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   300篇
  免费   9篇
  国内免费   4篇
安全科学   7篇
废物处理   5篇
环保管理   73篇
综合类   32篇
基础理论   95篇
环境理论   1篇
污染及防治   60篇
评价与监测   21篇
社会与环境   16篇
灾害及防治   3篇
  2023年   2篇
  2022年   5篇
  2021年   4篇
  2020年   4篇
  2019年   1篇
  2018年   5篇
  2017年   9篇
  2016年   14篇
  2015年   6篇
  2014年   5篇
  2013年   14篇
  2012年   12篇
  2011年   19篇
  2010年   18篇
  2009年   16篇
  2008年   17篇
  2007年   22篇
  2006年   16篇
  2005年   24篇
  2004年   9篇
  2003年   11篇
  2002年   13篇
  2001年   8篇
  2000年   7篇
  1999年   5篇
  1998年   2篇
  1997年   4篇
  1996年   3篇
  1995年   1篇
  1994年   6篇
  1993年   2篇
  1992年   1篇
  1991年   3篇
  1990年   2篇
  1989年   1篇
  1988年   2篇
  1987年   2篇
  1986年   3篇
  1985年   1篇
  1984年   2篇
  1983年   1篇
  1981年   1篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1971年   1篇
  1966年   1篇
  1963年   1篇
  1934年   1篇
排序方式: 共有313条查询结果,搜索用时 17 毫秒
221.
The concept of a knowledge-based approach to policy making (also referred to as 'evidence-based policy making' or 'science meets policy') has been around for 10 years, and is widely 'signed up to' by Governments. This paper examines the theory and the practice at national government (using the UK as a case study) and European levels, looking at how the knowledge-based approach has been applied in waste and resources management. There is general agreement that a knowledge-(or evidence-) based approach to policy making is a 'good thing'; however putting the concept into practice has proven challenging and is still evolving. The linkages between researchers and policy makers need to be further strengthened, as does the 'demand' for evidence from policy; requiring policy specialists to articulate their requirements for evidence sufficiently well in advance, and to do so routinely, is still an area of weakness. Using a model developed by the UK's Department for Environment, Food and Rural Affairs (Defra), we examine in detail some of the implications of changing the question from 'is this good research on waste and resources issues?' to 'is this good evidence for waste and resources policy?'. The paper also provides recommendations for further work required to achieve this at a European level, and for priority areas where international co-ordination of waste and resources research could add most value to policy.  相似文献   
222.
Sexual selection acting on male traits through female mate choice is commonly inferred from female association preferences in dichotomous mate choice experiments. However, there are surprisingly few empirical demonstrations that such association preferences predict the likelihood of females reproducing with a particular male. This information is essential to confirm association preferences as good predictors of mate choice. We used green swordtails (Xiphophorus helleri) to test whether association preferences predict the likelihood of a female reproducing with a male. Females were tested for a preference for long- or short-sworded males in a standard dichotomous choice experiment and then allowed free access to either their preferred or non-preferred male. If females subsequently failed to produce fry, they were provided a second unfamiliar male with similar sword length to the first male. Females were more likely to reproduce with preferred than non-preferred males, but for those that reproduced, neither the status (preferred/non-preferred) nor the sword length (long/short) of the male had an effect on brood size or relative investment in growth by the female. There was no overall preference based on sword length in this study, but male sword length did affect likelihood of reproduction, with females more likely to reproduce with long- than short-sworded males (independent of preference for such males in earlier choice tests). These results suggest that female association preferences are good indicators of female mate choice but that ornament characteristics of the male are also important.  相似文献   
223.
The measurement of travel costs in recreational demand modeling has been a contentious issue for many decades. This article explores the use of a number of alternative methods of incorporating time costs in the travel cost modeling process. Travel cost values where the opportunity cost of time is excluded, where it is included as a percentage of the individual's reported wage rate and where it based on an estimated wage from a secondary data source (the European Community Household Panel) are compared and then used in a conditional logit model to estimate the demand for whitewater kayaking in Ireland. We then evaluate the effect of different treatments of the cost of travel time on the welfare impacts of a number of different management scenarios for kayaking rivers in Ireland, and find that statistically significant differences emerge.  相似文献   
224.
Wellbore integrity is one of the key performance criteria in the geological storage of CO2. It is significant in any proposed storage site but may be critical to the suitability of depleted oil and gas reservoirs that may have 10’s to 1000’s of abandoned wells. Much previous work has focused on Portland cement which is the primary material used to seal wellbore systems. This work has emphasized the potential dissolution of Portland cement. However, an increasing number of field studies (e.g., Carey et al., 2007), experimental studies (e.g., Kutchko et al., 2006) and theoretical considerations indicate that the most significant leakage mechanism is likely to be flow of CO2 along the casing–cement microannulus, cement–cement fractures, or the cement–caprock interface.In this study, we investigate the casing–cement microannulus through core-flood experiments. The experiments were conducted on a synthetic wellbore system consisting of a 5-cm diameter sample of cement that was cured with an embedded rectangular length of steel casing that had grooves to accommodate fluid flow. The experiments were conducted at 40 ° C and 14 MPa pore pressure for 394 h. During the experiment, 6.2 l of a 50:50 mixture of supercritical CO2 and 30,000 ppm NaCl-rich brine flowed through 10-cm of limestone before flowing through the 6-cm length cement–casing wellbore system. Approximately 59,000 pore volumes of fluid moved through the casing–cement grooves. Scanning electron microscopy revealed that the CO2–brine mixture impacted both the casing and the cement. The Portland cement was carbonated to depths of 50–250 μm by a diffusion-dominated process. There was very little evidence for mass loss or erosion of the Portland cement. By contrast, the steel casing reacted to form abundant precipitates of mixed calcium and iron carbonate that lined the channels and in one case almost completely filled a channel. The depth of steel corroded was estimated at 25– 30μm and was similar in value to results obtained with a simplified corrosion model.The experimental results were applied to field observations of carbonated wellbore cement by Carey et al. (2007) and Crow et al. (2009) to show that carbonation of the field samples was not accompanied by significant CO2–brine flow at the casing–cement interface. The sensitivity of standard-grade steel casing to corrosion suggests that relatively straight-forward wireline logging of external casing corrosion could be used as a useful indicator of flow behind casing. These experiments also reinforce other studies that indicate rates of Portland cement deterioration are slow, even in the high-flux CO2–brine experiments reported here.  相似文献   
225.
