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821.
The need to implement sustainable resource management regimes for semi-arid and arid rangelands is acute as non-adapted grazing strategies lead to irreversible environmental problems such as desertification and associated loss of economic support to society. In these sensitive ecosystems, traditional sectoral, disciplinary approaches will not work to attain sustainability: achieving a collective vision of how to attain sustainability requires interactive efforts among disciplines in a more integrated approach. 相似文献
822.
C. H. Huang 《Environmental Fluid Mechanics》2009,9(3):359-366
In the condition of free convection, the Charnock relation is inadequate. In this paper we extend the Charnock relation to
include the effect of free convection on the roughness length. As a result, the singularity in the Monin–Obukhov similarity
theory can be avoided. This paper shows two approaches to derive the roughness length formula in the forced and free convections.
The first approach is based on the mixing length theory and the use of the observational data of the vertical velocity variance.
We introduce a new vertical velocity scale based on the vertical velocity variance; this velocity variance is well behaved
in the atmospheric boundary layer and easy to obtain from field experiments. The second approach is based on the theoretical
framework of Sykes et al. (Q R Met Soc, 119: 409–421). From that framework, we develop a theory to obtain the roughness length
formula. The results of these two approaches are in agreement with each other. In the past, a multiplication factor associated
with free convection was considered to be a constant. This paper shows that this multiplication factor is, in fact, also dependent
on the depth of the mixing height. In previous studies, experimental works were often conducted without taking into account
the depth of the mixing height. Not taking into account the mixing height in the estimation of the roughness length in free
convection would result in an inaccurate estimate of the roughness length and hence the drag coefficient.
An erratum to this article can be found at 相似文献
823.
This paper estimates the impact of climate change on the prevalence of criminal activity in the United States. The analysis is based on a 30-year panel of monthly crime and weather data for 2997 US counties. I identify the effect of weather on monthly crime by using a semi-parametric bin estimator and controlling for state-by-month and county-by-year fixed effects. The results show that temperature has a strong positive effect on criminal behavior, with little evidence of lagged impacts. Between 2010 and 2099, climate change will cause an additional 22,000 murders, 180,000 cases of rape, 1.2 million aggravated assaults, 2.3 million simple assaults, 260,000 robberies, 1.3 million burglaries, 2.2 million cases of larceny, and 580,000 cases of vehicle theft in the United States. 相似文献
824.
This paper explores the characteristics of 238 patents on 90 inventions contributed by major multinational innovators to the “Eco-Patent Commons”, which provides royalty-free access to third parties to patented innovations on green technologies. We compare the pledged patents to other patents in the same technologies or held by the same multinationals to investigate the motives of the contributing firms as well as the potential for such commons to encourage innovation and diffusion of climate change related technologies. We find pledged patents to protect environmentally friendly technologies and to be of similar value as the average patent in a pledging firm's patent portfolio but of lower value than other patents in their class. Our analysis of the impact of the patent commons on diffusion of patented technologies suggests that making patents accessible royalty-free did not result in any significant increase in diffusion as measured by citing patents. This study, therefore, indirectly provides evidence on the role of patents in the development and diffusion of green technologies. 相似文献
825.
Extremely damaging snowstorms, those causing more than $1 million in property losses across the US, were studied, and the spatial and temporal characteristics of the storm activity during 1949–2001 were defined. There were 155 catastrophic snowstorms and they caused insured losses of $21.6 billion (2001 dollars). The northeastern US had the nation's maximum storm occurrences (79 storms), greatest total losses ($7.3 billion), and highest storm intensity. Two-thirds of all US losses occurred in the Northeast, Southeast, and Central climate regions, and storm occurrences and losses were least in the western US. The incidence of storms peaked during the 1976–1985 period and exhibited no up or down trend during 1949–2001. However, losses had a significant upward time trend, as did storm sizes and intensity. New York and Pennsylvania had the greatest number of storms with fewest in Montana, Idaho, and Utah. Time distribution of losses in the northeastern and southeastern US were U-shaped with flat time trends for 1949–2001. Losses in the western regions and Deep South had distinct upward trends in losses, storm intensity, and storm size. More than 90 percent of all storm losses in the western US have occurred since 1980. These findings indicate that rapidly growing population and property at risk have been major factors in increasing losses as well as atmospheric changes leading to greater storm intensity and size. 相似文献
826.
