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151.
Normative models of choice predict no preference when unequally priced options of identical quality are temporarily offered
for the same low price, yet several studies using nonhuman subjects have found a preference in this context. Paradoxically,
subjects have preferred the stimulus associated with typically higher acquisition cost. Here, preference tests were conducted for gray jays (Perisoreus canadensis) choosing between temporarily identical options, which were color coded to represent typical conditions. During no-choice
trials, subjects were offered either a cheap or an expensive food reward, by positioning the reward either 1.9 or 60 cm into
a tunnel. During intermittent free-choice trials, subjects chose between color-coded but otherwise identical options (same
reward, both cheap). Jays preferred the stimulus associated with lower cost, unlike subjects in previous studies. To reconcile these conflicting findings, we model choice as a trade-off between
state and predation. We explore how alternative mechanisms of valuation may lead to preference in either direction (i.e.,
for greater workload vs lower predation risk). Our models accommodate observed paradoxical preferences in both directions. 相似文献
152.
David L. Naftz 《Journal of the American Water Resources Association》1988,24(4):869-877
ABSTRACT: The ability of batch-extraction experiments to predict postmining ground water quality was evaluated. As a basis for evaluation, mineralogical and water quality data were used to identify the geochemical reactions that controlled the major-ion chemistry in batch-extraction experiments. The experiments used water and spoil material collected from a surface-coal mine in the Powder River basin of northeast Wyoming. The batch-extraction experiments consisted of a 2:1 solid:liquid ratio of ground water and spoil material (by weight). The chemical composition of the resulting batch-extracts was determined after a contact time of 24 hours. Thermodynamically-favorable reactions included calcite precipitation, gypsum dissolution, and formation of kaolinite as a result of orthoclase feldspar hydrolysis. Three reaction models were consistent with the therinodynanuc and mineralogic data. In general, the extracts had smaller major-ion concentrations than did the water samples collected from the spoil aquifer. Correction ratios were calculated from these experiments and could be used in combination with additional batch-extractions at existing or future lease areas to predict the quality of the ground water after mining. 相似文献
153.
Agricultural producer participation and spatial coordination of land use decisions are key components for enhancing the effective delivery of ecosystem services from private land. However, inducing participation in Payment for Ecosystem Services schemes for coordinating land management choices is challenging from a policy design perspective owing to transaction costs associated with participation. This paper employs a laboratory experiment to investigate the impact of such costs on participation and land use in the context of an Agglomeration Bonus (AB) scheme. The AB creates a coordination game with multiple Nash equilibria related to alternative spatially-coordinated land use patterns. The experiment varies transaction costs between two levels (high and low), which affects the risks and payoffs of coordinating on the different equilibria. Additionally, an option to communicate is implemented between neighbors arranged on a local network to facilitate spatial coordination. Results indicate a significant difference in participation and performance under high and low transaction costs, with lower uptake and performance when transaction costs are high. These effects are, however, impacted by transaction costs faced in the past. Communication improves both AB participation rates and performance with the effect being greater for participants facing high transaction costs. 相似文献
154.
Deflector Designs for Fish Habitat Restoration 总被引:1,自引:0,他引:1
Paired current deflectors are structures that are installed on each bank of a river to locally reduce the width of the channel, thereby creating flow acceleration and promoting scouring. These instream habitat structures have been used extensively in restoration projects to create pool habitat for fish, but there are many discrepancies in deflector design recommendations in terms of orientation, height, and length. Our objectives were to (1) examine how the angle, height, and length of paired deflectors affect scour hole dimensions and potential for bank erosion; and (2) test the applicability to paired deflectors of existing equations for scour hole depth and volume. Three deflector angles (45°, 90°, and 135°), two deflector heights (with flow under and over the deflector height), and two lengths (reducing the width by 25% and 50%) were investigated using uniform sand in a laboratory flume. Results showed a 26–30% smaller scour depth resulting from 45° deflectors than from 90° deflectors and a 5–10% smaller scour depth for 135° deflectors compared to 90° deflectors. The volume of scour and the potential for bank erosion were greater when flow was under the height of the deflectors rather than overtopping and when the length of deflector was increased. When flow was under the deflector height, 135° deflectors had the highest amount of bank erosion; whereas during overtopping flow conditions, 90° deflectors had the greatest bank erosion potential. Values predicted by the model of Kuhnle and others were closest to observed scour depth and volume measurements. The assumption that upstream-oriented deflectors always generate the largest scour should be revised. 相似文献
155.
