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241.
242.
Madhu Vadali Chao Ma Neil A. Duffie Xiaochun Li Frank E. Pfefferkorn 《Journal of Manufacturing Processes》2012,14(3):307-315
The objective of this work is to predict the final roughness of metal surfaces that have undergone pulsed laser micro polishing. The motivation for pulsed laser micro polishing is to reduce the surface roughness of parts whose surface texture can approach the feature size. Being able to predict the magnitude of the polishing and frequency (wavelength) content of the surface will assist in the design of optimal processing parameters with minimal experiments. Laser pulses are used to create shallow melt pools with a controlled size (e.g., depth) and duration in order to allow surface tension forces to “pull down” asperities with small radius of curvature. There is no ablation occurring in the process being modeled. The melt depth and duration are predicted with a transient, two-dimensional axisymmetric heat transfer model with temperature-dependent material properties. The surface of the melt pool is analytically modeled as oscillations of stationary capillary waves with damping resulting from the forces of surface tension and viscosity. Above a critical spatial frequency, fcr, a significant reduction in the amplitude of the spatial Fourier components is expected. The work described in this paper extends the concept of critical frequency to a physics-based prediction methodology for predicting the spatial frequency content and surface roughness after polishing, given the features of the original surface, the material properties, and laser parameters. The proposed prediction methodology was validated using line polishing data for stainless steel 316L and area polishing results for pure nickel, Ti6Al4V, and Al-6061-T6. The predicted average surface roughnesses were within 12% of the values measured on the polished surfaces. 相似文献
243.
Lindsay Stark Nafessa Kassim Thalia Sparling Dale Buscher Gary Yu Neil Boothby 《Disasters》2015,39(2):295-315
This paper presents an evaluation of the long‐term impact of microfinance programmes on Acehnese children during the post‐tsunami recovery. The study, conducted from June to August 2010, examined the impact of microfinance programming six years after the tsunami. The sample consisted of 185 microfinance participants, with a comparison group of 192 individuals who did not participate in microfinance programmes. All respondents were parents, interviewed through a structured survey. The study used four child protection indicators—diet, health, childcare and education—in contrast to traditional repayment rate indicators. The primary results were insignificant with respect to all four child protection indicators, suggesting that, with respect to these indicators, there was no long‐term difference between the impact of microfinance on beneficiaries' children and non‐beneficiaries' children. These findings signify a need for microfinance actors to move beyond traditional indicators of economic success to evaluate the social changes microfinance programmes are presumed to effect. 相似文献
244.
245.
Neil LeBlanc Réjean Tremblay Jeff Davidson Thomas Landry Mary McNiven 《Marine Biology》2008,153(6):1141-1152
This study examined the effects of two selection treatments (elevated water temperature and air exposure) on the genetic and
physiological characteristics of the juvenile marine mussel, Mytilus edulis (<10 mm). Genetic effects were measured on five allozymes and fitness assessed using physiological tests to estimate energy
balance (scope for growth) as well as size, growth and survival. The in vitro treatments resulted in 48% mortality from an
air exposure of 11 h at 27°C and 76% mortality from a 6-h exposure to 33°C water. Survivors (n = 1,152) of each treatment along with controls (n = 2,304) were measured and randomly placed in compartmentalized cages. Mussels were deployed to three bays in Prince Edward
Island, Canada and monitored over a 10-month period. Initially, both of the treatments had an effect on mussel size and increased
the heterozygosity of the surviving mussels. Physiological analyses after 3 months in the field showed that the two treated
mussels showed lower metabolic rate that the control group. After 10 months in the field, the treated mussels were larger
and had lower mortality than the untreated control mussels. Unexplained environmental interaction in each of the bays had
an effect on allelic frequencies and heterozygosity. Overall, the results demonstrate that simple husbandry techniques can
be used to increase the productivity of mussel seed and heterozygosity measures can be used to assess fitness. However, more
field data is needed to determine the consistency of the increased productivity and if the increased productivity justifies
the costs of a selective treatment. Furthermore, because the level of heterozygosity in juvenile mussel populations can vary
considerably, both spatially and temporally, it may be effective as a warning of future natural mass mortality when overall
heterozygosity levels are found to be low. 相似文献
246.
247.