Nikolaos M. Fyllas Patrizia I. Politi Panayiotis G. Dimitrakopoulos 《Ecological modelling》2010,221(11):1494-1504
This study aims to provide a quantitative framework to model the dynamics of Mediterranean coniferous forests by integrating existing ecological data within a generic mathematical simulator. We developed an individual-based vegetation dynamics model, constrained on long-term field regeneration data, analyses of tree-rings and seed germination experiments. The simulator implements an asymmetric competition algorithm which is based on the location and size of each individual. Growth is parameterized through the analysis of tree-rings from more than thirty individuals of each of the three species of interest. A super-individual approach is implemented to simulate regeneration dynamics, constrained with available regeneration data across time-since-disturbance and light-availability gradients. The study concerns an insular population of an endemic to Greece Mediterranean fir (Abies cephalonica Loudon) on the island of Cephalonia (Ionian Sea) and two interacting populations of a Mediterranean pine (Pinus brutia Ten.) and a more temperate-oriented pine (Pinus nigra Arn. ssp. pallasiana) on the island of Lesbos (NE Aegean Sea), Greece. The model was validated against plot-level observations in terms of species standing biomass and regeneration vigour and adequately captured regeneration patterns and overall vegetation dynamics in both study sites. The potential effects of changing climatic patterns on the regeneration dynamics of the three species of interest were subsequently explored. With the assumption that a warmer future would probably cause changes in the duration of cold days, we tested how this change would affect the overall dynamics of the study sites, by focusing on the process of cold stratification upon seed germination. Following scenarios of a warmer future and under the current model parameterization, changes in the overall regeneration vigour controlled by a reduction in the amount of cold days, did not alter the overall dynamics in all plant populations studied. No changes were identified in the relative dominance of the interacting pine populations on Lesbos, while the observed reduction in the amount of emerging seedlings of A. cephalonica on Cephalonia did not affect biomass yield at later stages of stand development. 相似文献
827.
C.M.L. Hermans I.R. Geijzendorffer M.J. Metzger P.H. Vereijken A. Verhagen 《Ecological modelling》2010,221(18):2177-2187
Long-term future development of European agriculture within the global market is highly uncertain, but can potentially have large impacts on the future of agricultural businesses, rural communities and amenities such as traditional landscapes and biodiversity. Despite great uncertainties it is of interest to explore the extent of these potential changes. This paper provides an explorative scenario of the European crop production in a liberalised world without European Union (EU) market interventions. The results do not form a prediction or a business as usual scenario, but rather a plausible and salient thought-experiment of a possible future based on the consistent integration of current conceptual and quantitative models.Future scenarios for climate, demography, technology and global demand for agricultural commodities are used to assess the competitiveness of European agriculture. Regional economic competitiveness is determined by combining indicators for the economic strength of farms in a region and population pressure on agricultural land, and subsequently used to determine where agricultural production is likely to sustain under the market liberalisation scenario. The method is illustrated for the 27 EU member state countries for three commodities: wheat, potato and milk (relying on grass).Results include maps of the dominant wheat, potato and milk producing regions across Europe as projected for 2050. They show that due to increased agricultural productivity, less agricultural land will be needed to supply the European demand for food and feed. In addition, production will concentrate in those regions which have a comparative advantage. This potentially leads to a strong polarisation between north-western Europe and southern Europe, which faces negative impacts of climate change and central and northern Europe where agricultural businesses lag in economic strength and farm size. A contrasting policy intervention scenario illustrates how differences in demand and productivity result in an expansion of the agricultural area, especially for the production of wheat.Although the complete liberalisation scenario may seem unlikely, and the underlying assumptions have great uncertainty, the results help identify and map market pressures on agricultural land use across regions in Europe. As such, it stimulates policy debate on the desired future for the European agricultural sector and the trade-offs between economic competitiveness under global market conditions and policy intervention. In addition, it provides a basis for the planning of alternative economic strategies for agriculturally less competitive regions. 相似文献
828.
