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161.
Summary Preferred ambush sites of fishing spiders Dolomedes triton (Pisauridae) were investigated, primarily with respect to aquatic vegetation and wave action, at five locations differing in these variables along the shore of Dow Lake (near Athens, Ohio). The linear density of spiders correlated positively with the presence of aquatic vegetation. D. triton most often stood at a distance from shore proportional to the width of the zone of floating and emergent vegetation (Fig. 2). Usually they positioned their bodies in the horizontal plane on floating living or dead plant parts. Spider density was negatively correlated with the amplitude of wind-generated waves (Fig. 4). The maximum energy of these waves measured on breezy days was at a frequency of 1.4 Hz, with no components exceeding 10 Hz (Fig. 5). Spiders could discriminate high-amplitude (up to 40 mm) wind waves from prey waves, probably since the latter have substantially higher frequencies (Figs. 3, 5). 相似文献
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Horst Behrendt Matthias Kornmilch Dieter Opitz Oliver Schmoll Gaby Scholz 《Regional Environmental Change》2002,3(1-3):107-117
The nutrient discharges from point and diffuse sources in more than 200 German river basins were estimated for the periods
1983–1987 and 1993–1997 employing the MONERIS model. This model distinguishes between six diffuse pathways and point source
emissions from waste water treatment plants and direct industrial discharges. It was estimated that the total nitrogen input
into the German river systems amounts to about 819,000 t N year–1 in the period 1993 to 1997. These emissions have decreased since the mid-eighties by about 266,000 t N year–1, mainly caused by the reduction of point discharges. For phosphorus the emissions have been reduced by 56,290 t P year–1 and amount to 37,250 t P year–1 in the period 1993–1997. Based on emission data a retention module estimates riverine nutrient loads. The comparison of the
model output with the observed loads shows a deviation as low as 30% and 50% for nitrogen and phosphorus, respectively. The
regional resolution of the model indicates the relative importance of different pathways for phosphorus and nitrogen input
into river systems.
Electronic Publication 相似文献
166.
Because of its potential harmful impact on the environment, disposal of sewage sludge is becoming a major problem all over the world. Today the available disposal measures are at the crossroads. One alternative would be to continue its usage as fertiliser or to abandon it. Due to the discussions about soil contamination caused by sewage sludge, some countries have already prohibited its application in agriculture. In these countries, thermal treatment is now presenting the most common alternative. This report describes two suitable methods to directly convert sewage sludge into useful energy on-site at the wastewater treatment plant. Both processes consist mainly of four devices: dewatering and drying of the sewage sludge, gasification by means of fluidised bed technology (followed by a gas cleaning step) and production of useful energy via CHP units as the final step. The process described first (ETVS-Process) is using a high pressure technique for the initial dewatering and a fluidised bed technology utilising waste heat from the overall process for drying. In the second process (NTVS-Process) in addition to the waste heat, solar radiation is utilised. The subsequent measures--gasification, gas cleaning and electric and thermal power generation--are identical in both processes. The ETVS-Process and the NTVS-Process are self-sustaining in terms of energy use; actually a surplus of heat and electricity is generated in both processes. 相似文献
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Waste management strategies in mining projects will depend to a large extent on the characteristics of the operational process, the type of ore and prevailing socio-environmental conditions, amongst other issues. The expenditures required by the management scheme and the implementation of remediation programs will be determined by the extent that the above issues were considered in the planning phase of the project. Several works have been published in the literature concerning the analysis of waste management programs and environmental impacts associated with uranium projects around the world. However, the vast majority do not report a comprehensive assessment integrating the various relationships among operational process, environmental impact, remediation strategy and costs. This study, divided into two papers, presents a detailed critical analysis of the waste management strategies adopted in two uranium production centres in Brazil, i.e., the Poços de Caldas Project (Part I) and the Caetité Project (Part II). The operational processes are described and the environmental impacts of the generated wastes as well as the adopted management strategies and costs are examined. Also, in Part II, a comparison between both production centres is made emphasizing the impacts of environmental and social-economical issues on the overall assessment. 相似文献
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Eckart Steffen Horst Malchow Alexander B. Medvinsky 《Environmental Modeling and Assessment》1997,2(1-2):43-48
The dynamic behaviour of a model plankton community is described by solutions of a generalized predator‐prey model. The qualitative changes due to variations of parameters are considered and the existence of multistability and catastrophic behaviour is noted. Local and global bifurcations of the system are displayed. A seasonal variation of a parameter is introduced and the resulting dynamics are considered, such as quasiperiodic solutions or chaotic attractors. 相似文献