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   20467篇
  免费   182篇
  国内免费   201篇
安全科学   534篇
废物处理   995篇
环保管理   2419篇
综合类   2687篇
基础理论   5315篇
环境理论   5篇
污染及防治   5650篇
评价与监测   1657篇
社会与环境   1466篇
灾害及防治   122篇
  2023年   95篇
  2022年   220篇
  2021年   218篇
  2020年   142篇
  2019年   177篇
  2018年   328篇
  2017年   323篇
  2016年   535篇
  2015年   365篇
  2014年   584篇
  2013年   1755篇
  2012年   676篇
  2011年   868篇
  2010年   809篇
  2009年   800篇
  2008年   893篇
  2007年   983篇
  2006年   875篇
  2005年   724篇
  2004年   730篇
  2003年   707篇
  2002年   674篇
  2001年   911篇
  2000年   632篇
  1999年   394篇
  1998年   274篇
  1997年   246篇
  1996年   291篇
  1995年   270篇
  1994年   250篇
  1993年   233篇
  1992年   240篇
  1991年   208篇
  1990年   214篇
  1989年   219篇
  1988年   197篇
  1987年   158篇
  1986年   126篇
  1985年   138篇
  1984年   169篇
  1983年   153篇
  1982年   193篇
  1981年   134篇
  1980年   119篇
  1979年   152篇
  1978年   118篇
  1977年   107篇
  1976年   100篇
  1975年   83篇
  1974年   88篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
241.
This paper uses a sensitivity framework approach to look at the probabilistic impacts of climate change on 20-year return period flood peaks, by applying a set of typical response surfaces alongside the probabilistic UK Climate Projections (UKCP09) for 10 river-basin regions over Scotland. The first paper of the pair used the same approach for 10 river-basin regions over England and Wales. This paper develops the methodology for Scotland, by first enabling better estimation of the response type of Scottish catchments. Then, as for England and Wales, the potential range of impacts is shown for different types of catchment in each river-basin region in Scotland, and regional average impact ranges are estimated. Results show clear differences in impacts between catchments of different types and between regions. The Argyll and West Highland regions show the highest impacts, while the North-East Scotland region shows the lowest impacts. The overall ranges are generally smaller for Scotland than England and Wales.  相似文献   
242.
Renewable and alternative fuels have numerous advantages compared with fossil fuels as they are renewable and biodegradable and provide food and energy security and foreign exchange savings besides addressing environmental concerns and socio-economic issues (Yaliwal et al. 2013. International Journal of Sustainable Engineering, doi:10.1080/19397038.2013.801530. Zhu et al. 2011a, Applied Thermal Engineering 31 (14–15): 2271–2278; Zhu et al. 2011b, Fuel 90: 1743-1750; Banapurmath, Tewari, and Hosmath 2008, Renewable Energy 33: 2007-2018; Banapurmath 2009, “Performance, Combustion and Emission Characteristics of a Single Cylinder Direct Injection CI Engine Operated on Dual Fuel Mode Using Honge Oil and Producer Gas.” PhD thesis, 1–195; Banapurmath et al. 2011, Waste and Biomass Valorization 2: 1–11). In this context, the main objective of the present work is to study methods of biofuel production such as Honge oil methyl ester (HOME) using a conventional transesterification process and bioethanol from the Calliandra calothyrsus shrub using a new pretreatment method known as hydrothermal explosion. Further, experimental investigations were carried out on a single-cylinder, four-stroke, direct-injection stationary diesel engine operating in a dual-fuel mode using HOME, bioethanol and producer gas combinations to determine its performance, combustion and emission characteristics. The performance of the dual-fuel engine was analyzed at optimized engine conditions. HOME-Bioethanol (BE) blends such as HOME+ 5% bioethanol (BE5), HOME+ 10% bioethanol (BE10) and HOME+ 15% bioethanol (BE15) were prepared by adding bioethanol to HOME (on volume basis) in different proportions ranging from 5 to 15% with an increment of 5%. In this present work, the effect of different BE blends on the performance of producer gas fuelled dual fuel engine was studied. Experimental investigation on dual fuel engine using BE5-Producer gas operation resulted in up to 4–9% increased brake thermal efficiency with decreased hydrocarbon (HC), carbon monoxide (CO) and marginally increased nitric oxide (NOx) emission levels compared to HOME-Producer gas, BE10-producer gas and BE15-producer gas mode of operation. However, it was observed that, the overall performance of BE-producer gas operation was found to be lower compared to diesel-producer gas operation.  相似文献   
243.
