全文获取类型
收费全文 | 13692篇 |
免费 | 202篇 |
国内免费 | 144篇 |
专业分类
安全科学 | 520篇 |
废物处理 | 602篇 |
环保管理 | 2055篇 |
综合类 | 1639篇 |
基础理论 | 3617篇 |
环境理论 | 5篇 |
污染及防治 | 3672篇 |
评价与监测 | 1006篇 |
社会与环境 | 833篇 |
灾害及防治 | 89篇 |
出版年
2023年 | 70篇 |
2022年 | 139篇 |
2021年 | 120篇 |
2020年 | 119篇 |
2019年 | 136篇 |
2018年 | 227篇 |
2017年 | 253篇 |
2016年 | 366篇 |
2015年 | 265篇 |
2014年 | 356篇 |
2013年 | 1063篇 |
2012年 | 470篇 |
2011年 | 666篇 |
2010年 | 535篇 |
2009年 | 593篇 |
2008年 | 678篇 |
2007年 | 690篇 |
2006年 | 615篇 |
2005年 | 538篇 |
2004年 | 474篇 |
2003年 | 502篇 |
2002年 | 459篇 |
2001年 | 594篇 |
2000年 | 397篇 |
1999年 | 255篇 |
1998年 | 184篇 |
1997年 | 195篇 |
1996年 | 187篇 |
1995年 | 214篇 |
1994年 | 181篇 |
1993年 | 149篇 |
1992年 | 161篇 |
1991年 | 148篇 |
1990年 | 158篇 |
1989年 | 156篇 |
1988年 | 116篇 |
1987年 | 103篇 |
1986年 | 82篇 |
1985年 | 113篇 |
1984年 | 104篇 |
1983年 | 112篇 |
1982年 | 104篇 |
1981年 | 105篇 |
1980年 | 79篇 |
1979年 | 86篇 |
1978年 | 58篇 |
1977年 | 58篇 |
1976年 | 54篇 |
1975年 | 58篇 |
1973年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Mortimer MJ 《Environmental management》2008,41(5):640-653
Political and legal conflicts between the need for targeted private forest conservation and the continued assurance of private
property rights in the U.S. presents a seemingly intractable resource management problem. Scandinavian use of habitat protection
areas on private forests offers an additional tool that may be suitable for solving the historical and on-going tension found
within U.S. efforts to reconcile desires to maintain lands in a forested condition while also respecting private property
rights. This article presents a comparative cross-sectional policy analysis of Sweden, Finland, and the U.S., supported with
a supplemental case example from the Commonwealth of Virginia. Similarities in all three countries among forest ownership
patterns, use of public subsidies, and changing attitudes towards conservation are generally encouraging. Additionally, Virginia’s
current consideration and development of state-wide forest policies focused on forestland and open space conservation suggests
both a need and an opportunity to systematically assess the applicability of the Nordic forest reserve approach to local private
forest conservation. Future research at a high-resolution, and specifically at the state level, should focus on the social
and political factors that would ultimately determine the viability of a forest reserve program. 相似文献
82.
We demonstrate an approach for evaluating the level of protection attained using a variety of forms and levels of past, current,
and proposed Air Quality Standards (AQSs). The U.S. Clean Air Act requires the establishment of ambient air quality standards
to protect health and public welfare. However, determination of attainment of these standards is based on ambient pollutant
concentrations rather than prevention of adverse effects. To determine if a given AQS protected against adverse effects on
vegetation, hourly ozone concentrations were adjusted to create exposure levels that “just attain” a given standard. These
exposures were used in combination with a physiologically-based tree growth model to account for the interactions of climate
and ozone. In the evaluation, we used ozone concentrations from two 6-year time periods from the San Bernardino Mountains
in California. There were clear differences in the level of vegetation protection achieved with the various AQSs. Based on
modeled plant growth, the most effective standards were the California 8-hr average maximum of 70 ppb and a seasonal, cumulative,
concentration-weighted index (SUM06), which if attained, resulted in annual growth reductions of 1% or less. Least effective
was the 1-hr maximum of 120 ppb which resulted in a 7% annual reduction. We conclude that combining climate, exposure scenarios,
and a process-based plant growth simulator was a useful approach for evaluating effectiveness of current or proposed air quality
standards, or evaluating the form and/or level of a standard based on preventing adverse growth effects. 相似文献
83.
84.
