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381.
Luis E Rodríguez-Gómez Sebastián Delgado Manuel Alvarez Samuel Elmaleh 《Water environment research》2005,77(2):193-198
Sulfide generation should be avoided during wastewater transportation. The efficiency of nitrate dosing for the inhibition of sulfide generation was evaluated during reclaimed wastewater transport with two nitrate doses, 2.5 and 5 mg/L nitrate-nitrogen (NO3-N). A calcium nitrate [Ca(NO3)2] solution was injected at the beginning of the 61-km-long gravity pipe, which is part of the Reclaimed Wastewater Reuse System of South Tenerife (Spain). During transportation, after dissolved oxygen depletion, a denitrification process took place. With the 5 mg/L NO3-N dose, nitrate was not completely removed at the end of the pipe, whereas with 2.5 mg/L NO3-N, a complete denitrification was achieved. Sulfide generation was completely inhibited with the 5 mg/L dose. However, with 2.5 mg/L, sulfide generation was not completely inhibited but delayed and minimized to a great extent. Denitrification was stoichiometrically limited by the availability in biodegradable matter. An empirical equation enables one to predict the nitrate concentration. 相似文献
382.
This article provides a case study of small-scale private sector provision of water supply in Paraguay, where the Government has sought sector policy reforms that would encourage private investment in drinking water supply. Ironically, while the Government has focused almost entirely on garnering the interest of large private international water companies, much smaller local firms have already made significant investments in drinking water services for the poor, all without any participation or encouragement from the Government. Outside Paraguay's two major cities, Asunción and Ciudad del Este, large numbers of aguateros currently provide piped potable water to lower-income people. Though the aguateros have little legal footing — they are in many respects informal and unregulated —they have constructed as much as one third of all the new drinking water connections in these two cities over the past 20 years. The small-scale water systems in Paraguay offer a model of financial, economic, and water-use efficiency. This article asserts that an abundance of groundwater resources, cheap access to electricity for pumping, and a spirit of informal investment, among other variables, has spawned widespread use of this approach. This article documents and analyzes the features of these independent small-scale water providers in Paraguay and the efficiency they bring to the use of water resources in meeting drinking water demands among the poor. It also cautions against policies that may trample on such entrepreneurial spirit in the name of State-managed privatization. 相似文献
383.
Enrique Morán-Tejeda Antonio Ceballos-Barbancho José Manuel Llorente-Pinto Juan Ignacio López-Moreno 《Regional Environmental Change》2012,12(1):17-33
Land-use and land-cover changes have attracted substantial scientific interest in recent years because of their marked influence
on hydrological cycles. In developed countries of the Mediterranean basin, the generalized revegetation and forest growth
in mountainous areas that occurred during the last five decades are negatively affecting the evolution of water resources
in headwaters. In this study, changes in land cover in the Duero River Basin (northern Spain) during the last 50 years were
analyzed and their role in hydrological evolution was estimated. For this purpose, step-wise linear regressions were developed
to estimate the evolution of runoff as a function of climate (precipitation and temperatures). The results show a significant
expansion of forest cover in the headwaters, although it has been more extensive in the mountains to the north of the basin
than to the south. River discharges in the headwaters underwent a generalized decline during the study period (1961–2006),
but precipitation over the same period did not show an appreciable trend. In the absence of noticeable trends in removal of
water for human consumption, our results indicate that revegetation is contributing to the observed hydrological decline.
Our hypothesis is confirmed because of the greater divergence in the evolution of precipitation and runoff in the northern
headwaters (more forest growth) than in the south headwaters (less forest growth). Results suggest that further increases
in forest area will enhance hydrological decline and highlight the importance of integrating land-cover information in water
availability assessments in a region where water is a strategic resource. 相似文献
384.
385.
Manuel H Johnson Frederick W Bell James T Bennett 《Journal of Environmental Economics and Management》1980,7(3):256-271
This study updates and expands the empirical analysis of natural resource scarcity published in 1963 by Harold Barnett and Chandler Morse (“Scarcity and Growth: The Economics of Natural Resource Availability,” Johns Hopkins Press). Unit extraction costs are measured for all extractive products, four major subgroups (agriculture, minerals, forestry, and fishing), and selected individual commodities. The efficacy of the unit cost measure of resource scarcity is addressed and a critique of alternative scarcity indicators is provided. Unit cost appears to be the most practical scarcity index because there are adequate checks against its theoretical shortcomings and data are readily available which contain fewer deficiencies than other indexes. On the basis of the Barnett and Morse definition of relative scarcity, the empirical evidence does not support the need for public actions justified solely on the basis of increasing resource scarcity. 相似文献
386.
387.
Félix-Valenzuela Leticia Molina-Chavarria Alejandro Enríquez-Hernández Carmen Itzé Bolado-Martínez Enrique Durazo-Arvizu María de los Ángeles Dórame-Castillo Roberto Cano-Rangel Manuel Alberto Mata-Haro Verónica 《Food and environmental virology》2020,12(4):355-360
Food and Environmental Virology - Norovirus (NoV) is an important etiological agent of diarrhea in children and adults. In Mexico, NoV screening is not routinely performed. NoV is highly infectious... 相似文献
388.
The sequential extraction procedures described by Tessier et al., McGrath and Cegarra, and Gimeno-García et al. were compared
to investigate trace element (As, Cr, Cu, Pb, and Zn) partitioning patterns and extraction efficiency in three contaminated
soils from Mediterranean regions of Spain. Soils were selected from Onda (Castellón) (S1), Aznalcóllar (Sevilla) (S2), and
Silla (Valencia) (S3). S1 was a soil contaminated with Pb and Zn after dumping of wastes from the manufacture of ceramic tiles,
S2 was polluted accidentally with a highly acid and As-concentrated sludge from mining activities, and S3 was a soil with
a high Cr content from tannery sludge disposal. Trace element distribution in the soils—soluble, exchangeable, organically
bound, precipitated with carbonates, bound to iron and manganese oxides, and precipitated with sulfides fractions—varied significantly
according to the extraction procedure used. In addition, different extraction efficiencies were found for the three sequential
extraction procedures compared. Finally, the trace elements studied showed different and specific distribution patterns between
the various soil fractions examined. 相似文献
389.
390.
It is predicted that climate change will drive extinctions of some reptiles and that the number of these extinctions will depend on whether reptiles are able to change their distribution. Whether the latitudinal distribution of reptiles may change in response to increases in temperature is unknown. We used data on reptile distributions collected during the 20th century to analyze whether changes in the distributions of reptiles in Spain are associated with increases in temperature. We controlled for biases in sampling effort and found a mean, statistically significant, northward shift of the northern extent of reptile distributions of about 15.2 km from 1940-1975 to 1991-2005. The southern extent of the distributions did not change significantly. Thus, our results suggest that the latitudinal distributions of reptiles may be changing in response to climate change. 相似文献