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   325篇
  免费   61篇
  国内免费   2篇
安全科学   68篇
废物处理   11篇
环保管理   63篇
综合类   31篇
基础理论   102篇
污染及防治   82篇
评价与监测   7篇
社会与环境   15篇
灾害及防治   9篇
  2024年   1篇
  2022年   1篇
  2021年   3篇
  2020年   2篇
  2019年   15篇
  2018年   17篇
  2017年   17篇
  2016年   21篇
  2015年   13篇
  2014年   32篇
  2013年   13篇
  2012年   8篇
  2011年   10篇
  2010年   8篇
  2009年   39篇
  2008年   24篇
  2007年   22篇
  2006年   18篇
  2005年   23篇
  2004年   25篇
  2003年   24篇
  2002年   18篇
  2001年   13篇
  2000年   7篇
  1999年   6篇
  1998年   2篇
  1997年   1篇
  1996年   1篇
  1993年   1篇
  1985年   2篇
  1978年   1篇
排序方式: 共有388条查询结果,搜索用时 500 毫秒
261.
Abstract: Pheromone‐based monitoring is a promising new method for assessing the conservation status of many threatened insect species. We examined the versatility and usefulness of pheromone‐based monitoring by integrating a pheromone–kairomone trapping system and pitfall trapping system in the monitoring of two saproxylic beetles, the hermit beetle Osmoderma eremita (Coleoptera: Scarabaeidae) and its predator Elater ferrugineus (Coleoptera: Elateridae), which live inside hollow trees. We performed mark–recapture studies of both species with unbaited pitfall traps in oak hollows combined with pheromone‐baited funnel traps suspended from oak branches to intercept dispersing individuals. For O. eremita, the integrated trapping system showed that the population in the study sites may be considerably higher than estimates based on extrapolation from pitfall trapping alone (approximately 3400 vs. 1100 or 1800 individuals, respectively). Recaptures between odor‐baited funnel traps showed that males and females had similar dispersal rates, but estimating the number of dispersing individuals was problematic due to declining recapture probability between subsequent capture events. Our conservative estimate, assuming a linear decrease in capture probability, suggested that around 1900 individuals, or at least half of the O. eremita population, may perform flights from their natal host trees, representing higher dispersal rates than previous estimates. E. ferrugineus was rarely caught in pitfall traps. One hundred thirty‐nine individuals, likely almost exclusively females, were caught in odor‐baited funnel traps with approximately 4% recapture probability. If recapture probability over consecutive capture events follows that of O. eremita, this would correspond to a total population size of 2500–3000 individuals of the predator; similar to its supposed prey O. eremita. Our results demonstrate that pheromone‐based monitoring is a valuable tool in the study of species or life‐history stages that would otherwise be inaccessible.  相似文献   
262.
We propose the wildlife premium mechanism as an innovation to conserve endangered large vertebrates. The performance‐based payment scheme would allow stakeholders in lower‐income countries to generate revenue by recovering and maintaining threatened fauna that can also serve as umbrella species (i.e., species whose protection benefits other species with which they co‐occur). There are 3 possible options for applying the premium: option 1, embed premiums in a carbon payment; option 2, link premiums to a related carbon payment, but as independent and legally separate transactions; option 3, link premiums to noncarbon payments for conserving ecosystem services (PES). Each option presents advantages, such as incentive payments to improve livelihoods of rural poor who reside in or near areas harboring umbrella species, and challenges, such as the establishment of a subnational carbon credit scheme. In Kenya, Peru, and Nepal pilot premium projects are now underway or being finalized that largely follow option 1. The Kasigau (Kenya) project is the first voluntary carbon credit project to win approval from the 2 leading groups sanctioning such protocols and has already sold carbon credits totaling over $1.2 million since June 2011. A portion of the earnings is divided among community landowners and projects that support community members and has added over 350 jobs to the local economy. All 3 projects involve extensive community management because they occur on lands where locals hold the title or have a long‐term lease from the government. The monitoring, reporting, and verification required to make premium payments credible to investors include transparent methods for collecting data on key indices by trained community members and verification of their reporting by a biologist. A wildlife premium readiness fund would enable expansion of pilot programs needed to test options beyond those presented here. Mejora de la Conservación, Servicios del Ecosistema y Calidad de Vida Local Mediante un Mecanismo de Compensación de Vida Silvestre  相似文献   
263.
Abstract: Urban development is the most common form of land conversion in the United States. Using a before–after control‐impact study design, we investigated the effects of urbanization on larval and adult stages of southern two‐lined salamanders (Eurycea cirrigera) and northern dusky salamanders (Desmognathus fuscus). Over 5 years, we estimated changes in occupancy and probabilities of colonization and survival in 13 stream catchments after urbanization and in 17 catchments that were not urbanized. We also examined effects of proportion of urbanized area in a catchment and distance of the salamander population to the nearest stream on probabilities of colonization and survival. Before urbanization, adult and larval stages of the two salamander species occupied nearly all surveyed streams, with occupancy estimates ranging from 1.0 to 0.78. Four years after urbanization mean occupancy of larval and adult two‐lined salamanders had decreased from 0.87 and 0.78 to 0.57 and 0.39, respectively. Estimates of mean occupancy of larval northern dusky salamanders decreased from 1.0 to 0.57 in urban streams 4 years after urbanization; however, adult northern dusky salamander occupancy remained close to 1.0 in urban streams over 5 years. Occupancy estimates in control streams were similar for each species and stage over 5 years. Urbanization was associated with decreases in survival probabilities of adult and larval two‐lined salamanders and decreases in colonization probabilities of larval dusky salamanders. Nevertheless, proportion of impervious surface and distance to nearest stream had little effect on probabilities of survival and colonization. Our results imply that in the evaluation of the effects of urbanization on species, such as amphibians, with complex life cycles, consideration of the effects of urbanization on both adult and larval stages is required.  相似文献   
264.
