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221.
A study has been made of the relationships between the characteristics of the riparian vegetation (floristic composition,
structure and diversity) and the spatial–temporal variation of the quality of the stream waters in a basin under a semiarid
Mediterranean climate in the southeastern Iberian Peninsula. The plant communities of the high reaches present greater specific
richness and diversity (S
mean= 7.0 ± 3.4 and H′mean= 2.0 ± 0.7) than do those of the middle and low reaches (S
mean= 4.5 ± 1.6 and H′mean= 1.8 ± 0.6). One zone reached the highest specific richness (S= 12, H′= 3.2), which, apart from being situated in the intermediate stretch of the basin, represents a transitional state (ecotone)
between the Salix and Tamarix communities. The characteristics of the waters analyzed indicate very high rates of erosion and runoff due to the nature
of the soils (easily eroded marls) and to agricultural expansion and mining since the 16th century. The present-day riparian
vegetation is not adequate to absorb the nitrates added to the basin by crop fertilization, reaching extremely high values,
particularly during the dry period (between 1.2 and 42.5 mg/liter). Sewage dumping at three sampling stations did not appear
to affect the specific composition of the woody vegetation. In the zones with watercourses, water salinity was low during
the period of greater water flow, but considerably higher in the dry season (the upper limit was some 1.2 mS/m), resulting
in a predominance of salt cedars over willows. Three types of saltcedar areas were distinguished: subhalophilous, which barely
changes its chemical composition over the season; halophilous, which develops over strongly mineralized waters and markedly
alters in chemical composition during the dry season; and hyperhalophilous, where salinity is extraordinarily high and quite
constant throughout the year. A direct relationship was found between the dominance of Tamarix africana and abundance of NaCl. 相似文献
222.
Mercury in sediments and vegetation in a moderately contaminated salt marsh
(Tagus Estuary, Portugal) 总被引:1,自引:1,他引:0
Jo?ao Can′ario Carlos Vale Laurier Poissant Marta Nogueir Martin Pilote Vasco Branco 《环境科学学报(英文版)》2010,22(8):1151-1157
Depth variations of total mercury (Hg) and methylmercury (MeHg) concentrations were studied in cores from non-colonized
sediments, sediments colonized by Halimione portulacoides, Sarcocornia fruticosa and Spartina maritima and belowground biomass,
in a moderately contaminated salt marsh (Tagus Estuary, Portugal). Concentrations in belowground biomass exceeded up to 3 (Hg) and
15 (MeHg) times the levels in sediments, and up to 198 (Hg) and 308 (MeHg) times those found in aboveground parts. Methylmercury
in colonized sediments reached 3% of the total Hg, 50 times above the maximum values found in non-colonized sediments. The absence
of correlations between total Hg concentrations in sediments and the corresponding MeHg levels suggested that methylation was only
dependent on the environmental and microbiological factors. The analysis of belowground biomass at high-depth resolution (2 cm)
provided evidence that Hg and MeHg were actively absorbed from sediments, with higher enrichment factors at layers where higher
microbial activity was probably occurring. The results obtained in this study indicated that the biotransformation of Hg to the toxic
MeHg could increase the toxicity of plant-colonized sediments. 相似文献
223.
Soil carbon sequestration in a changing global environment 总被引:1,自引:0,他引:1
Felipe Macías Marta Camps Arbestain 《Mitigation and Adaptation Strategies for Global Change》2010,15(6):511-529
Throughout its long history the Earth has undergone warm periods with high atmospheric concentrations of greenhouse gases
(GHG), and has responded with different buffering mechanisms whereby atmospheric C has been transferred to other geochemical
compartments. Strategies for the mitigation and adaptation to the current climatic forcing may thus be generated by the acceleration
of such natural mechanisms, especially those involved in short cycles, mainly in the biosphere and the pedosphere. Although
these contain smaller C stocks than other compartments (< 0.01% of the total C), they circulate large amounts of C from the
atmosphere through photosynthesis and mineral weathering (e.g., 120 Pg C are circulated through terrestrial ecosystems and
total C in the atmospheric compartment is 805 Pg C). Increased C sequestration can thus be achieved in terrestrial ecosystems,
by: (1) favouring growth of biomass; (2) promoting and facilitating carbonation processes; (3) reducing erosion and favouring
pedogenesis; (4) developing organic matter-rich horizons; (5) recovering degraded or contaminated soils, and/or (6) managing
waste by use of systems that minimize emissions of GHG. Within the latter option, the following actions are considered here
in more detail: 1) production of Technosols, and 2) production of biochar. All of the above options should form part of a
strategy for the mitigation and adaptation to global climate change. In this review, we analyze those focused on promoting
soil conservation, soil restoration and soil formation. 相似文献
224.
Mónica Martínez-Martínez Marta Diez-Valcarce Marta Hernández David Rodríguez-Lázaro 《Food and environmental virology》2011,3(2):92-98
Synthetic multiple-target RNA and DNA oligonucleotides were constructed for use as quantification standards for nucleic acid
amplification assays for human norovirus genogroup I and II, hepatitis E virus, murine norovirus, human adenovirus, porcine
adenovirus and bovine polyomavirus. This approach overcomes the problems related to the difficulty of obtaining practical
quantities of viral RNA and DNA from these viruses. The quantification capacity of assays using the standards was excellent
in each case (R
2 > 0.998 and PCR efficiency > 0.89). The copy numbers of the standards were equivalent to the genome equivalents of representative
viruses (murine norovirus and human adenovirus), ensuring an accurate determination of virus presence. The availability of
these standards should facilitate the implementation of nucleic acid amplification-based methods for quantitative virus detection. 相似文献
225.
