全文获取类型
收费全文 | 170篇 |
免费 | 27篇 |
国内免费 | 24篇 |
专业分类
安全科学 | 49篇 |
废物处理 | 4篇 |
环保管理 | 47篇 |
综合类 | 52篇 |
基础理论 | 29篇 |
污染及防治 | 12篇 |
评价与监测 | 6篇 |
社会与环境 | 9篇 |
灾害及防治 | 13篇 |
出版年
2024年 | 1篇 |
2023年 | 6篇 |
2022年 | 9篇 |
2021年 | 5篇 |
2020年 | 8篇 |
2019年 | 5篇 |
2018年 | 8篇 |
2017年 | 13篇 |
2016年 | 11篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 9篇 |
2012年 | 19篇 |
2011年 | 23篇 |
2010年 | 14篇 |
2009年 | 12篇 |
2008年 | 11篇 |
2007年 | 7篇 |
2006年 | 12篇 |
2005年 | 6篇 |
2004年 | 2篇 |
2003年 | 6篇 |
2002年 | 3篇 |
2001年 | 3篇 |
2000年 | 6篇 |
1999年 | 3篇 |
1998年 | 2篇 |
1997年 | 3篇 |
1996年 | 1篇 |
排序方式: 共有221条查询结果,搜索用时 171 毫秒
121.
Joshua M. Peschel Patricia K. Haan Ronald E. Lacey 《Journal of the American Water Resources Association》2006,42(5):1371-1389
ABSTRACT: Soils represent a fundamental abiotic parameter in defining the characteristics of an ecosystem. The U.S. Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS) produces the most detailed digital spatial soil datasets that are publicly available. The Soil Survey Geographic (SSURGO) database contains basic attributes for the continuous coverage of soils across the United States. In its standard format, the SSURGO database is incompatible for use within the ArcView Soil and Water Assessment Tool (SWAT). A modified version of the State Soil and Geographic (STATSGO) database is the template soils dataset used by ArcView SWAT. This paper presents the methodology and development of a SSURGO database preprocessor extension for the ArcView SWAT model. A case study for the Upper Sabinal River Watershed near Uvalde, Texas, is given. Results indicate that hydro‐logic output parameter differences occur when comparing the STATSGO and SSURGO database information in the ArcView SWAT model under identical modeling conditions. Specifically, the SSURGO model produced a greater daily mean water yield with evapotranspiration and surface runoff being found consistently lower across the watershed. The most likely causes assigned to this phenomenon were higher percolation and resulting ground water return flow values due to significantly larger saturated hydraulic conductivity values associated with the SSURGO 2.x database. 相似文献
122.
123.
124.
Tracey N. Johnson Patricia L. KennedyTim DelCurto Robert V. Taylor 《Agriculture, ecosystems & environment》2011,144(1):338-346
In 2006-2010, effects of four different cattle stocking rates (0, 14.4, 28.8, and 43.2 animal unit months) were compared, representing 0%, 20%, 32%, and 46% utilization of vegetation by domestic livestock, on vegetation structure (as indexed by visual obstruction), and songbird population and apparent nest density, community composition, and diversity in a Pacific Northwest bunchgrass prairie in northeastern Oregon, USA. Overall paddock-level visual obstruction decreased and structural heterogeneity increased with increasing stocking rates, and those effects carried over 1 year after grazing had ceased. Most species were able to locate nesting sites regardless of differences in visual obstruction, except western meadowlark and vesper sparrow, for which obstruction was lower in paddocks with higher stocking rates. Apparent nest density for grasshopper sparrows was negatively affected by higher stocking rates. Grazing effects on absolute songbird population density were restricted to negative effects of higher stocking rates on savannah sparrows, but this relationship was not observed until 1 year after grazing had ceased. Songbird community composition differed between control and heavily-grazed paddocks, driven by an increase in the proportion of horned larks and a decrease in the proportion of savannah sparrows in heavily-grazed paddocks from pre-treatment to post-treatment years. Bird diversity indices were unaffected by stocking rate. Negative effects of high stocking rates on densities of two species and the absence of any clear positive effect for the other three species suggest high stocking rates as applied in this experiment may not provide suitable habitat for all grassland songbirds. The absence of negative responses of density to low and moderate stocking rates suggests these grazing regimes generally provided suitable habitat for all species. 相似文献
125.
