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   98699篇
  免费   1420篇
  国内免费   2710篇
安全科学   4038篇
废物处理   3677篇
环保管理   14805篇
综合类   23641篇
基础理论   27597篇
环境理论   73篇
污染及防治   18368篇
评价与监测   5793篇
社会与环境   4049篇
灾害及防治   788篇
  2022年   951篇
  2021年   963篇
  2020年   770篇
  2019年   980篇
  2018年   1336篇
  2017年   1429篇
  2016年   2409篇
  2015年   2085篇
  2014年   2956篇
  2013年   9732篇
  2012年   2711篇
  2011年   3180篇
  2010年   3610篇
  2009年   3726篇
  2008年   2655篇
  2007年   2482篇
  2006年   2787篇
  2005年   2640篇
  2004年   2926篇
  2003年   2745篇
  2002年   2342篇
  2001年   2738篇
  2000年   2308篇
  1999年   1714篇
  1998年   1546篇
  1997年   1501篇
  1996年   1591篇
  1995年   1682篇
  1994年   1572篇
  1993年   1393篇
  1992年   1396篇
  1991年   1342篇
  1990年   1292篇
  1989年   1247篇
  1988年   1091篇
  1987年   1014篇
  1986年   1011篇
  1985年   1084篇
  1984年   1173篇
  1983年   1186篇
  1982年   1184篇
  1981年   1106篇
  1980年   951篇
  1979年   937篇
  1978年   833篇
  1977年   730篇
  1976年   658篇
  1974年   630篇
  1973年   656篇
  1972年   671篇
排序方式: 共有10000条查询结果,搜索用时 281 毫秒
61.

While progress has been made in reducing external nutrient inputs to the Baltic Sea, further actions are needed to meet the goals of the Baltic Sea Action Plan (BSAP), especially for the Baltic Proper, Gulf of Finland, and Gulf of Riga sub-basins. We used the net anthropogenic nitrogen and phosphorus inputs (NANI and NAPI, respectively) nutrient accounting approach to construct three scenarios of reduced NANI-NAPI. Reductions assumed that manure nutrients were redistributed from areas with intense animal production to areas that focus on crop production and would otherwise import synthetic and mineral fertilizers. We also used the Simple as Necessary Baltic Long Term Large Scale (SANBALTS) model to compare eutrophication conditions for the scenarios to current and BSAP-target conditions. The scenarios suggest that reducing NANI-NAPI by redistributing manure nutrients, together with improving agronomic practices, could meet 54–82% of the N reductions targets (28–43 kt N reduction) and 38–64% P reduction targets (4–6.6 kt P reduction), depending on scenario. SANBALTS output showed that even partial fulfillment of nutrient reduction targets could have ameliorating effects on eutrophication conditions. Meeting BSAP targets will require addressing additional sources, such as sewage. A common approach to apportioning sources to external nutrients loads could enable further assessment of the feasibility of eutrophication management targets.

  相似文献   
62.
Fifty percent of the dry zone areas in Sri Lanka have fluoride levels above 1 ppm. This paper discusses the ground conditions and recommends an appropriate range of fluoride in drinking water which can support preventive practices for improving the oral health of children 8-years old and younger. In efforts to address the Chronic Kidney Disease of Unknown etiology (CKDU), water treatment to reduce contaminant level in potable water has been implemented. Such treatment would also remove fluoride and has resulted in potable water with various fluoride levels, depending on concentrations in the raw water. While it is important to reduce fluoride levels, it is important to have appropriate residual levels for prevention of dental caries. It needs, however, to be noted fluoride in excess can cause dental fluorosis. In Sri Lanka's dry zone areas increasing prevalence of dental fluorosis with decreasing prevalence of dental caries has been noted. Consumption of tea and powdered milk could increase total intake of fluoride. Fluoridated toothpaste, when used properly, may, however, result in negligible intake of fluoride. Sri Lanka's hot tropical climate which results in substantial intake of fluids reinforces the need to consider reduction in water fluoride. Consideration of local studies and international standards indicate fluoride levels should be in the range of 0.225–0.500 ppm. In the range of 0.225–0.500 ppm, the prevalence of dental fluorosis and caries was only 14% and 8%, respectively, in an endemic district. When fluoride levels are above 0.500 ppm, the issue of dental fluorosis shall need to be addressed. When levels are below 0.225 ppm, oral health care services shall need to be directed at preventing dental caries.  相似文献   
63.