Identifying effective adaptation strategies for coastal communities dependent on marine resources and impacted by climate change can be difficult due to the dynamic nature of marine ecosystems. The task is more difficult if current and predicted shifts in social and economic trends are considered. Information about social and economic change is often limited to qualitative data. A combination of qualitative and quantitative models provide the flexibility to allow the assessment of current and future ecological and socio-economic risks and can provide information on alternative adaptations. Here, we demonstrate how stakeholder input, qualitative models and Bayesian belief networks (BBNs) can provide semi-quantitative predictions, including uncertainty levels, for the assessment of climate and non-climate-driven change in a case study community. Issues are identified, including the need to increase the capacity of the community to cope with change. Adaptation strategies are identified that alter positive feedback cycles contributing to a continued decline in population, local employment and retail spending. For instance, the diversification of employment opportunities and the attraction of new residents of different ages would be beneficial in preventing further population decline. Some impacts of climate change can be combated through recreational bag or size limits and monitoring of popular range-shifted species that are currently unmanaged, to reduce the potential for excessive removal. Our results also demonstrate that combining BBNs and qualitative models can assist with the effective communication of information between stakeholders and researchers. Furthermore, the combination of techniques provides a dynamic, learning-based, semi-quantitative approach for the assessment of climate and socio-economic impacts and the identification of potential adaptation strategies.  相似文献   
244.
Water represents 71% of all earth area and about 97% of this water is salty water. So, only 3% of the overall world water quantity is freshwater. Human can benefit only from 1% of this water and the remaining 2% freeze at both poles of earth. Therefore, it is important to preserve the freshwater through increasing the plants consuming salty water. The future prosperity of feed resources in arid and semi-arid countries depends on economic use of alternative resources that have been marginalized for long periods of time, such as halophytic plants, which are one such potential future resource. Halophyte plants can grow in high salinity water and soil and to some extent during drought. The growth of these plants depends on the contact of the salted water with plant roots as in semi-desert saline water, mangrove swamps, marshes, and seashores. Halophyte plants need high levels of sodium chloride in the soil water for growth, and the soil water must also contain high levels of salts, as sodium hydroxide or magnesium sulfate. There are many uses for halophyte plants, including feed for animals, vegetables, drugs, sand dune stabilizers, wind shelter, soil cover, wetland cultivation, laundry detergents, and paper production. This paper will focus on the use of halophytes as a feed additive for animals. In spite of the good nutritional value of halophytes, some anti-nutritional factors as nitrates, nitrite complexes, tannins, glycosides, phenolic compounds, saponins, oxalates, and alkaloids may be present in some of them. The presence of such anti-nutritional agents makes halophytes unpalatable to animals, which tends to reduce feed intake and nutrient use. Therefore, the negative effects of these plants on animal performance are the only objection against using halophytes in animal feed diets. This review article highlights the beneficial impact of considering halophytes in animal feeding on saving freshwater and illustrates its nutritive value for livestock from different aspects.  相似文献   
245.
Abstract

The main objective of this study is the degradation of a synthetic solution of atrazine by a modified vermiculite catalyzed ozonation, in a rotating packed bed (RPB) reactor. A 0.5?L RPB reactor was used to perform the experiments, using a Central Composite Design (CCD) response surface to construct the quadratic model based on the factors: pH, catalyst concentration and reactor rotation frequency. The response variable was the removal of the organic load measured in terms of Chemical Oxygen Demand (COD). After the complete quadratic model was constructed through the response surface, the COD degradation process had an optimal removal of 41% under the following conditions: pH 8.0, rotation of 1150?rpm and catalyst concentration 0.66?g L?1.  相似文献   
246.
Environmental Science and Pollution Research - The objective of this study was to evaluate the effect of salinity on the acute and sub-chronic toxicity of silver nanoparticles (AgNPs) in Persian...  相似文献   
247.
Environmental Science and Pollution Research - Hydroxyurea (HDU), a class of antineoplastic drugs, has a powerful efficacy in the treatment of several types of malignancies. However, it has...  相似文献   
248.
Environmental Science and Pollution Research - Bisphenol-A is widely used chemical in industry and unfortunately often detected in natural waters. Considered as an emerging pollutant, bisphenol-A...  相似文献   
249.
250.
The purpose of the study reported here was to investigate the relative resistance of yeast species to various metallic and metalloid ions, with a view to gaining more knowledge on this subject, as resistant species may become dominant in habitats contaminated with the relevant metals. Saccharomyces cerevisiae, Candida albicans and Candida tropicalis were grown in media containing different concentrations of mercury (as HgCl(2)), cadmium (as CdCl(2)), lead (as Pb(CH(3)COO)(2)), arsenic (as Na(2)HAsO(4)) and selenium (as Na(2)SeO(3)) for various intervals. Invariably, the two Candida species turned out to be more resistant to all the metals studied than S. cerevisiae. The metal showing the highest toxicity for these species was mercury, with cadmium being the second, lead, the third and arsenic and selenium being the least toxic elements. Strains showing resistance to mercury were isolated, even in the case of S. cerevisiae.  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