全文获取类型
收费全文 | 116篇 |
免费 | 4篇 |
国内免费 | 9篇 |
专业分类
废物处理 | 1篇 |
环保管理 | 27篇 |
综合类 | 23篇 |
基础理论 | 37篇 |
污染及防治 | 28篇 |
评价与监测 | 10篇 |
社会与环境 | 2篇 |
灾害及防治 | 1篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2020年 | 1篇 |
2019年 | 1篇 |
2018年 | 3篇 |
2017年 | 5篇 |
2016年 | 8篇 |
2015年 | 9篇 |
2014年 | 5篇 |
2013年 | 8篇 |
2012年 | 2篇 |
2011年 | 8篇 |
2010年 | 10篇 |
2009年 | 9篇 |
2008年 | 14篇 |
2007年 | 7篇 |
2006年 | 5篇 |
2005年 | 6篇 |
2004年 | 2篇 |
2003年 | 4篇 |
2002年 | 2篇 |
2001年 | 4篇 |
2000年 | 2篇 |
1996年 | 1篇 |
1995年 | 2篇 |
1994年 | 2篇 |
1993年 | 1篇 |
1990年 | 1篇 |
1988年 | 1篇 |
1987年 | 1篇 |
1983年 | 1篇 |
1964年 | 1篇 |
排序方式: 共有129条查询结果,搜索用时 15 毫秒
61.
Submerged aquatic vegetation has the potential to greatly improve water quality through the removal of nutrients, particulates
and trace metals. The efficiency of this removal depends heavily upon the rate of vertical mixing, which dictates the timescale
over which these constituents remain in the canopy. Continuous dye injection experiments were conducted in a flume with model
vegetation to characterize vertical mass transport in vegetated shear flows. Through the absorbance–concentration relationship
of the Beer–Lambert Law, digital imaging was used to provide high-resolution concentration profiles of the dye plumes. Vertical
mass transport is dominated by the coherent vortices of the vegetated shear layers. This is highlighted by the strong periodicity
of the transport and its simple characterization based on properties of the shear layer. For example, the vertical turbulent
diffusivity is directly proportional to the shear and thickness of the layer. The turbulent diffusivity depends upon the size
of the plume, such that the rate of plume growth is lower near the source. In the far-field, mass is mixed more than twice
as rapidly as momentum. Finally, plume size is dictated predominantly by X, a dimensionless distance that scales upon the
number of vortex rotations experienced by the plume. 相似文献
62.
Gonzalez-Ocampo H Romero-Schmidt H Serrano-Pinto V Arguelles C Salinas F Rodríguez A Castellanos A Ortega-Rubio A 《Journal of environmental biology / Academy of Environmental Biology, India》2004,25(1):27-38
Aquaculture offers a major opportunity for the economic development of Baja California Sur (BCS), Mexico. The severely limited freshwater supply and the geographic isolation of the state place limits on other productive activities. Despite the aridity, the natural vegetation of BCS is diverse and structurally complex with a high percentage (20%) of endemic species. In this work we compare the environmental impacts produced by two kinds of aquaculture systems: coastal ponds vs. inland ponds. Construction and operation of coastal ponds does not require destruction of the natural vegetation and, as is true for inland ponds. Coastal ponds are also compatible with conservation of mangroves, sea grasses and sensitive habitats for fish and mollusks. To reduce the negative impacts of aquaculture and to protect the vegetation of Baja California Sur, we recommend the use of coastal ponds for shrimp production. 相似文献
63.
Greenhouse experiments were conducted to determine the effects of sand burial on survival and growth of seedlings ofCirsium pitcheri. In 1992–1993, seedlings were buried to depths of 0, 25, 50, 75, and 100% of their height while in 1993–1994, the seedlings
were buried to depths of 0, 4 cm (single burial), 4 cm (repeated burial of 1 cm every 8 days), 8 cm (single burial) and 8
cm (repeated burial of 2 cm every 8 days). Several physiological traits, net photosynthetic rate, chlorophyll a∶b ratio, leaf
area, number and length of leaves, number of internodes, amount of tillering, and biomass, were measured. The results showed
that all seedlings died in the complete (100%) burial, 20% died in the 75% burial and none died in the 0, 25 and 50% burial
treatments. Burial of seedlings to a depth of 25% stimulated their growth but 75% burial significantly decreased the total
dry weight. Repeated burial treatments exhibited significantly greater stimulation of growth than single burial. Surviving
seedlings grew through the sand deposit by elongating the stem and leaf petioles, increasing the number of nodes and the length
of internodes. This elongation occurred at the expense of development of the root system indicating that available energy
was re-allocated to above-ground parts. 相似文献
64.
It has been suggested that actively expressed genes are primarily located in early replicating bands. This hypothesis is supported by cytogenetic and pregnancy outcome data from four consecutive cases of prenatally detected de novo marker chromosomes. Two fetuses with major anomalies had large early replicating bands, while the marker in a third phenotypically normal fetus was late replicating. In the fourth case, a ring marker chromosome had only a small early replicating region. Pregnancy termination was elected. While no structural malformations were apparent, potential intellectual function in this case remains unresolved. An understanding of the relationship between genomic organization and chromosome banding is critical in counseling for prenatally detected de novo marker chromosomes. Replicational banding is particularly helpful in recognizing genes that may be actively expressed and result in developmental abnormality. 相似文献
65.