Phyllanthus niruri is a plant that is used to prevent calcium oxalate crystallisation and to block the stone formation in urolithiasis. Contaminants in the environment can be readily taken up by medicinal plants due to their ability to absorb chemicals into their tissues. If contaminated plants are ingested, they have the potential to negatively affect human and environmental health. The aim of this study was to assess contamination in the soil and the medicinal plant P. niruri by cadmium (Cd) in ceramic industrial areas of Monte Carmelo, Brazil. Soil samples and plant samples (divided in root, shoot and leaves) were collected from a contaminated monitoring site and from a rural area (which was used as a reference site for comparative purposes). The Cd concentrations of the samples were analysed with an atomic absorption spectrometer. P. niruri was found to be sensitive to soil contamination by Cd that was attributed to ceramic industrial emissions. The results revealed that Cd bioaccumulation in the roots and shoots of P. niruri was associated with a significant increase (p?<?0.05) in the concentration of active lignan compounds (phyllanthin and hypophyllanthin) in the leaves. The identification of high concentrations of Cd and active lignan compounds suggests a risk of contamination of the site and the risk of a high dose of Cd to people exposed at the site.  相似文献   
64.
In the present study, personal exposure to fine particulate matter (particulate matter with an aerodynamic diameter <2.5 μm [PM2.5]) concentrations in an urban hotspot (central business district [CBD]) was investigated. The PM monitoring campaigns were carried out at an urban hotspot from June to October 2015. The personal exposure monitoring was performed during three different time periods, i.e., morning (8 a.m.?9 a.m.), afternoon (12.30 p.m.–1.30 p.m.), and evening (4 p.m.–5 p.m.), to cover both the peak and lean hour activities of the CBD. The median PM2.5 concentrations were 38.1, 34.9, and 40.4 µg/m3 during the morning, afternoon, and evening hours on the weekends. During weekdays, the median PM2.5 concentrations were 59.5, 29.6, and 36.6 µg/m3 in the morning, afternoon, and evening hours, respectively. It was observed that the combined effect of traffic emissions, complex land use, and micrometeorological conditions created localized air pollution hotspots. Furthermore, the total PM2.5 lung dose levels for an exposure duration of 1 hr were 8.7 ± 5.7 and 12.3 ± 5.2 µg at CBD during weekends and weekdays, respectively, as compared with 2.5 ± 0.8 µg at the urban background (UB). This study emphasizes the need for mobile measurement for short-term personal exposure assessment complementing the fixed air quality monitoring.

Implications: Personal exposure monitoring at an urban hotspot indicated space and time variation in PM concentrations that is not captured by the fixed air quality monitoring networks. The short-term exposure to higher concentrations can have a significant impact on health that need to be considered for the health risk–based air quality management. The study emphasizes the need of hotspot-based monitoring complementing the already existing fixed air quality monitoring in urban areas. The personal exposure patterns at hotspots can provide additional insight into sustainable urban planning.  相似文献   
65.
Following the renewed effort at achieving a new green revolution for Africa, emphasis has been placed on modernizing smallholder agriculture through the deployment of improved inputs especially mechanized technologies. In Ghana, the government has in the last decade emphasized the provision of subsidized mechanized ploughing services to farmers alongside a rapidly growing private sector tractor service market. While mechanized technology adoption rates have increased rapidly, the deployment of these technologies has been without critical analysis of the impacts on production patterns and local agrarian systems. This paper examines the distributional impacts of agriculture mechanization on cropping patterns and farm sizes of smallholder farmers in northern Ghana using Geographic Information Systems (GIS) techniques, and semi-structured interviews with smallholder farmers (n=60). Specifically, comparative analysis of the field sizes and cropping patterns of participant farmers prior to and after the adoption of mechanized technologies was conducted. In-depth interviews were used to contextualize the experiences of smallholder farmers toward understanding how mechanization may be impacting traditional agriculture. Our findings reveal a mechanization paradox in which farm sizes are expanding, while cropping patterns are shifting away from traditional staple crops (pearl millet and sorghum bicolor) to market-oriented crops (maize, rice and groundnuts). This transition we argue, has adverse implications on the cultural dimension of food security, the organization of social life, and climate change adaptation. We recommend a retooling of the current agricultural policy focus to ensure context sensitivity for a more robust battle against food insecurity.  相似文献   
66.
