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   1842篇
  免费   32篇
  国内免费   173篇
安全科学   90篇
废物处理   114篇
环保管理   168篇
综合类   453篇
基础理论   406篇
环境理论   1篇
污染及防治   519篇
评价与监测   134篇
社会与环境   137篇
灾害及防治   25篇
  2023年   22篇
  2022年   69篇
  2021年   31篇
  2020年   22篇
  2019年   31篇
  2018年   79篇
  2017年   49篇
  2016年   55篇
  2015年   69篇
  2014年   54篇
  2013年   176篇
  2012年   85篇
  2011年   107篇
  2010年   80篇
  2009年   97篇
  2008年   95篇
  2007年   86篇
  2006年   70篇
  2005年   66篇
  2004年   88篇
  2003年   80篇
  2002年   53篇
  2001年   105篇
  2000年   48篇
  1999年   34篇
  1998年   23篇
  1997年   12篇
  1996年   11篇
  1995年   23篇
  1994年   9篇
  1993年   11篇
  1992年   16篇
  1991年   10篇
  1990年   12篇
  1989年   10篇
  1988年   6篇
  1987年   7篇
  1985年   8篇
  1984年   10篇
  1983年   7篇
  1980年   6篇
  1975年   8篇
  1974年   10篇
  1973年   7篇
  1972年   12篇
  1971年   5篇
  1966年   5篇
  1965年   5篇
  1959年   5篇
  1957年   5篇
排序方式: 共有2047条查询结果,搜索用时 31 毫秒
991.
To better understand sublethal effects of harmful algal blooms (HABs) on fish, mummichog, Fundulus heteroclitus (L.), were exposed in the laboratory to varying, environmentally relevant densities of Pfiesteria shumwayae (Glasgow et Burkholder, CCMP 2089, dinoflagellate) and Chaetoceros concavicornis (Mangin, CCMP 169, diatom). Two experiments were conducted during the spring of 2003 and 2004 to quantitatively examine the effects of acute (2 h) P. shumwayae and C. concavicornis algal exposure on mummichog brain activity using c-Fos expression as a marker of altered neuronal activity. Brains from HAB-exposed fish were removed, sectioned, and stained using immunocytochemistry prior to quantifying neuronal c-Fos expression. Fish exposed to P. shumwayae and C. concavicornis showed increased c-Fos expression compared to unexposed control fish. A significant dose-response relationship was observed, with increased labeling in brains of fish exposed to higher cell densities for both HAB species tested (P ≤ 0.01). Increased labeling was found in the telencephalon, optic lobes, midbrain, and portions of the medulla. The greatest increases in expression were observed in the telencephalon of P. shumwayae-exposed fish, and in the telencephalon and optic lobes of C. concavicornis-exposed fish (P ≤ 0.01). These increases in c-Fos expression are consistent with other physical and chemical stress exposures observed in fish. Neuronal stress, evidenced by c-Fos expression, demonstrates a sublethal effect of exposure and changes in brain activity in fish exposed to HAB species.  相似文献   
992.
环保企业往往涉及许多化学品的处理与处置,对企业员工来说,是带有一定危险性的行业.因此,安全生产至关重要,而企业职工的安全心理教育也是刻不容缓的.本文以大连东泰产业废弃物处理有限公司为例,分析了此类环保企业员工可能存在的一些不良安全心理,指出了安全教育的重要性和紧迫性,并结合其他企业安全生产的经验,提出了制定必要的奖惩制度、优化企业管理水平、解决工作紧张给职工带来的心理问题、加强职工心理素质的培养和训练,提高其沟通减压的能力等提升企业员工安全心理健康发展、提高员工安全意识的方法和措施.  相似文献   
993.
