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   13110篇
  免费   142篇
  国内免费   111篇
安全科学   360篇
废物处理   344篇
环保管理   1964篇
综合类   3271篇
基础理论   3099篇
环境理论   6篇
污染及防治   3311篇
评价与监测   580篇
社会与环境   363篇
灾害及防治   65篇
  2018年   123篇
  2017年   128篇
  2016年   184篇
  2015年   155篇
  2014年   200篇
  2013年   959篇
  2012年   307篇
  2011年   434篇
  2010年   309篇
  2009年   408篇
  2008年   448篇
  2007年   479篇
  2006年   435篇
  2005年   326篇
  2004年   347篇
  2003年   383篇
  2002年   323篇
  2001年   467篇
  2000年   323篇
  1999年   217篇
  1998年   154篇
  1997年   146篇
  1996年   179篇
  1995年   177篇
  1994年   201篇
  1993年   180篇
  1992年   183篇
  1991年   181篇
  1990年   208篇
  1989年   194篇
  1988年   166篇
  1987年   163篇
  1986年   148篇
  1985年   165篇
  1984年   147篇
  1983年   159篇
  1982年   160篇
  1981年   163篇
  1980年   149篇
  1979年   145篇
  1978年   142篇
  1977年   129篇
  1976年   136篇
  1975年   114篇
  1974年   142篇
  1973年   125篇
  1972年   125篇
  1971年   105篇
  1970年   106篇
  1967年   116篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
In previous research on unemployment, conflicting evidence has been found for a ‘reverse causation interpretation’, indicating that prolonged unemployment is a consequence of psychological distress instead of the reverse. The present longitudinal study was conducted to test this reverse causation explanation. A second issue addressed in this study was whether getting a job or not depends more strongly on subjective or psychological factors than on objective factors (e.g. a person's biographical background, length of unemployment). Two independent samples were examined: Sample 1 (n = 635) consisted of school-leavers, and sample 2 (n = 467) consisted of subjects who had been unemployed for more than one year. Some support was found for the reverse causation explanation. In addition, more than objective factors, a strong job orientation and a problem focused coping style appeared to be a precursor of success in the labour market. Accordingly, getting a job seems to be primarily a function of one's own efforts.  相似文献   
992.
993.
Early in 1992, Bangladesh experienced an influx of Burmese refugees, reaching a total of 263,000 by May. As the health and nutritional status of the refugee population was reportedly poor, a need was felt to collect dependable data through epidemiological surveillance, on which interventions could be based. The nutritional and health status of children was dramatically poor in all camps surveyed and a deterioration was expected in the coming monsoon. Several problem areas could be identified. Based on these findings it was possible to undertake appropriate action and to avert threatening calamities. Epidemiological surveillance is an important monitoring tool to provide reliable data on the health and nutritional status of refugee populations and to help the organizations involved to prioritize and evaluate their actions.  相似文献   
994.
Many important groundwater aquifers cross state and national boundaries. The flow of water in these aquifers is not influenced by the boundaries but may be materially influenced by mans activities on one or both sides of a boundary. Interstate and international problems may develop because of excessive groundwater lowering on one side of a boundary affecting water users on the opposite side of the line. Similarly, intensive groundwater development along a surface stream may influence the amount of surface water that flows across a boundary. A third type of problem may develop when pumping on one side of the boundary induces poor quality water into an aquifer on the other side of the boundary. Several specific interstate and international aquifer problems are briefly described.  相似文献   
995.
ABSTRACT A methodology for predicting the spatial and temporal levels of conservative water quality constituents within a multibasin water resource system is presented. Dissolved solids, sulfates, and chlorides are the constituents used during this investigation; however, any other conservative ion or mineral can be incorporated into the simulation model. The methodology is tested on the proposed Texas Water System. The water quality model, QNET-I, utilizes monthly canal and river flows and reservoir storage levels calculated by the Texas Water Development Board's systems simulation model. Discharge-concentration relationships are developed for each source of water in the system, including significant waste-water discharges. Reservoirs in the system are assumed to be completely mixed with respect to conservative constituents. A mass balance analysis is performed for each node and each month during the simulation period. The output from the water quality simulation is a table of the concentrations of the conservative water quality constituents at each demand point in the system and in each reservoir and canal for every month the system is in operation. The desired quality of the water at the demand locations is used to determine the economic utility of transporting and mixing water from various sources.  相似文献   
996.
This paper serves as a literature review of manganese in fresh water. The major aspects of manganese occurrence discussed are: (1) sources, (2) geochemistry, (3) manganese-iron relationships, (4) effects on the fauna and flora and (5) detection.  相似文献   
997.
ABSTRACT
Three main issues are discussed: the demands for additional water stemming from population dispersion; supply alternatives to large-scale interbasin transfers; and the displacement of agriculture from nonprofit regions. It is concluded that population dispersion is unlikely to increase aggregate water demands; that large additional supplies are available from other sources at lesser costs; and that a very likely consequence of large-scale transfers will be the displacement of agriculture in other parts of the country.  相似文献   
998.
ABSTRACT. .Eighteen rural lakes in Lubbock County were sampled on a routine basis following runoff-producing rainfall for a period of approximately eighteen months to determine whether or not runoff from intensively farmed agricultural areas contained significant concentrations of nitrates, phosphates, herbicides, or insecticides. An additional fifteen lakes lying within a triangle bounded by the cities of Plainview, Canyon, and Hereford, Texas, were sampled one time during the summer of 1969 to provide additional data regarding the nature and extent of the potential problem in an area with a different soil type and a slightly different cropping pattern. Based on results of detailed analyses of approximately two hundred samples of water collected from the lakes and an equal number of sediment samples collected from the same lakes at the same time, it appears that the concentrations of all chemical pollutants in runoff from agricultural lands in the High Plains are well below the allowable concentrations for drinking water.  相似文献   
999.
ABSTRACT .Many growing municipalities near irrigated agriculture are advocating a transfer of water now utilized for irrigation to municipal use. Alternatives are presented whereby this water can be transferred to municipal use in exchange for treated sewage effluent. The irrigation water would in effect be cycled through the municipal system prior to use on the farms. A case study of the Tucson region illustrates the relevant legal, economic and technical aspects. Effluent could be delivered to irrigators in Avra Valley at a cost less than that now paid for water pumped from declining water tables. In return the City of Tucson could import ground water now being used for irrigation through an existing pipeline which presently cannot be used because of a court injunction obtained by the irrigators. It appears that such an exchange agreement could be made without modification of existing statutory law. Similar exchange arrangements may prove to be feasible in other regions containing irrigated agriculture. Increased efficiency of water use can be achieved avoiding external effects which commonly arise in a direct transfer and are difficult to evaluate. High quality water is allocated to municipal use whereas nutrient-rich sewage effluent is transferred to irrigation.  相似文献   
1000.
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