2022年 | 127篇 |
2021年 | 140篇 |
2020年 | 141篇 |
2019年 | 150篇 |
2018年 | 127篇 |
2017年 | 175篇 |
2016年 | 227篇 |
2015年 | 189篇 |
2014年 | 197篇 |
2013年 | 277篇 |
2012年 | 283篇 |
2011年 | 249篇 |
2010年 | 168篇 |
2009年 | 187篇 |
2008年 | 141篇 |
2007年 | 184篇 |
2006年 | 164篇 |
2005年 | 133篇 |
2004年 | 123篇 |
2003年 | 104篇 |
2002年 | 84篇 |
2001年 | 72篇 |
2000年 | 87篇 |
1999年 | 46篇 |
1998年 | 34篇 |
1997年 | 38篇 |
1996年 | 14篇 |
1995年 | 13篇 |
1994年 | 8篇 |
1993年 | 16篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1975年 | 1篇 |
1963年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有4081条查询结果,搜索用时 15 毫秒
71.
《The Journal of Applied Poultry Research》2008,17(2):305-314
Limited data on pollutant emissions from poultry operations are available to assess the effect of these operations on the environment and to put their contribution in perspective with other sources of pollutants. To alleviate this problem, numerous studies at various poultry facilities have been undertaken to improve the knowledge base in quantifying emissions of NH3 and size-fractionated particulate matter (PM). For these emission data to be of practical use for government agencies and policy makers, the emission rates must be reported as an emission factor with a production unit that enables the emissions from one poultry operation to be correlated to another poultry operation. This paper presents a compilation of NH3 and PM emission data from several studies in the form of emission factor on a per-500 kg of live weight or animal unit basis. In addition, best management practices that lower pollutant emissions from poultry operations have been reported along with their effectiveness at reducing NH3 and PM. Unfortunately, the compiled data were insufficient to characterize the variability in emissions caused by differences in house design, suggesting that more studies are needed to complete a comprehensive emission inventory. Once complete, this inventory will enable poultry producers to estimate emissions from their facilities and, if necessary, select management practice(s) to lessen their emissions of NH3, PM, or both. 相似文献
72.
73.
74.
75.
笔者以恩施州为例,运用生物量清单法估算森林碳汇量,运用数学模型估算CO2年排放量。计算出2015年恩施州森林碳汇量100.80万t,CO2年排放量237.61万t,净排放量136.41万t。得出按目前的经济发展速度和恩施州森林年增长量,在2015年CO2不会成为恩施州经济发展的制约因素。但从环境保护这方面出发,同时考虑发展以碳汇为目的的林业经济,恩施州应该加大对森林的管理力度,实行增汇减排措施,并对恩施州森林碳汇发展方向提出相关建议与措施。 相似文献
76.
Abstract. Field margins are a valuable resource in the farmed landscape, providing numerous environmental benefits. We present a preliminary analysis of the carbon mitigation potential of different field margin management options for Great Britain, calculated using data from long-term experiments and literature estimates. The carbon sequestration potential of the individual options investigated here varies from 0.1 to 2.4% of 1990 UK CO2 -C emissions, or 0.7–20% of the Quantified Emission Limitation Reduction Commitment (QELRC). The scenarios investigated covered three possible margin widths and options for the management of margins at each width (viz. grass strips, hedgerows and tree strips). Scenarios involving margin widths of 2, 6 or 20 m would require approximately 2.3, 6.7 or 21.3% of the total arable area of Great Britain, respectively. Scenarios including tree strips offered the greatest potential for carbon sequestration, since large amounts would be accumulated in above-ground biomass in addition to that in soil. We also accounted for the possible impacts of changed land management on trace gas fluxes, which indicated that any scenario involving a change from arable to grass strip, hedgerow or tree strip would significantly reduce N2 O emissions, and thus further increase carbon mitigation potential. There would also be considerable potential for including the scenarios investigated here with other strategies for the alternative management of UK arable land to identify optimal combinations. We assumed that it would take 50–100 years for soil carbon to reach a new equilibrium following a land use change. More detailed analyses need to be conducted to include environmental benefits, socioeconomic factors and the full system carbon balance. 相似文献
77.
EMDI-UF混合胶刨花板制造工艺条件的研究 总被引:2,自引:0,他引:2
介绍了东北林业大学人造板研究所在降低人造板游离甲醛释放量的研究成果,利用可乳化异氰酸酯(EMDI)与脲醛树脂(UF)混合胶制造刨花板,使产品达到E1级标准要求。研究结果表明:混合胶的施胶量为7%,采用6%的UF和1%的EMDI是比较适合的比例。将它们混合到一起,不加酸性固化剂,搅拌均匀后喷洒到刨花上,比较适宜的板坯含水率不应超过14%,在175℃下热压4.5min,所粘结的刨花板各项性能都符合GB4897—92—等品和E1级板标准的要求。与UF胶刨花板相比,混合胶刨花板的耐水性得到明显改善,甲醛释放量可降低到7.88mg/100g板。 相似文献
78.
79.
80.