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131.
Analysis of bank erosion on the Merced River,Yosemite Valley,Yosemite National Park,California, USA 总被引:1,自引:0,他引:1
Channel changes from 1919 to 1989 were documented in two study reaches of the Merced River in Yosemite National Park through
a review of historical photographs and documents and a comparison of survey data. Bank erosion was prevalent and channel width
increased an average of 27% in the upstream reach, where human use was concentrated. Here, trampling of the banks and riparian
vegetation was common, and banks eroded on straight stretches as frequently as on meander bends. Six bridges in the upper
reach constrict the channel by an average of 38% of the original width, causing severe erosion. In the downstream control
reach, where human use was minimal, channel widths both decreased and increased, with a mean increase of only 4% since 1919.
Bank erosion in the control reach occurred primarily on meander bends. The control reach also had denser stands of riparian
vegetation and a higher frequency of large woody debris in channels. There is only one bridge in the lower reach, located
at the downstream end. Since 1919, bank erosion in the impacted upstream reach contributed a significant amount of sediment
(74,800 tonnes, equivalent to 2.0 t/km2/yr) to the river. An analysis of 75 years of precipitation and hydrologic records showed no trends responsible for bank erosion
in the upper reach. Sediment input to the upper reach has not changed significantly during the study period. Floodplain soils
are sandy, with low cohesion and are easily detached by lateral erosion. The degree of channel widening was positively correlated
with the percentage of bare ground on the streambanks and low bank stability ratings. Low bank stability ratings were, in
turn, strongly associated with high human use areas. Channel widening and bank erosion in the upper reach were due primarily
to destruction of riparian vegetation by human trampling and the effect of bridge constrictions on high flow, and secondarily
to poorly installed channel revetments. Several specific recommendations for river restoration were provided to park management. 相似文献
132.
Terrie K. Boguski Robert G. Hunt William E. Franklin 《Resources, Conservation and Recycling》1994,12(3-4)
Life cycle inventory (LCI) is becoming more widely used as a tool to evaluate the resource and energy use and the environmental releases associated with various products. The methodology for handling different recycling scenarios is also becoming increasingly important. Several different methods exist for handling recycling in an LCI. The method described in this paper uses mathematical models to show that the same basic equations can be used to handle a variety of recycling options for multi-product systems. 相似文献
133.
William Towers 《Journal of Environmental Planning and Management》1994,37(4):447-460
Patterns of sewage sludge disposal will undergo dramatic changes in the next decade because of recent EC legislation; land utilization is likely to increase as a result. The legislation as applied in the UK is discussed and the current situation in Scotland is outlined. A rule‐based risk assessment classification has been formulated and by applying it to the Scottish National Soils Inventory database, national and regional estimates of land availability for sludge utilization have been obtained. The relationship of these area estimates with the projected sludge volumes and the long‐term implications are discussed. In addition, the impact of potential policy changes are described. The need for incorporating objective strategic analyses of this type into the restructuring of the Scottish water industry is advocated. 相似文献
134.
135.
William H. Parker 《环境质量管理》1994,3(4):421-431
EG&G is a Fortune 200 company with annual sales of $2.7 billion. It designs and manufactures laboratory and field-test instruments and electronic and mechanical components for commercial customers. EG&G provides systems engineering, precision component manufacturing, and test-site operating and management services to many government agencies and laboratories. It employs 34,000 people worldwide. Recognizing the need to improve its business practices as they related to environmental excellence, EG&G initiated policies, procedures, and programs to establish itself as an environmentally responsible company. Waste reduction was designated priority number one in EGG's environmental program. Our major customers are also making waste reduction a high visibility program. For example, on August 3, 1993, the president signed Executive Order 12856 making pollution prevention at federal facilities a goal of this administration. This article describes the EG&G Waste Reduction Pays (WARP) program, developed for use by all its operating entities, and why it is a model program to implement Executive Order 12856. It also depicts how the implementation of the program at federal facilities differs, in some respects, from that at other EG&G operating units. 相似文献
136.