Robert?R.?HearneEmail author C.?Alejandro?Santos 《Environment, Development and Sustainability》2005,7(3):303-318
Ecotourism has been identified as a low impact means to provide income generating opportunities that are complementary to
nature conservation as well as the welfare of the local population. The Maya Biosphere Reserve in Peten, Guatemala is one
of Central America's largest and most isolated protected areas. And although the area is contains a well-visited archeological
site, it has not been developed for ecotourism. In this study choice experiments are used to analyze the preferences toward
alternative scenarios of ecotourism of two important stakeholder groups: foreign tourists and educated local residents. Results
demonstrate that these two populations of have unequal but similar preference orderings, especially toward: improved national
park management and the presence of guides for wildlife viewing. These stakeholder groups had different opinions toward paved
access roads and the presence of illegal colonists within the protected area. Both populations favored an entrance fee toward
the absence of an entrance fee. These preferences were generally consistent across other socioeconomic indicators.
Readers should send their comments on this paper to: BhaskarNath@aol.com within 3 months of publication of this issue. 相似文献
156.
Mountain biking is an increasingly popular leisure pursuit. Consequences are trail degradation and conflicts with hikers and other users. Resource managers often attempt to resolve these problems by closing trails to mountain biking. In order to estimate the impact of these developments, a model has been devised that predicts the effects of changes in trail characteristics and introduction of access fees, and correlates these with biker preference on trail selection. It estimates each individual's per-ride consumer's surplus associated with implementing different policies. The surplus varies significantly as a function of each individual's gender, budget, and interest in mountain biking. Estimation uses stated preference data, specifically choice experiments. Hypothetical mountain bike trails were created and each surveyed biker was asked to make five pair-wise choices. A benefit-transfer simulation is used to show how the model and parameter estimates can be transferred to estimate the benefits and costs to mountain bikers in a specific area. 相似文献
157.
The research activities in the project Assessing the Influence of Real Releases on Explosions (AIRRE) included a unique series of large-scale explosion experiments with high-momentum jet releases directed into congested geometries with subsequent ignition. The primary objective for the AIRRE project was to gain improved understanding of the effect that realistic releases and turbulent flow conditions have on the consequences of accidental gas explosions in the petroleum industry. A secondary objective was to develop a methodology that can facilitate safe and optimal design of process facilities. This paper presents selected results from experiments involving ignition of a highly turbulent gas cloud, generated by a large-scale, pressurised release of natural gas. The paper gives an overview of the effect on maximum explosion overpressures of varying the ignition position relative to the release point of the jet and a congested region placed inside the flammable cloud, with either a high or a medium level of congestion. For two of the tests, involving a jet release and the medium congestion rig, the maximum overpressures significantly exceeded those obtained in a quiescent reference test. The paper presents detailed results for selected tests and discusses the effect of the initial flow field generated by realistic releases – including turbulence, net flow and concentration gradients – on relevant explosion phenomena. 相似文献
158.
159.
Gas-liquid interface measurements were conducted in a strongly turbulent free-surface flow (i.e., stepped cascade). Local void fractions, bubble count rates, bubble size distributions and gas-liquid interface areas were measured simultaneously in the air-water flow region using resistivity probes. The results highlight the air-water mass transfer potential of a stepped cascade with measured specific interface area over 650 m–1 and depth-average specific area up to 310 m–1. A comparison between single-tip and double-tip resistivity probes suggests that simple robust single-tip probes may provide accurate, although conservative, gas-liquid interfacial properties. The latter device may be used in the field and in prototype plants.
Notation
a = specific interface area (m–1); a
mean = depth-average specific interface area (m–1): a
mean=frac1Y
90limits
sup>
Y
90
sup
0(1–C)dy; C = local void fraction; C
gas = dissolved gas concentration (kg m–3); C
mean = depth-average mean air concentration defined as: C
mean=1–d/Y
90; C
s = saturation concentration (kg m–3); D = dimensionless air bubble diffusivity (defined by [1]); d = equivalent clear-water flow depth (m): d=limits
sup>
Y
90
sup
0(1–C) dy; dab = air bubble diameter (m); dc = critical flow depth (m); for a rectangular channel: d
c=sqrt[3]q
w
2/g; F = air bubble count rate (Hz); F
max = maximum bubble count rate (Hz), often observed for C=50%; g = gravity acceleration (m s–2); h = step height (m); K
L = liquid film coefficient (m s–1); K = integration constant defined as: K=tanh
–1
sqrt0.1)+(2D)–1 [1]; L = chute length (m); N = velocity distribution exponent; ———– *Corresponding author, E-mail: h.chanson@mailbox.uq.edu.au
Q
w = water discharge (m3 s–1); q
w = water discharge per unit width m2 s–1); t = time (s); V = local velocity (m s–1); V
c = critical flow velocity (m s–1); for a rectangular channel: V
c=sqrt[3]q
w
g
V
max = maximum air-water velocity (m s–1); V
90 = characteristic air-water velocity (m s–1) where C = 90%; W = channel width (m); x = longitudinal distance (m) measured along the flow direction (i.e., parallel to the pseudo-bottom formed by the step edges); y = distance (m) normal to the pseudo-bottom formed by the step edges; Y90 = characteristic distance (m) where C=0.90; Y
98 = characteristic distance (m) where C=0.98; = slope of pseudo-bottom by the step edges; = diameter (m). 相似文献
160.