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   20171篇
  免费   249篇
  国内免费   162篇
安全科学   537篇
废物处理   841篇
环保管理   2589篇
综合类   3589篇
基础理论   4911篇
环境理论   16篇
污染及防治   5391篇
评价与监测   1379篇
社会与环境   1191篇
灾害及防治   138篇
  2023年   112篇
  2022年   233篇
  2021年   297篇
  2020年   173篇
  2019年   203篇
  2018年   344篇
  2017年   392篇
  2016年   547篇
  2015年   409篇
  2014年   609篇
  2013年   1865篇
  2012年   716篇
  2011年   892篇
  2010年   715篇
  2009年   712篇
  2008年   846篇
  2007年   890篇
  2006年   786篇
  2005年   639篇
  2004年   595篇
  2003年   577篇
  2002年   517篇
  2001年   583篇
  2000年   465篇
  1999年   272篇
  1998年   220篇
  1997年   206篇
  1996年   228篇
  1995年   246篇
  1994年   233篇
  1993年   230篇
  1992年   230篇
  1991年   215篇
  1990年   221篇
  1989年   191篇
  1988年   172篇
  1987年   145篇
  1986年   165篇
  1985年   168篇
  1984年   182篇
  1983年   180篇
  1982年   166篇
  1981年   177篇
  1980年   161篇
  1979年   159篇
  1978年   123篇
  1977年   128篇
  1974年   115篇
  1973年   95篇
  1972年   114篇
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
991.
A system has been developed to automatically measure the effects of air pollutants in the ambient air on the rate of CO2 exchange by intact leaves of citrus trees growing in the field. A miniaturized system utilizing the same nondispersive infrared CO2 analyzer has been designed to study individually the effects of different concentrations of air pollutants on photosynthesis and respiration by plants.  相似文献   
992.
This Report, published as Informative Report No. 7 of the Air Pollution Control Association’s TI-5 Public Utilities Committee, began to move through the 14 step approval procedure of APCA’s Technical Council in February 1964 Comments made by members of the Technical Council were considered in the preparation of the final report. It is now published as representing the best thinking of the Association. It is an extremely timely and informative report.  相似文献   
993.
994.
The importance of fuels combustion was brought into sharp focus recently in a report on air pollution to the United States Senate in which it was stated, “These processes replace usable air with potentially harmful pollutants, and the capability of the atmosphere to disperse and dilute these pollutants—especially in urban areas where people, vehicles, and industries congregate in even greater numbers—is strictly limited.”1 The overwhelming burden of emissions of sulfur compounds, as well as nitrogen compounds and particulate matter in the U. S. today, originates from the burning of coal and fuel oil in stationary combustion sources. Thus, combustion has a large influence on the quality of the atmosphere in most urban areas. The air pollution effects of these contaminants are many and varied and all are objectionable and undesirable. Without a doubt, the most serious air pollution problem in the nation today is that created by the combustion of fossil fuels.  相似文献   
995.
Informative Report No. 8 on soap and detergent manufacture is one of a series of survey reports prepared by APCA’s Tl-2 Committee on air pollution problems and control methods encountered in the chemical industry today.  相似文献   
996.
Industry, government, and the public have come a long way in establishing the dialogue that is necessary if the reservations each has had of the others’ motives are to be dispelled. However, each tends to fall into a routine of accusations, charges, counter charges, and rebuttals. This paper deals with the action which must be forthcoming from industry if good community relations are to be maintained and the public interest is to be served.  相似文献   
997.
998.
Photochemical oxidant injury to ponderosa pine (Pinus ponderosa Laws) is a severe problem in the southern California mountains. Three-year-old ponderosa pines fumigated in controlled environment chambers with ozone at 0.15, 0.30, or 0.45 ppm had apparent photosynthesis rates reduced by 10, 70, and 85%, respectively, after 30 days exposure. A fumigation with 0.30 ppm ozone for 33 days depressed the cold perchloric acid extracted polysaccharides of both current and one-year-old needles by 40%. The 80% ethanol soluble sugar concentration of current year, ozone-injured needles increased 16% and that of the one-year-old needles decreased slightly. Both carbohydrate fractions of control trees in carbon-filtered air increased moderately. Higher, endogenous concentrations of ascorbic acid in needles did not protect the tissue from ozone injury. Apparent photosynthesis rate was a sensitive index for ozone dosage response. Needle carbohydrate depletion probably induces premature abscission.  相似文献   
999.
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   
1000.
A different approach to mathematically modeling large-scale atmospheric processes is presented. Whereas past approaches have been to develop a model based on an accumulation of information from a specific geographical area, resulting in a model applicable to that area only, we have developed a general mathematical model applicable to any geographical area. The model’s applicability is controlled by specifying the input information describing the meteorological situation and pollution source configuration. A rectangular array of grid points is used to specify both the wind field, by using stream functions, and the average source strength of some pollutant for the area represented by the grid. The diffusion problem is divided into two areas: transport by the mean wind field, and dispersion based on travel time and distance as described by empirical equations. Trajectories of pollutants are traced backwards from the points of interest in the course of the calculations and the contributions of all sources that affect the points of interest are accumulated. The model requires an array of source strength information. An inventory of pollution sources in the State of Connecticut was compiled and maps of source strengths were prepared for five pollutants on a 5000-ft grid-square array. Maps of sulfur dioxide and carbon monoxide source strengths are presented with the resulting concentration distribution for “typical” meteorological conditions. The model permits the changing of meteorological or source values at predetermined intervals so that diurnal changes are incorporated in the calculations. The model has not been verified, but the values of pollution concentration are the right order of magnitude and the resulting patterns are as expected.  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