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   7594篇
  免费   215篇
  国内免费   1787篇
安全科学   390篇
废物处理   439篇
环保管理   646篇
综合类   3023篇
基础理论   1876篇
污染及防治   2292篇
评价与监测   360篇
社会与环境   342篇
灾害及防治   228篇
  2024年   6篇
  2023年   69篇
  2022年   255篇
  2021年   199篇
  2020年   140篇
  2019年   153篇
  2018年   276篇
  2017年   362篇
  2016年   419篇
  2015年   320篇
  2014年   348篇
  2013年   529篇
  2012年   808篇
  2011年   679篇
  2010年   327篇
  2009年   317篇
  2008年   420篇
  2007年   363篇
  2006年   347篇
  2005年   571篇
  2004年   664篇
  2003年   589篇
  2002年   182篇
  2001年   159篇
  2000年   157篇
  1999年   153篇
  1998年   114篇
  1997年   132篇
  1996年   87篇
  1995年   106篇
  1994年   68篇
  1993年   66篇
  1992年   61篇
  1991年   55篇
  1990年   32篇
  1989年   16篇
  1988年   7篇
  1987年   6篇
  1986年   6篇
  1985年   2篇
  1984年   3篇
  1983年   3篇
  1982年   3篇
  1981年   2篇
  1975年   2篇
  1974年   2篇
  1972年   2篇
  1966年   2篇
  1961年   1篇
  1957年   1篇
排序方式: 共有9596条查询结果,搜索用时 234 毫秒
991.
This paper deals with the various factors that condition underdevelopment in the world. It suggests some alternatives and points out the potential opportunities that both the developed and the underdeveloped world will have in the coming years to change the gloomy prospects that we see today. The present paper outlines the trends in historical priorities in development, changing as they pass from economic development to social development to ecological conservation – the three pillars of Sustainable Development.The paper analyses the importance of geography, a very relevant and often neglected conditioning factor. Also, it analyses the role of socio-economic conditioning factors like political immaturity, demographics, land ownership and external debt.Furthermore, the current opportunities for economic take-off are presented, from cash surpluses to low interest rates, from natural resource management to tourism or migration, from the Information Revolution to liberalisation of agricultural markets. Current obstacles are also analysed. The paper, on the basis of current facts and figures, reaches the conclusion that there is a structural need for sustained development aid for most poor countries, but it must be distributed in a more rational way.Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.  相似文献   
992.
“Measuring Sustainability”: A Multi-Criterion Framework   总被引:4,自引:0,他引:4  
So far, the elementary question of whether one country’s or region’s economy is moving towards sustainability or away from it cannot be answered with unanimous consensus on the ‘measuring rod(s)’ to be employed. The main assumption of this article is that sustainability assessment needs a set of multi-dimensional indicators. From this assumption a question arises: how could such indicators be aggregated? Often, some indicators improve while others deteriorate. For instance, when incomes grow, SO2 might go down while CO2 increases. It has to be noted that this is the classical conflictual situation studied in multi-criteria decision theory. The use of a multi-criterion framework for making operational the ‘measuring of sustainability’ is discussed here by means of illustrative examples and more formal arguments.  相似文献   
993.
For some time now, ecological economists have been putting forward a ‘threshold hypothesis’ – the notion that when macroeconomic systems expand beyond a certain size, the additional cost of growth exceeds the flow of additional benefits. In order to support their belief, ecological economists have developed a number of similar indexes to measure and compare the benefits and costs of growth (e.g., the Index of Sustainable Economic Welfare and the Genuine Progress Indicator). In virtually every instance where an index of this type has been calculated for a particular country, the movement of the index appears to reinforce the existence of the threshold hypothesis. Of late, a number of observers have expressed concerns about whether these alternative indexes reflect concrete reality or the prejudices of ecological economists. In view of these concerns, this paper closely examines the valuation methods used in the calculation the Index of Sustainable Economic Welfare, the Genuine Progress Indicator, and the Sustainable Net Benefit Index. It is argued that a consistent and more robust set of valuation techniques is required in order for these alternative indexes to gain broad acceptability.*Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.  相似文献   
994.
Using a case study, involving turtle-based ecotourism, we explore the role of ecotourism in promoting environmental learning and in sustaining conservation of nature. Mon Repos Conservation Park (an important marine turtle rookery involved in ecotourism) in Queensland, Australia, was selected for this study and visitors were surveyed using a structured questionnaire. The reported on-site experiences of respondents are analysed to identify important factors that alter their stated conservation attitudes and behaviours. The impact of these factors (such as the amount of environmental education that respondents claimed they obtained, sighting of sea turtles, nationality) is quantified using regression analyses. There has been little previous quantification of such influences. The study reveals that a considerable amount of environmental knowledge is gained by visitors to Mon Repos. The ecotourism experience, involving environmental education and seeing of turtles, was found to have positive and statistically significant impacts on the visitors' stated desire and intended behaviour to protect sea turtles. The study reveals the importance of learning and the interaction of tourists with wildlife as a contributor to their pro-conservation sentiments and actions. It shows how ecotourism can support nature conservation. Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue.  相似文献   
995.