265.
为主动减小热带气旋灾害,给将来热带气旋调控的工程实践奠定理论基础。从RossHoffman对热带气旋调控减灾的研究出发,引出了作为非线性最优控制技术的四维变分天气控制版本。简要介绍了条件非线性最优扰动(CNOP)的概念,在此基础上,重点介绍了CNOP方法与四维变分方法相比改进方面的主要应用,它可以利用控制过程中的观测数据,从而在天气控制方面优于四维变分技术。进一步研究了CNOP在热带气旋控制中的另外两个应用,即对初始扰动发展为热带气旋的反演以及利用CNOP寻求产生最大垂直风切变的扰动。新的非线性最优控制技术可称为"非线性最优强迫变分(NOFV)"或"非线性最优强迫扰动(NOFP)"方法,它可以使控制尽可能接近观测。研究表明,CNOP方法在热带气旋调控减灾中大有用武之地。  相似文献   
266.
On the basis of justice and exchange theories, the authors propose that employees offset their levels of work–family conflict (WFC) with their levels of pay satisfaction. Results based on two waves of data indicate that pay satisfaction has a negative relationship with WFC after controlling for actual pay and other work‐related and family‐related variables. Analysis of pay satisfaction dimensions reveals that satisfaction with benefits and pay structure are negatively related to WFC, whereas satisfaction with pay level and pay raise are not. Number of dependents and level of education moderate the relationship between pay satisfaction and WFC; specifically, having more dependents and higher education attenuates the relationship between pay satisfaction and WFC. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
267.
Lattice Boltzmann model for agrochemical transport in soils   总被引:2,自引:0,他引:2  
Agrochemical transport in soils is complicated and involves physical, chemical and biochemical reactions; its mathematical modelling remains a challenging task. This paper presents a lattice Boltzmann model to simulate the agrochemical movement. The lattice Boltzmann model is a microscopic and process-based model, simulating the transport process by tracking chemical particles. The model presented in this paper is for one-dimensional vertical leaching and assumes that the chemical particles at the microscopic level move in five directions: one stagnant, two in vertical direction and two in an internal horizontal direction bounded by two reactive walls. Reactions at the walls are assumed to take place at two different rates, one in fast rate where the chemicals in the solution and on the wall are in an instant equilibrium, and the other in slow rate where the mass exchange rate between the chemicals in the solution and on the wall is a first-order kinetic. The reactions on both walls are assumed to occur instantly when the chemical particles moving in the internal direction hit the walls. To test the model, we measured the leaching of atrazine through soil columns in the laboratory. The results simulated with the lattice Boltzmann model are compared with the measured breakthrough curves and the non-equilibrium two-site convection-dispersion model; they all show close agreement. The transport parameters needed in the models are obtained from the measurement of adsorption isotherm of atrazine, bromide leaching in the same soil columns and calibration.  相似文献   
268.
The microecosystem approach and an adequate system of quantitative methods have been used to study the relationship between the chorologic changes in the structure and functions of edificator tree stand and other components of the pine (Pinus sylvestris L.) forest cenoecosystems of the Transural and Northern Turgai regions. Significant correlations of the density of pine undergrowth with the litter thickness; of its growth with root competition, stand closeness, and, to a lower degree, photosynthetically active radiation (PAR); and of the numbers of small mammals and groups of soil mesofauna with herbaceous phytomass have been found. The possibility of the synthesis of population-ecological, synecological, and biogeocenological methods has been demonstrated.  相似文献   
269.
Marine protected areas (MPAs) are one tool that can be used in the comprehensive management of human activities in areas of the ocean. Although researchers have supported using MPAs as an ecosystem management tool, scientific research on MPAs in areas other than fisheries and fisheries management is limited. This paper presents a model for designing marine protected areas that protect important components of the ecosystem while minimizing economic impacts on local communities. This model combines conservation principles derived specifically for the marine environment with economic impact assessment. This integrated model allows for consideration of both fishery and non-fishery resources and activities such as shipping and recreational boating. An illustration of the model is presented that estimates the total economic impacts on Massachusetts' coastal counties of restricting fishing and shipping at certain sites in an area in the southern Gulf of Maine. The results suggest that the economic impacts on the region would differ according to the site in which shipping and fishing were restricted. Restricting activities in certain sites may have considerable impacts on local communities. The use of the model for evaluating and comparing potential MPA sites is illustrated through an evaluation of three different policy scenarios. The scenarios demonstrate how the model could be used to achieve different goals for managing resources in the region: protecting important components of the ecosystem, minimizing economic impacts on the local region, or a combination of the two.  相似文献   
270.
Tropospheric O3 has been implicated in the declining health of forest ecosystems in Europe and North America and has been shown to have negative consequences on human health. We have measured tropospheric ozone (O3) in the lower canopy through the use of passive monitors located in five woodlots along a 150 km urban–rural transect, originating in the large urban complex of Toronto, Canada. We also sampled foliage from 10 mature sugar maple trees in each woodlot and measured the concentration of a number of phenolic compounds and macronutrients. O3 concentrations were highest in the two rural woodlots, located approximately 150 km downwind of Toronto, when compared to the woodlots found within the Greater Toronto Area. Foliar concentrations of three flavonoids, avicularin, isoquercitrin, and quercitrin, were significantly greater and nitrogen concentrations significantly lower at these same rural woodlots, suggesting some physiological disruption is occurring in those sites where exposure to tropospheric O3 is greater. We suggest that foliar phenolics of sugar maple may be a biochemical indicator of tropospheric ozone exposure.  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