全文获取类型
收费全文 | 34214篇 |
免费 | 362篇 |
国内免费 | 246篇 |
专业分类
安全科学 | 916篇 |
废物处理 | 1360篇 |
环保管理 | 4374篇 |
综合类 | 5365篇 |
基础理论 | 9488篇 |
环境理论 | 26篇 |
污染及防治 | 9351篇 |
评价与监测 | 2190篇 |
社会与环境 | 1546篇 |
灾害及防治 | 206篇 |
出版年
2022年 | 335篇 |
2021年 | 332篇 |
2020年 | 222篇 |
2019年 | 286篇 |
2018年 | 565篇 |
2017年 | 534篇 |
2016年 | 796篇 |
2015年 | 625篇 |
2014年 | 937篇 |
2013年 | 2574篇 |
2012年 | 1146篇 |
2011年 | 1580篇 |
2010年 | 1232篇 |
2009年 | 1222篇 |
2008年 | 1529篇 |
2007年 | 1613篇 |
2006年 | 1394篇 |
2005年 | 1155篇 |
2004年 | 1131篇 |
2003年 | 1053篇 |
2002年 | 1042篇 |
2001年 | 1309篇 |
2000年 | 901篇 |
1999年 | 583篇 |
1998年 | 439篇 |
1997年 | 449篇 |
1996年 | 452篇 |
1995年 | 515篇 |
1994年 | 459篇 |
1993年 | 411篇 |
1992年 | 426篇 |
1991年 | 385篇 |
1990年 | 382篇 |
1989年 | 418篇 |
1988年 | 354篇 |
1987年 | 305篇 |
1986年 | 278篇 |
1985年 | 310篇 |
1984年 | 286篇 |
1983年 | 325篇 |
1982年 | 324篇 |
1981年 | 273篇 |
1980年 | 244篇 |
1979年 | 273篇 |
1978年 | 230篇 |
1977年 | 196篇 |
1976年 | 203篇 |
1975年 | 196篇 |
1974年 | 173篇 |
1972年 | 200篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Eshleman KN Wigington PJ Davies TD Tranter M 《Environmental pollution (Barking, Essex : 1987)》1992,77(2-3):287-295
Field studies of chemical changes in surface waters associated with rainfall and snowmelt events have provided evidence of episodic acidification of lakes and streams in Europe and North America. Modelling these chemical changes is particularly challenging because of the variability associated with hydrological transport and chemical transformation processes in catchments. This paper provides a review of mathematical models that have been applied to the problem of episodic acidification. Several empirical approaches, including regression models, mixing models and time series models, support a strong hydrological interpretation of episodic acidification. Regional application of several models has suggested that acidic episodes (in which the acid neutralizing capacity becomes negative) are relatively common in surface waters in several regions of the US that receive acid deposition. Results from physically based models have suggested a lack of understanding of hydrological flowpaths, hydraulic residence times and biogeochemical reactions, particularly those involving aluminum. The ability to better predict episodic chemical responses of surface waters is thus dependent upon elucidation of these and other physical and chemical processes. 相似文献
92.
Wigington PJ Davies TD Tranter M Eshleman KN 《Environmental pollution (Barking, Essex : 1987)》1992,78(1-3):29-35
Episodic acidification is practically a ubiquitous process in streams and drainage lakes in Canada, Europe and the United States. Depressions of pH are often smaller in systems with low pre-episode pH levels. Studies on European surface waters have reported episodes most frequently with minimum pH levels below 4.5. In Canada and the United States, studies have also reported a number of systems that have had minimum pH levels below 4.5. In all areas, change in water flowpath during hydrological events is a major determinant of episode characteristics. Episodic acidification is also controlled by a combination of other natural and anthropogenic factors. Base cation decreases are an important contributor to episodes in circumneutral streams and lakes. Sulphate pulses are generally important contributors to episodic acidification in Europe and Canada. Nitrate pulses are generally more important to episodic acidification in the Northeast United States. Increases in organic acids contribute to episodes in some streams in all areas. The sea-salt effect is important in near-coastal streams and lakes. In Canada, Europe and the United States, acidic deposition has increased the severity (minimum pH reached) of episodes in some streams and lakes. 相似文献
93.
Reynolds B Stevens PA Adamson JK Hughes S Roberts JD 《Environmental pollution (Barking, Essex : 1987)》1992,77(2-3):157-165
Data are presented demonstrating how clearfelling has changed soil and stream water aluminium chemistry. For soil waters, a strong empirical relationship was observed between inorganic aluminium (Al(inorg)) and total inorganic anion (TIA) concentrations. Before felling, chloride and sulphate accounted for the largest proportion of the TIA concentration. After felling, in soils where nitrification was active, nitrate became increasingly important. Where this led to an increase in TIA, Al(inorg) concentrations increased. Over five years, nitrate concentrations have fallen, along with TIA, resulting in a sympathetic decline in Al(inorg). Streams draining clearfelled areas initially became more acid, although chloride and sulphate concentrations decreased. Stream water nitrate concentrations increased soon after felling and remained higher than controls for up to four years. While nitrate concentrations were high, Al(inorg) remained unchanged. Subsequently, as nitrate and TIA decreased, Al(inorg) also declined to concentrations below those in the control stream. Clearfelling upland forests will not necessarily result in immediate improvements in water quality, although long-term benefits may be seen before canopy-closure of the next crop. 相似文献
94.