Removal of nitrogen in wastewater before discharge into receiving water courses is an important consideration in treatment systems. However, nitrogen removal efficiency is usually limited due to the low carbon/nitrogen (C/N) ratio. A common solution is to add external carbon sources, but amount of liquid is difficult to determine. Therefore, a combined wood-chip-framework substrate (with wood, slag and gravel) as a slow-release carbon source was constructed in baffled subsurface-flow constructed wetlands to overcome the problem. Results show that the removal rate of ammonia nitrogen (NH4+-N), total nitrogen (TN) and chemical oxygen demand (COD) could reach 37.5%–85%, 57.4%–86%, 32.4%–78%, respectively, indicating the combined substrate could diffuse sufficient oxygen for the nitrification process (slag and gravel zone) and provide carbon source for denitrification process (wood-chip zone). The nitrification and denitrification were determined according to the location of slag/gravel and wood-chip, respectively. Nitrogen removal was efficient at the steady phase before a shock loading using slag-wood-gravel combined substrate because of nitrification–denitrification process, while nitrogen removal was efficient under a shock loading with wood-slag-gravel combined substrate because of ANAMMOX process. This study provides a new idea for wetland treatment of high-strength nitrogen wastewater.  相似文献   
994.
湖南攸县稻米镉(Cd)富集特征及原因解析   总被引:2,自引:0,他引:2  
攸县大米富镉(Cd)问题受到社会的广泛关注.通过实地调查和采样分析,应用路径分析模型(PA),多元回归分析和K-means聚类方法分析Cd在土壤-稻米系统中的富集特征,潜在风险和主要影响因子.结果显示攸县稻米Cd平均含量为0.47 mg·kg~(-1),约为国家粮食安全质量标准的2.5倍.稻米Cd富集因子(PUF)服从自然对数分布,变化范围较大.回归分析和PA分析显示土壤pH、土壤Mn和土壤Zn含量为影响PUF变化的主要环境因子,其中土壤Mn对PUF的影响主要体现在对稻米Cd的直接作用,土壤pH和土壤Zn对PUF的影响主要是通过影响土壤Cd含量而间接影响稻米Cd含量.K-means聚类分析显示土壤pH=5.6和土壤Mn含量=333 mg·kg-1可作为研究区对生产严重超标Cd米的土壤进行治理的初步调控阈值.  相似文献   
995.
This paper presents a systematic framework for optimal utilization of by-products generated during crude palm oil refining processes. Three by-products are considered in the supply chain network: soapstock, palm fatty acid distillate (PFAD) and spent bleaching earth (SBE). These by-products, generated from neutralization, deodorization and bleaching processes, are viable feedstocks to other commercial industries such as animal feed, biodiesel, lubricant and soap. The case study is formulated as Mixed Integer Linear Programming (MILP) and integrated into the framework with the objective to maximize the refinery's profit as well as moving towards a conscious mindset of zero waste. This is the first time that such framework is developed and applied for the palm oil industry. The framework is called as Industry to Industry By-products Exchange Network (I2IBEN). An illustrative case study demonstrates a significant potential profit of MYR182, 893 per month.  相似文献   
996.
Prokopy, Linda Stalker, Z. Asligül Göçmen, Jing Gao, Shorna Broussard Allred, Joseph E. Bonnell, Kenneth Genskow, Alicia Molloy, and Rebecca Power, 2011. Incorporating Social Context Variables Into Paired Watershed Designs to Test Nonpoint Source Program Effectiveness. Journal of the American Water Resources Association (JAWRA) 47(1):196‐202. DOI: 10.1111/j.1752‐1688.2010.00508.x Abstract: In a traditional paired watershed study, watersheds are selected to be as similar as possible so that conclusions may be drawn about the performance of Best Management Practices. We have extended the paired watershed concept to examine the effectiveness of watershed management programs by adding comparative criteria for social characteristics. For four different 8 or 11/12 digit hydrologic unit code (HUC) watersheds in the Midwest, we have piloted a systematic method for selecting paired subwatersheds. First, we developed a list of 11 key variables. Next, a factor analysis was conducted to determine the underlying structure of the 11 input variables. Finally, in each of the four watersheds, potential paired subwatersheds (all 14 digit HUCs) were selected using the factors in a cluster analysis. Informal interviews were then held with key informants in each watershed to provide qualitative assessments of criteria that could impact the comparability of the subwatersheds. This method for selecting paired watersheds should be helpful for other researchers to test the effectiveness of watershed management programs focused on behavior change.  相似文献   
997.
