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   173篇
  免费   9篇
  国内免费   2篇
安全科学   3篇
废物处理   4篇
环保管理   49篇
综合类   18篇
基础理论   63篇
污染及防治   9篇
评价与监测   2篇
社会与环境   15篇
灾害及防治   21篇
  2022年   4篇
  2021年   1篇
  2020年   5篇
  2019年   6篇
  2018年   11篇
  2017年   8篇
  2016年   5篇
  2015年   6篇
  2014年   8篇
  2013年   26篇
  2012年   5篇
  2011年   11篇
  2010年   8篇
  2009年   8篇
  2008年   14篇
  2007年   11篇
  2006年   5篇
  2005年   3篇
  2004年   7篇
  2003年   3篇
  2002年   3篇
  2001年   5篇
  2000年   3篇
  1999年   2篇
  1998年   6篇
  1997年   5篇
  1993年   2篇
  1992年   2篇
  1989年   1篇
排序方式: 共有184条查询结果,搜索用时 15 毫秒
141.
Disaster resettlement, as a mitigation and preparedness measure, entails significant economic, physical, and social impacts, which continue to challenge understanding of recovery from major events, especially regarding the extent of the context and environmental efforts to rebuild livelihoods. Based on a case study of Qinling Mountains, China, this research investigates the effects of disaster resettlement from a livelihoods perspective. Methodologically, it proposes a framework that combines the pressure–state–response framework and the sustainable livelihoods approach, and it employs a structural equation model to examine how specific factors affect disaster resettlement. The results indicate that conflicts may occur during and after resettlement owing to the difference or disparity between the concerns of resettled peasants and those of the government. Consequently, the risks related to livelihoods need to be taken seriously. Effective risk communication is critical to bridge the gap between different stakeholders. The paper concludes with some practical and policy recommendations.  相似文献   
142.
Smallholder Agroforestry Systems For Carbon Storage   总被引:3,自引:0,他引:3  
Most smallholder agroforestry systems in Southeast Asia are tree- and species-rich systems producing non-wood and wood products for both home use and market sale. Due to their high biomass, these systems contain large carbon (C) stocks. While the systems of individual farmers are of limited size, on a per area basis smallholder systems accumulate significant amounts of C, equaling the amount of C stored in some secondary forests of similar age. Their ability to simultaneously address smallholders’ livelihood needs and store large amounts of C makes smallholder systems viable project types under the Clean Development Mechanism (CDM) of the Kyoto Protocol, with its dual objective of emissions reduction and sustainable development. Smallholder systems have not developed in areas where enabling conditions do not exist. A CDM project that facilitates a minimum threshold of enabling conditions that make smallholder agroforestation possible should qualify for C credits. To secure smallholder confidence, the agroforestry systems promoted through a CDM project must be socially and economically viable independent of C payments. To assure system productivity and profitability, projects should provide farmers with technical and marketing assistance. Additionally, project sites should meet the following preconditions: areas of underutilized low-biomass landuse systems available for rehabilitation; smallholders interested in tree farming; accessible markets for tree products; supportive local governments; sufficient infrastructure; and transparent and equitable relationships between project partners. Questions of leakage and additionality should not be problematic and can be addressed through the project design, establishment of quantifiable baseline data and facilitating enabling conditions. However, smallholder-focused CDM projects would have high transaction costs. The subsequent challenge is thus to develop mechanisms that reduce the costs of: (a) making information (e.g., technology, markets) more accessible to multiple clients; (b) facilitating and enforcing smallholder agreements and (c) designing feasible monitoring systems.  相似文献   
143.
汽车代用燃料及应用前景   总被引:4,自引:0,他引:4  
介绍了已经开发使用的代用燃料氢气,甲醇,乙醇,新配方汽油,天然气,液化石油气,电动汽车等,并对代用燃料车和汽油车的环境安全性,成本,能耗消耗等方面作了比较,指出天然气,液化石油气是当前最有前途的代用燃料。  相似文献   
144.
Tree lizards (Urosaurus ornatus) vary in throat fan (dewlap) color. Earlier, we described five dewlap types (Orange, Orange-Blue, Yellow, Yellow-Blue, and Blue), and reported that only males had blue in the dewlap and that presence or absence of a discrete blue patch was correlated with male alternative reproductive phenotypes in a central Arizona population. Here, with a modified scheme characterizing two dewlap elements, background color (orange, yellow, blue) and blue patch occurrence, we assessed: (1) sexual, annual, and geographic variation in the frequencies of dewlap elements; (2) simple habitat correlates; and (3) the effects of laboratory rearing regime on dewlap type. Within a population, frequencies of males and females expressing orange or yellow backgrounds did not differ, suggesting that control of background is similar in the sexes. Within several populations, frequencies of the dewlap elements did not differ across years (and probably generations), indicating that phenotype frequencies are relatively stable. Among five populations frequencies of background colors varied, as did frequencies of male types (blue patch present or absent). Dewlap frequencies did not correlate with habitat (boulders or mesquite trees), although few populations were sampled. In male and female offspring reared from eggs to sexual maturity in a common-garden laboratory study, background color frequencies in both sexes and blue patch frequencies in males differed among offspring from different populations. Offspring frequencies matched respective parental population frequencies. Results suggest that among-population variation in frequencies of the two dewlap elements are mediated by differences in genetics, in maternal effects, or both. Thus, differences in male behavior functionally linked to the blue patch also may be controlled by genetic or maternal effects. Received: 17 January 1997 / Accepted after revision: 30 August 1997  相似文献   
145.
