首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   11615篇
  免费   48篇
  国内免费   32篇
安全科学   139篇
废物处理   547篇
环保管理   1306篇
综合类   1472篇
基础理论   3326篇
环境理论   3篇
污染及防治   2196篇
评价与监测   926篇
社会与环境   1751篇
灾害及防治   29篇
  2022年   69篇
  2021年   87篇
  2020年   41篇
  2019年   57篇
  2018年   648篇
  2017年   632篇
  2016年   601篇
  2015年   157篇
  2014年   230篇
  2013年   540篇
  2012年   434篇
  2011年   1007篇
  2010年   618篇
  2009年   701篇
  2008年   900篇
  2007年   1160篇
  2006年   279篇
  2005年   319篇
  2004年   277篇
  2003年   329篇
  2002年   351篇
  2001年   261篇
  2000年   208篇
  1999年   95篇
  1998年   89篇
  1997年   74篇
  1996年   61篇
  1995年   81篇
  1994年   66篇
  1993年   56篇
  1992年   57篇
  1991年   59篇
  1990年   71篇
  1989年   54篇
  1988年   42篇
  1987年   38篇
  1986年   46篇
  1985年   46篇
  1984年   62篇
  1983年   39篇
  1982年   46篇
  1981年   36篇
  1980年   44篇
  1979年   44篇
  1975年   30篇
  1974年   30篇
  1973年   33篇
  1972年   39篇
  1971年   30篇
  1969年   31篇
排序方式: 共有10000条查询结果,搜索用时 562 毫秒
971.
Barriers and bridges to implement policies about sustainable development and sustainability commonly depend on the past development of social–ecological systems. Production of metals required integration of use of ore, streams for energy, and wood for bioenergy and construction, as well as of multiple societal actors. Focusing on the Swedish Bergslagen region as a case study we (1) describe the phases of natural resource use triggered by metallurgy, (2) the location and spatial extent of 22 definitions of Bergslagen divided into four zones as a proxy of cumulative pressure on landscapes, and (3) analyze the consequences for natural capital and society. We found clear gradients in industrial activity, stream alteration, and amount of natural forest from the core to the periphery of Bergslagen. Additionally, the legacy of top-down governance is linked to today’s poorly diversified business sector and thus municipal vulnerability. Comparing the Bergslagen case study with other similar regions in Russia and Germany, we discuss the usefulness of multiple case studies.  相似文献   
972.
Gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM) and particulate bound mercury (PBM) were measured on the University of Mississippi campus from July 2011 to June 2012. It is believed to be the first time that concentrations of atmospheric mercury species have been documented in northern Mississippi, and at a location with relatively large and sudden swings in population. The mean concentration (±1SD) of GEM was 1.54 ± 0.32 ng m−3; levels were lower and generally more stable during the winter (1.48 ± 0.22) and spring (1.46 ± 0.27) compared with the summer (1.56 ± 0.32) and fall (1.63 ± 0.42). Mean concentrations for GOM and PBM were 3.87 pg m−3 and 4.58 pg m−3, respectively; levels tended to be highest in the afternoon and lowest in the early morning hours. During the fall and spring academic semesters concentrations and variability of GOM and PBM both increased, possibly from vehicle exhaust. There were moderate negative correlations with wind speed (all species) and humidity (GOM and PBM). Backward air mass trajectory modeling for the ten highest peaks for each mercury species revealed that the majority of these events occurred from air masses that passed through the northern continental US region. Overall, this study illustrates the complexity of temporal fluctuations of airborne mercury species, even in a small town environment.  相似文献   
973.
The effect of aquatic vegetation (Spyrogira sp. and Zannichellia palustris), light exposure and water quality (secondary-treated wastewater vs. ultrapure water) on the removal efficiency of six antibiotics (sulfonamides and tetracyclines) is studied in laboratory-scale reactors. After 20 d of treatment, 3–59% of sulfonamides were eliminated in the reactors exposed to light. Removal was about 10% in unplanted reactors in darkness. The elimination of tetracycline (TC) and oxytetracycline (OTC) ranged between 83% and 97% in both planted and unplanted reactors. However, in dark unplanted reactors, OTC was largely removed (88%) while only 15% of TC was eliminated. These results suggest that TC was mainly removed by photodegradation whereas biodegradation or hydrolysis process seems to be significant processes for OTC. Sulfonamides were mainly eliminated by biodegradation or indirect photodegradation processes. Pseudo-first order kinetics removal rates ranged from 0.003 and 0.007 d?1 for Sulfamethazine and TC in the covered control reactors to 0.13 and 0.21 d?1 for TC and OTC in the uncovered control reactors, with half-lives from 3 to 350 d. A TC photodegradation product was tentatively identified in uncovered reactors. This study highlights the important role played by light exposure in the elimination of antibiotics in polishing ponds.  相似文献   
974.
Abstract