Wood chip bioreactors are receiving increasing attention as a means of reducing nitrate in subsurface tile drainage systems. Agrochemicals in tile drainage water entering wood chip bioreactors can be retained or degraded and may affect denitrification. The degradation of 5 mg L atrazine, enrofloxacin, and sulfamethazine under denitrifying conditions in wood chips from an in situ reactor was determined. The impact of these chemicals on denitrifying microorganisms was assessed using the denitrification potential assay, most probable number (MPN), and quantitative polymerase chain reaction targeting the gene of the denitrifiers. Initial half-lives for these chemicals in the aqueous phase were 0.98 d for atrazine, 0.17 d for enrofloxacin, and 6.2 d for sulfamethazine. Similar rates of disappearance in autoclaved and nonautoclaved wood chip solutions during the first 48 h suggested sorption was the dominant mechanism. The presence of atrazine did not impair denitrification potential, the MPN, or the copy number. The denitrifier MPN and copy number in sulfamethazine- and enrofloxacin-treated microcosms were less than the control within the first 5 d after chemical addition, whereas the denitrification potentials were not affected. However, after 45 d the denitrification rate, MPN and gene copy numbers for sulfamethazine and enrofloxacin were similar to that of the no-chemical control, indicating that acclimation of the denitrifier population to the antibiotic or reduced bioavailability over time allowed recovery of the denitrifier population.  相似文献   
998.
Recent papers have shown that climate change affects many species, including birds. Several papers from different areas have devoted attention to the negative correlation between the dates of breeding and year, and also negative correlation between the dates of breeding and air spring temperatures. Recent work give some firm evidence for postulating causal relationship between spring temperature and laying dates. We used 31 years (1979-2009) of data from blackcap Sylvia atricapilla in Mokrice area, Northwestern Croatia to assess whether there has been any systematic change in breeding phenology through time.Among environmental factors possibly affecting the breeding date, consideration was given to mean monthly air temperatures (April-May). Over the past three decades, the breeding date of blackcap in our study population has changed significantly: They started breeding progressively earlier (11.77 days). Two regression analysis with laying date as criterion variable showed that spring temperatures can significantly predict variation of laying date and that there are also some other unknown factors which significantly explain variation of laying date. We conclude that blackcaps across Northwestern Croatia are breeding earlier and that mean air spring temperatures is probably the most important factor causing it, among other factors.  相似文献   
999.
1000.
Considering high-moisture municipal solid waste (MSW) of China, a steam dried MSW gasification and melting process was proposed, the feasibility was tested, and the mass and energy balance was analyzed. Preliminary experiments were conducted using a fixed-bed drying apparatus, a 200 kg per day fluidized-bed gasifier, and a swirl melting furnace. Moisture percentage was reduced from 50% to 20% roughly when MSW was dried by slightly superheated steam of 150°C?C350°C within 40 min. When the temperature was less than 250°C, no incondensable gas was produced during the drying process. The gasifier ran at 550°C?C700°Cwith an air equivalence ratio (ER) of 0.2?C0.4. The temperature of the swirl melting furnace reached about 1240°C when the gasification ER was 0.3 and the total ER was 1.1. At these conditions, the fly ash concentration in the flue gas was 1.7 g·(Nm3)?1, which meant over 95% fly ash was trapped in the furnace and discharged as slag. 85% of Ni and Cr were bound in the slag, as well as 60% of Cu. The mass and energy balance analysis indicates that the boiler heat efficiency of an industrial MSW incineration plant reaches 86.97% when MSW is dried by steam of 200°C. The boiler heat efficiency is sensitive to three important parameters, including the temperature of preheated MSW, the moisture percentage of dried MS Wand the fly ash percentage in the total ash.  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