全文获取类型
收费全文 | 1473篇 |
免费 | 198篇 |
国内免费 | 1165篇 |
专业分类
安全科学 | 131篇 |
废物处理 | 100篇 |
环保管理 | 98篇 |
综合类 | 1750篇 |
基础理论 | 276篇 |
污染及防治 | 449篇 |
评价与监测 | 22篇 |
社会与环境 | 9篇 |
灾害及防治 | 1篇 |
出版年
2024年 | 2篇 |
2023年 | 24篇 |
2022年 | 67篇 |
2021年 | 68篇 |
2020年 | 80篇 |
2019年 | 79篇 |
2018年 | 103篇 |
2017年 | 95篇 |
2016年 | 108篇 |
2015年 | 129篇 |
2014年 | 140篇 |
2013年 | 162篇 |
2012年 | 185篇 |
2011年 | 166篇 |
2010年 | 153篇 |
2009年 | 152篇 |
2008年 | 147篇 |
2007年 | 161篇 |
2006年 | 166篇 |
2005年 | 113篇 |
2004年 | 93篇 |
2003年 | 77篇 |
2002年 | 64篇 |
2001年 | 48篇 |
2000年 | 43篇 |
1999年 | 31篇 |
1998年 | 29篇 |
1997年 | 33篇 |
1996年 | 31篇 |
1995年 | 25篇 |
1994年 | 18篇 |
1993年 | 18篇 |
1992年 | 5篇 |
1991年 | 11篇 |
1990年 | 3篇 |
1989年 | 2篇 |
1987年 | 1篇 |
1986年 | 2篇 |
1979年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有2836条查询结果,搜索用时 406 毫秒
991.
Set-aside management: How do succession, sowing patterns and landscape context affect biodiversity? 总被引:1,自引:0,他引:1
Teja Tscharntke Péter BatáryCarsten F. Dormann 《Agriculture, ecosystems & environment》2011,143(1):37-44
European Union (EU) member states set aside between 5 and 15% of arable land during the last two decades, but abolition of the set-aside scheme in 2008 caused a sudden loss in habitat availability and biodiversity in agricultural landscapes. Management of set-aside has many facets and in this perspective paper we focus on the biodiversity effects of successional age, sowing strategies and landscape context. Young, 1-2-year-old set-asides have been initially considered to be too ephemeral to have any conservation value. However, when a rich seed and bud bank is available, a species-rich natural (secondary) succession can be observed. Arable (annual) weed communities in the first two years of succession can even include endangered plant species with associated rare insect consumers. Furthermore, many bird species benefit from early-successional habitats, whereas small mammal communities are richer in older habitats. If the local plant species pool is poor, sowings of diverse mixtures from regional seed collections can be recommended. Set-aside managers using species-rich sowings often experience that dominant weeds suppress the less competitive annual species. This trend to species-poor communities can be avoided by intraspecific aggregation of competitively weak species. Broadening the spatial scale from the plot to the landscape, efficiency of set-aside is highest in simple landscapes, where set-aside exhibits greatest effect in enhancement of biodiversity and associated services such as pollination and biological control. In complex landscapes, however, additional set-aside does not add much to the high level of biodiversity and ecological processes already present. Twenty percent of semi-natural, non-crop habitat appears to be a rough threshold for enhancing biodiversity and sustaining services such as pollination and biological control, but improved set-aside management should have the potential to reduce the percentage of semi-natural non-crop habitat needed. EU policy should tailor set-aside schemes for the maintenance of biodiversity and also consider that management efficiency is higher in simple than complex landscapes. 相似文献
992.
993.
中温(32~35℃)环境下,通过对固含率为15%三种不同粒径的发酵物料(0.5 cm以下、1~2 cm、3~5 cm)的厌氧消化过程分析,并且对固含率20%、25%、30%与带消化液回流的厌氧发酵实验研究,结果表明:三种不同粒径发酵物料产气量最大的是<0.5 cm,其次依次为1~2 cm,3~5 cm,考虑到粒径小容易酸化的原因,选择秸秆厌氧消化的粒径范围0.5~2.0 cm;小麦秸秆无回流间歇发酵的产气率可达到每立方米发酵物料2~3 m3/d,带消化液回流的厌氧发酵产气率达到2.2 m3/(m3.d);初始固含率8%的发酵物料经过消化液回流、排剩,最终发酵物的固含率为16.4%;小麦秸秆无回流间歇发酵产甲烷潜能最大达249.0 m3/t,对应的固含率为25%,带消化液回流的厌氧发酵产甲烷潜能达223.06 m3/t。 相似文献
994.