Measurements of gaseous H2O2 and peroxyacetyl nitrate (PAN) concentrations in air are given for a site in rural southern England over an approximately 4-year period. In both cases the data show both diurnal and seasonal patterns. Temperature and wind direction had clear influences on the recorded concentrations of both species. There was an indication of increasing H2O2 concentrations with time. The use of a two-dimensional global model confirmed that this would be expected to occur alongside growth in ozone formation. It is suggested that, during photochemical episodes, the sequential build-up of ozone, PAN and H2O2 could be important in influencing the ability of vegetation to resist the effects of aggressive pollutants. 相似文献
95.
As a consequence of decreases in the emission rate of sulphur in eastern North America in the late 1970s and early 1980s, sulphate deposition in central Ontario declined by about 40%, but has remained constant for about six years. Plastic Lake, a small, dilute lake on the Precambrian shield that the authors have studied since 1979, acidified between the start of the study and about 1986, but since then has not changed. The authors also monitored the chemistry of streamwater draining the Plastic Lake catchment. Water quality of runoff from an upland site improved rapidly (pH and alkalinity increased, SO4(2-) and Al decreased), but two factors offset these improvements. A small wetland area downstream reversed most of these changes, resulting in a constant output of strong acid from the catchment. In addition, in extremely dry years (1983, 1987, 1989) there were very high concentrations of SO4(2-) in the streamwater, suggesting substantial re-oxidation of reduced S in the catchment. 相似文献
96.
Comparative impacts of forest harvest and acid precipitation on soil and streamwater acidity 总被引:1,自引:0,他引:1
Hornbeck JW 《Environmental pollution (Barking, Essex : 1987)》1992,77(2-3):151-155
Annual H+ budgets were calculated for a catchment with a 65-year-old spruce-fir forest, and for an adjacent catchment at three years after a whole-tree harvest. In the harvested catchment sinks for H+ due to weathering and mineralization reactions were 85% greater, and sources of H+ due to biomass uptake were 60% greater than in the undisturbed catchment. There was an overall net consumption of 550 eq H+ ha(-1) year(-1) at year 3 after harvest compared to a net generation of 520 eq H+ ha(-1) year(-1) for the 65-year-old forest. Soil pH increased by 0.2-0.4 units soon after harvest, but there was little change in pH of streamwater from the harvested watershed. The whole-tree harvest resulted in a total production of about 30,000 eq H+ ha(-1) due to biomass removal. In contrast, wet and dry deposition at rates measured in this study could add more than 50,000 eq H+ ha(-1) in the 65-year period before the next harvest. Reducing the intensity of harvest may lessen long-term impacts of these sources of H+ on acidification of soils and streams. 相似文献
97.
This paper documents the rapid expansion and changes in food aid flows to Sub-Saharan Africa up to mid-1985. Trends for Sub-Saharan Africa as a whole and for the more seriously affected countries are examined, as are the comparative experiences of food aid of individual countries in the region. Table 11 lists the Sub-Saharan African countries and indicates the most seriously affected food-short countries, as defined by the WFP/FAO task force. It should be borne in mind that some practical problems exist in compiling data on food aid. These include lack of availability of reliable data, especially of most recent data; lack of common terminology and definitions; and different accounting systems. These data problems are sometimes a source of confusion. However, the basic facts are clear: food aid gradually emerged during the early 1980s as a resource too often of considerable significance to many countries of Sub-Saharan Africa. These trends were only accelerated with the crisis of 1984-1985. These facts provide a point of reference for further analysis of the sources of the crisis, its actual dimensions and consequences. 相似文献
98.
Taylor AJ 《Disasters》1986,10(1):70-73
This paper was prepared in 1978 on the basis of a review of sociological and anthropological fieldwork conducted up to that time. Although theoretical in presentation its conclusions are formulated in accordance with the author's own extensive observations of organizational response to natural disasters in developing countries, especially those having sudden onset. Practical implications for co-ordination agencies and pre-disaster training are drawn. 相似文献
99.
Environment, Development and Sustainability - This study describes the results of groundwater table variation in Thanjavur District before and after the monsoon seasons. Groundwater-level data... 相似文献
100.
Shahpari Ghazal Sadeghi Hossein Ashena Malihe García-León David 《Environment, Development and Sustainability》2022,24(3):4110-4127
Environment, Development and Sustainability - In the last two decades, recurring drought becomes a challenge for Iran’s economy, which is located in a drought-prone area, and it has been... 相似文献