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71.
小型砂滤池在废水处理中的应用 总被引:1,自引:0,他引:1
本文通过湿式除尘后的废水治理及工程实例,探讨了小型砂滤池在废水处 理中应用的可行性。 相似文献
72.
D. van der Laan O. F. R. van Tongeren W. H. van der Putten G. Veenbaas 《Journal of Coastal Conservation》1997,3(2):179-190
In coastal foredunes marram grass (Ammophila arenaria) is used to stabilize windblown sand. The development of traditionally plantedAmmophila into a more natural foredune vegetation may take 5 – 10 yr. For economic reasons, traditional planting may be replaced by
alternative techniques such as planting seeds or disk-harrowing rhizome fragments. In this paper, we compare the initial vegetation
development of traditionally planted stands with stands established from seeds and from rhizomes.
The experiments were conducted on an artificial foredune originating from dredged sea sand. The total experimental area covered
more than 100 ha and the vegetation development was studied for 6 yr. The data were analysed bya priori grouping of plant species according to their ecology, as well as by Principal Components Analysis (PCA) and Redundancy Analysis
(RA) of the percentage ground cover per plant species.
Comparing ecological groups of plants showed that all planting methods delivered equal numbers of plant species that are indicative
for coastal dunes. PCA and RA showed that methods based on the use of rhizome material resulted in a higher percentage cover
of clonal perennials (Calammophila baltica, Festuca rubra ssp.arenaria, Carex arenaria andCirsium arvense) than the traditionally planted stands and the stands obtained from seeds. The latter two were characterized by the dominance
of annuals, bi-annuals and (mostly nonrhizomatous) perennials.
Initially, the rates of succession were highest in the stands obtained from rhizomes. However, after 3 – 6 yr there were no
differences between the various stands. During the first four years, the percentage cover by rhizomatous foredune plants developed
faster than that of annuals, bi-annuals and perennials. After 6 yr, the latter contributed almost as much to the percentage
cover as the clonal species.
Nomenclature: van der Meijden et al. (1990) for plant species. The plant species were classified into ecological groups according to van
der Meijden et al. (1991) and Mennema et al. (1980). 相似文献
73.
74.
研究了浸油沙层的导热性能对浸油沙层闪点和燃点的影响。选用柴油作为燃料液体,铜粉和沙子的混合物代表沙层,浸油沙层的导热系数由混合物中的沙子和铜粉比例控制。实验结果表明,浸油沙层的导热性能对其着火特性有重要影响。不加铜粉时,存在一个使混合物的闪点与燃点最小的沙油质量比。随着铜粉添加量的增加,闪点与燃点的最小值点逐渐消失。这可能是加入细铜粉使混合物的表面平整造成的。在最小点后,随铜粉添加量的增加,也就是随混合物的导热性能的改善,混合物的闪点与燃点增大。但当沙子与铜粉的质量比达到1:1时,闪点与燃点随沙油质量比的变化出现了一个最大值,之后闪点和燃点随沙油质量比的增加而降低。这些现象的出现可能是导热能力、毛细现象和混合物内部的空隙三者共同作用的结果。 相似文献
75.
Removal of NAPLs from the unsaturated zone using steam: prevention of downward migration by injecting mixtures of steam and air 总被引:1,自引:0,他引:1
Steam injection for remediation of porous media contaminated by nonaqueous phase liquids has been shown to be a potentially efficient technology. There is, however, concern that the technique may lead to downward migration of separate phase contaminant. In this work, a modification of the steam injection technology is presented, where a mixture of steam and air was injected. In two-dimensional experiments with unsaturated porous medium contaminated with nonaqueous phase liquids, it was demonstrated how injection of pure steam lead to severe downward migration. Similar experiments, where steam and air were injected simultaneously, resulted in practically no downward migration and still rapid cleanup was achieved. The processes responsible for the prevention of downward migration when injecting steam-air mixtures were analyzed using a nonisothermal multiphase flow and transport model. Hereby, three mechanisms were identified and it was demonstrated how the effectiveness of these mechanisms depended on the air-to-steam mixing ratio. 相似文献
76.
长庆气田——呼和浩特输气管道工程生态环境保护及恢复对策 总被引:1,自引:0,他引:1
针对管道工程的特点,尤其是管道工程穿越脆弱沙地生态系统的特点,在分析管道沿线生态环境现状及特点的基础上,重点从沙地生态系统的演替规律出发,分析了管道工程沙地段的主要环境问题,借鉴当地已有的生态恢复的成功经验,进一步提出了穿越脆弱沙地生态系统管道工程项目的生态保护和恢复对策。 相似文献
77.