Martha W. Gilliland Lee Becker Ralph Cady Joe Gabig James Gilley Richard A. Kern Arley Larson Quang M. Nguyen William Powers Raymond Supalla 《Journal of the American Water Resources Association》1985,21(2):281-290
Substantial conflict exists over water management and allocation in the Platte River Basin of Nebraska. An interdisciplinary computer simulation model, representing the water quantity, water quality, environmental, and economic dimensions of the conflict, was developed in order to analyze the tradeoffs among allocation scenarios. Most importantly, decisionmakers and interest groups were involved in model development. Simulation results for a base case and two scenarios are presented. One scenario favors protection of instream flow for wildlife; the other favors water diversions for agriculture. Impacts of the instream flow scenario, as measured by the amount of land irrigated, groundwater levels, the amount of wildlife habitat for cranes and catfish, and net agricultural benefits did not differ greatly from those of the base case. However, impacts of the diversion scenario were substantial. On the negative side, instream flows and wildlife habitat declined an average of 39 percent; while, on the positive side, groundwater levels and net agricultural benefits each increased 6 percent. The modeling process was successful insofar as it promoted an understanding among the highly diverse interest groups of the systems nature of the Basin. One agreement on a water diversion schedule among three of the parties has been reached, partly as a result of this process. More comprehensive compromises have not yet been forged. Our experience, however, indicates that modeling success at the policymaking level depends more on the extent to which the policymakers understand the model than it does on model sophistication. 相似文献
137.
ABSTRACT: Variability in bedload-transport rates during constant water discharge is an inherent part of the bedload-transport process. Although this variability has been measured extensively in the laboratory, similar information generally is not available from field measurements. During a four-day period of nearly constant water discharge, four sets of consecutively collected bedload samples, ranging from 43 to 120 samples, were obtained at the same cross channel location using a standard 65-pound Helley-Smith bedload sampler. When the measured transport rates are converted to dimensionless rates and plotted as cumulative frequency distributions, they show good agreement with a theoretical probability distribution function of rates derived for the case of ripples on dunes. The distributions show that during constant water discharge individual measured rates at a fixed point vary from near zero to four times the mean rate, and 60 percent of the sampled rates will be less than the mean. Because of the large variation in transport rates that occurs at every location in the cross section, many observations are required to establish an accurate estimate of the mean rate at any given location. 相似文献
138.
William M. Alley 《Journal of the American Water Resources Association》1985,21(1):105-114
ABSTRACT: The Palmer Drought Severity Index (PDSI) is perhaps the most widely used regional drought index. However, there is considerable ambiguity about its value as a measure of hydrologic drought. In this paper the PDSI for climatic divisions in New Jersey is compared to the occurrence within each climatic division of streamflows in their lower quartile for the month (streamflow index), and ground-water levels in their lower quartile for the month (ground-water index). These indices are found to have distinct properties. It is not uncommon for PDSI values to indicate “severe” or “extreme” drought at times when the streamflow or groundwater index is above its lower quartile at many stations within the climatic division. The PDSI values and groundwater index indicate more persistent subnormal conditions than the streamflow index for truncation levels yielding the same total duration of drought over a period. The ground-water index tends to indicate a later beginning to droughts and of the three indices is the most conservative indicator of a drought's end. Drought timing and duration properties for the ground-water index are found to be highly influenced by the average depth to water in the well. Overall, the three indices of drought can provide three very different characterizations of drought. In particular, the results indicate that considerable caution should be exercised in drawing conclusions about hydrologic drought from the PDSI. 相似文献
139.
We followed selection guidelines commonly used by management agencies to select mountain quail (Oreortyx pictus) as an indicator species for an ecological guild of birds. We then evaluated the ability of mountain quail to indicate the presence of other species from the guild and to index the quality of the habitat for other species. The ability of quail to indicate the presence of species from the ecological guild varied widely within and among vegetation types. Species compositions of the ecological guild were more consistent in comparisons of sites within vegetation types than they were in comparisons of sites between vegetation types. Mountain quail habitat was significantly different from the habitats of sympatric species from the guild for 14 of 15 multivariate contrasts. We suggest that managers use indicator species with caution. If indicators are used, they should be applied to guilds composed of species that closely share ecological affinities. The habitat of the indicator species should overlap extensively with those of all other guild members. The use of indicators should be restricted to very similar sites within the same general vegetation type. 相似文献
140.
William W-G. Yeh Chuching Wang 《Journal of the American Water Resources Association》1987,23(4):569-580
ABSTRACT: This paper presents a method for estimating aquifer dispersivities in solute transport models. Sensitivity equations are derived for the calculation of sensitivity coefficients. A modified Gauss-Newton algorithm is used to perform the least-squares minimization. A statistical procedure is outlined to assess reliability of the estimated parameters. The solute transport model is solved by the upstream weighted, multiple cell balance method which combines the concepts of local mass balance and finite element approximations. A one-dimensional solute transport problem in a vertical column system is first used to illustrate the inverse technique. A second example considers the parameter identification problem for three-dimensional solute transport with a unidirectional steady and uniform flow field. The third example solves the parameter identification problem in a three-dimensional, stream-aquifer, solute transport system with steady state flow. Numerical experiments are conducted to study data requirements for parameter identification. 相似文献