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121.
Constructed wetlands are one method under investigation for the remediation of trace element-contaminated agricultural drainwater. A greater understanding of the retention of trace elements by the bulk soil and soil constituents is necessary for their safe and effective use. To determine the capacity of soil, calcite, and goethite-coated quartz sand for retention of As, Mo, and V under field conditions, an in situ method was used whereby permeable bags containing those minerals were placed near the sediment surface of a flow-through constructed wetland for 3 or 12 mo. Accumulations of As, Mo, and V occurred on goethite-coated sand. Concentrations of Mo on goethite-coated sand were much higher in samples from a wetland cell with a water depth of 15 cm (38.23 +/- 7.27 mg kg(-1)) compared with those from a cell with a water depth of 3 cm (8.30 +/- 1.45 mg kg(-1)). Calcite sorbed no As and low amounts of Mo and V, indicating that it is not an important sink for those elements under these conditions. In soil bags, total As and V concentrations showed little change over 12 mo. Molybdenum accumulated in the soil bags, resulting in total concentrations (12 mo) of 27.22 +/- 2.69 mg kg(-1) and 11.42 +/- 1.35 mg kg(-1) at water depths of 15 and 3 cm, respectively. Nearly half of the Mo accumulation on soil became water soluble after air-drying. This has important implications for systems that may undergo changes in redox status, possibly resulting in large fluxes of water-soluble Mo. 相似文献
122.
F. Edwin. Harvey 《Journal of the American Water Resources Association》2005,41(2):447-460
ABSTRACT: Where data are available, hydrologic studies may use precipitation's stable oxygen and hydrogen isotope composition to investigate streamflow, ground water/surface water interaction, and ground water recharge. Paleoclimate studies utilize the δ18Oprecipitation‐Tair relationship, in conjunction with lake sediments, fossils, or old ground waters, for example, to estimate pale‐otemperatures. Ecological studies utilize precipitation and soil water isotope composition to track moisture uptake in plants, and to trace species migration patterns. Such studies require that the isotopic composition of precipitation be known. Oxygen‐18 (δ18O) and deuterium (δ2H) data for precipitation are lacking in the semi‐arid portion of the north‐central U.S. Great Plains, and thus there is a need to establish additional meteoric water lines as isotope input functions across the region, as well as to develop better understanding of the isotopic climate linkages that control oxygen and hydrogen isotope ratios in precipitation. This study determined the δ18O and δ2H composition of precipitation in the Pawnee Grasslands of northeastern Colorado from 1994 through 1998 using archived National Atmospheric Deposition Program samples. The resulting local water line follows the relationship δ2H = 7.86 δ18O‐7.66, and the data show a δ18Oweekly ‐ Tweekly relationship of δ18O = 0.560‐T (°C)‐18.8. 相似文献
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124.
The experience of the International Expert Panel on Environment for the Xiaolangdi dam/reservoir project in China (XEP) showed that the Panel meetings resulted in a marked improvement in project environmental performance by all parties participating in project implementation, with no parties exempt from the Panel's evaluations. Unfortunately the Loan Agreement authorizes use of the Panel only through the project stages of final design and construction, hence the 12th Panel meeting, which matched project construction completion, ended this series. The Panel has recommended that some meetings of the Panel be held during the project's operations stage in order to maintain continuing attention to environmental needs. The XEP experience showed that the XEP, in addition to monitoring project environmental performance, was very valuable for (i) training of Chinese staff involved in project implementation, and (ii) serving in the role as expert consultant for guiding the work of the Chinese participants. The XEP experience also showed the need for making a clear separation between evaluation, the overall resettlement program per se, and the environmental effects of the program. The Panel recommended that the Ministry of Water Resources and World Bank cooperate in sponsoring a book on The Environmental History of the Xiaolangdi Project, including both dam construction as well as resettlement problems, which would serve as a very valuable reference for guiding environmental planning for future dam projects in China (Ludwig, H.F. 1994–2000). 相似文献
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128.
The purpose of this research is to study the temporal and spatial sediment delivery to and within the stream network following a wildfire on a chaparral watershed in Arizona, USA. Methods include interpretation of channel processes (aggradation, degradation) from sequential aerial photographs, field measurements of sediment delivery, and overland flow from ten microwatersheds having different vegetation cover (no vegetation, chaparral cover, and bare with vegetation buffer strips). The response of the watershed to the fire was very complex. The fire reduced the chaparral cover to zero in most locations and severe erosion led to filling of the channels by sediment. With vegetation recovery, sediment delivery from the watershed practically ceased. Vegetation buffer strips were mainly responsible for arresting the sediment delivered from bare hillslopes. Relatively clear water, entering the channels, caused degradation in the tributaries that delivered the sediment into the main stream at El Oso Creek. Due to high water infiltration by immense volumes of sediment deposits in the middle reach, the sediment from the tributaries was deposited as in-channel fans. In contrast, the upper reach of El Oso Creek behaved similarly to the tributaries. It aggraded after the fire and was followed by degradation. The low reach of El Oso Creek is degrading because it is still adjusting base level to the incision of the master stream. Implications of this study are that land managers, concerned to avoid severe erosion and sedimentation following disturbance, should concentrate on the establishment and enhancement of vegetation buffer strips along channel banks. 相似文献
129.
Assigning money amounts to represent intrinsic value of precious eco-systems in developing countries
Harvey F. Ludwig 《The Environmentalist》2006,26(3):143-145
Conclusion The need is urgent, if the ongoing rapid degradation of the remaining precious eco-systems of the developing countries are
to be put under control while there is still time, for developing a procedure by which the real world intrinsic meaningfulness
to people of precious eco-systems is recognized by assigning them monetary values to be considered in benefit/cost analyses.
The procedures recommended by the U.S. Corps of Engineers and Resources of the Future for use in the USA seem to be much too
complex for application in developing countries in the foreseeable future. Rather a very pragmatic approach is recommended
based on actual experience in money outlays for such protection in USA projects, with the amounts modified to suit developing
country conditions. Hopefully the IAAs (Multilateral Development Banks, Bilaterials, U.N. Agencies) will carry out the recommended
R&D studies to produce a prescribed methodology recognized by economic, environmental, and political decision makers of both
the IAAs and the DCs to be appropriate for use in planning and evaluating DC projects. 相似文献
130.
Summary We test the hypothesis that cross-species variation in home range size across primates is determined by the metabolic needs of the animals occupying the home range and by their diet. Metabolic needs are calculated from published records of group structure, time spent in different activities and the metabolic costs of those activities. Data from 20 species demonstrate clear relationships between home range, diet and metabolic needs. Although correlations are in the expected directions, simple models relating diet to home range size and metabolic needs do not predict the functional relationships found. This may be because the data are inadequate or because the models are wrong. An empirical relationship between relative home-range size and diet distinguishes between the arboreal and terrestrial species in the sample. 相似文献