ABSTRACT: The Nebraska Sand Hills have a unique hydrologic system with very little runoff and thick aquifers that constantly supply water to rivers, lakes, and wetlands. A ground water flow model was developed to determine the interactions between ground water and streamflow and to simulate the changes in ground water systems by reduced precipitation. The numerical modeling method includes a water balance model for the vadose zone and MOD‐FLOW for the saturated zone. The modeling results indicated that, between 1979 and 1990, 13 percent of the annual precipitation recharged to the aquifer and annual ground water loss by evapotranspiration (ET) was only about one‐fourth of this recharge. Ground water discharge to rivers accounts for about 96 percent of the streamflow in the Dismal and Middle Loup rivers. When precipitation decreased by half the average amount of the 1979 to 1990 period, the average decline of water table over the study area was 0.89 m, and the streamflow was about 87 percent of the present rate. This decline of the water table results in significant reductions in ET directly from ground water and so a significant portion of the streamflow is maintained by capture of the salvaged ET. 相似文献
78.
Dunes that are protected because of their very rich and diverse plant communities are often exposed to excessive visitor pressure.
The effects of trampling on the habitat must be known from a conservation viewpoint but also are important for management.
To determine the response of plant assemblages to trampling by people, an experimental study was conducted on the state-owned
dunes at Quiberon (Brittany, France). Indices of resistance and resilience were used to compare three typical plant communities
belonging to the various landscape units: mobile dune, semifixed dune, and fixed dune. The strong contrasts between communities
belonging to different successional stages reflect their ecological functioning. The mobile dune and semifixed dune with their
low resistance contrasted with the fixed dune. Only the vegetation cover of the semifixed dune benefited from long-term trampling
and had a very high resilience (134%). This response could be explained by a good balance of two opposite factors: soil compaction
increasing soil stability and moisture content, and vegetation destruction. Because of their low resilience, trampling seems
to be harmful for fixed dunes in the long term. The tourist pressure seems easier to integrate in to the mobile dunes and
the semifixed dunes if periods of recovery are included in the management. 相似文献
79.
P. C. E. M. de Rooij-van der Goes C. van Dijk W. H. van der Putten P. D. Jungerius 《Journal of Coastal Conservation》1997,3(2):133-142
In stabilized dunesAmmophila arenaria (marram grass) degenerates due to a process involving soil-borne pathogens and parasites. This leads to exposure of the sand
surface so that wind erosion may create blowouts.Ammophila rejuvenates on the edges of the blowouts, where the sand has accumulated. We tested the hypothesis that such rejuvenation
of plants may be related to a reduction of the plant-parasitic nematodes and fungal propagules during the process of wind-driven
transport.
Field measurements in blowouts during storm events indicated that the drifted sand contained relatively low numbers of plant
pathogenic fungi and plant-parasitic nematodes. A wind tunnel experiment showed that drifting sand may indeed reduce the numbers
of fungi and nematodes. Although most fungi were attached to sand particles, they were also affected by the wind-borne sand
movement. Sand that had been deposited by wind was made up of a larger proportion of large-sized particles. In our experiment
the relatively small particles were lost during transport.
Stirring the soil (part of the forces of natural winds) by mixing for 15 min. with a propeller mixer at 1500 rpm significantly
reduced the number of nematodes and fungi. Both sand movement in the wind tunnel and intensive stirring of the sand enhanced
the growth ofAmmophila test plants in a bioassay. It was concluded that in wind-blown sand the pathogen inoculum is reduced. Therefore, serious
consideration should be given to allowing controlled reactivation of blowouts to rejuvenate decliningAmmophila in stabilized foredunes.
Implications for dune management are briefly discussed.
Nomenclature: van der Meijden (1990) for vascular plants. Nematodes were identified to the genus level according to Bongers (1988). The
allocation of nematodes to feeding groups was according to Yeates et al. (1993). Nomenclature of fungi according to Domsch
et al. (1980) was used throughout this study except forFusarium. Species of the latter genus were identified according to Nelson et al. (1983). 相似文献
80.
H. Doing 《Journal of Coastal Conservation》1995,1(2):145-172
This paper is a summary and elaboration of an earlier publication in Dutch on the compilation of a landscape-ecological map,
scale 1 : 50 000, of the Dutch coast. It is argued that such an integrated map is the best basis for the conservation and
management of the coastal dunes and salt marshes. It may be combined with local more detailed vegetation maps, some examples
of which are mentioned in the context of management.
The Dutch North Sea coast is a ca. 350 km long chain of sandy beaches and sand dunes, from only 100 m to more than 10 km wide.
On sheltered stretches of dune coasts along estuaries in the Southwest and on the Wadden Sea islands, salt marshes have developed.
The small-scale gradient structure of the beach-dune-salt marsh complex is emphasized. 相似文献