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   311篇
  免费   6篇
  国内免费   2篇
安全科学   15篇
废物处理   14篇
环保管理   60篇
综合类   40篇
基础理论   66篇
环境理论   1篇
污染及防治   83篇
评价与监测   22篇
社会与环境   13篇
灾害及防治   5篇
  2023年   2篇
  2021年   4篇
  2020年   4篇
  2019年   7篇
  2018年   9篇
  2017年   4篇
  2016年   15篇
  2015年   8篇
  2014年   8篇
  2013年   39篇
  2012年   13篇
  2011年   17篇
  2010年   19篇
  2009年   12篇
  2008年   17篇
  2007年   16篇
  2006年   19篇
  2005年   9篇
  2004年   6篇
  2003年   10篇
  2002年   10篇
  2000年   4篇
  1999年   5篇
  1998年   4篇
  1997年   5篇
  1996年   2篇
  1995年   7篇
  1993年   2篇
  1991年   1篇
  1990年   6篇
  1988年   1篇
  1987年   5篇
  1986年   1篇
  1984年   2篇
  1982年   1篇
  1981年   1篇
  1980年   3篇
  1979年   2篇
  1978年   1篇
  1974年   1篇
  1969年   1篇
  1968年   1篇
  1962年   1篇
  1959年   2篇
  1958年   1篇
  1957年   4篇
  1956年   1篇
  1955年   1篇
  1936年   1篇
  1931年   1篇
排序方式: 共有319条查询结果,搜索用时 15 毫秒
111.
Field studies of pesticide effects on birds often utilize indicator species with the purpose of extrapolating to other avian taxa. Little guidance exists for choosing indicator species to monitor the presence and/or effects of contaminants that are labile in the environment or body, but are acutely toxic, such as anticholinesterase (anti-ChE) insecticides. Use of an indicator species that does not represent maximum exposure and/or effects could lead to inaccurate risk estimates. Our objective was to test the relevance of a priori selection of indicator species for a study on pesticide exposure to birds inhabiting fruit orchards. We used total plasma ChE activity and ChE reactivation to describe the variability in anti-ChE pesticide exposure among avian species in two conventionally managed fruit orchards. Of seven species included in statistical analyses, the less common species, chipping sparrow (Spizella passerina), showed the greatest percentage of exposed individuals and the greatest ChE depression, whereas the two most common species, American robins (Turdus migratorius) and gray catbirds (Dumatella carolinensis), did not show significant exposure. Due to their lower abundance, chipping sparrows would have been an unlikely choice for study. Our results show that selection of indicator species using traditionally accepted criteria such as abundance and ease of collection may not identify species that are at greatest risk. Our efforts also demonstrate the usefulness of conducting multiple-species pilot studies prior to initiating detailed studies on pesticide effects. A study such as ours can help focus research and resources on study species that are most appropriate.  相似文献   
112.
The Environmental Liability Directive (ELD) establishes a framework of liability based on the ‘polluter-pays’ principle to prevent and remedy environmental damage. The ELD requires the testing of appropriate equivalency methods to assess the scale of compensatory measures needed to offset damage. The aim of this paper is to contribute to fill the existing knowledge gap on the application of the value equivalency approach for damage compensation in this context. We analyze the toxic spill damaging the Doñana National Park (Spain) in 1998. The welfare losses associated with the resource damage are estimated using non-market valuation and compared to the value of the compensatory measures taken after the accident. Our results show that the in-kind compensation may have been insufficient to offset the welfare losses. We conclude that a more comprehensive knowledge of the human welfare effects caused by environmental damage is of substantial importance to determine compensatory remediation, as insufficient information in this respect can lead to erroneous decisions causing loss to society.  相似文献   
113.
From 1999 through 2010, a team of scientists and engineers systematically reviewed approximately eight million classified and unclassified documents at Los Alamos National Laboratory (LANL) that describe historical off-site releases of radionuclides and chemicals in order to determine the extent to which a full-scale dose reconstruction for releases is warranted and/or feasible. As a part of this effort, a relative ranking of historical airborne and waterborne radionuclide releases from LANL was established using priority index (PI) values that were calculated from estimated annual quantities released and the maximum allowable effluent concentrations according to The U.S. Nuclear Regulatory Commission (USNRC). Chemical releases were ranked based on annual usage estimates and U.S. Environmental Protection Agency (USEPA) toxicity values. PI results for airborne radionuclides indicate that early plutonium operations were of most concern between 1948 and 1961, in 1967, and again from 1970 through 1973. Airborne releases of uranium were found to be of most interest for 1968, from 1974 through 1978, and again in 1996. Mixed fission products yielded the highest PI value for 1969. Mixed activation product releases yielded the highest PI values from 1979 to 1995. For waterborne releases, results indicate that plutonium is of most concern for all years evaluated with the exception of 1956 when (90)Sr yielded the highest PI value. The prioritization of chemical releases indicate that four of the top five ranked chemicals were organic solvents that were commonly used in chemical processing and for cleaning. Trichloroethylene ranked highest, indicating highest relative potential for health effects, for both cancer and non-cancer effects. Documents also indicate that beryllium was used in significant quantities, which could have lead to residential exposures exceeding established environmental and occupational exposure limits, and warrants further consideration. In part because of the close proximity of residents to LANL, further study of historical LANL releases and the potential impact to public health is recommended for those materials with the largest priority index values; namely, plutonium, uranium, and selected chemicals.  相似文献   
114.

