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61.
In this study the frequencies of PM10 (as key urban pollutant) in 14 key environmental protection cities in northern China were analyzed. It follows that the PM10 concentration in the high-frequency period is higher with an extent 0.009–0.066 mg m−3 than in the low-frequency period of 2001–2002. Further the impacts of three kinds of dust events on the PM10 concentration in four cities (Beijing, Hohhot, Xi’an and Lanzhou) were explored. The results showed that different kinds of dust events have different influences on variation of PM10 concentration in these four cities. In Lanzhou and Hohhot, which are near the source areas of dust events, the contribution degree of these three dust events to the PM10 is: floating dust>dust storm>blowing dust. Whereas, in Beijing and Xi’an situated in dust event passing areas, the mean value of PM10 concentration is higher in blowing dust than in floating dust (no dust storm). In addition, the influences of dust events on PM10 concentration are different in the cities on different dust event paths. In Beijing and Hohhot (on the northern path), the high PM10 concentration is usually caused by blowing dust. But in both Lanzhou and Xi’an (on the western/northwestern path) the high PM10 pollution concentration is usually caused by floating dust.  相似文献   
62.
Conservation of the Northern Spotted Owl under the Northwest Forest Plan   总被引:2,自引:0,他引:2  
Abstract:  Development of the Northwest Forest Plan (NWFP) was motivated by concerns about the overharvest of late-seral forests and the effects of intensive forest management on the long-term viability of the Northern Spotted Owl ( Strix occidentalis caurina ). Following several years of intense political and legal debates, the final NWFP was approved in 1994. Even though the plan evolved with a broad ecosystem perspective, it remained anchored in the Spotted Owl reserve design proposed in 1990. Based on a criterion of stable or increasing populations, a decade later it remains unclear whether the enactment of the NWFP has improved the conservation status of Spotted Owls. The results of intensive monitoring of several Spotted Owl populations for over a decade suggest a continuing range-wide decline even though rates of timber harvest have declined dramatically on federal lands. The cause of the decline is difficult to determine because the research needed to establish cause and effect relations has not been done. One plausible hypothesis is that the owl's life history greatly constrains its rate of population growth even when habitat is no longer limiting. Since enactment of the NWFP, new threats have arisen, including the movement of Barred Owls ( S. varia ) into the range of the Spotted Owl, political pressure to increase levels of timber harvest, and recent changes to forest laws that eliminate the requirement to assess the viability of wildlife populations on U.S. Department of Agriculture Forest Service lands. At this time is appears that Spotted Owl conservation rests critically on continued implementation of the protections afforded by the NWFP and the U.S. Endangered Species Act.  相似文献   
63.
基于2013年潮白新河(天津段)水体COD、NH+4-N、TN和TP的监测数据,通过研究影响研究区水质变化的主要因素,按照农作物的生长周期(将全年分为播种期、生长期和收获期)分析我国北方闸控河流水质时间变化特征和空间变化特征。结果表明,农业面源污染是该流域的主要污染源;在气候、闸坝调度和污染来源的共同作用下,各监控断面水质变化较大,各监测指标值存在明显时空差异。其中,COD和TN污染负荷由大到小为播种期、收获期、生长期,NH+4-N和TP污染负荷由大到小为播种期、生长期、收获期。不同时段水质的空间分析表明,河流上游NH+4-N、TN和TP污染负荷偏高,河流中、下游COD污染较严重。因此,在分析北方闸控河流水质状况时,应综合考虑影响水质的主要因素,分时段、分河段进行水质评价。  相似文献   
64.
Mercury(Hg) remains a key contaminant of concern in Arctic biota, and monitoring of Hg concentrations in seabird tissues will be an effective approach to track the effects of implementing the Minamata Convention. We examined trends in total Hg(THg) in liver and egg tissues of two Arctic seabirds, thick-billed murres(Uria lomvia) and northern fulmars(Fulmarus glacialis), between 1976 and 2013 to assess whether both tissues showed similar patterns of Hg change. Hepatic THg was consistently higher than egg THg, and both species had similar egg THg concentrations, but fulmars had higher hepatic THg than murres.Murre THg concentrations showed more relative variation through time than fulmars.We suggest that egg THg better reflects exposure of birds to THg in local, Arctic prey,whereas liver THg may incorporate longer term, year-round THg exposure. Additional analysis of THg distribution in Arctic seabirds post-laying would help inform interpretation of long-term trends.  相似文献   
65.