Naphthenic acids are naturally-occurring, aliphatic or alicyclic carboxylic acids found in petroleum. Water used to extract bitumen from the Athabasca oil sands becomes toxic to various organisms due to the presence of naphthenic acids released from the bitumen. Natural biodegradation was expected to be the most cost-effective method for reducing the toxicity of the oil sands process water (OSPW). However, naphthenic acids are poorly biodegraded in the holding ponds located on properties leased by the oil sands companies. In the present study, chemical oxidation using ozone was investigated as an option for mitigation of this toxicity. Ozonation of sediment-free OSPW was conducted using proprietary technology manufactured by Seair Diffusion Systems Inc. Ozonation for 50min generated a non-toxic effluent (based on the Microtox bioassay) and decreased the naphthenic acids concentration by approximately 70%. After 130min of ozonation, the residual naphthenic acids concentration was 2mgl(-1): <5% of the initial concentration in the filtered OSPW. Total organic carbon did not change with 130min of ozonation, whereas chemical oxygen demand decreased by approximately 50% and 5-d biochemical oxygen demand increased from an initial value of 2mgl(-1) to a final value of 15mgl(-1). GC-MS analysis showed that ozonation resulted in an overall decrease in the proportion of high molecular weight naphthenic acids (n> or = 22). 相似文献
85.
Photolysis of 14C-sulfadiazine in aqueous solution under simulated sunlight followed first-order kinetics. The impact of H2O2, humic acid, fulvic acid and acetone to enhance the photodegradation of sulfadiazine (SDZ) was studied. Six photoproducts, 4-OH-SDZ, 5-OH-SDZ, N-formyl-SDZ, 4-[2-iminopyrimidine-1(2H)-yl] aniline, 2-aminopyrimidine, and aniline were identified. Extrusion of SO2 was found to be the main degradation process during irradiation. These photoproducts can occur in water and soil upon sunlight exposure, when soil is treated with SDZ contained in manure. Due to photodegradation the experimental half-life of the SDZ in water was 32h and in the presence of photosensitizers the half-life values were 19.3-31.4h, 17.2-31.4h, 12.6-29.8h, and 3.8-30.7h for H2O2, humic acid, fulvic acid, and acetone, respectively depending on the concentration of the photosensitizers. The presence of photosensitizers markedly reduced SDZ persistence, indicating that indirect photolytic processes are important factors governing the photodegradation of SDZ in aqueous environments. Investigation revealed further persistence behavior of SDZ in manure. The half-life value of SDZ in manure was 158h. 相似文献
86.
Bergin MS Russell AG Odman MT Cohan DS Chameides WL 《Journal of the Air & Waste Management Association (1995)》2008,58(10):1351-1359
Isolating the effects of an individual emissions source on secondary air pollutants such as ozone and some components of particulate matter must incorporate complex nonlinear processes, be sensitive to small emissions perturbations, and account for impacts that may occur hundreds of kilometers away. The ability to evaluate these impacts is becoming increasingly important for efficient air quality management. Here, as part of a recent compliance enforcement action for a violation of the Clean Air Act and as an evaluation of ozone response to single-source emissions plumes, two three-dimensional regional photochemical air quality models are used to assess the impact on ozone from approximately 2000 to 3000 excess t/month of nitrogen oxides emitted from a single power plant in Ohio. Periods in May, July, and August are evaluated. Two sensitivity methods are applied: the "brute-force" (B-F) method and the decoupled direct method (DDM). Using DDM, maximum 1-hr averaged ozone concentrations are found to increase by up to 1.8, 1.3, and 2.2 ppbv during May, July, and August episodes, respectively, and concentration increases greater than 0.5 ppbv occur in Ohio, Pennsylvania, Maryland, New York, West Virginia, Virginia, and North and South Carolina. B-F results for the August episode show a maximum 1-hr averaged ozone concentration increase of 2.3 ppbv. Significant localized decreases are also simulated, with a maximum of 3.6 ppbv in Ohio during the August episode and decreases of 0.50 ppbv and greater in Ohio, Pennsylvania, Maryland, West Virginia, and Virginia. Maximum increases are compared with maximum decreases for the August period using second-order DDM and are found, in aggregate, to be greater in magnitude by 42%. When evaluated during hours when ozone concentrations exceed 0.060 ppm, the maximum increases in ozone are higher than decreases by 82%. The spatial extent of ozone increase in both cases is about triple that of reduction. 相似文献
87.
George P. Ingersoll M. Alisa Mast Donald H. Campbell David W. Clow Leora Nanus John T. Turk 《Atmospheric environment (Oxford, England : 1994)》2008,42(24):6098-6113
Seasonal snowpack chemistry data from the Rocky Mountain region of the US was examined to identify long-term trends in concentration and chemical deposition in snow and in snow-water equivalent. For the period 1993–2004, comparisons of trends were made between 54 Rocky Mountain Snowpack sites and 16 National Atmospheric Deposition Program wetfall sites located nearby in the region. The region was divided into three subregions: Northern, Central, and Southern. A non-parametric correlation method known as the Regional Kendall Test was used. This technique collectively computed the slope, direction, and probability of trend for several sites at once in each of the Northern, Central, and Southern Rockies subregions. Seasonal Kendall tests were used to evaluate trends at individual sites.Significant trends occurred during the period in wetfall and snowpack concentrations and deposition, and in precipitation. For the comparison, trends in concentrations of ammonium, nitrate, and sulfate for the two networks were in fair agreement. In several cases, increases in ammonium and nitrate concentrations, and decreases in sulfate concentrations for both wetfall and snowpack were consistent in the three subregions. However, deposition patterns between wetfall and snowpack more often were opposite, particularly for ammonium and nitrate. Decreases in ammonium and nitrate deposition in wetfall in the central and southern rockies subregions mostly were moderately significant (p<0.11) in constrast to highly significant increases in snowpack (p<0.02). These opposite trends likely are explained by different rates of declining precipitation during the recent drought (1999–2004) and increasing concentration. Furthermore, dry deposition was an important factor in total deposition of nitrogen in the region. Sulfate deposition decreased with moderate to high significance in all three subregions in both wetfall and snowpack. Precipitation trends consistently were downward and significant for wetfall, snowpack, and snow-telemetry data for the central and southern rockies subregions (p<0.03), while no trends were noted for the Northern Rockies subregion. 相似文献
88.