Background

The vertical migration of phytoplankton was investigated in natural waters using in situ fluorescence profiling, chlorophyll a concentrations and life counts at two study sites differing in coloured dissolved organic matter (cDOM) concentrations. The data from the corresponding water depths (50-cm intervals down to 10 m) and times (hourly, before dawn to sunset, several days) were related to the highly resolved (2 nm) underwater ultraviolet radiation (UVR)/photosynthetic active radiation (PAR) transparency (290 to 700 nm).

Results

Chlorophyll a maxima of mainly motile dinoflagellates were observed in situ at all days and at both study sites (open marine, brackish waters), independent on prevailing weather conditions or cDOM concentrations. Phytoplankton migration was triggered solely by irradiance in the 400- to 700-nm wavelength range (PAR) at the particular water depth, irrespective of PAR/UVR ratios and surface UVR (290 to 400 nm), after an illumination period of about 40 min. Interestingly, the PAR tolerance levels of the phytoplankton, which have been lower in cDOM-rich waters, matched their light acclimation values determined by parallel PAM measurements.

Conclusions

The response of the phytoplankton to PAR is not a sufficient protection strategy versus increasing UVR levels, which might have wide ecological implications beyond the level of primary producers to impact important ecosystem functions such as the delicate trophic interactions.  相似文献   
115.
Phragmites australis Trin., and/or aggressive species, Typha spp. Tidally influenced wetlands that have subtidal perimeter ditches have significantly less (P < 0.05) P. australis in the wetland interior than those without perimeter ditches. Fractured regression analyses show that 6 years after construction, P. australis invasion can be extensive. Linear regression analysis suggests that, if conditions remain favorable for P. australis colonization, constructed wetlands could be overrun in 40 years.  相似文献   
116.
117.
One of the key challenges in the total maximum daily load (TMDL) development process is how to define the critical condition for a receiving waterbody. The main concern in using a continuous simulation approach is the absence of any guarantee that the most critical condition will be captured during the selected representative hydrologic period, given the scarcity of long-term continuous data. The objectives of this paper are to clearly address the critical condition in the TMDL development process and to compare continuous and event-based approaches in defining critical condition during TMDL development for a waterbody impacted by both point and nonpoint source pollution. A practical, event-based critical flow-storm (CFS) approach was developed to explicitly addresses the critical condition as a combination of a low stream flow and a storm event of a selected magnitude, both having certain frequencies of occurrence. This paper illustrated the CFS concept and provided its theoretical basis using a derived analytical conceptual model. The CFS approach clearly defined a critical condition, obtained reasonable results and could be considered as an alternative method in TMDL development.  相似文献   
118.
Recent research has suggested that the fate of biologically active compounds (BACs) originating from point sources such as wastewater treatment plants is fundamentally different from that of similar compounds released from nonpoint sources through runoff from agricultural landscapes. Downstream from wastewater treatment plants, BACs will degrade via a variety of mechanisms; however, their concentration in the water adjacent to the point of discharge may not decrease over time, as the compounds are continually released. In contrast, in agricultural systems, BACs are episodically introduced to surface water during snowmelt and rainstorm events, and under these circumstances, may be found in water for only hours or days after a storm event. Recent research in our laboratories as well as others, has suggested that sediments play an important role in the persistence of herbicides and steroids in watersheds after nonpoint source loading events. Conceptually, the sediment serves as both a sink and a source, equilibrating with BACs during storm events then slowly releasing them back into the water over time, long after the initial pulse of chemicals has moved downstream.  相似文献   
