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471.
Robert D. Mutch Jr. Joanna I. Scott David J. Wilson 《Environmental monitoring and assessment》1993,24(1):45-70
As contamination moves through a fractured rock aquifer, it tends to diffuse from the flowing fracture water into the rock's essentially stagnant pore water. This process tends both to retard a contamination plume's advance through a fractured rock aquifer and to substantially increase the difficulty of purging contamination from the aquifer. A mathematical model has been developed to evaluate the potential impact of this phenomenon upon water quality restoration in fractured rock aquifers. The numerical modeling reveals that cleanup of fractured rock aquifers will, in many cases, require many decades, even centuries, to achieve, particularly where substantial improvements in water quality are sought. The parameters which most strongly govern the degree to which matrix diffusion prolongs the aquifer restoration process are the rock's matrix porosity, fracture spacing, and matrix diffusivity, the chemical identity of the contaminant(s), and the length of time the aquifer has been contaminated.Since sedimentary rocks tend to have both relatively high matrix porosities and matrix diffusivities, it can be particularly difficult to purge contamination from sedimentary rock aquifers. Crystalline rocks, in contrast, typically have lower matrix porosities and matrix diffusivities, and therefore undergo more rapid cleanup. However, even in crystalline rocks, attainment of very high degrees of water quality improvement may be problematic. Numerical modeling also indicates that conventional groundwater pump and treat programs are not likely to be very effective in speeding up aquifer restoration if the rate limiting step in the process is diffusion of contaminants from the rock matrix. 相似文献
472.
Bustard CJ Durham M Lindsey C Starns T Baldrey K Martin C Schlager R Sjostrom S Slye R Renninger S Monroe L Miller R Chang R 《Journal of the Air & Waste Management Association (1995)》2002,52(8):918-926
The overall objective of this project was to determine the cost and impacts of Hg control using sorbent injection into a Compact Hybrid Particulate Collector (COHPAC) at Alabama Power's Gaston Unit 3. This test is part of a program funded by the U.S. Department of Energy's National Energy Technology Laboratory (NETL) to obtain the necessary information to assess the costs of controlling Hg from coal-fired utility plants that do not have scrubbers for SO2 control. The economics will be developed based on various levels of Hg control. Gaston Unit 3 was chosen for testing because COHPAC represents a cost-effective retrofit option for utilities with existing electrostatic precipitators (ESPs). COHPAC is an EPRI-patented concept that places a high air-to-cloth ratio baghouse downstream of an existing ESP to improve overall particulate collection efficiency. Activated carbons were injected upstream of COHPAC and downstream of the ESP to obtain performance and operational data. Results were very encouraging, with up to 90% removal of Hg for short operating periods using powdered activated carbon (PAC). During the long-term tests, an average Hg removal efficiency of 78% was measured. The PAC injection rate for the long-term tests was chosen to maintain COHPAC cleaning frequency at less than 1.5 pulses/bag/hr. 相似文献
473.
S. Christensen P. Ambus J.R.M. Arah H. Clayton B. Galle D.W.T. Griffith K.J. Hargreaves L. Klenzedtsson A.-M. Lind M. Maag A. Scott U. Skiba K.A. Smith M. Welling F.G. Wienhold 《Atmospheric environment (Oxford, England : 1994)》1996,30(24):4183-4190
The soil in a drained fjord area, reclaimed for arable farming, produced N2O mainly at 75–105 cm depth, just above the ground water level. Surface emissions of N2O were measured from discrete small areas by closed and open-flow chamber methods, using gas chromatographic analysis and over larger areas by integrative methods: flux gradient (analysis by FTIR), conditional sampling (analysis by TDLAS), and eddy covariance (analysis by TDLAS). The mean emission of N2O as determined by chamber procedures during a 9-day campaign was 162–202 μg N2ONm−2h−1 from a wheat stubble and 328–467 μg N2ONm−2 h−1 from a carrot field. The integrative approaches gave N2O emissions of 149–495 μg N2ONm−2 h−1, i.e. a range similar to those determined with the chamber methods. Wind direction affected the comparison of chamber and integrative methods because of patchiness of the N2O emission over the area. When a uniform area with a single type of vegetation had a dominant effect on the N2O gradient at the sampling mast, the temporal variation in N2O emission determined by the flux gradient/FTIR method and chamber methods was very similar, with differences of only 18% or less in mean N2O emission, well below the variation encountered with the chamber methods themselves. A detailed comparison of FTIR gradient and chamber data taking into account the precise emission footprint showed good agreement. It is concluded that there was no bias between the different approaches used to measure the N2O emission and that the precision of the measurements was determined by the spatial variability of the N2O emission at the site and the variability inherent in the individual techniques. These results confirm that measurements of N2O emissions from different ecosystems obtained by the different methods can be meaningfully compared. 相似文献
474.
