全文获取类型
收费全文 | 20703篇 |
免费 | 237篇 |
国内免费 | 130篇 |
专业分类
安全科学 | 520篇 |
废物处理 | 889篇 |
环保管理 | 2780篇 |
综合类 | 3406篇 |
基础理论 | 5850篇 |
环境理论 | 10篇 |
污染及防治 | 5333篇 |
评价与监测 | 1288篇 |
社会与环境 | 860篇 |
灾害及防治 | 134篇 |
出版年
2021年 | 138篇 |
2019年 | 128篇 |
2018年 | 237篇 |
2017年 | 256篇 |
2016年 | 408篇 |
2015年 | 315篇 |
2014年 | 471篇 |
2013年 | 1606篇 |
2012年 | 575篇 |
2011年 | 823篇 |
2010年 | 675篇 |
2009年 | 670篇 |
2008年 | 844篇 |
2007年 | 871篇 |
2006年 | 768篇 |
2005年 | 668篇 |
2004年 | 649篇 |
2003年 | 629篇 |
2002年 | 611篇 |
2001年 | 767篇 |
2000年 | 575篇 |
1999年 | 326篇 |
1998年 | 261篇 |
1997年 | 278篇 |
1996年 | 280篇 |
1995年 | 333篇 |
1994年 | 304篇 |
1993年 | 285篇 |
1992年 | 277篇 |
1991年 | 278篇 |
1990年 | 295篇 |
1989年 | 278篇 |
1988年 | 250篇 |
1987年 | 241篇 |
1986年 | 222篇 |
1985年 | 200篇 |
1984年 | 255篇 |
1983年 | 211篇 |
1982年 | 271篇 |
1981年 | 219篇 |
1980年 | 184篇 |
1979年 | 201篇 |
1978年 | 184篇 |
1977年 | 153篇 |
1976年 | 138篇 |
1975年 | 143篇 |
1974年 | 159篇 |
1973年 | 162篇 |
1972年 | 148篇 |
1971年 | 146篇 |
排序方式: 共有10000条查询结果,搜索用时 16 毫秒
891.
Flora of the still unchanged or slightly modified floodplains is particularly valuable. Such are the natural, periodically flooded riparian ecosystems within the Mid-Pripyat river valley in Belarus. Distinctive elements of that area are ‘periodic islands’, which arise from the most elevated parts of the riverbed during flooding and have a specific microtopography. The aim of the research was to recognize floristic composition and ecological conditions of the ‘islands.’ Noted plants were mainly photophilous, by clearly varied in soil moisture, acidity and fertility requirements. 相似文献
892.
P. M. S. Jayathilaka Peeyush Soni Sylvain R. Perret H. P. W. Jayasuriya Vilas M. Salokhe 《Regional Environmental Change》2012,12(1):55-68
Climate change is the main global challenge of this century; it is therefore imperative to identify its effects on agriculture
in developing countries. This research makes spatial assessment of climate change effect on major plantation crops in Sri
Lanka, with emphasis on crop suitability of tea, rubber, and coconut. Geo-referenced maps of spatial and temporal changes
in crop suitability and production potentials are generated and compared. Data pertaining to six agro-ecological zones under
the study area are analyzed for a period of 1980–2007. Crop suitability maps are generated amalgamating yield maps and climatic
factors maps using AHP in multi-criteria analysis under two time frames of 1980–1992 and 1993–2007. Percent change in crop
suitability and crop yield classes is calculated based on five crop suitability and five crop yield classes during two time
frames. Dynamics of climatic parameters and crop yield are recognized using geo-referenced maps. The suitability maps of the
two time frames are compared to identify the changes with each crop in conjunction with changes in the prevailing climate
and yield. Geographic shift of suitability, yield, and climate classes are examined. Net gain or loss in crop production is
quantified. Long-term annual rainfall significantly decreased in mid-country wet zone, whereas the mean temperature of the
study area increased by 1.4°C. Results clearly showed that the climate and yield can be meaningfully related to the crop suitability
and management. 相似文献
893.
The results are presented that have been obtained during long-term studies (1991–2009) on the efficiency of natural reproduction
of the beluga, Russian sturgeon, stellate sturgeon, and sterlet in different spawning zones of the Volga. The influence of
major environmental factors on the formation of the offspring of these fishes is analyzed. It is shown that the productivity
of Volga spawning grounds varies depending on the river flow volume during spring floods and the abundance of active spawners.