119.
Wind erosion processes affect soil surfaces across all land uses worldwide. Understanding the spatial and temporal scales of wind erosion is a challenging undertaking because these processes are diverse and highly variable. Wind tunnels provide a useful tool as they can be used to simulate erosion at small spatial scales. Portable wind tunnels are particularly valued because erosion can be simulated on undisturbed soil surfaces in the field. There has been a long history of use of large portable wind tunnels, with consensus that these wind erosion simulation tools can meet real world aerodynamic criteria. However, one consequence of striving to meet aerodynamic reality is that the size of the tunnels has increased, making them logistically difficult to work with in the field and resulting in a tendency to homogenise naturally complex soil surfaces. This homogenisation is at odds with an increasing awareness of the importance that small scale processes have in wind erosion. To address these logistical and surface homogenisation issues we present here the development and testing of a micro wind tunnel (MWT) designed to simulate wind erosion processes at high spatial resolution. The MWT is a duct-type design—0.05 m tall 0.1 m wide and with a 1.0 m working section. The tunnel uses a centrifugal motor to suck air through a flow‐conditioning section, over the working section and then through a sediment collection trap. Simulated wind velocities range from 5 to 18 m s?1, with high reproducibility. Wind speeds are laterally uniform and values of u * at the tunnel bed (calculated by measuring the pressure gradients within the MWT) are comparable with those of larger tunnels in which logarithmic profiles can be developed. Saltation sediment can be added. The tunnel can be deployed by a single person and operated on slopes ranging from 0 to 10°. Evidence is presented here that the MWT provides new and useful understanding of the erodibility of rangelands, claypans and ore stockpiles.  相似文献   
120.
Although bycatch of seabirds and other long-lived species is a critical conservation issue in world fisheries, case studies documenting significant reductions in the mortality of these low-productivity species in a fishery are rare. We studied progress toward seabird conservation in the Alaskan longline fisheries, one of the largest and most diverse demersal fisheries. We generated annual seabird bycatch rates in 4 target fisheries and all fisheries combined from 23 years of fisheries observer data. We used 0-inflated negative binomial models to evaluate variables influencing seabird bycatch per unit effort (BPUE) in 2 target fisheries. Following adoption of streamer lines, at first voluntarily and then mandatorily, seabird BPUE was reduced by 77–90%, preventing mortality of thousands of birds per year. Despite this, BPUE increased significantly in 2 of 4 target fisheries since streamer lines were adopted. Although night setting yielded significant reductions (74–97%) in seabird BPUE and significant increases (7–11%) in fish catch per unit effort over daytime setting, nighttime setting increased the BPUE of Northern Fulmar (Fulmarus glacialis) by 40% and nontarget fish species by 5–17%. Thus, best practices to prevent seabird mortalities in longline fisheries varied by species assemblage and fishery. Our results inform global efforts toward fisheries bycatch reduction by illustrating that successful conservation requires fishery-specific solutions, strong industry support, constant vigilance in analysis and reporting observer data, and ongoing outreach to fleets, especially to vessels with anomalously high BPUE.  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