PROBLEM: Most investigations of injuries among Chinese populations are focused on urban or better developed areas, fewer on rural or poor areas. METHODS: From September 21 to 27, 2002, an epidemiological investigation of eight kinds of injury-related events was carried out among 1,944 students in 39 classes randomly sampled from middle schools in Lijin County, a rural area. The eight kinds of events were: (a) traffic accidents, (b) poisoning, (c) fall, (d) burn or scald, (e) blunt or sharp tools contact, (f) electrical contact, (g) animal or insect bites, and (h) non-fatal drowning. RESULTS: The total incidence rate of eight kinds of injuries in the previous year was 21.1%. The incidence rate among boys was 24.2%, while that among girls was 17.4%, which was significant (chi-square=13.4, P<0.05). The incidence rate among junior high school students was 23.1%, while that among senior high school students was 15.5%, which was also significant (chi-square=13.2, P<0.05). A case-control study of 410 students with at least one of eight kinds of injury events indicated that students' gender and their mothers' health status were related to their injuries. CONCLUSION: The injury incidence rate in a rural area was less than other results in urban or developed areas. Students' gender and mothers' health status were important factors associated with the occurrence of injury. IMPACT ON INDUSTRY: In order to improve the surroundings of the growing population of adolescents, some preventive measures should be put forward, especially to the high-risk students of injury.  相似文献   
996.
OBJECTIVE: To study the present situation, characteristics, and main problems of the traffic safety in the mountain areas of Southwest China. METHODS: A study was done on the traffic status of Wulong County, Chongqing Municipality, by means of document review, field investigation, and inquiry. RESULTS: The traffic crashes and deaths in Wulong County were increasing since 1999. From 1997 to 2001, there occurred 126 severe and very severe traffic crashes resulting in 175 deaths and 411 serious injuries, which accounted for 9.4% of total crashes, 96.1% of total deaths, and 48.4% of total serious injuries, respectively. The severe and very severe traffic crashes were highest in 2000. One part for 83 km in length accounting for 3.0% of No. 319 National Highway was responsible for 54.5% of very severe traffic crashes, which closely related to conditions of the road itself and its environment and defective execution of traffic laws. CONCLUSIONS: Wulong County, one of the mountain counties in Southwest China, is now facing a complex and serious road traffic situation and serious traffic safety, with a high incidence of severe and very severe road traffic crashes. The crashes closely relate to imperfect road design, defective execution of traffic laws, imperfect management, and environmental factors.  相似文献   
997.
Corn distillers’ dry grain, corncob powder, hardwood powder, and sugar beet pulp were separately anionized by oxidation with sodium hypochlorite in aqueous solution. Solid reaction products instantly precipitated upon admixing each of the above-oxidized materials with soy protein isolate. Infrared spectra and differential scanning calorimetry supported the hypothesis that soy protein isolate complexed with all of the above-oxidized polysaccharides. Reaction products with either oxidized corn distillers’ dry grain or oxidized sugar beet pulp provided hard, brittle pellets with tensile strengths as high as 9.5 MPa, suggesting that these materials could be viable as biodegradable plastics.  相似文献   
998.
Biocomposites were made by a novel high volume processing technique named biocomposite sheet molding compound panel (BCSMCP) manufacturing process. This process design was inspired by the commercial glass fiber–polyester resin composite fabrication method called sheet molding compounding (SMC). This process yields continuous production of biocomposites on a large scale, and thus can be easily adopted in industries. A unique fiber dispersion method, which enabled uniform distribution of natural fibers, was used in this process. Consistency of the process was tested by evaluating the repeatability of the resultant materials mechanical properties. The low cost biocomposites produced as a result of the processing will be used for various panel applications such as housing and transportation. The molded samples were tested for various mechanical and thermal properties, in accordance with ASTM procedures. The biocomposites were made with various natural fibers including, big blue stem grass, jute, and industrial hemp. By combining different natural fibers in varying mass fractions, hybrid biocomposites were made using this process. Grass fiber reinforced polyester biocomposites processed by the SMC line showed very promising results.  相似文献   
999.
1000.
Increased environmental awareness and interest in long-term sustainability of material resources has motivated considerable advancements in composite materials made from natural fibers and resins, or biocomposites. In spite of these developments the lower stiffness and strength of biocomposites has limited their applications to non-load-bearing components. This paper presents an overview of a study aimed at showing that the shortcomings of biocomposites can be overcome through hybrid material designs and efficient structural configurations to make them suitable for load bearing structural components. Hybrid blends of natural and synthetic fibers can significantly improve the characteristics of biocomposites with minimal cost and environmental impact, and hierarchical cellular designs can maximize material efficiency in structural components. Periodic and hierarchical cellular plate designs made from natural fibers and unsaturated polyester resin were evaluated experimentally and analytically. Stiffness, strength, and dimensional stability of all-biocomposite and hybrid natural–synthetic material systems were evaluated through material tests while structural performance of cellular plate designs was assessed through flexural tests on laboratory-scale samples. The experimental results were correlated with analytical models for short-fiber composites and cellular structures. The results showed that biocomposites have adequate short-term performance and that they can efficiently compete with housing panels made from conventional structural materials.  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