Scott Nunes Peter A. Zugger Anne L. Engh Kurt O. Reinhart Kay E. Holekamp 《Behavioral ecology and sociobiology》1997,40(3):199-207
We examined the effects of food provisioning on the natal dispersal behavior of Belding's ground squirrels (Spermophilus beldingi). We provided extra food to adult and yearling females in their maternal territories during pregnancy and lactation, and
to offspring of these females in their natal areas for 6 weeks after weaning. We used unprovisioned young of unprovisioned
mothers as controls. Provisioning influenced the probability of dispersal from the natal area by female but not male S. beldingi. All surviving male S.␣beldingi dispersed by 55 weeks of age, regardless of whether they and their mothers received extra food. By contrast, we observed
a significant trend, beginning 3 weeks after weaning and continuing through the yearling year, for a greater proportion of
provisioned than control female S. beldingi to emigrate from the natal area. Competition for food did not appear to influence natal dispersal of females. However, overall
population density, density of females weaning litters, and rates of aggression and vigilance among these females, were higher
in provisioned than control areas, suggesting that competition for non-food resources was unusually intense in provisioned
areas. We propose that juvenile female, but not juvenile male, S. beldingi may emigrate from the natal site to increase access to areas with low densities of conspecifics. Together with findings of
earlier workers, our results suggest that spatial and temporal distributions of environmental resources are important influences
on the dispersal behavior of female ground squirrels.
Received: 28 February 1996 / Accepted after revision: 16 October 1996 相似文献
475.
Scott B. Terrill 《Behavioral ecology and sociobiology》1987,21(1):1-11
Summary I investigated the effect of restricted food and social dominance on nocturnal migratory activity (Zugunruhe) in dark-eyed juncos (Junco hyemalis) in late fall and winter. Highly restricted food tended to increase Zugunruhe in both dominant and subordinate members of pairs, however, subordinates showed significantly more migratory activity than dominants or solitary controls. Further, subordinate birds continued Zugunruhe after dominants and solitary controls had ceased this activity for the remainder of the winter. From mid-December through mid-January when birds had access to food ad lib, migratory activity decreased significantly. These results indicate that toward the end of fall migration, migratory behavior is subject to ecological and social conditions that influence the probability of overwinter survival. Presumably, such a system enables these birds to minimize the distance of migration; at the same time, they are able to track a relatively unpredictable, temperate, winter environment by prolonging migration if necessary. 相似文献
476.
477.
