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   12687篇
  免费   83篇
  国内免费   30篇
安全科学   212篇
废物处理   930篇
环保管理   1874篇
综合类   1277篇
基础理论   3824篇
环境理论   4篇
污染及防治   2382篇
评价与监测   1229篇
社会与环境   1021篇
灾害及防治   47篇
  2023年   14篇
  2022年   23篇
  2021年   30篇
  2020年   32篇
  2019年   35篇
  2018年   1532篇
  2017年   1426篇
  2016年   1272篇
  2015年   202篇
  2014年   100篇
  2013年   271篇
  2012年   583篇
  2011年   1504篇
  2010年   809篇
  2009年   741篇
  2008年   1014篇
  2007年   1363篇
  2006年   162篇
  2005年   140篇
  2004年   135篇
  2003年   189篇
  2002年   193篇
  2001年   84篇
  2000年   84篇
  1999年   57篇
  1998年   61篇
  1997年   43篇
  1996年   47篇
  1995年   44篇
  1994年   50篇
  1993年   44篇
  1992年   30篇
  1991年   31篇
  1990年   23篇
  1989年   17篇
  1988年   27篇
  1987年   26篇
  1986年   15篇
  1985年   30篇
  1984年   32篇
  1983年   40篇
  1982年   27篇
  1981年   29篇
  1980年   17篇
  1979年   18篇
  1978年   8篇
  1977年   12篇
  1974年   8篇
  1972年   9篇
  1971年   6篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Costa Rica is internationally recognized for its abundant biodiversity and being a leader in the promotion of education strategies for biodiversity conservation. We interviewed staff from 16 institutions developing key environmental communication, education, and participation projects for biodiversity conservation in the country. Through content analysis, hierarchical cluster analysis and Chi-square tests, we examined the characteristics of the projects carried out by these institutions and developed a typology of four categories derived from six variables: primary audience, content, project purpose, location, scale, and facility. Then, we designed a conceptual model describing the integration of conservation and economic development in the educational projects. We found two key approaches related to this integration: vision of nature protection which aims to inform audiences of ecological concepts and focuses on schoolchildren and vision of sustainability which engages adult audiences and is management-oriented. Education for community-based environmental management may serve as a good example of educational projects which integrate conservation and economic development, implementing a vision of sustainability.  相似文献   
32.
This paper reports environmental analysis results of food and tannery Tunisian companies to identify the features of environmental management system (EMS) that is implemented recently. EMS via ISO 14001 has become one of the principal tools used by companies to handle environmental aspects and impacts through their various complex activities interacted with environment. While several companies have implemented and maintained a formal EMS, it has related mainly to their benefits in short term without responding to the sustainable development recommendations and practices. This study focuses on the strong linkage between the EMS effectiveness of food–tannery Tunisian companies and sustainability. A proactive environmental management approach is proposed and adopts a qualitative and quantitative assessment for factor analysis. It provides a strategic EMS framework and principles for sustainability to evolve the future enterprises’ benefits that has a clear influence on environmental performance in long term.  相似文献   
33.
Brazil is considered one of the world’s leading producers of biofuels given the predominance of ethanol fuel in its energy matrix. However, despite the prominence of Brazil in ethanol production, the vast majority of biodiesel production plants in Brazil use methanol instead of ethanol as the alcohol for transesterification reaction, as is generally the case in the rest of the world. The aim of this paper is therefore to examine the transesterification process in the Brazilian biodiesel production in terms of sustainability. In this regard, it was necessary to evaluate the way in which the industrial process is currently carried out, the role of government incentives or subsidies for the use of ethanol to produce biodiesel, and the investments of companies in technology development for the same purpose. This study presents indications that the development of the biodiesel market in Brazil is still oriented toward a production model which is inconsistent with the environmental and social aspects of sustainability.  相似文献   
34.
Overuse of nitrogen (N) fertilizers in agriculture activities has caused severe water pollution in China. The lack of data at producer level hampers decision makers in the development and implementation of efficient policies to curb excessive N-fertilizer use. In a survey of 300 farm households in the Liangzihu Lake basin, we identified factors associated with farmers’ decisions on N-fertilizer use and application rate. Household survey and multiple linear regression models indicate that the average application rate in the study region is 229 kg N ha?1, which exceeds the recommended rate for maximum profit for cereal crops (maize, wheat, and rice) in China of 150–180 kg N ha?1. High N-application rates are associated with low farmland productivity (coefficient = ?15.66, p = 0.02), a high share of off-farm income (coefficient = 27.14, p = 0.003), and a low education level of the household head (coefficient = ?10.83, p = 0.039). Neither physical infrastructure nor access to input markets appears to be related to N-application rates. It may be concluded that excessive use of N in agriculture of Central China is mainly a problem of insufficient awareness and high share of off-farm income.  相似文献   
35.
In the present paper, the optimum design of a PV system used to operate a water pumping system was determined for Oman. The system design focused on the environmental conditions of Sohar city. The implementation and measurement of the designed system are presented to prove the effectiveness of the proposed system. The results show that the system can provide the required power at peak hours, leading to a substantial reduction in the sizing of the PV system. Consequently, the investment capital costs 2400 USD, and the cost of energy is equal to 0.309 USD/kWh. Furthermore, the results indicate that the system annual yield factor is 2024.66 kWh/kWp and that the capacity factor is 23.05 %, which is encouraging since the latter is typically 21 %. The system capital cost and the cost of energy are worth comparing to a diesel generator. A comparison is made between the proposed system and several others in the literature. The comparison indicated that the system cost of energy is promising.  相似文献   
36.
