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   265篇
  免费   32篇
  国内免费   30篇
  2023年   1篇
  2022年   3篇
  2021年   12篇
  2020年   24篇
  2019年   20篇
  2018年   17篇
  2017年   20篇
  2016年   14篇
  2015年   16篇
  2014年   13篇
  2013年   25篇
  2012年   11篇
  2011年   11篇
  2010年   9篇
  2009年   18篇
  2008年   12篇
  2007年   16篇
  2006年   14篇
  2005年   8篇
  2004年   8篇
  2003年   8篇
  2002年   4篇
  2001年   4篇
  2000年   5篇
  1999年   4篇
  1998年   3篇
  1997年   3篇
  1996年   2篇
  1995年   3篇
  1994年   1篇
  1992年   3篇
  1991年   3篇
  1990年   1篇
  1987年   1篇
  1986年   2篇
  1984年   2篇
  1983年   2篇
  1979年   4篇
排序方式: 共有327条查询结果,搜索用时 812 毫秒
91.
John Clifton-Brown  Astley Hastings  Moritz von Cossel  Donal Murphy-Bokern  Jon McCalmont  Jeanette Whitaker  Efi Alexopoulou  Stefano Amaducci  Larisa Andronic  Christopher Ashman  Danny Awty-Carroll  Rakesh Bhatia  Lutz Breuer  Salvatore Cosentino  William Cracroft-Eley  Iain Donnison  Berien Elbersen  Andrea Ferrarini  Judith Ford  Jörg Greef  Julie Ingram  Iris Lewandowski  Elena Magenau  Michal Mos  Martin Petrick  Marta Pogrzeba  Paul Robson  Rebecca L. Rowe  Anatolii Sandu  Kai-Uwe Schwarz  Danilo Scordia  Jonathan Scurlock  Anita Shepherd  Judith Thornton  Luisa M. Trindade  Sylvia Vetter  Moritz Wagner  Pei-Chen Wu  Toshihiko Yamada  Andreas Kiesel 《Global Change Biology Bioenergy》2023,15(5):538-558
Demand for sustainably produced biomass is expected to increase with the need to provide renewable commodities, improve resource security and reduce greenhouse gas emissions in line with COP26 commitments. Studies have demonstrated additional environmental benefits of using perennial biomass crops (PBCs), when produced appropriately, as a feedstock for the growing bioeconomy, including utilisation for bioenergy (with or without carbon capture and storage). PBCs can potentially contribute to Common Agricultural Policy (CAP) (2023–27) objectives provided they are carefully integrated into farming systems and landscapes. Despite significant research and development (R&D) investment over decades in herbaceous and coppiced woody PBCs, deployment has largely stagnated due to social, economic and policy uncertainties. This paper identifies the challenges in creating policies that are acceptable to all actors. Development will need to be informed by measurement, reporting and verification (MRV) of greenhouse gas emissions reductions and other environmental, economic and social metrics. It discusses interlinked issues that must be considered in the expansion of PBC production: (i) available land; (ii) yield potential; (iii) integration into farming systems; (iv) R&D requirements; (v) utilisation options; and (vi) market systems and the socio-economic environment. It makes policy recommendations that would enable greater PBC deployment: (1) incentivise farmers and land managers through specific policy measures, including carbon pricing, to allocate their less productive and less profitable land for uses which deliver demonstrable greenhouse gas reductions; (2) enable greenhouse gas mitigation markets to develop and offer secure contracts for commercial developers of verifiable low-carbon bioenergy and bioproducts; (3) support innovation in biomass utilisation value chains; and (4) continue long-term, strategic R&D and education for positive environmental, economic and social sustainability impacts.  相似文献   
92.
The nitrogen (N) cycle is essentially 'leaky'. The losses of small amounts of nitrate to waters and of ammonia and nitrous oxide to the atmosphere are a part of the global biogeochemical N cycle. However, intensive agricultural production, industry and vehicle use have more tem change and health concerns. Research has identified agricultural practices that cause large losses of N and, in some cases, developed solutions. This paper discusses the problems of maintaining productivity while reducing N losses, compares conventional with low input (integrated) and organic farming systems, and discusses wider options. It also looks at the need to integrate studies on N with other environmental impacts, set in the context of the whole farm system, to provide truly sustainable agricultural systems.  相似文献   
93.

Background

In the backdrop of conflicting reports (some studies reported adverse outcomes of biomass fuel use whereas few studies reported absence of any association between adverse health effect and fuel use, may be due to presence of large number of confounding variables) on the respiratory health effects of biomass fuel use, this cross sectional survey was undertaken to understand the role of fuel use on pulmonary function.

Method

This study was conducted in a village of western India involving 369 randomly selected adult subjects (165 male and 204 female). All the subjects were interviewed and were subjected to pulmonary function test. Analysis of covariance was performed to compare the levels of different pulmonary function test parameters in relation to different fuel use taking care of the role of possible confounding factors.

