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   2959篇
  免费   80篇
  国内免费   28篇
安全科学   140篇
废物处理   123篇
环保管理   883篇
综合类   290篇
基础理论   690篇
环境理论   1篇
污染及防治   641篇
评价与监测   175篇
社会与环境   88篇
灾害及防治   36篇
  2023年   15篇
  2022年   20篇
  2021年   31篇
  2020年   20篇
  2019年   36篇
  2018年   55篇
  2017年   51篇
  2016年   70篇
  2015年   62篇
  2014年   64篇
  2013年   308篇
  2012年   118篇
  2011年   157篇
  2010年   117篇
  2009年   128篇
  2008年   166篇
  2007年   155篇
  2006年   138篇
  2005年   102篇
  2004年   91篇
  2003年   109篇
  2002年   99篇
  2001年   63篇
  2000年   53篇
  1999年   26篇
  1998年   46篇
  1997年   35篇
  1996年   49篇
  1995年   52篇
  1994年   39篇
  1993年   48篇
  1992年   39篇
  1991年   25篇
  1990年   27篇
  1989年   22篇
  1988年   26篇
  1987年   19篇
  1986年   20篇
  1985年   30篇
  1984年   24篇
  1983年   26篇
  1982年   39篇
  1981年   37篇
  1980年   32篇
  1979年   21篇
  1978年   25篇
  1977年   12篇
  1976年   9篇
  1974年   7篇
  1972年   9篇
排序方式: 共有3067条查询结果,搜索用时 31 毫秒
101.
ABSTRACT: Export coefficients (kg/km2/yr) for dissolved ortho-phosphate (OP), total phosphorus (TP), total inorganic nitrogen (TIN), and total nitrogen (TN) were derived for watersheds in Wisconsin using data bases available for 17 basins from the U.S. Environmental Protection Agency — National Eutrophication Survey, U.S. Geological Survey, and the Wisconsin Department of Natural Resources. Three general land use categories, representative of most regions in Wisconsin, were established: forest, mixed, and agricultural. Data for the 17 basins indicated greater exports of OP. TP, TIN, and TN as the percentage of forest decreased and agriculture increased. These region-specific coefficients are compared to the values reported in the literature representing much broader areas of the U.S.  相似文献   
102.
Indonesia is a major exporter of tropical hardwoods. The country's goal is to establish integrated wood industries by reducing the export of unprocessed sawlogs. The value of hardwood sawlog exports has decreased by twothirds in 1986 dollars since 1978, while the value of hardwood sawnwood and plywood exports has increased sixfold. Sawlog exports are now banned. This article contrasts the official governmental policy on forest industry development with the operational realities of doing business in Indonesia.  相似文献   
103.
An important goal of the Reagan administration has been to shift responsibility for many public programs from the US federal government to the states. This New Federalism seeks to restore a proper balance to the federal system and to ensure an effective working partnership between the states and the federal government. Such a partnership is especially important for many environmental laws because these laws often give states primary responsibility for the control and abatement of pollution.This research examines the extent to which the Reagan administration has succeeded in improving intergovernmental environmental relations in terms of state implementation of the Clean Water Act. Data from a 1985 survey of directors of state water quality control programs are compared with responses to a similar survey that the US General Accounting Office conducted in 1979. The latter survey found considerable dissatisfaction on the part of state directors with the quality of their relations with the US Environmental Protection Agency. Although some improvement can be noted between 1979 and 1985, the Reagan administration's efforts to improve intergovernmental relations appear to have been of limited consequence, to the possible detriment of effective implementation of the Clean Water Act.  相似文献   
104.
Food habits of white-tailed deer (Odocoileus virginianus) were examined from January to November 1984 via fecal-pellet analysis at Valley Forge National Historical Park (VFNHP), which represents an island habitat for deer surrounded by extensive urbanization, in southeastern Pennsylvania. In addition, use of fields by deer was compared to food habits. Herbaceous vegetation (forbs, leaves of woody plants, and conifer needles) was the predominant food type in all seasons except fall. Acorns and graminoids (grasses and sedges) were important food resources in fall and spring, respectively. Use of woody browse (twigs) was similar among seasons. Field use was relatively high during fall, winter without snow cover (<20 cm), and spring when food resources in fields were readily available. In contrast, use of fields was lowest in summer when preferred woodland foods were available and in winter with snow cover when food in fields was not readily accessible. Patterns of food-type use by deer at VFNHP indicate the year-round importance of nonwoody foods and field habitats to deer populations on public lands such as national parks in the northeastern United States.  相似文献   
105.