Practical recommendations are proposed for enhancing sturgeon reproduction in the Volga. 相似文献
894.
The levels of total lipids, peroxidation products, and antioxidant activity in the liver were studied in fish species living in unequally polluted areas of the Rybinsk Reservoir and differing in their ecology and taxonomic position: the bream (Abramis brama L.), roach (Rutilus rutilus L.), burbot (Lota lota L.), and zander (Stizostedion lucioperca L.). The fish from polluted water areas were characterized by higher levels of total lipids and malonic dialdehyde and a deficiency of antioxidants. It is shown that the test parameters depend on the type of feeding and mode of life of the fish species. 相似文献
895.
J. B. Koogler R. S. Sholtes A. L. Danis C. I. Harding 《Journal of the Air & Waste Management Association (1995)》2013,63(4):211-214
In conjunction with a 15-month air quality survey of Jacksonville, Fia., a mathematical model has been developed to describe the dispersion of atmospheric pollutants. The source inventory used with the model was compiled, in part, from the data obtained from the sampling of all major sources within the area. The major sources were considered separately from the one-mile square area sources which accounted for the remainder of the emissions. Meteorological data was recorded continuously in the city including vertical temperature observations to 750 ft. The model was compiled in FORTRAN and can be used for both gaseous and particulate pollutants, by utilizing proper decay rates. The variant nature of meteorological parameters and emission rates are considered. The ground level concentrations of several pollutants which were determined for 24 hr periods at 11 sites and continuously at two other sites were used to check the model. A limited tracer study was carried out in conjunction with the project. 相似文献
896.
H. P. Sanderson R. Thomas Morris Katz 《Journal of the Air & Waste Management Association (1995)》2013,63(6):328-330
Field experience with the lead acetate impregnated paper tape sampler has indicated that large errors may arise in this method due to fading of the color of the precipitated lead sulfide spots. This fading is due to the action of light, sulfur dioxide, ozone, on other substances capable of oxidizing lead sulfide. The moisture content or relative humidity of the air sample must be maintained at an appropriate level to ensure reaction with the impregnated paper tape. The effects of the factors have been investigated in laboratory experiments with known concentrations of H2S. A number of antioxidants were studied in relation to the stability of the resultant spots to light and oxidation Orthophenyl phenol was found to be the most effective antioxidant for this purpose. A number of necessary precautions to be employed in the use of the lead acetate method are recommended and the limitations are discussed. 相似文献
897.
P. R. Miller J. R. Parmeter Jr. Brigitta H. Flick C. W. Martinez 《Journal of the Air & Waste Management Association (1995)》2013,63(6):435-438
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
898.
899.
D. F. Adams R. K. Koppe 《Journal of the Air & Waste Management Association (1995)》2013,63(6):410-415
Light aircraft and helicopters have been occasionally used to conduct aerial traverses for a single pollutant or atmospheric tracer. The continuous analyzer or sample collector is temporarily tied down with a seat belt or hand held. Flight variables are visually observed and written on the recorder chart, a notebook or possibly voice-recorded on a portable tape recorder. The versatile airborne instrumentation package described can measure and record up to 27 pollutant and flight variables from a Cessna Skymaster center-line thrust, light twin. Real-time analysis instrumentation include non-dispersive infrared analyzers for CO2, CO, and hydrocarbons, conductivity and coulometric analyzers for sulfur dioxide and sulfur-containing gases, and Charlson-Ahlquist visual range nephelometer. A Battelle “bulk sampler” is used to collect particulates for weighing and microscopic examination. Indicated air speed, altitude, rate of climb, magnetic heading, temperature, and relative humidity are continuously measured. All variables are sequentially recorded on a 7-track, 200 bit per second, 27-channel, magnetic tape data logging system. Measured variables are recorded once each 0.3 to 0.8 sec—equivalent to 33-100 ft of traversedepending upon the number of variables recorded (i.e., between 9 and 27) when flying at 90 mph. Tape data are reduced directly by IBM 360 computer to a digital print-out or from tape to an X-Y analog plot. 相似文献
900.
This annotated bibliography was prepared for the purpose of directing interested persons to some of the more helpful references in the field of air pollution meteorology. It obviously is not a complete listing. The reader who requires more information is directed to the references in the articles listed. 相似文献