Heidi C. Pearson 《Behavioral ecology and sociobiology》2009,63(10):1437-1446
In societies characterized by a high degree of fission-fusion dynamics, individuals adjust their grouping patterns according
to the shifting balance of costs and benefits associated with grouping. This study examines influences on fission-fusion dynamics
for dusky dolphins (Lagenorhynchus obscurus) in Admiralty Bay, New Zealand. This area is an important foraging habitat for dusky dolphins during the winter and spring.
Admiralty Bay has little predation risk, but nearshore mussel farms may infringe on available habitat. I used generalized
estimating equations to determine the influences of coordinated foraging, predation risk, and presence of mussel farms on
party size, rate of fission-fusion, and behavioral state. I conducted 168 boat-based group focal follows totaling 168 h. The
proportion of individuals observed foraging was positively related to party size and rate of party fusion. Resting had no
effect on party size and did not vary according to location. Near mussel farms, traveling decreased, and rate of party fission
decreased. I conclude that (1) coordinated foraging strategies are a primary influence on fission-fusion dynamics within this
population, (2) dolphins may respond to decreased predation risk by not adjusting party size or location during resting, and
(3) areas near mussel farms are not used for traveling. 相似文献
66.
67.
Sediment phosphorus extractants for phosphorus-31 nuclear magnetic resonance analysis: a quantitative evaluation 总被引:2,自引:0,他引:2
Ahlgren J De Brabandere H Reitzel K Rydin E Gogoll A Waldebäck M 《Journal of environmental quality》2007,36(3):892-898
The influence of pre-extractant, extractant, and post-extractant on total extracted amounts of P and organic P compound groups measured with 31P nuclear magnetic resonance (31P-NMR) in lacustrine sediment was examined. The main extractants investigated were sodium hydroxide (NaOH) and sodium hydroxide ethylenediaminetetraacetic acid (NaOH-EDTA) with bicarbonate buffered dithionite (BD) or EDTA as pre-extractants. Post extractions were conducted using either NaOH or NaOH-EDTA, depending on the main extractant. Results showed that the most efficient combination of extractants for total P yield was NaOH with EDTA as pre-extractant, yielding almost 50% more than the second best procedure. The P compound groups varying the most between the different extraction procedures were polyphosphates and pyrophosphates. NaOH with BD as pre-extractant was the most efficient combination for these compound groups. 相似文献
68.
Flume experiments were conducted with rigid and flexible model vegetation to study the structure of coherent vortices (a manifestation
of the Kelvin–Helmholtz instability) and vertical transport in shallow vegetated shear flows. The vortex street in a vegetated
shear layer creates a pronounced oscillation in the velocity profile, with the velocity near the top of a model canopy varying
by a factor of three during vortex passage. In turn, this velocity oscillation drives the coherent waving of flexible canopies.
Relative to flows over rigid vegetation, the oscillation in canopy geometry has the effect of decreasing the amount of turbulent
vertical momentum transport in the shear layer. Using a waving plant to determine phase in the vortex cycle, each vortex is
shown to consist of a strong sweep at its front (during which the canopy is most deflected), followed by a weak ejection at
its rear (when the canopy height is at a maximum). Whereas in unobstructed mixing layers the vortices span the entire layer,
they encompass only 70% of the flexibly obstructed shear layer studied here. 相似文献
69.
Exchange flow between open water and floating vegetation 总被引:1,自引:1,他引:0
This study describes the exchange flow between a region with open water and a region with a partial-depth porous obstruction,
which represents the thermally-driven exchange that occurs between open water and floating vegetation. The partial-depth porous
obstruction represents the root layer, which does not penetrate to the bed. Initially, a vertical wall separates the two regions,
with fluid of higher density in the obstructed region and fluid of lower density in the open region. This density difference
represents the influence of differential solar heating due to shading by the vegetation. For a range of root density and root
depths, the velocity distribution is measured in the lab using PIV. When the vertical wall is removed, the less dense water
flows into the obstructed region at the surface. This surface flow bifurcates into two layers, one flowing directly through
the root layer and one flowing beneath the root layer. A flow directed out of the vegetated region occurs at the bed. A model
is developed that predicts the flow rates within each layer based on energy considerations. The experiments and model together
suggest that at time- and length-scales relevant to the field, the flow structure for any root layer porosity approaches that
of a fully blocked layer, for which the exchange flow occurs only beneath the root layer. 相似文献
70.
Easy-liberatable cyanide has to be analysed if soils and waters are contaminated by cyanide. The aim of this study was to determine easy-liberatable cyanide in these environmental samples using a micro-distillation apparatus by means of a modified digestion vessel. Pure aqueous solutions of different cyanide species, five contaminated and uncontaminated soil samples and two water samples were analysed by micro-distillation according to the German standards. Recovery was determined by analysis of spiked samples. When using the modified digestion vessels, the pH of 4 which is demanded by the standard method can be adjusted. The recovery of potassium cyanide and weakly-complexed zinc-cyanide ranged from 93–101% for standards, and from 87–98% for spiked samples. In contrast, the recovery of strong iron-cyanide complexes was below 4% both for pure solutions and spiked samples. The precision of the method expressed as a relative standard deviation was 25% in cases of very low easy-liberatable cyanide contents (< 1 mg CN kg?1) and below 12% in case of high easy-liberatable cyanide contents (> 1 mg CN kg?1) for contaminated soils. The determination of easily-liberatable cyanide in soils and waters using micro-distillation combined with the modified digestion sample is an alternative to other distillation methods. 相似文献