The high seas provide a variety of ecosystem services that benefit society. There have, however, been few attempts to quantify the human welfare impacts of changes to the delivery of these benefits. We assessed the values of several key ecosystem service benefits derived from protecting ecosystems in the high seas of the Flemish Cap through choice experiments conducted in Canada, Norway, and Scotland. Rather than solely eliciting public willingness to pay, we also explored the determinants of variance in the estimates of willingness to pay. We aimed to determine how much respondents were willing to pay for high-seas ecosystems conservation, which factors influence individuals’ willingness to pay, and whether individuals in Canada had a higher willingness to pay relative to those living in Norway and Scotland. This latter point captures distance-decay effects. On average, the public placed positive value on conserving high-seas ecosystems and on developing economic activities related to the exploitation and exploration of marine resources, despite a lack of awareness and familiarity with these environments. Distance-decay effects on willingness to pay were not clear. Scots had the highest willingness to pay and the Norwegians the lowest willingness to pay for all attributes, with the only exception being willingness to pay for a large increase in new jobs, in which case Canadians’ willingness to pay was higher than Scots’. The public's willingness to pay was influenced by sociodemographic characteristics and their perceptions of high-seas ecosystems. Our results provide evidence of the impacts of high-seas governance on human welfare and that improved governance could increase the value people place on high-seas ecosystems and the services they produce.  相似文献   
66.
This document describes a basis for the establishment of marine sediment quality guidelines for regulatory applications. It outlines a geochemical basis for identifying potential anomalies in the presence of inorganic contaminants in marine sediments and a biological or ecotoxicological basis for determining concentrations unlikely to result in adverse biological effects. These approaches are discussed in an exploratory fashion. It is intended that both approaches could be combined in a manner that takes account of sedimentary nature and composition as a conceptual and practical approach to the establishment of guidelines for regulatory applications associated with the protection of the marine environment.  相似文献   
67.
Vegetation conditions, i.e., plant cover, species richness, and the presence of exotic species, are compared along a high-use trail (Berg Lake Trail--BLT) and a low use trail (Mt. Fitzwilliam Trail--FWT) in Canada's Mt. Robson Provincial Park. We established 71 paired quadrats (1 m x 1 m), and assessed the amount of vegetation cover and species richness by four main lifeforms, i.e., woody species, herbaceous species, ferns, and moss, lichen and fungi. The following hypotheses were tested: (1) differences exist between control and trailside quadrats in vegetation cover, species richness and floristic diversity, and (2) differences exist between the high and low-use trails in the above-mentioned three parameters. Results show that for the majority of variables the differences between the control and trailside quadrats are statistically not significant. Variables showing significant differences are relative vegetation cover (for BLT only), exposed soil (BLT and FWT), herbaceous cover (FWT), moss, lichen and fungi cover (BLT), overall species richness (BLT), and herbaceous species richness (BLT). Ruderal and exotic species are present but only on trailside quadrats of the high-use trail. Results indicate that the Park administration's strategy to disperse use in the Mt. Robson Provincial Park should be examined critically, and some guidelines for acceptability of changes should be developed.  相似文献   
68.
ABSTRACT: Wildfires in 1988 burned over 2000 square miles of the greater Yellowstone area in Montana and Wyoming in the largest fires in the history of Yellowstone National Park (YNP). A four-year postfire study to estimate fire-related changes in suspended sediment transport on the Yellowstone River and its principal tributary in YNP, the Lamar River, benefitted from a recently completed three-year prefire baseline study. Both studies took daily depth-integrated samples from April through September. Fire-related changes in suspended sediment were distinguished from natural climatic variations by two methods: comparison of forecast postfire sediment loads estimated with prefire sediment-rating equations to measured postfire loads; and by postfire changes in suspended sediment load expressed per unit volume runoff. Both methods indicated postfire sediment increases that varied according to season. The higher elevation Lamar River basin had little postfire increase in spring snowmelt season sediment but large increases in summer sediment load. The Yellowstone River had postfire increases in sediment load for the spring but did not reflect the large summer increases of its upstream tributary. The reasons for the difference in postfire snowmelt sediment response are unclear but may relate to basin elevation differences, the effects of unburned watersheds, and cooler postfire springs. The few high streamflow snowmelt events in the postfire period mitigated postfire sediment increases.  相似文献   
69.
Cumulative environmental change or cumulative effects may result from the additive effect of individual actions of the same nature or the interactive effect of multiple actions of a different nature. This article reviews conceptual frameworks of cumulative environmental change and describes analytical and institutional approaches to cumulative effects assessment (CEA). A causal model is a common theoretical construct, although the frameworks vary in their emphasis on different components of the model. Two broad approaches to CEA are distinguished: one scientific and the other planning oriented. These approaches should not be interpreted as competing paradigms but rather different interpretations of the scope of CEA. Each approach can provide a distinct but complementary contribution to the analysis, assessment, and management of cumulative effects. A comparison of the institutional and legislative response to CEA in Canada and the United States shows that Canada is following the American example of incorporating the analysis and assessment of cumulative effects into regulatory actions and administrative procedures that also govern environmental impact assessment.  相似文献   
70.
This study assesses the relative dominance of vision and hearing in judgments of environments, and examines whether the sound sensitivity of the judge alters relative sensory dominance. Six sets of four composite (auditory-plus-visual) videotaped environmental displays were created from unisensory visual and auditory components with known levels of evoked affect. These displays, in a 2 (high, low) × 2 (high, low) Pleasure and/or Arousal format, were presented to 70 participants. The results indicate that visual cues dominate auditory cues in judgments of Pleasure, but that the degree of dominance is highly variable. Arousal judgments were not consistently related to visual or auditory cues. Sound sensitivity does not appear to influence the relative dominance of vision.  相似文献   
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