A laboratory scale two‐stage sequencing batch reactor (TSSBR) was used to study the effectiveness of pH as a real‐time control parameter in swine wastewater treatment. A Ringlace media was inserted into the A/O (Anoxic/Oxic) reactor for bacteria immobilization. The TSSBR was subjected to three levels of organic loading. The pH and ORP (Oxidation Reduction Potential) patterns obtained were consistent with distinct features, enabling the real‐time control strategy to effectively set a flexible aeration time pending on influent concentration, hence resulting in flexible cycle time and HRT (Hydraulic Retention Time) for the system. The real‐time process ensured a removal efficiency of over 99% and 95%, respectively, for ammonia and TOC (Total Organic Carbon). For NO3 ‐N and PO4 ‐3, the run with influent TOC = 4,000 mg/L yielded the most efficient removal of 61% and 95%, respectively. Test results suggest that pH can be a viable tool for on‐line real‐time control of a biological treatment process.  相似文献   
975.
A series of partitioning agents were studied to determine their ability to separate organic sulfur compounds by gas chromatography. Several columns showed promise, but did not separate organic sulfur compounds from normally occurring atmospheric hydrocarbons. Higher concentrations of organic sulfur compounds in stack gases are separated as metallic salts in a series of impingers. The nature of the precipitated sulfur compound can be determined by gas chromatography after regeneration of the compound by addition of acid to the metallic precipitate.  相似文献   
976.
The Pennsylvania Air Pollution Commission has developed a regulatory program based upon the control of local air pollution problems and reduction of pollutant levels in air basins. The geographical boundaries of 10 air basins have been established. The Commission’s air basin regulations will provide for the reduction of over-all pollutant levels and for emergency procedures in the event of adverse meteorological conditions. The paper discusses the format and objectives of the program.

In order to effectively enforce the air basin regulations and maintain the necessary surveillance of the state’s air quality, a "computerized real time on-line integrated air monitoring-data handling system" has been designed. The system will incorporate a network to constantly monitor the air in each air basin.The primary objectives of the system are: 1. Constant surveillance of air pollution in the air basins.

2. Provide information on air pollution potential alerts.

3. Aid in further development of air quality criteria and regulations.

The air monitoring network is estimated to include approximately 25 remote stations. Each remote will contain air pollution and meteorological sampling equipment and hardware to telemeter to a central station. The data will be transmitted over leased telephone lines. The central station in Harrisburg will contain the necessary hardware to receive and process data, calculate and display results and permit supervisory control of the network. Output options will include immediate display of edited data, command and alarm information, and presentation of statistical results.

Although the air monitoring system is one of the principle ingredients of the program, the air basin concept encompasses other component systems designed to knit together the entire air pollution control program in Pennsylvania.  相似文献   
977.
A portable, battery-operated, electro-optical dust analyzer operating on the principle of light scattering from individual dust particles in air drawn through a high-intensity light field has been developed for monitoring dust levels where external power may be unavailable. The instrument counts and size-discriminates airborne particles over two size ranges upwards of 0.3 microns with immediate readout. A dilution mechanism permits analysis of particulate concentrations as high as 2400 particles/cm3 on each channel. The self-contained Ni-Cd batteries are rechargeable. Total weight, including batteries and all components, is approximately 14 Ib. Total power used, mainly for pumping a filtered air sheath at 300 cm/sec and for the light source, is less than 34 watts. Another unique feature is the flow system designed for turbulence suppression.

Electronic calibration in terms of number of particles/cm3 for each size range is accomplished in the laboratory by means of a pulse generator with respect to which the readout indicator is calibrated for count. The input voltages to the pulse-height discriminators are appropriately attenuated for various pulse amplitudes simulating the output of the light-sensitive pickup, a photomultiplier tube.Pulse height as a function of particle size was measured for polystyrene latex beads ranging from 0.3 to 2 microns in diameter. Good correlation is obtained with results from commercial analyzers.

Field surveys have been undertaken with the CAES prototype analyzer at various sites in central Pennsylvania and at numerous sampling points within the cities of Pittsburgh and Philadelphia. Particulate concentrations as high as 1400 particles/ cm3 have been measured at a coal cleaning plant.  相似文献   
978.
This paper presents a simplified analysis to determine the variables that affect the empirical correlation factor used in the lead peroxide method. The rate of sulfation has been determined from two different models. In the first model, the mass transfer rate is calculated from the gas phase resistance alone whereas in the second model, the diffusion resistance in the gel phase is assumed to be the rate limiting step. Although the gas phase and the gel phase resistances may be both important in the actual case, it has been found that the correlation factor based on the first model is adequate to describe general experimental observations. Reasonable agreement has been obtained between the measured and the calculated va|ue of the correlation factor.  相似文献   
979.
Pollutants sampled during the burning of 30 lb ponderosa pine fuel beds yielded emission factors for CO, hydrocarbon gases, and par-ticulate matter of 146, 8.4, and 9.1 lb/ton of fuel, respectively. When similar beds were treated with diammonium phosphate flame retardant, these factors increased to 166, 11.7, and 19.3 lb/ton of fuel, respectively.

Gas chromatographic analysis of hydrocarbon gases showed that 15-40% of this material was composed of methane and eth-ylene. Ethane and acetylene were the next most abundant materials, with photochemically important materials constituting minor portions of this gaseous component. Fuel beds treated with flame retardant produced more oiefins, and this production lasted throughout the smoldering phase of burning.

These tests showed that the smoldering phase of combustion is of major importance to air pollutant production during slash burning. The initial 80% of the fuel burned accounted for only 20-30% of HC and CO emissions. This suggests that a rapid mop-up of slash burns could substantially reduce air pollutant production.  相似文献   
980.
Vanadium compounds are toxic pollutants which require engineering control in the design stage. In the lower Delaware River Valley, the main sources are presently the combustion of vanadium rich fuel oils and the catalytic processing of high vanadium crudes. These and other Industrial emissions, result in atmospheric vanadium concentrations which have varied from 0.133 μg/m3 to 0.557 μg/m3 between 1958 and 1969. Compounds of vanadium, principally with oxygen and sulfur, are considered. The dominance of oxygen compounds over sulfur compounds as derived from equilibrium data, and the tendency of vanadium oxides to move toward vanadium’s maximum valence of +5, indicate the prevalence of V205 as the emission compound.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号