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   14618篇
  免费   247篇
  国内免费   2032篇
安全科学   360篇
废物处理   1101篇
环保管理   1587篇
综合类   3902篇
基础理论   3885篇
环境理论   1篇
污染及防治   3546篇
评价与监测   1202篇
社会与环境   1080篇
灾害及防治   233篇
  2024年   13篇
  2023年   88篇
  2022年   238篇
  2021年   214篇
  2020年   173篇
  2019年   144篇
  2018年   1630篇
  2017年   1585篇
  2016年   1460篇
  2015年   462篇
  2014年   384篇
  2013年   528篇
  2012年   890篇
  2011年   1771篇
  2010年   1042篇
  2009年   945篇
  2008年   1246篇
  2007年   1552篇
  2006年   286篇
  2005年   236篇
  2004年   180篇
  2003年   239篇
  2002年   283篇
  2001年   147篇
  2000年   146篇
  1999年   170篇
  1998年   140篇
  1997年   126篇
  1996年   113篇
  1995年   122篇
  1994年   83篇
  1993年   70篇
  1992年   58篇
  1991年   35篇
  1990年   18篇
  1989年   9篇
  1988年   16篇
  1987年   4篇
  1986年   7篇
  1985年   2篇
  1984年   17篇
  1983年   11篇
  1982年   9篇
  1981年   3篇
  1935年   2篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
The quality of education in Kenya’s public elementary schools has continued to drop, which is an ironic outcome in the wake of the introduction of tuition-exempt primary education. This removal of tuition costs led to a surge in primary education enrollment that overwhelmed the existing educational infrastructure. Overcapacity in classrooms led to frustrated teachers and mediocre delivery of content amid the overstretched resources and limited education budget. To remedy this situation, the government has begun introducing various information and communication technologies (ICTs) in schools to supplement current resources. This comes with mixed results. This paper aims to demonstrate effective strategies for integrating low-cost ICT-based materials in schools in developing countries through a community of practice. Three schools were used to illustrate integration of sustainable ICT-based education in a style of classroom characteristic in developing schools. Development and use of prerecorded DVD-based content was proposed as an effective solution. A comparative study was undertaken to evaluate the differences in student comprehension and educator delivery of education involving a digital, ICT-integrated classroom and a traditional, analog-type teaching method classroom to underscore the empirical evidence of the effectiveness of introducing a low-cost ICT-based program. This study also shows that teachers are better positioned to lead the design and development of appropriate and innovative materials. Furthermore, to cope with the immense amount of materials that need developing to correspond with the curriculum, it shows that with the emergence of a community of practice of teachers, many suitable low-cost materials can be developed. This takes place through an iterative collaboration as opposed to traditional top-down approaches, which have a proven record of failure.  相似文献   
102.
Sustainability science is a solution-oriented discipline. Yet, there are few theory-rich discussions about how this orientation structures the efforts of sustainability science. We argue that Niklas Luhmann’s social system theory, which explains how societies communicate problems, conceptualize solutions, and identify pathways towards implementation of solutions, is valuable in explaining the general structure of sustainability science. From Luhmann, we focus on two key concepts. First, his notion of resonance offers us a way to account for how sustainability science has attended and responded to environmental risks. As a product of resonance, we reveal solution-oriented research as the strategic coordination of capacities, resources, and information. Second, Luhmann’s interests in self-organizing processes explain how sustainability science can simultaneously advance multiple innovations. The value logic that supports this multiplicity of self-organizing activities as a recognition that human and natural systems are complex coupled and mutually influencing. To give form to this theoretical framework, we offer case evidence of renewable energy policy formation in Texas. Although the state’s wealth is rooted in a fossil-fuel heritage, Texas generates more electricity from wind than any US state. It is politically antagonistic towards climate-change policy, yet the state’s reception of wind energy technology illustrates how social and environmental systems can be strategically aligned to generate solutions that address diverse needs simultaneously. This case demonstrates that isolating climate change—as politicians do as a separate and discrete problem—is incapable of achieving sustainable solutions, and resonance offers researchers a framework for conceptualizing, designing, and communicating meaningfully integrated actions.  相似文献   
103.
104.
粮食安全:我国农业现代化的任务与标志   总被引:8,自引:0,他引:8  
解决10多亿人吃饭问题是我国农业第一主题,是农业现代化的首要任务,而粮食安全水平是我国农业现代化的重要标志,因此,在我国农业现代化进程中,必须强化商品粮基地建设;不断提高种粮科学技术的经济效益、粮食转化效益,保护和改善粮食生产者和主产区经济利益和经济状况,建立健全国家粮食安全保障体系,提高我国粮食安全水平。  相似文献   
105.
Polybrominated diphenyl ethers (PBDEs) have been determined in 30 samples, including soil, biota and plant collected from an electronic waste recycling site and its vicinage towns. Polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzo-furans (PCDD/Fs) were also simultaneously analyzed in 20 samples. PBDEs were detected in all soil samples and the highest was up to 789 ng/g dry weight (dw). The toxic equivalency (TEQ) of PCBs and PCDD/Fs detected in E-waste recycling site is significant higher than those in the vicinage samples. Biota and plant were also contaminated with high level of PBDEs, PCBs and PCDD/Fs in this area. High levels of the three kinds of organic compounds in the environmental samples showed that the E-waste recycling have induced serious environmental problems.  相似文献   
106.