226.
This study examines the extent to which human resource (HR) training (content and context) is contingent on business strategy (i.e. classified according to Miles and Snow (1984) typology—‘Designing strategic human resource systems’, Organizational Dynamics, 13 , 36–52) as well as the characteristics of the work process. Sixty‐five Spanish organizations (i.e. 65 senior executives and 65 senior HR officers) participated in the study. Using primarily factorial and cluster analyses, support was found to the assertion that companies adopting a particular type of training strategy/policy have a high degree of internal consistency amongst the training objectives sought. In terms of work processes and training, results indicate that under work processes where the content of work provides for enrichment and for long‐term results, companies tend to adopt training strategies where emphasis is on enhancement of individual specialized skills aimed at improving direct productivity. By contrast, firms who use work processes that are characterized by repetitive and routine tasks, de‐emphasize this type of training content. Results also indicae that limited level of contingencies exist between training policies and business strategy, especially when time dimension is also accounted for. While the theory suggests that organizations that have their HR training fit (contingent) on their business strategy are more effective, the empirical results portrayed in this study shows a more complex picture. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
227.
Fdez-Güelfo LA Alvarez-Gallego C Sales D García LI 《Waste management (New York, N.Y.)》2012,32(3):382-388
The influence of particle size and organic matter content of organic fraction of municipal solid waste (OFMSW) in the overall kinetics of dry (30% total solids) thermophilic (55 °C) anaerobic digestion have been studied in a semi-continuous stirred tank reactor (SSTR). Two types of wastes were used: synthetic OFMSW (average particle size of 1 mm; 0.71 g Volatile Solids/g waste), and OFMSW coming from a composting full scale plant (average particle size of 30 mm; 0.16 g Volatile Solids/g waste).A modification of a widely-validated product-generation kinetic model has been proposed. Results obtained from the modified-model parameterization at steady-state (that include new kinetic parameters as K, YpMAX and θMIN) indicate that the features of the feedstock strongly influence the kinetics of the process. The overall specific growth rate of microorganisms (μmax) with synthetic OFMSW is 43% higher compared to OFMSW coming from a composting full scale plant: 0.238 d−1 (K = 1.391 d−1; YpMAX = 1.167 L CH4/gDOCc; θMIN = 7.924 days) vs. 0.135 d−1 (K = 1.282 d−1; YpMAX = 1.150 L CH4/gDOCc; θMIN = 9.997 days) respectively.Finally, it could be emphasized that the validation of proposed modified-model has been performed successfully by means of the simulation of non-steady state data for the different SRTs tested with each waste. 相似文献
228.
Trait-mediated effects on flowers: artificial spiders deceive pollinators and decrease plant fitness 总被引:1,自引:0,他引:1
Although predators can affect foraging behaviors of floral visitors, rarely is it known if these top-down effects of predators may cascade to plant fitness through trait-mediated interactions. In this study we manipulated artificial crab spiders on flowers of Rubus rosifolius to test the effects of predation risk on flower-visiting insects and strength of trait-mediated indirect effects to plant fitness. In addition, we tested which predator traits (e.g., forelimbs, abdomen) are recognized and avoided by pollinators. Total visitation rate was higher for control flowers than for flowers with an artificial crab spider. In addition, flowers with a sphere (simulating a spider abdomen) were more frequently visited than those with forelimbs or the entire spider model. Furthermore, the presence of artificial spiders decreased individual seed set by 42% and fruit biomass by 50%. Our findings indicate that pollinators, mostly bees, recognize and avoid flowers with predation risk; forelimbs seem to be the predator trait recognized and avoided by hymenopterans. Additionally, predator avoidance by pollinators resulted in pollen limitation, thereby affecting some components of plant fitness (fruit biomass and seed number). Because most pollinator species that recognized predation risk visited many other plant species, trait-mediated indirect effects of spiders cascading down to plant fitness may be a common phenomenon in the Atlantic rainforest ecosystem. 相似文献
229.
230.
Studies of the Slovakian Danube have indicated profound changes in the structures of several invertebrate assemblages in the section of the river bypassed by the Gab?íkovo hydroelectric project in 1992 and in adjacent floodplain water bodies. The present study investigates the relationship between hydrological connectivity and species diversity in the old main channel and adjacent left-bank water bodies, using resident cladocerans as indicators of the ecological integrity of the river-floodplain system. The work aimed to quantify cladoceran habitat preferences using habitat values (HV) and indication weights (IW) calculated from data accumulated during long-term monitoring of planktonic communities of the Danube floodplain (1,840.5–1,804 rkm) and supplemented with data from the literature. Although not listed as an indicator group in the European Union Water Framework Directive, cladocerans are shown to be highly apposite in the ecological assessment of river-floodplain systems. Of 71 recorded cladoceran species, 19 taxa showed a preference for eupotamal habitats, 24 species preferred eupotamal B/parapotamal waters, and 28 cladocerans were found to prefer the plesiopotamal/paleopotamal habitat type. Identified habitat types follow a gradient of hydrological connectivity with the main river channel, ranging from the eupotamal to more or less isolated floodplain water bodies. A secondary aim was to use the calculated values to assess the ecological integrity of the river-floodplain system. The key element of this procedure is the calculation of the Floodplain Index (FI) (Chovanec et al. Large Rivers, 15(1–4), 169–185 2005) from the summation of the habitat values and indication weights of all species present at the sampling sites. Calculated index values indicate the extent of disruption to lateral connectivity in the floodplain area. 相似文献