Chlorpyrifos (O, O-diethyl O-3,5,6-trichloropyridin-2-yl phosphorothioate) and carbaryl (1-naphthyl methylcarbamate) are often applied concurrently as insecticides in food production. The aim of this study was to research their migration behavior in a real environment. We researched the leaching of both pesticides by setting up field lysimeters on a farm with the typical soil used in fruit production today. In order to analyze the variables involved in this process, we performed complementary adsorption studies, we performed complementary adsorption studies using batches and undisturbed soil laboratory columns for both compounds. The results for pesticide transport through the lysimeters showed that less than 1% of chlorpyrifos was recovered in the leachates, while almost 17% was recovered for carbaryl. Having completed the experiment in undisturbed laboratory columns, soil analysis showed that chlorpyrifos mainly remained in the first 5 cm, while carbaryl moved down to the lower sections. These results can be explained in view of the sorption coefficient values (KD) obtained in horizons A and B for chlorpyrifos (393 and 184 L kg?1) and carbaryl (3.1 and 4.2 L kg?1), respectively. By integrating the results obtained in the different approaches, we were able to characterize the percolation modes of these pesticides in the soil matrix, thus contributing to the sustainable use of resources.  相似文献   
67.
Waste accumulation is a grave concern and becoming a transboundary challenge for environment. During Covid-19 pandemic, diverse type of waste were collected due to different practices employed in order to fight back the transmission rate of the virus. Covid-19 was proved to be capricious catastrophe of this 20th century and even not completely eradicated from the world. The havoc created by this imperceptible quick witted, pleomorphic deadly virus can't be ignored. Though a number of vaccines have been developed by the scientists but there is a fear of getting this virus again in our life. Medical studies prove that immunity drinks will help to reduce its reoccurrences. Coconut water is widely used among all drinks available globally. Its massive consumption created an incalculable pile of green coconut shells around the different corners of the world. This practice generating enormous problem of space acquisition for the environment. Both the environment and public health will benefit from an evaluation of quantity of coconut waste that is being thrown and its potential to generate value added products. With this context, present article has been planned to study different aspects like, coconut waste generation, its biological properties and environmental hazards associated with its accumulation. Additionally, this review illustrates, green technologies for production of different value added products from coconut waste.  相似文献   
68.
Cassava starch waste hydrolysates (CSWHs) with different degrees of polymerisation, i.e., CSWHs-1, CSWHs-2 and CSWHs-3, were prepared through the hydrolysis of cassava starch waste with thermostable a-amylase from Thermococcus sp. HJ21. The prepared CSWHs were then used as a carbon source for curdlan production with Alcaligenes faecalis ATCC 31749. The amount of curdlan produced and the glucosyltransferase activity during curdlan synthesis increased more obviously when CSWHs-2 was used as the carbon source than when glucose was used. Using both carbon sources, the maximum curdlan production was observed at day 5, and the maximum glucosyltransferase activity was observed at day 4. Glucosyltransferase activity decreased thereafter, and biomass continued to increase until the end of the experiment (day 6). Results indicated that the enhanced curdlan production with CSWHs as the carbon source was highly correlated with glucosyltransferase activity.  相似文献   
69.
Environmental Economics and Policy Studies - Streets are an essential element of cities, and their design has a profound impact on their functionality to the movement of people and their...  相似文献   
70.
Journal of Material Cycles and Waste Management - Material flow analysis (MFA) is a well-established tool for supporting decisions on nutrient management. This paper shows the importance of the...  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