In the face of fundamental land‐use changes, the potential for trophy hunting to contribute to conservation is increasingly recognized. Trophy hunting can, for example, provide economic incentives to protect wildlife populations and their habitat, but empirical studies on these relationships are few and tend to focus on the effects of benefit‐sharing schemes from an ex post perspective. We investigated the conditions under which trophy hunting could facilitate wildlife conservation in Ethiopia ex ante. We used a choice experiment approach to survey international trophy hunters’ (n = 224) preferences for trips to Ethiopia, here operationalized as trade‐offs between different attributes of a hunting package, as expressed through choices with an associated willingness to pay. Participants expressed strong preferences and, consequently, were willing to pay substantial premiums for hunting trips to areas with abundant nontarget wildlife where domestic livestock was absent and for arrangements that offered benefit sharing with local communities. For example, within the range of percentages considered in the survey, respondents were on average willing to pay an additional $3900 for every 10 percentage points of the revenue being given to local communities. By contrast, respondents were less supportive of hunting revenue being retained by governmental bodies: Willingness to pay decreased by $1900 for every 10 percentage points of the revenue given to government. Hunters’ preferences for such attributes of hunting trips differed depending on the degree to which they declared an interest in Ethiopian culture, nature conservation, or believed Ethiopia to be politically unstable. Overall, respondents thus expressly valued the outcomes of nature conservation activities—the presence of wildlife in hunting areas—and they were willing to pay for them. Our findings highlight the usefulness of insights from choice modeling for the design of wildlife management and conservation policies and suggest that trophy hunting in Ethiopia could generate substantially more financial support for conservation and be more in line with conservation objectives than is currently the case.  相似文献   
226.
227.
We compare existing nontimber forest product extraction systems in Petén, Guatemala, and West Kalimantan, Indonesia, to identify key ecological, socioeconomic, and political factors in the design and implementation of extractive reserves. Ecological parameters include the spatial and temporal availability of harvested products and the sustainability of harvesting practices from both a population and an ecosystem perspective. Socioeconomic and political factors include the presence or absence of well-defined resource tenure rights, physical and social infrastructure, markets, and alternative land uses. We conclude that although extractive reserves can play a significant role in preserving tropical forests as a part of a broader land-use spectrum, their effectiveness is highly dependent on prevailing local ecological, socioeconomic, and political conditions. Ultimately, extractive reserves should be regarded as one component of an overall approach to the problem of tropical deforestation.  相似文献   
228.
This paper reports on the results of a survey of environmental management and technical measures amongst almost 2000 European firms. Logit analysis is undertaken to determine the effects of firm characteristics, commercial conditions, perceived environmental impacts, expected benefits and stakeholder pressures on the probability of having an environmental management system in place. Subsequently, determinants of the likelihood of undertaking environmental actions in five environmental areas are estimated. There is a positive effect of environmental management on the likelihood of undertaking technical measures to reduce environmental impacts in some (but not all) areas, as well as a positive role for integrated environmental management strategies.  相似文献   
229.
Biodegradation has been identified as a major loss process for organic contaminants in soils and, as a result, microbial strategies have been developed for the remediation of contaminated land. Prediction of the biodegradable fraction would be important for determining bioremediation end-points in the clean-up of contaminated land. The aim of this study was to investigate the ability of a cyclodextrin extraction to predict the extent to which polycyclic aromatic hydrocarbons (PAHs) would be degraded microbiologically in field contaminated soils; further testing the robustness and reproducibility of this extraction in chemically complex systems. Dichloromethane and hydroxypropyl-beta-cyclodextrin (HPCD) extractable fractions were measured together with the PAH biodegradable fraction in each of the six field contaminated soils. The amounts of PAHs degraded by the catabolic activity of the indigenous microflora in each of the soils were correlated with HPCD-extractable PAH concentrations. The regressions showed that the amounts of lower molecular weight PAHs extracted by the HPCD were not significantly (P > 0.05) different to the amounts that were degraded. However, higher molecular weight PAHs that were extracted by HPCD did differ significantly (P < 0.05) from the amounts degraded. Although the HPCD extraction did overestimate the microbially degradable fraction of the higher molecular weight PAHs, overall the correlations between the HPCD extractable fraction and the microbially degradable fraction were very close, with mean values of the slope of line for the six soils equalling 1. This study further describes the robust and reproducible nature of the aqueous-based soil extraction technique reliably measuring the extent to which PAHs will be microbially degraded in soil.  相似文献   
230.
A simple method for preparing prometaphase chromosomes from amniotic fluid cell cultures is described. The technique is based upon several key steps including: (1) reduced colcemid concentration, (2) reduced exposure to trypsin-EDTA, and (3) maintaining cells in single suspension by adjusting cell concentration appropriately. Chromosomes with banding resolution up ot 800 bands per haploid set can be routinely produced. The described methodology is particularly useful in defining and establishing the clinical significance of subtle structural aberrations.  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