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   20004篇
  免费   1611篇
  国内免费   4693篇
安全科学   2732篇
废物处理   486篇
环保管理   3205篇
综合类   13024篇
基础理论   2082篇
环境理论   9篇
污染及防治   1705篇
评价与监测   1024篇
社会与环境   1190篇
灾害及防治   851篇
  2024年   78篇
  2023年   319篇
  2022年   623篇
  2021年   807篇
  2020年   806篇
  2019年   678篇
  2018年   585篇
  2017年   742篇
  2016年   893篇
  2015年   928篇
  2014年   1096篇
  2013年   1303篇
  2012年   1528篇
  2011年   1671篇
  2010年   1158篇
  2009年   1266篇
  2008年   953篇
  2007年   1431篇
  2006年   1407篇
  2005年   1198篇
  2004年   1038篇
  2003年   972篇
  2002年   841篇
  2001年   713篇
  2000年   620篇
  1999年   599篇
  1998年   392篇
  1997年   331篇
  1996年   225篇
  1995年   222篇
  1994年   184篇
  1993年   167篇
  1992年   114篇
  1991年   72篇
  1990年   48篇
  1989年   27篇
  1988年   36篇
  1987年   25篇
  1986年   17篇
  1985年   14篇
  1984年   25篇
  1983年   19篇
  1982年   23篇
  1981年   14篇
  1980年   22篇
  1979年   20篇
  1974年   8篇
  1973年   9篇
  1972年   7篇
  1971年   11篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
691.
分析了环保工程总承包项目质量管理中存在的主要问题,提出了提高项目质量管理水平的主要措施。  相似文献   
692.
论述了生态工业园区政策法规建设中存在的问题,并提出了建立健全生态工业园区政策法规的建议。  相似文献   
693.
论述了为实现全面建设小康社会的发展目标,必须走跨越式发展之路。  相似文献   
694.
Ammonia emissions from two contrasting seabird colonies in Scotland were measured, based on the determination of atmospheric concentrations downwind of the colonies. Atmospheric concentrations of ammonia (NH3) across the downwind plume were compared with the inverse application of a Gaussian dispersion model (ID) to calculate the modelled NH3 emission that would generate the measured cross-wind-integrated plume concentration. In parallel, a tracer gas (sulphur hexafluoride, SF6) was released from the colonies with air samples taken to allow determination of SF6 concentrations. On the basis of the known emission rate of SF6, the magnitude of ammonia emissions was estimated by the cross-wind-integrated tracer ratio (TR) of NH3/SF6 concentrations. Coupled with data on annual bird attendance, the measurements indicate annual emissions from the Isle of May and the Bass Rock of 18 and 132 tonnes NH3-N year–1, respectively. The measured NH3 emissions were compared with estimates of seabird nitrogen excretion to estimate the proportion of excreted N that is volatilised as NH3 (FNr). The emission estimates of the two methods compared favourably, giving 4 and 6 kg NH3-N h–1 (FNr = 15%) for the Isle of May for the ID and TR methods, respectively, and 21 and 25 kg NH3-N h–1 (FNr = 50%) for the Bass Rock for the ID and TR methods, respectively. The results provide the first measurement-based estimates to allow regional up scaling of ammonia emissions from seabirds.  相似文献   
695.
This paper provides the background to this special issue, outlining the extent to which the global atmospheric nitrogen cycle has been modified by human activity and outlining the range of effects. The global total emissions of reduced and oxidized nitrogen, amount to 124 Tg N, and exceed those from natural sources (34 Tg N) by almost a factor of four showing the extent to which anthropogenic activity has taken over the global N cycle. Of the 124 Tg N, 70 Tg N is emitted in the oxidized form, largely as NO and 70% of which results directly from anthropogenic activity. The remaining 54 Tg N is emitted as NH3, (66% anthropogenic). The enhanced nitrogen emissions are associated with a range of local, regional and global issues including, acidification, eutrophication, climate change, human health and tropospheric O3. The paper also places the Global Nitrogen Enrichment (GaNE) research programme in the UK in a wider perspective.  相似文献   
696.