We studied the effects of inter-annual variability and serial correlation on the statistical power of monitoring schemes to detect trends in biomass of bream (Abramis brama) in Lake Veluwemeer (The Netherlands). In order to distinguish between 'true' system variability and sampling variability we simulated the development of the bream population, using estimates for population structure and growth, and compared the resulting inter-annual variabilities and serial correlations with those from field data. In all cases the inter-annual variability in the field data was larger than in simulated data (e.g. for total biomass of all assessed bream sigma = 0.45 in field data, and sigma = 0.03-0.14 in simulated data) indicating that sampling variability decreased statistical power for detecting trends. Moreover, sampling variability obscured the inter-annual dependency (and thus the serial correlation) of biomass, which was expected because in this long-lived population biomass changes are buffered by the many year classes present. We did find the expected serial correlation in our simulation results and concluded that good survey data of long-lived fish populations should show low sampling variability and considerable inter-annual serial correlation. Since serial correlation decreases the power for detecting trends, this means that even when sampling variability would be greatly reduced, the number of sampling years to detect a change of 15%.year(-1) in bream populations (corresponding to a halving or doubling in a six-year period) would in most cases be more than six. This would imply that the six-year reporting periods that are required by the Water Framework Directive of the European Union are too short for the existing fish monitoring schemes. 相似文献
89.
McFarland MJ Olivas AC Atkins SG Kennedy RL Patel K 《Journal of the Air & Waste Management Association (1995)》2007,57(11):1317-1325
Maintenance of Department of Defense (DoD) weapon systems, conducting battlefield training exercises as well as meeting military construction and/or demolition schedules, invariably generate fugitive air emissions, many of which are visible. Although there is no codified federal method for quantifying fugitive emissions opacity, many state and local air regulatory agencies have instituted enforceable fugitive emission opacity standards at DoD facilities. The current study focused on comparing the performance of the digital opacity compliance system (DOCS) with U.S. Environment Protection Agency Method 9 (Method 9) certified human observers in quantifying the visible opacity associated with fugitive emissions produced using a commercial fog generator. By systematically repositioning both DOCS cameras and Method 9-certified observers during field testing, differences in method performance as a function of observational locations were documented. At both the 30- and 300-ft off-set distances, opacity levels reported by the DOCS technology and Method 9-certified smoke readers were found to be statistically different at the 99% confidence level. Alternatively, at the 90- and 150-ft off-set distances, results suggested that there was an insignificant difference at the 99% confidence level between the two methods. Comparing the magnitude of the each method's standard deviation suggested that, at the 30-ft off-set distance, the DOCS technology was consistently more precise than Method 9-certified readers regardless of the observer's downwind distance. However, at the 90, 150, and 300-ft off-set distances, method precision seemed to vary as a function of both off-set and downwind distance. The primary factor affecting the consistency in opacity measurements appeared to be the impact of ground-level air turbulence on fog plume dispersion and transport. Field observations demonstrated that localized wind shear played a critical and decisive role in how and to what extent fugitive emissions opacity could be determined, regardless of the method selected. 相似文献
90.
T. Lubjuhn Wolfgang Winkel Jörg Thomas Epplen Jörg Brün 《Behavioral ecology and sociobiology》2000,48(1):12-17
One of the most interesting aspects of the mating system of pied flycatchers is the regular occurrence of polygyny. Here we
present data on the reproductive success of polygynously paired pied flycatcher males compared to monogamous males based on
paternity analyses through DNA fingerprinting. Males paired with two females suffered a higher loss in reproductive output
per female compared to monogamous males due to (1) a greater proportion of unhatched eggs in their broods, (2) greater nestling
mortality and (3) a greater probability of being cuckolded. Nevertheless, the number of fledglings was significantly greater
for polygynous males. Based on the number of nestlings that returned for subsequent breeding seasons, however, the reproductive
success of monogamous and polygynous males did not differ significantly. These data raise the question as to why males attempt
polygyny.
Received: 16 August 1999 / Received in revised form: 15 March 2000 / Accepted: 18 March 2000 相似文献