106.
ABSTRACT: Survey data collected in the San Joaquin Valley of southern California and the Grand Valley of western Colorado reveal that residents of both areas believe that a severe sustained drought is likely to occur within the next 20–25 years and that their communities would be seriously impacted by such an event. Although a severe sustained drought affecting the Colorado River Basin would cause major economic and social disruptions in these and other communities, residents express little support for water management alternatives that would require significant shifts in economic development activities or in water use and allocation patterns. In particular, residents of these areas express little support for strategies such as construction and growth moratoriums, mandatory water conservation programs, water transfers from low-to high-population areas, water marketing, or reallocations of water from agricultural to municipal/industrial uses. This rejection of water management strategies that would require a departure from “business as usual” with respect to water use and allocations severely restricts the capacity of these and similar communities to respond effectively should a severe sustained drought occur.  相似文献   
107.
ABSTRACT: Historically ephemeral washes in the Las Vegas Valley have become perennial streams in the urbanized area, and the primary source of these perennial flows appears to be the overirrigation of ornamental landscaping and turf. Overirrigation produces direct runoff to the washes via the streets and results in high ground water levels in some areas. Elevated ground water levels result in discharge to the washes because of changes in the natural balance of the hydrologic system and construction site and foundation dewatering. In recognition of the resource potential of these flows within the Las Vegas Valley, of the potential for dry weather flows to convey pollutants from the Valley to Lake Mead, and of the need to characterize dry weather flows under the stormwater discharge permit program, the quantity and quality of dry weather flow in Flamingo Wash was investigated during the period September 1990 through May 1993. This paper focuses on the resource potential of the flow (quantity and quality) as it relates to the interception and use of this water within the Valley. Economic and legal issues associated with the interception and use of this resource are not considered here.  相似文献   
108.
109.
ABSTRACT The use of satellite telemetry is playing a major role in the collection of hydrologic data. Advancing technology and availability of government satellites have permitted many agencies to take advantage of new procedures for acquiring data from automated remote data collection stations. Experiments with Earth satellite technology started in the 1960's and 1970's, with the polar-orbiting National Aeronautics and Space Administration Nimbus and Landsat satellites. Subsequent advancements took place through the development phase to operational systems using the Geostationary Operational Environmental Satellite (GOES) of the National Oceanic and Atmospheric Administration. This satellite system supports more than 2,500 active telemetry sites, of which approximately 1,200 are Geological Survey stream-gaging stations for the collection of hydrologic data. A satellite data collection system is made up of three primary components; a small battery-operated radio, and Earth-orbiting satellite, and an Earth receive and data processing station. The data relay satellites' vast aerial view of the Earth's surface gives satellite telemetry a large advantage over ground-based systems for the collection of real-time hydrologic data for flood warning, reservoir management, irrigation water control, hydropower generation, and the operation of hydrologic stations.  相似文献   
110.
ABSTRACT: Heat pulse velocity techniques were developed for effective monitoring of water movement in aspen (Populus tremuloides), subalpine fir (Abies lasiocarpa), and Englemann spruce (Picea engelmannif). Water loss was monitored in replicated trees of each species for one year. These data were used to modify the plant activity index (a reflection of the ability of plants to transpire water at various times during a year) and the crop coefficient (a reflection of differences in consumptive use rates of water by different vegetation types when all other factors are held constant) for each species within the model ASPCON, a deterministic, lumped-parameter model describing the hydrology of aspen to conifer succession. Results of the modeling in dicate 18.6 cm net loss of moisture available for streamflow when spruce replaced aspen, and a loss of 7.2 cm when fir forests replaced aspen. The aspen to conifer successional trend appears, therefore, to be significantly reducing water yields in the western United States.  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