机动车加油过程中气液两相流动特性的CFD数值模拟 总被引:2,自引:2,他引:0
随着环保法规的不断完善,机动车加油过程中所产生的油气排放污染问题越来越受到重视.国外自20世纪90年代中后期开始采用数值模拟手段对机动车的加油过程进行研究,而国内迄今尚处于空白阶段.对机动车加油过程所涉及的"加油枪喷嘴+加油管+油箱+回气管"物理体系进行适当简化,采用商业计算流体动力学(CFD)软件Fluent中提供的VOF气液两相流模型和RNG k-ε湍流模型,在基于Gambit软件确定网格划分方案和进行适当的边界条件设置后,建立了合理可行的加油过程气液两相流动CFD数值模拟模型,讨论了加油速度对油箱内气相空间静压力的影响,揭示了汽油在加油管内的回流现象.结果表明,加油枪的流量越大,油箱内气相空间的静压总体上也逐渐增大;同时油箱内气相空间的静压总体上可以划分为3个较为明显的阶段.而当加油流量较大时,往往会引起汽油在加油管油帽段内回流,从而使得加油枪过早跳枪.本研究为国内自主开展机动车加油以及油气排放污染控制技术和设备方面的研究开发奠定了一定基础. 相似文献
126.
Food restrictions early in life can have adverse effects on the development of adult avian song structure. Nutritional deficiencies
during brain development are thought to impair the growth of neural circuits responsible for learning and production of song
in adulthood. Thus, the quality of song may reflect the quality of the singer due to the costs associated with neural development
early in life. Recent investigations have focused on domesticated laboratory strains of zebra finches where early dietary
deficiencies have significantly reduced the complexity of song and its sexual attractiveness. Domesticated zebra finches may
be more sensitive to the early effects of moderate under-nutrition on song complexity than their non-domesticated counterparts.
In an aviary experiment with non-domesticated zebra finch stock, we found that song complexity when measured by a linear combination
of six variables was reduced in food-restricted birds, with syllable rate and maximum syllable frequency as the principal
variables affected. The restriction had no effect on learning accuracy when song phrases of experimental birds were compared
to those of their fathers.This result demonstrates that early nutrition may differentially affect the development of neural
processes that influence learning accuracy and song complexity. While the finding of negative effects of dietary restriction
on song complexity is robust for zebra finches and is not an artefact of domestication, it does not explain why some nutritionally
stressed populations of wild zebra finches have more complex songs than those from other regions of Australia characterised
by greater food availability. 相似文献
127.
Volker Berding Stefan Schwartz Michael Matthies 《Environmental science and pollution research international》1999,6(1):37-43
The interdependencies of parameters applied in the models of EUSES are visualised in a directed connectivity graph. The parameters
(inputs, defaults, state variables, outputs) are represented by boxes (nodes) and their relations by lines (edges). The visualisation,
on the one hand, clarifies the complexity of the models in EUSES and, on the other hand, creates an overview and transparency.
The parameters’ relations to each other can be recognised faster, and the models can be better understood. The complexity
was quantified by the number (variety), kind (substance parameter, physico-chemical parameter, concentration, other parameters),
and depth (dimension) of the parameter and the number of relations (connectivity). The variety of EUSES (without the modelsSimple Treat andSimple Box whose interior structure is not documented and without the effect and risk characterisation) amounts to 466, the connectivity
to 961, and the maximal dimension is 21. 相似文献
128.
129.
Modeling of Vertical Solute Dispersion in a Sediment Bed Enhanced by Wave‐Induced Interstitial Flow1
Qin Qian Vaughan R. Voller Heinz G. Stefan 《Journal of the American Water Resources Association》2009,45(2):343-354
Abstract: Mass (solute) transport in a stream or lake sediment bed has a significant effect on chemical mass balances and microbial activities in the sediment. A “1D vertical dispersion model” is a useful tool to analyze or model solute transfer between river or lake water and a sediment bed. Under a motionless water column, solute transfer into and within the sediment bed is by molecular diffusion. However, surface waves or bed forms create periodic pressure waves along the sediment/water interface, which in turn induce flows in the pores of the sediment bed. The enhancement of solute transport by these interstitial periodic flows in the pores has been incorporated in a 1D depth‐dependent “enhanced dispersion coefficient (DE).” Typically, DE diminishes exponentially with depth in the sediment bed. Relationships have been developed to estimate DE as a function of the characteristics of sediment (particle size, hydraulic conductivity, and porosity) and pressure waves (wave length and height). In this paper, we outline and illustrate the calculation of DE as well as the penetration depth (dp) of the flow effect. Sample applications to illustrate the computational procedure are provided for dissolved oxygen transfer into a stream gravel bed and release of phosphorus from a lake bed. The sensitivity of the results to input parameter values is illustrated, and compared with the errors obtained when interstitial flow is ignored. Maximum values of DE near the sediment surface can be on the order of 1 cm2/s in a stream gravel bed with standing waves, and 0.001 cm2/s in a fine sand lake bed under progressive surface waves, much larger than molecular diffusion coefficients. 相似文献
130.
在实际生产过程中,有很多情况能使气体燃料与空气混合,达到可燃浓度,此时若有点火源存在,就可能酿成燃烧、爆炸灾害,造成严重的财产损失和人员伤亡.选取甲烷作为研究对象,选用空气作为氧化性气体,对其进行数值模拟.获得了不同时刻爆燃的压力场、温度场、密度场的变化数据,为工程上防爆、抑爆、泄爆提供了理论基础和数据. 相似文献