I conducted a detailed morphological analysis of the Japanese horned beetle Trypoxylus dichotomus septentrionalis to clarify the allometric relationship between horn length and body size and examined its mating success and reproductive behaviour in the field. The relationship between horn and body size was not discontinuous at the switch point body size, but the slope of the linear relationship changed at the switch point. Shape of the allometric relationship was initially steep and became flatten around the switch point in both linear and log scales; that is, minor males showed a positive relationship and major males showed a negative one. Major males gained more mating success than minor males. Within major males, individuals with larger horn or body size had higher mating success than individuals with smaller ones. Within minor males there were no differences in horn and body size between mated and unmated individuals. Although sneak-like behaviours were exhibited by both morphs, it is likely that these behaviours rarely lead to direct benefit. These results suggest that dimorphic allometry of T. dichotomus is consistent with the hypothesis of a continuous reaction norm that meets a ceiling, which restrains further allometric growth.  相似文献   
146.
Adult dung beetles (Onthophagus acuminatus) exhibit continuous variation in body size resulting from differential nutritional conditions experienced during larval development. Males of this species have a pair of horns that protrude from the base of the head, and the lengths of these horns are bimodally distributed in natural populations. Males growing larger than a threshold body size develop long horns, and males that do not achieve this size grow only rudimentary horns or no horns at all. Previous studies of other horned beetle species have shown that horned and hornless males often have different types of reproductive behavior. Here I describe the mating behaviors of the two male morphs of O. acuminatus during encounters with females. Females excavate tunnels beneath dung, where they feed, mate and provision eggs. Large, horned males were found to guard entrances to tunnels containing females. These males fought with all other males that attempted to enter these tunnels. In contrast, small, hornless males encountered females by sneaking into tunnels guarded by other males. In many instances, this was accomplished by digging new tunnels that intercepted the guarded tunnels below ground. Side-tunneling behavior allowed sneaking males to enter tunnels beneath the guarding male, and mate with females undetected. Both overall body size and relative horn length significantly affected the outcome of fights over tunnel ownership. These results suggest that alternative reproductive tactics may favor divergence in male horn morphology, with long horns favored in males large enough to guard tunnels, and hornlessness favored in smaller males that adopt the “sneaking” behavioral alternative. Received: 12 October 1996 / Accepted after revision: 8 August 1997  相似文献   
147.
Organic synthesis is usually performed in solution to dissolve both reactants and catalysts and to deliver heat. Here, we show that glycerol, which is a non-toxic, biodegradable, and recyclable liquid manufactured from renewable sources, has a high potential to serve as alternative green solvent for organic reactions. Several catalytic and non-catalytic reactions were successfully performed in glycerol. High products yields and selectivities were achieved. Besides solubility of the reactants and the catalysts and easy separation of the product, glycerol offers several other benefits such as catalyst recycling, microwave assisting reaction, and biphasic and emulsion modes.  相似文献   
148.
Sperm traits often show extreme variation both between and within species. Between-species variation may often be interpreted in the context of a sperm competition theory, but within-species variation has remained unexplained. Previous studies on intraspecific variation in sperm traits have focused on a limited set of variables and may have failed to explain observed variation because of potential trade-offs between different sperm traits. We report on variation in number, size, motility and longevity of sperm in the frog Crinia georgiana, a species where sperm competition is common. We found intrapopulation variation in sperm size and motility and interpopulation variation in relative sperm number and size. When we combined relative sperm number and size into one variable, and motility and longevity into another, we found significant interpopulation variation in these variables as well. We also detected considerable intra- and significant interpopulation variation in cumulative sperm quality, a combination of all four sperm traits. Furthermore, a significant effect of the interaction between population origin and male size on sperm characteristics indicated interpopulation variation in the strength of selection acting on sperm traits of males adopting different mating strategies. We discuss heterogeneity in the reproductive environment, a complex genetic background in the determination of sperm characteristics and varying levels of developmental noise as potential contributors to the observed variation in sperm traits.  相似文献   
149.
The paper concerns the comparative analysis of combustion characteristics of different alternative fuels such as Fischer-Tropsch Synthetic Paraffinic Kerosene (FT-SPK), cryogenic methane, bioethanol, biomethanol, biobutanol, dimethyl ether, biodiesel and conventional aviation kerosene Jet-A as well as analysis of emissions of NOx, CO, CO2, H2O, HNOy (y = 2,3) and organics for gas turbine engine operating on these fuels. The analysis has shown that the usage of all considered alternative fuels results in the increase of H2O emission, compared to kerosene-fueled combustor, and, as consequence, in the growth of water vapor supersaturation that can increase the rate of the H2O vapor condensation and enhance the formation of contrails and cirrus clouds in the atmosphere. The usage of all considered alternative fuels except FT-SPK, cryogenic methane and dimethyl can increase the CO2 emission compared to using of kerosene. Emission of N-containing species can be reduced upon the usage of considered alternative fuels, except dimethyl ether, for which one can expect the increase in the emissions of HNO2 and HNO3 approximately by 10%. The emission of CO decreases for all fuels except biodiesel. The major decrease can be achieved upon the replacement of kerosene to bioethanol.  相似文献   
150.
The October 2005 earthquake in northern Pakistan severely affected the livelihoods of 1.5 million people. With the destruction of material assets and communications infrastructure, the quake had a devastating impact on people's way of life in this remote mountainous region. This paper explores livelihood revival interventions undertaken during the earthquake response, and considers how differentiated livelihood outcomes were achieved. In addressing this objective the paper examines livelihood rehabilitation schemes in terms of structural aspects, working strategies, key factors, strengths of interventions and the role of human agency in influencing livelihood trajectories of quake‐affected communities. Primary data for this study was gathered in northern Pakistan between October 2008 and January 2009. The study identifies structural shortcomings and strengths of the programmes attempting to revive the livelihoods of poor and vulnerable households. It identifies how households in two villages made the most of opportunities to improve their lives and move towards favourable outcomes.  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