Eric J Bergman Robert A Garrott Scott Creel John J Borkowski Rosemary Jaffe E G R Watson 《Ecological applications》2006,16(1):273-284
Within predator-prey systems behavior can heavily influence spatial dynamics, and accordingly, the theoretical study of how spatial dynamics relate to stability within these systems has a rich history. However, our understanding of these behaviors in large mammalian systems is poorly developed. To address the relationship between predator selection patterns, prey density, and prey vulnerability, we quantified selection patterns for two fine-scale behaviors of a recovering wolf (Canis lupus) population in Yellowstone National Park, Wyoming, USA. Wolf spatial data were collected between November and May from 1998-1999 until 2001-2002. Over four winters, 244 aerial locations, 522 ground-based telemetry locations, 1287 km of movement data from snow tracking, and the locations of 279 wolf kill sites were recorded. There was evidence that elk (Cervus elaphus) and bison (Bison bison) densities had a weak effect on the sites where wolves traveled and made kills. Wolf movements showed a strong selection for geothermal areas, meadows, and areas near various types of habitat edges. Proximity to edge and habitat class also had a strong influence on the locations where elk were most vulnerable to predation. There was little evidence that wolf kill sites differed from the places where wolves traveled, indicating that elk vulnerability influenced where wolves selected to travel. Our results indicate that elk are more vulnerable to wolves under certain conditions and that wolves are capable of selecting for these conditions. As such, vulnerability plays a central role in predator-prey behavioral games and can potentially impact the systems to which they relate. 相似文献
478.
Low level liquid radioactive waste discharges from the Sellafield nuclear fuel reprocessing plant in north west England had
generated environmental inventories of about 3 × 1016 Bq of137Cs, 6.8 × 1014 Bq of239,240Pu and 8.9 × 1014 Bq of241Am by 1990. Most of the239,240Pu and241Am and about 10% of the137Cs has been retained in a deposit of fine marine sediment close to the discharge point. The quantities of radionuclides discharged
annually from Sellafield decreased by two orders of magnitude from the mid-1970s to 1990 but estimated critical group internal
and external exposure decreased by less than one order of magnitude over this period. This indicates that during the period
of reduced discharges, radionuclides already in the environment from previous releases continued to contribute to the critical
group exposure and highlights the need to understand processes controlling the environmental distribution of the radionuclides.
Redistribution of the contaminated marine sediment is potentially of major significance in this context, in particular if
it results in transport of radionuclides to intertidal areas, where contact with the human population is relatively likely.
A review is presented of published work relating to Sellafield waste radionuclides in Irish Sea sediments. Data on temporal
and spatial trends in radionuclide concentrations and activity ratios are collated from a number of sources to show that the
dominant mechanism of radionuclide supply to intertidal areas is by redistribution of the contaminated marine sediment. The
implications of this mechanism of supply for trends in critical group radiation exposure are considered. 相似文献
479.
480.
Comparative accumulation of (109)Cd and (75)Se from water and food by an estuarine fish (Tetractenos glaber) 总被引:1,自引:0,他引:1
Few data are available on the comparative accumulation of metal(loid)s from water and food in estuarine/marine fish. Smooth toadfish (Tetractenos glaber), commonly found in estuaries in south-eastern Australia, were separately exposed to radio-labelled seawater (14kBqL(-1) of (109)Cd and 24kBqL(-1) of (75)Se) and food (ghost shrimps; Trypaea australiensis: 875Bqg(-1)(109)Cd and 1130Bqg(-1)(75)Se) for 25 days (uptake phase), followed by exposure to radionuclide-free water or food for 30 days (loss phase). Toadfish accumulated (109)Cd predominantly from water (85%) and (75)Se predominantly from food (62%), although the latter was lower than expected. For both the water and food exposures, (109)Cd was predominantly located in the gut lining (60-75%) at the end of the uptake phase, suggesting that the gut may be the primary pathway of (109)Cd uptake. This may be attributed to toadfish drinking large volumes of water to maintain osmoregulation. By the end of the loss phase, (109)Cd had predominantly shifted to the excretory organs - the liver (81%) in toadfish exposed to radio-labelled food, and in the liver, gills and kidney (82%) of toadfish exposed to radio-labelled water. In contrast, (75)Se was predominantly located in the excretory organs (gills, kidneys and liver; 66-76%) at the end of the uptake phase, irrespective of the exposure pathway, with minimal change in percentage distribution (76-83%) after the loss phase. This study emphasises the importance of differentiating accumulation pathways to better understand metal(loid) transfer dynamics and subsequent toxicity, in aquatic biota. 相似文献