The distribution and impacts of different nitrogen pollutants are inextricably linked. To understand the problem fully, the interactions between the different pollutants need to be taken into account. This is particularly important when it comes to abatement techniques, since measures to reduce emissions of one nitrogen pollutant can often lead to an increase in another. This project represents a step towards greater understanding of these issues by linking together new and existing nitrogen flux models into a larger framework. The modelling framework has been constructed and some of the nitrogen flows between fields, farms and the atmosphere have been modelled for a UK study area for typical farm management scenarios.  相似文献   
697.
Amino acids constitute one of the largest inputs of organic nitrogen (N) to most polar soils and have been hypothesized to be important in regulating vegetational succession and productivity in Arctic ecosystems. Our understanding of amino acid cycling in these soils, however, is poor. The aim of this study was to investigate the size and rate of turnover of the amino acid pool in a range of Arctic and Antarctic soils. Our results indicate that in polar soils with either high or low ornithogenic inputs the amino acid pool is small in comparison to the inorganic N pool (NO3 and NH+4). The free amino acid pool constituted only a small proportion of the total dissolved organic nitrogen (DON) pool in these soils. Here we show that these low concentrations may be due to rapid use by the soil microbial community in both Arctic and Antarctic soils. The turnover of the amino acid pool in soil was extremely rapid, with a half-life ranging from 2 to 24 h, indicating that this N pool can be turned over many hundred times each summer when polar soils are frequently unfrozen. The implications of amino acids in N cycling and plant and microbial nutrition are discussed.  相似文献   
698.
Impact of Land Use on Soluble Organic Nitrogen in Soil   总被引:5,自引:0,他引:5  
Although it has been hypothesized that soluble organic nitrogen (SON) plays a central role in regulating productivity in some terrestrial ecosystems, the factors controlling the size of the SON pool in soil remain poorly understood. Therefore our principal aim in this work was to assess the impact of seven different land use systems (rough and managed grassland, deciduous and coniferous woodland, heathland, wetland and tilled land) on the size of the SON and inorganic N (NO 3 , NH 4 + ) pools in the surface soil layer (0–15 cm). After extraction with deionised water, we found that in most cases the size of the water extractable organic N (WEON) pool was similar in size to the inorganic N pool. In contrast, the KCl extractable organic N (KClEON) pool constituted the dominant form of soluble N in soils under all land uses, perhaps indicating that significant amounts were held on the soil exchange phase. In contrast to inorganic N, which varied significantly with land use, the size of the KClEON and WEON pool was similar for all land uses with the exception of KClEON in tilled land, where significantly lower amounts were observed. We conclude that SON constitutes an important soil N pool in a broad range of land uses, and that its role in microbial N assimilation, plant nutrition and ecosystem responses to atmospheric N deposition warrants further attention. SAFRD, University of Newcastle, Newcastle-upon-Tyne, NE1 7RU, U.K.  相似文献   
699.
南充市空气中可吸入颗粒物污染水平分析   总被引:3,自引:1,他引:3  
本文在连续1年又5个月同步采样的基础上,测得南充市市辖三城区5个采样监测点环境空气中PM10的浓度及其时空变化进行了分析。结果表明,PM10的日平均浓度范围为0.020~1.030mg/m^3,超标率达38.0%;周日均浓度在0.040~0.520mg/m^3之间,超标率达到了37.8%。空气污染最重为嘉陵城区,其次为高坪城区,再次为石油学院、炼油厂和市府二院。浓度季节变化特征表现为冬季最高,其次为秋季,再次为春季,最轻为夏季。  相似文献   
700.
城市污水除磷技术发展   总被引:8,自引:4,他引:8  
侯红娟  周琪 《四川环境》2004,23(6):41-44,49
磷是水体富营养化的一个主要限制因素,控制出水中磷的浓度尤其重要。污水除磷方法有生物除磷、化学除磷及生态除磷,也可将各种方法组合使用,如生物一化学除磷、生物一生态除磷等,实际应用中应根据具体情况选择适宜的除磷方法。  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