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401.
402.
Wigand C McKinney RA Chintala MM Charpentier MA Groffman PM 《Journal of environmental quality》2004,33(3):1144-1151
Coastal salt marshes are a buffer between the uplands and adjacent coastal waters in New England (USA). With increasing N loads from developed watersheds, salt marshes could play an important role in the water quality maintenance of coastal waters. In this study we examined seasonal relationships between denitrification enzyme activity (DEA) in salt marshes of Narragansett Bay, Rhode Island, and watershed N loadings, land use, and terrestrial hydric soils. In a manipulative experiment, the effect of nutrient enrichment on DEA was examined in a saltmeadow cordgrass [Spartina patens (Aiton) Muhl.] marsh. In the high marsh, DEA significantly (p < 0.05) increased with watershed N loadings and decreased with the percent of hydric soils in a 200-m terrestrial buffer. In the low marsh, we found no significant relationships between DEA and watershed N loadings, residential land development, or terrestrial hydric soils. In the manipulation experiment, we measured increased DEA in N-amended treatments, but no effect in the P-amended treatments. The positive relationships between N loading and high marsh DEA support the hypothesis that salt marshes may be important buffers between the terrestrial landscape and estuaries, preventing the movement of land-derived N into coastal waters. The negative relationships between marsh DEA and the percent of hydric soils in the adjacent watershed illustrate the importance of natural buffers within the terrestrial landscape. Denitrification enzyme activity appears to be a useful index for comparing relative N exposure and the potential denitrification activity of coastal salt marshes. 相似文献
403.
Bird SB Herrick JE Wander MM Wright SF 《Environmental pollution (Barking, Essex : 1987)》2002,116(3):445-455
To measure and manage for C sequestration in heterogeneous rangeland systems, we need to more fully understand spatial patterns of soil resources. Spatial distributions of aggregate stability and soil carbon were investigated in a semiarid rangeland in New Mexico, USA. Soil was analyzed from plant interspaces, black grama (Bouteloua eriopoda (Torr.) Torr.), and mesquite (Prosopis glandulosa Torr.) in a landscape-replicated study. Aggregate stability at the 250 microm scale, carbonate C, organic C and N, C:N ratio, and glomalin, were all highest under mesquite. Soil C:N ratio was the best predictor of aggregate stability. Estimates of metric tons of C per hectare in the top 10 cm were highly variable at patch and landscape scales, varying from 4.2 to 10.5 under mesquite and from 3.0 to 7.0 in interspaces. High variability of aggregate stability and soil C has important implications for C sequestration. We argue that this multi-scale soil heterogeneity must be considered when measuring and managing for C sequestration. 相似文献
404.
The origin of faeces by means of biomarker detection 总被引:6,自引:0,他引:6
Bull ID Lockheart MJ Elhmmali MM Roberts DJ Evershed RP 《Environment international》2002,27(8):647-654
405.
Ecological Compensation in Dutch Highway Planning 总被引:13,自引:0,他引:13
The ecological compensation principle was introduced by the Dutch government in 1993. This principle is designed to enhance
the input of nature conservation interests in decision-making on large-scale development projects and to counterbalance the
ecological impacts of such developments when implemented. This article evaluates the application of the Dutch compensation
principle in highway planning. Six current highway projects reveal consistent implementation of this principle, although provincial
policies on compensation and a national method for identifying compensation measures are still under development. As the planning
process has not yet been completed for all the projects, no general conclusions can be drawn on the impact of the compensation
principle on highway decision-making. Nevertheless, several examples show that the principle stimulates project initiators
to develop alternative routes or route sections in order to avoid or reduce ecological impacts and the need for coherent compensation
measures. If the compensation principle is to be properly implemented in the context of highway planning, particular attention
should be paid to the following aspects: (1) sequential assessment of overall project legitimacy and the necessity of intersecting
protected areas and compensation measures, (2) the initiator's attempts to avoid and mitigate ecological impacts in developing
alternative routes prior to compensation for impacts, and (3) the role of uncertain ecological impacts in identifying compensation
measures, especially those concerning habitat isolation. 相似文献
406.
407.
408.
John Zink公司向市场推出一种可以利用烟道气循环减少燃气锅炉NOx排放量的燃烧器.在现场试验中 该燃烧器NOx的排放体积分数稳定达到×- 最低达到×-. 该技术被称作冷燃料法 因为烟道气与燃料气混合使燃料气的热值从Bt u/英尺降至 Btu/英尺 使绝热火焰温度降低 从而减少NOx的产生量.该技术的关键是一个具有专利权的文丘里喷嘴.该喷嘴可利用燃料气的驱动力将烟道气循环引入燃料管线中 从而避免使用风扇. 由于技术简单 该法的投资要低于其他方法.对于一个 MM Btu/h的典型燃气锅炉 该法去除t NOx的费 《化工环保》2001,21(6):371
John Zink公司向市场推出一种可以利用烟道气循环减少燃气锅炉NOx排放量的燃烧器 .在现场试验中,该燃烧器NOx的排放体积分数稳定达到30×10-6,最低达到10×1 0-6. 该技术被称作冷燃料法,因为烟道气与燃料气混合使燃料气的热值从1200 Bt u/英尺3降至400 Btu/英尺3,使绝热火焰温度降低,从而减少NOx的产生量.该技术的关键是一个具有专利权的文丘里喷嘴.该喷嘴可利用燃料气的驱动力将烟道气循环引入燃料管线中,从而避免使用风扇. 由于技术简单,该法的投资要低于其他方法.对于一个100 MM Btu/h的典型燃气锅炉,该法去除1 t NOx的费用为527美元,而常规烟道气循环法则需要1 120美元,选择性催化还原法则需要3148美元.该技术可适用于任何一种常规燃烧器. 相似文献
409.
410.
Controls over foliar N:P ratios in tropical rain forests 总被引:13,自引:0,他引:13
Correlations between foliar nutrient concentrations and soil nutrient availability have been found in multiple ecosystems. These relationships have led to the use of foliar nutrients as an index of nutrient status and to the prediction of broadscale patterns in ecosystem processes. More recently, a growing interest in ecological stoichiometry has fueled multiple analyses of foliar nitrogen:phosphorus (N:P) ratios within and across ecosystems. These studies have observed that N:P values are generally elevated in tropical forests when compared to higher latitude ecosystems, adding weight to a common belief that tropical forests are generally N rich and P poor. However, while these broad generalizations may have merit, their simplicity masks the enormous environmental heterogeneity that exists within the tropics; such variation includes large ranges in soil fertility and climate, as well as the highest plant species diversity of any biome. Here we present original data on foliar N and P concentrations from 150 mature canopy tree species in Costa Rica and Brazil, and combine those data with a comprehensive new literature synthesis to explore the major sources of variation in foliar N:P values within the tropics. We found no relationship between N:P ratios and either latitude or mean annual precipitation within the tropics alone. There is, however, evidence of seasonal controls; in our Costa Rica sites, foliar N:P values differed by 25% between wet and dry seasons. The N:P ratios do vary with soil P availability and/or soil order, but there is substantial overlap across coarse divisions in soil type, and perhaps the most striking feature of the data set is variation at the species level. Taken as a whole, our results imply that the dominant influence on foliar N:P ratios in the tropics is species variability and that, unlike marine systems and perhaps many other terrestrial biomes, the N:P stoichiometry of tropical forests is not well constrained. Thus any use of N:P ratios in the tropics to infer larger-scale ecosystem processes must comprehensively account for the diversity of any given site and recognize the broad range in nutrient requirements, even at the local scale. 相似文献