In 2014, there was virtually no summer in northern and central-southern Italy. Storm after storm battered the peninsula, triggering floods and landslides from Veneto to Puglia. We studied the coverage of “the year without a summer” in Italy by analyzing the content of 171 news articles from two influential online newspapers. Our software-based analysis enabled us to observe that the two newspapers hardly ever mentioned climate change in their coverage of the weather anomaly that affected Italy in the summer of 2014. This type of coverage is in line with climate science, according to which there is no evidence of a climate change-related influence on summer precipitation patterns in Southern Europe—whereas such influence has been documented for northern Europe. We compared our results with a recent paper, which documented that the same online dailies chose to represent the particularly hot summer of 2012 in Italy as a direct consequence of climate change. We corroborated this comparison also on the basis of a preliminary analysis we performed on the media coverage of the exceptionally hot and arid summer of 2015 in Italy.  相似文献   
37.
This study aimed at investigating the retention of Pb and Cd in soils and the geochemical factors influencing the adsorption of these pollutants. Soil samples were air-dried and ground to pass through a 2-mm sieve, and different soil extracts were prepared for chemical analysis (organic matter, cation exchange capacity and pH). Total Pb and Cd were extracted with diacid using digestion method and determined by atomic adsorption spectrophotometer (AAS) after filtration. Results revealed that the heavy metals retention ratio (RR) of the Rhodic ferralsol, Xanthic ferralsol and Mollic gleysol (2) were very high for Cd (>80 %) and was relatively low (generally < 60 %) for Pb. In contrast, RRs for the Plinthic gleysol and the Mollic gleysol (1) were relatively low (<60 %), regardless of the heavy metal concerned. Multiple regression equations indicated for Pb and Cd concentrations different linear relationships over simple linear regression, when pH, organic matter, clay percentage and cation exchange capacity (CEC) were used as independent variables. Results indicate that organic matter exerts major influences on the retention of Pb and Cd in soils, while CEC, clay content and pH have a minor influence in this process in the Ntem watershed. From these observations, the application of soil organic matter could be a solution in protecting shallow aquifers from heavy metal pollution and thus insuring that they are not a hazard to public health.  相似文献   
38.
Increasing environmental issues, economic and cultural differences, the regulatory framework and the great attention to social responsibility, have forced companies to face the challenge of sustainability. Thus, the adaption of a proper marketing strategy in order to achieve a sustainable competitive advantage in the market (specially export markets) has become an important principle in accepting companies. In this regard, this study is a systematic literature review, which investigated 102 published articles in international journals between 1964 and 2015. In the literature review, the main focus was on key issues such as sustainability, marketing strategies, financial and market export performance. In this article, at first, the concept of sustainability from different aspects was collected and described. Then, external factors, such as competitive intensity, public concern, regulations, technology, cultural/social, and economic, as well as internal factors, such as managers, employees, stakeholders, affecting sustainability, were studied. Finally, adaption of export marketing strategies in order to achieve sustainability export performance is discussed.  相似文献   
39.
The vulnerability of forest ecosystem services to climate change is expected to depend on landscape characteristic and management history, but may also be influenced by the proximity to the southern range limit of constituent tree species. In the Western Rhodopes in South Bulgaria, Norway spruce is an important commercial species, but is approaching its current southern limit. Using climate sensitive forest models, we projected the impact of climate change on timber production, carbon storage, biodiversity and soil retention in two representative landscapes in the Western Rhodopes; a lower elevation landscape (1000–1450 m a.s.l) dominated by mixed species forests, and a higher elevation landscape (1550–2100 m a.s.l.) currently dominated by spruce. In both landscapes climate change is projected to induce a shift in forest composition, with drought-sensitive species, such as Norway spruce, being replaced by more drought-tolerant species such as Scots pine and black pine at lower elevations. In the higher elevation landscape a reduction in spruce growth is projected, particularly under the more severe climate change scenarios. Under most climate scenarios a reduction in growing stock is projected to occur, but under some scenarios a moderate increase in higher elevation stands (>1500 m a.s.l.) is expected. Climate change is projected to negatively influence carbon storage potential across landscapes with the magnitude depending on the severity of the climate change scenario. The impact of climate change on forest diversity and habitat availability is projected to differ considerably between the two landscapes, with diversity and habitat quality generally increasing at higher elevations, and being reduced at lower elevations. Our results suggest that if currently management practices are maintained the sensitivity of forests and forest ecosystem services in the Western Rhodopes to climate change will differ between low and higher elevation sites and will depend strongly on current forest composition.  相似文献   
40.
European forestry is facing many challenges, including the need to adapt to climate change and an unprecedented increase in forest damage. We investigated these challenges in a Norway spruce-dominated mountain region in Central Europe. We used the model Sibyla to explore forest biomass production to the year 2100 under climate change and under two alternative management systems: the currently applied management (CM), which strives to actively improve the forest’s adaptive capacity, and no management (NM) as a reference. Because biodiversity is thought to have mostly positive effects on the adaptive capacity of forests and on the quality of ecosystem services, we explored how climate change and management affect indicators of biodiversity. We found a differential response across the elevation-climatic gradient, including a drought-induced decrease in biomass production over large areas. With CM, the support of non-spruce species and the projected improvement of their growth increased tree species diversity. The promotion of species with higher survival rates led to a decrease in forest damage relative to both the present conditions and NM. NM preserved the high density of over-matured spruce trees, which caused forest damage to increase. An abundance of dead wood and large standing trees, which can increase biodiversity, increased with NM. Our results suggest that commercial spruce forests, which are not actively adapted to climate change, tend to preserve their monospecific composition at a cost of increased forest damage. The persisting high rates of damage along with the adverse effects of climate change make the prospects of such forests uncertain.  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