Sebastian C. A. Ferse Marion Glaser Muhammad Neil Kathleen Schwerdtner Máñez 《Regional Environmental Change》2014,14(6):2053-2065
Small-scale fisheries in coral reef areas support the livelihoods of millions of people worldwide. Anthropogenic impacts such as overfishing and climate change increasingly threaten both the reef ecosystem and the livelihood security of the people that depend on the reefs. Adaptive management strategies are needed to adequately deal with these threats, but they require an understanding of the underlying drivers, which often originate and act on multiple levels. Using a social-ecological system approach, the coral reef fishery of the Spermonde Archipelago in South Sulawesi/Indonesia is assessed to identify key drivers and strategic leverage points for management. Under the influence of international markets and technological changes, several export-oriented fisheries have developed in the area that led to distinct subsequent peaks in fishing activity in a pattern of sequential marine resource exploitation. In response to stressors such as seasonality and overfishing of individual locations or species, a number of coping strategies have developed locally. These include extensive borrowing from fishing patrons, diversification of fishing methods, fishing migrations, and the crafting of local institutions to regulate fishing activity. However, the coping strategies hinder, and even decrease, the capacity of the system to adapt to future stressors and undermine the sustainability of the fishery. Potential strategies that target different levels of the fishery system in order to strengthen adaptive management are identified. 相似文献
248.
Barbara Toole-O’Neil 《Journal of the Air & Waste Management Association (1995)》2013,63(12):1716-1718
Abstract This paper summarizes information on the spatial and temporal variability of selected air toxics pollutants collected on a national basis primarily for a period encompassing 1990–2003. Spatial information on pollutant concentrations is characterized in terms of within-city and between-city variability. Temporal information is summarized as diurnal and seasonal variability and in multiyear trends. The information on variability is presented in the framework of a larger need for systematic documentation of information on air toxics pollutants to assess progress in air pollution control programs. 相似文献
249.
Craig A. Walling Nick J. Royle Jan Lindström Neil B. Metcalfe 《Behavioral ecology and sociobiology》2010,64(4):541-548
Sexual selection acting on male traits through female mate choice is commonly inferred from female association preferences
in dichotomous mate choice experiments. However, there are surprisingly few empirical demonstrations that such association
preferences predict the likelihood of females reproducing with a particular male. This information is essential to confirm
association preferences as good predictors of mate choice. We used green swordtails (Xiphophorus helleri) to test whether association preferences predict the likelihood of a female reproducing with a male. Females were tested
for a preference for long- or short-sworded males in a standard dichotomous choice experiment and then allowed free access
to either their preferred or non-preferred male. If females subsequently failed to produce fry, they were provided a second
unfamiliar male with similar sword length to the first male. Females were more likely to reproduce with preferred than non-preferred
males, but for those that reproduced, neither the status (preferred/non-preferred) nor the sword length (long/short) of the
male had an effect on brood size or relative investment in growth by the female. There was no overall preference based on
sword length in this study, but male sword length did affect likelihood of reproduction, with females more likely to reproduce
with long- than short-sworded males (independent of preference for such males in earlier choice tests). These results suggest
that female association preferences are good indicators of female mate choice but that ornament characteristics of the male
are also important. 相似文献
250.
J.A. Gillies V. Etyemezian H. Kuhns J.D. McAlpine J. King S. Uppapalli G. Nikolich J. Engelbrecht 《Atmospheric environment (Oxford, England : 1994)》2010,44(8):1043-1053
There is a dearth of information on dust emissions from sources that are unique to U.S. Department of Defense testing and training activities. Dust emissions of PM10 and PM2.5 from low-level rotary-winged aircraft travelling (rotor-blade ≈7 m above ground level) over two types of desert surfaces (i.e., relatively undisturbed desert pavement and disturbed desert soil surface) were characterized at the Yuma Proving Ground (Yuma, AZ) in May 2007. Fugitive emissions are created by the shear stress of the outflow of high speed air created by the rotor-blade. The strength of the emissions was observed to scale primarily as a function of forward travel speed of the aircraft. Speed affects dust emissions in two ways: 1) as speed increases, peak shear stress at the soil surface was observed to decline proportionally, and 2) as the helicopter's forward speed increases its residence time over any location on the surface diminishes, so the time the downward rotor-generated flow is acting upon that surface must also decrease. The state of the surface over which the travel occurs also affects the scale of the emissions. The disturbed desert test surface produced approximately an order of magnitude greater emission than the undisturbed surface. Based on the measured emission rates for the test aircraft and the established scaling relationships, a rotary-winged aircraft similar to the test aircraft traveling 30 km h?1 over the disturbed surface would need to travel 4 km to produce emissions equivalent to one kilometer of travel by a light wheeled military vehicle also traveling at 30 km h?1 on an unpaved road. As rotary-winged aircraft activity is substantially less than that of off-road vehicle military testing and training activities it is likely that this source is small compared to emissions created by ground-based vehicle movements. 相似文献