Gergely Forgács Saeid Alinezh Amir Mirabdollah Elisabeth Feuk-Lagerstedt Ilona Sárvári Horváth 《环境科学学报(英文版)》2011,23(10):1747-1753
A two-stage system was developed which combines the biological degradation of keratin-rich waste with the production of biogas. Chicken feather waste was treated biologically with a recombinant Bacillus megaterium strain showing keratinase activity prior to biogas production. Chopped, autoclaved chicken feathers (4%, W/V) were completely degraded, resulting in a yellowish fermentation broth with a level of 0.51 mg/mL soluble proteins after 8 days of cultivation of the recombinant strain. During the subsequent anaerobic batch digestion experiments, methane production of 0.35 Nm3/kg dry feathers (i.e., 0.4 Nm3/kg volatile solids of feathers), corresponding to 80% of the theoretical value on proteins, was achieved from the feather hydrolyzates, independently of the pre-hydrolysis time period of 1, 2 or 8 days. Cultivation with a native keratinase producing strain, Bacillus licheniformis resulted in only 0.25 mg/mL soluble proteins in the feather hydrolyzate, which then was digested achieving a maximum accumulated methane production of 0.31 Nm3/kg dry feathers. Feather hydrolyzates treated with the wild type B. megaterium produced 0.21 Nm3 CH4/kg dry feathers as maximum yield. 相似文献
995.
To investigate the effect of ultrasonic pretreatment on anaerobic digestion and sludge dewaterability and further to probe into the
influencing factors on sludge dewaterability, sludge flocs were stratified into four fractions: (1) slime; (2) loosely bound extracellular
polymeric substances (LB-EPS); (3) tightly bound EPS (TB-EPS); and (4) EPS-free pellets. The results showed that ultrasonic
pretreatment increased the anaerobic digestion efficiency by 7%–8%. Anaerobic digestion without ultrasonic pretreatment deteriorated
the sludge dewaterability, with the capillary suction time (CST) increased from 1.42 to 47.3 (sec L)/g-TSS. The application of ultrasonic
pretreatment firstly deteriorated the sludge dewaterability (normalized CST increased to 44.4 (sec L)/g-TSS), while subsequent
anaerobic digestion offset this effect and ultimately decreased the normalized CST to 23.2 (sec L)/g-TSS. The dewaterability of
unsonicated sludge correlated with protein (p = 0.003) and polysaccharide (p = 0.004) concentrations in the slime fraction, while
that of sonicated sludge correlated with protein concentrations in the slime and LB-EPS fractions (p < 0.05). Fluorescent excitationemission
matrix analysis showed that the fluorescence matters in the LB-EPS fraction significantly correlated with sludge dewaterability
during anarobic digestion. 相似文献
996.
997.
998.
添加外源微生物对城市生活垃圾堆肥腐熟的影响 总被引:1,自引:0,他引:1
文章探究高效、低成本的圾堆肥技术,为城市生活垃圾的无害化处理和资源化利用提供科学依据。以生活垃圾为原料,采用7 d翻堆一次的方式,进行为期45 d的堆肥试验。试验设常规和添加5%发酵剂堆肥处理,研究添加外源菌剂对城市生活垃圾堆肥过程中物理和化学特性变化的影响及对堆肥腐熟度的影响。结果显示添加5%菌剂的堆肥处理在堆肥24 h后温度达到53℃,堆肥过程中最高温度达到65℃,温度保持50℃以上达24 d;使堆肥C/N迅速下降,并在35 d后,该值稳定在12.2左右;铵态氮与硝态氮比值开始迅速上升,而后逐渐下降,最终比值稳定在1.2,油菜种子的发芽指数达到85%以上。说明添加5%外源微生物菌剂能加速城市垃圾堆肥腐熟进程。 相似文献
999.
微生物来源对餐厨垃圾厌氧消化产氢的影响很大。在添加剂抑制耗氢菌的前提下,单独一种接种的条件下,剩余污泥的产氢效果是最好的,氢气的浓度和产量都最大,分别为47.1%和100.0 mLH2/g VS,其次是矿化污泥和矿化垃圾,颗粒污泥体系氢气的产量最少,分别为88.6 mLH2/g VS,57.8 mLH2/g VS和36.8 mLH2/g VS,其中颗粒污泥体系产生了甲烷气体而另外3中反应体系中并未检测到甲烷。污泥和矿化污泥混合后,在实验时间内,能够提高氢气的产量到106.4 mLH2/g VS,其余的混合体系的氢气的浓度和产量都较单独的剩余污泥体系的差。 相似文献
1000.