While the world is going into different tourism expectations, the tourism understanding in Turkey is defined as tourism in the sea-sand-sun triangle. However, it is possible to contribute to the income and local development of the indigenous people by developing nature-based tourism. Besides, with the sustainable use and preservation of the natural-cultural assets, the damage of the traditional tourism industry on the natural and cultural environment could be reduced. In this study, it is aimed to bring up the nature-based tourism concept in Çanakkale by evaluating the nature-based tourism industry in the general of Turkey and assessing the natural-cultural resources that Çanakkale comprehends. The most important areas that have a nature-based tourism potential in Çanakkale and the tourism activities that are most suitable for these areas have been determined.  相似文献   
107.
This paper presents the technical aspects of a new methodology for assessing the susceptibility of society to drought. The methodology consists of a combination of inference modelling and fuzzy logic applications. Four steps are followed: (1) model input variables are selected—these variables reflect the main factors influencing susceptibility in a social group, population or region, (2) fuzzification—the uncertainties of the input variables are made explicit by representing them as ‘fuzzy membership functions’, (3) inference modelling—the input variables are used to construct a model made up of linguistic rules, and (4) defuzzification—results from the model in linguistic form are translated into numerical form, also through the use of fuzzy membership functions. The disadvantages and advantages of this methodology became apparent when it was applied to the assessment of susceptibility from three disciplinary perspectives: Disadvantages include the difficulty in validating results and the subjectivity involved with specifying fuzzy membership functions and the rules of the inference model. Advantages of the methodology are its transparency, because all model assumptions have to be made explicit in the form of inference rules; its flexibility, in that informal and expert knowledge can be incorporated through ‘fuzzy membership functions’ and through the rules in the inference model; and its versatility, since numerical data can be converted to linguistic statements and vice versa through the procedures of ‘fuzzification’ and ‘defuzzification’.  相似文献   
108.
Persistent organochlorine pesticides pollutants (OCPs) have been reported to occur at relatively high concentrations in some Chinese waters. In order to map the distribution of organochlorine pesticides in the surface water throughout China, samples were collected from over 600 sites in seven major river basins and three main internal rivers drainage areas during 2003 and 2004. The surface water samples were analyzed for the representative organochlorine pesticides contaminants including lindane (gamma-HCH), p,p'-DDT and heptachlor epoxide. In general, the most frequently detected compound was lindane, being detected in 83.9% of samples (mean=31.3 ng/l; range <0.17-860 ng/l), and the highest concentration was present in the Yellow River basin. p,p'-DDT was detected in 63.1% of the samples collected (mean=14.6 ng/l; range <0.14-368 ng/l) with the highest concentration present in the Huaihe River basin. Heptachlor epoxide was detected in only 9.3% of water samples (range <0.11-10 ng/l). Measured concentrations for the three compounds were low and rarely exceed the environment quality standard for surface water of China. Lindane was more frequently detected at much higher concentrations in the rivers of northern China compared with those of southern China. The sites with higher concentration of lindane and p,p'-DDT mainly occurred in the Yellow River and Huaihe River basins, so the results of this investigation indicate that the organochlorine pesticide contamination of Yellow River and Huaihe River basins should be of particular concern relative to the other basins. When compared with other regions of the world, it appears that the Chinese surface water is moderately polluted by lindane and p,p'-DDT.  相似文献   
109.
110.
The methane concentration profile from -1.5m depth in soil to 32m height in air was measured in alpine steppe located in the permafrost area. Methane concentrations showed widely variations both in air and in soil during the study period. The mean concentrations in atmosphere were all higher than those in soil, and the highest methane concentration was found in air at the height of 16m with the lowest concentration occurring at the depth of 1.5m in soil. The variations of atmospheric methane concentrations did not show any clear pattern both temporally and spatially, although they exhibited a more steadystable state than those in soil. During the seasonal variations, the methane concentrations at different depths in soil were significantly correlated (R^2〉0.6) with each other comparing to the weak correlations (R^2〈0.2) between the atmospheric concentra- tions at different heights. Mean methane concentrations in soil significantly decreased with depth. This was the compositive influence of the decreasing production rates and the increasing methane oxidation rates, which was caused by the descent soil moisture with depth. Although the methane concentrations at all depths varied widely during the growing season, they showed very distinct temporal variations in the non-growing season. It was indicated from the literatures that methane oxidation rates were positively correlated with soil temperature. The higher methane concentrations in soil during the winter were determined by the lower methane oxidation rates with decreasing soil temperatures, whereas methane production rates had no reaction to the lower temperature. Relations between methane contribution and other environmental factors were not discussed in this paper for lacking of data, which impulse us to carry out further and more detailed studies in this unique area.  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