Results

This study showed that biomass fuel use (especially wood) is an important factor for deterioration of pulmonary function (particularly in female). FEV1 (p < .05), FEV1 % (p < .01), PEFR (p < .05) and FEF25–75 (p < .01) values were significantly lower in biomass fuel using females than nonusers. Comparison of only biomass fuel use vs. only LPG (Liquefied Petroleum Gas) use and only wood vs. only LPG use has showed that LPG is a safer fuel so far as deterioration of pulmonary function is concerned. This study observes some deterioration of pulmonary function in the male subjects also, who came from biomass fuel using families.

Conclusion

This study concluded that traditional biomass fuels like wood have adverse effects on pulmonary function.  相似文献   
94.
The objectives of our research were to assess the soil enzyme activities in relation with soil physicochemical and oxide minerals in the coastal agroecosystem of Puducherry region, India. Soils from nine farms in organic (ORG), sustainable (SUS), and conventional (CON) farming were sampled. Organically managed farming system soils contain significantly higher amounts of soil total N, organic carbon, and a higher level of microbial biomass C and N. Urease, protease, β-glucosidase, cellulose, saccharase, xylanase, and alkaline phosphatase enzyme activities were higher in organic farming system soils compared to sustainable and conventional farming soils. In addition, silt, clay, Al2O3, CaO, Fe2O3, K2O, MgO, MnO, Na2O, and P2O5 oxides were higher in organic farming soil and they showed a significant positive correlation with soil enzyme activities. Our study revealed that soil enzyme activities and soil minerals were significantly affected by farm management practices. The organic farming system had improved the soil health, enzyme activities, and plant available nutrients in coastal agro-ecosystem.  相似文献   
95.
96.
97.
Recent studies have introduced the metric GWPbio, an indicator of the potential global warming impact of CO2 emissions from biofuels. When a time horizon of 100 years was applied, the studies found the GWPbio of bioenergy from slow‐growing forests to be significantly lower than the traditionally calculated GWP of CO2 from fossil fuels. This result means that bioenergy is an attractive energy source from a climate mitigation perspective. The present paper provides an improved method for quantifying GWPbio. The method is based on a model of a forest stand that includes basic dynamics and interactions of the forest's multiple carbon pools, including harvest residues, other dead organic matter, and soil carbon. Moreover, the baseline scenario (with no harvest) takes into account that a mature stand will usually continue to capture carbon if not harvested. With these methodological adjustments, the resulting GWPbio estimates are found to be two to three times as high as the estimates of GWPbio found in other studies, and also significantly higher than the GWP of fossil CO2, when a 100‐year time horizon is applied. Hence, the climate impact per unit of CO2 emitted seems to be even higher for the combustion of slow‐growing biomass than for the combustion of fossil carbon in a 100‐year time frame.  相似文献   
98.
风电作为清洁可再生绿色能源越来越受到世界各国的重视,其建设规模也在不断扩大,导致风电建设与鸟类保护的矛盾进一步凸显,如何协调风电发展与物种保护已成为生态学家和保护生物学家关注的热点主题。为了探究风机对鸟类物种、功能和谱系的影响,本研究于2019年1、3、4、5月,采用样线法对连山风电场的鸟类多样性进行了4次调查。根据样线离风机距离的远近设置4个梯度: 100~300 m有6条样线,300~500 m 有13条样线,500~700 m 有8条样线,>700 m 有5条样线。结果表明: 本次调查中记录了繁殖留鸟76种,隶属于11目31科,目、科中数量最多是雀形目(53种)和画眉科(12种)。鸟类物种丰富度、功能丰富度(FRic)和谱系多样性(Faith PD)随着离风机距离的增加呈增加趋势: 在500 m以内未显著增加,500 m外呈显著增加趋势;鸟类群落水平的扩散能力呈现出增加趋势。鸟类群落的平均成对功能和谱系距离的标准化效应值(SES.MFD和SES.MPD)均小于0,其中显著低于随机值的样线占比约为50%(P<0.05)。风力发电机对鸟类物种、功能和谱系的影响主要在前500 m的距离;本研究的4个梯度中,鸟类群落的功能和谱系结构均表现为聚集特征。研究证实,风机对鸟类的影响是多维度的,在评估风机对鸟类群落的影响时仅考虑物种多样性可能难以提供全面的信息。  相似文献   
99.
100.
The global push to achieve ecosystem restoration targets has resulted in an increased demand for native seeds that current production systems are not able to fulfill. In many countries, seeds used in ecological restoration are often sourced from natural populations. Though providing seed that is reflective of the genetic diversity of a species, wild harvesting often cannot meet the demands for large‐scale restoration and may also result in depletion of native seed resources through over harvesting. To improve seed production and decrease seed costs, seed production systems have been established in several countries to generate native seeds based on agricultural or horticultural production methods or by managing natural populations. However, there is a need to expand these production systems which have a primary focus on herbaceous species to also include slower maturing shrub and tree seed. Here we propose that to reduce the threat of overharvest on the viability of natural populations, seed collection from natural populations should be replaced or supplemented by seed production systems. This overview of seed production systems demonstrates how to maximize production and minimize unintended selection bias so that native seed batches maintain genetic diversity and adaptability to underpin the success of ecological restoration programs.  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