Ecological niche models (ENMs) have multiple applications in ecology, evolution and conservation planning. They relate the known locations of a species to characteristics of its environment (usually climate) over its geographical range. Most ENMs are trained using standard 30-year (1961-1990) or 50-year (1951-2000) baselines to represent current climate conditions. Species occurrence records used as input to the models, however, are frequently collected from time periods that differ from those from which the climate is derived. Since climate variability can be significant within and outside baselines, and the distributions of some plants and animals (e.g., annual plants, insects) can adjust to environmental conditions on much shorter time scales, this mismatch between collection records and climatic baselines may affect the utility and accuracy of model outputs. We investigated how the choice of baseline periods influenced modelling efforts, anticipating that climate baselines derived from the same temporal period as the species records would yield improved ENMs. Ten simulated species’ distributions were modelled using an ENM (Maxent) for (a) occurrences and climates within the same temporal period, based on eighteen 10-year baselines within the 20th century and (b) all available samples and climate baselines from 1951-2000 and 1961-1990. Each model was projected onto all the available 10-year climate scenarios and compared to the models trained on the corresponding scenario. We show that temporal mismatches of species occurrences and climate baselines can result in significantly poorer distribution models. Such temporal mismatch may be unavoidable for many studies, but we emphasize here the need to match the time range of samples and climate data whenever possible. 相似文献
829.
Perceived safety climate, job demands, and coworker support among union and nonunion injured construction workers 总被引:2,自引:0,他引:2
PROBLEM: This study evaluated injured construction workers' perceptions of workplace safety climate, psychological job demands, decision latitude, and coworker support, and the relationship of these variables to the injury severity sustained by the workers. METHODS: Injury severity was assessed using the Health Assessment Questionnaire (HAQ), which evaluates functional limitations. Worker perceptions of workplace variables were determined by two instruments: (a) the Safety Climate Measure for Construction Sites and (b) the Job Content Questionnaire (JCQ). RESULTS: The overall model explained 23% of the variance in injury severity, with unique contributions provided by union status, the Safety Climate Score, and Psychological Job Demands. A positive significant correlation was found between injury severity and the Safety Climate Scores (r = .183, P = .003), and between the Safety Climate Scores and union status (r = .225, P < .001). DISCUSSION: There were statistically significant differences between union and nonunion workers' responses regarding perceived safety climate on 5 of the 10 safety climate items. Union workers were more likely than nonunion workers to: (a) perceive their supervisors as caring about their safety; (b) be made aware of dangerous work practices; (c) have received safety instructions when hired; (d) have regular job safety meetings; and (e) perceive that taking risks was not a part of their job. However, with regard to the 49-item JCQ, which includes Coworker Support, the responses between union and nonunion workers were very similar, indicating an overall high degree of job satisfaction. However, workers who experienced their workplace as more safe also perceived the level of management (r = -.55, P < .001) and coworker (r = -.31, P < .001) support as being higher. IMPACT ON INDUSTRY: The findings of this study underscore the critical need for construction managers to alert workers to dangerous work practices and conditions more frequently, and express concern and praise workers for safe work in a manner that is culturally acceptable in this industry. Workplace interventions that decrease the incidence and severity of injuries, but that are flexible enough to meet a variety of potentially competing imperatives, such as production deadlines and client demands, need to be identified. 相似文献
830.
Ringrose S Chipanshi AC Matheson W Chanda R Motoma L Magole I Jellema A 《Environmental management》2002,30(1):98-109
For purposes of suggesting adaptive and policy options regarding the sustained use of forestry resources in Botswana, an analysis
of the whole countrywide satellite data (showing the mean present distribution of vegetation in terms of species abundance
and over all density) and the projection of vegetation cover changes using a simulation approach under different climatic
scenarios were undertaken. The analysis revealed that changes in vegetation cover types due to human and natural causes have
taken place since the first vegetation map was produced in 1971. In the southwest, the changes appear to be more towards an
increasing prevalence of thorn trees; in the eastern part of the country where widespread bush encroachment is taking place,
the higher population density suggests more human induced (agrarian-degradation) effects, while in the sparsely settled central
Kalahari region, changes from tree savanna to shrubs may be indicative of the possible influence of climate with the associated
effects of fires and local adaptations. Projection of future vegetation changes to about 2050 indicates degeneration of the
major vegetation types due to the expected drying. Based on the projected changes in vegetation, current adaptive and policy
arrangements are not adequate and as such a shift from the traditional adaptive approaches to community-based types is suggested.
Defining forestry management units and adopting different management plans for the main vegetation stands that are found in
Botswana are the major policy options. 相似文献