全文获取类型
收费全文 | 1035篇 |
免费 | 90篇 |
国内免费 | 144篇 |
专业分类
安全科学 | 52篇 |
废物处理 | 7篇 |
环保管理 | 255篇 |
综合类 | 475篇 |
基础理论 | 79篇 |
污染及防治 | 23篇 |
评价与监测 | 44篇 |
社会与环境 | 288篇 |
灾害及防治 | 46篇 |
出版年
2024年 | 6篇 |
2023年 | 12篇 |
2022年 | 32篇 |
2021年 | 45篇 |
2020年 | 24篇 |
2019年 | 30篇 |
2018年 | 36篇 |
2017年 | 47篇 |
2016年 | 44篇 |
2015年 | 51篇 |
2014年 | 31篇 |
2013年 | 75篇 |
2012年 | 72篇 |
2011年 | 89篇 |
2010年 | 56篇 |
2009年 | 55篇 |
2008年 | 47篇 |
2007年 | 62篇 |
2006年 | 57篇 |
2005年 | 35篇 |
2004年 | 48篇 |
2003年 | 36篇 |
2002年 | 34篇 |
2001年 | 18篇 |
2000年 | 37篇 |
1999年 | 31篇 |
1998年 | 11篇 |
1997年 | 19篇 |
1996年 | 18篇 |
1995年 | 15篇 |
1994年 | 22篇 |
1993年 | 10篇 |
1992年 | 7篇 |
1991年 | 3篇 |
1990年 | 6篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 5篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1980年 | 5篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1975年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 3篇 |
1971年 | 2篇 |
排序方式: 共有1269条查询结果,搜索用时 62 毫秒
621.
在强震区进行投资应注意的几个问题 总被引:2,自引:0,他引:2
在强震区进行投资时,除要考虑一般经济环境下的投资风险外,还要考虑特殊自然环境条件下的风险.区域的地震危险性、自然环境危害性和经济运行安全性都是在强震区投资活动中应综合考虑的因素,文中就如何控制强震区的投资风险提出了建议. 相似文献
622.
Sherman R. Ellis Gary W. Levings Lisa F. Carter Steven F. Richey Mary Jo Radell 《Journal of the American Water Resources Association》1993,29(4):617-646
ABSTRACT: The Rio Grande Valley National Water-Quality Assessment study unit encompasses about 45,700 square miles in Colorado, New Mexico, and Texas upstream from the gaging station Rio Grande at El Paso, Texas, and includes surface-water closed basins east of the Continental Divide in New Mexico, and the San Luis Closed Basin in Colorado. The mean annual precipitation ranges from less than 6 to more than 50 inches; potential evapo-transpiration ranges from less than 35 to more than 80 inches per year. Land use is mainly rangeland, forest land, and cropland. Total irrigated acreage in 1990 was about 914,000 acres and water use was about 3,410,000 acre-feet. Two structural settings are found in the study unit: alluvial basins and bedrock basins. The alluvial basins can have through-flowing surface water or be closed basins. The discussion of streamflow and water quality for the surface-water system is based on four river reaches for the 750 miles of the main stem. The quality of the ground water is affected by both natural process and human activities and by nonpoint and point sources. Nonpoint sources for surface water include agriculture, hydromodification, and mining operations; point sources are mainly discharge from wastewater treatment plants. Nonpoint sources for ground water include agriculture and septic tanks and cesspools; point sources include leaking underground storage tanks, unlined or manure-lined holding ponds used for disposal of dairy wastes, landfills, and mining operations. 相似文献
623.
Krishan P. Singh 《Journal of the American Water Resources Association》1990,26(6):901-911
ABSTRACT: In Illinois, a procedure has been developed to derive unit hydrographs for generating 100-year and probable maximum flood hydrographs, on the basis of 11 parameters that define the hydrograph shape very well. Regional regressions of these parameters with basin factors show very high correlation. Thus satisfactory values of parameters can be determined for ungaged areas or those with a few years' record. The nonlinearity in unit hydrographs derived from usual floods is largely attributed to mixing within-channel and overbank-flow flood events. To minimize the effects of nonlinearity and to derive unit hydrographa suitable for calculating spillway design floods, use of the proposed method of developing such hydrographs is recommended. 相似文献
624.
本文根据组合模式原理提出了一种用小震调制比(rm)异常区出现高频次的空间异常图,进行强地震中短期预报的方法,简称rs法。该方法在预报强震地点和时间上可望取得较好效果。本文在介绍该方法的基础上,应用该法对3次7级以上大震进行了回顾性检验。 相似文献
625.
The paper starts from an assessment of regional policy inspired by considerations of social justice. An effort is made to sketch the outline of a top‐down and bottom‐up approach and provide a new profile for regional planning, and for professional planners within the context of contemporary politico‐economic transformations. The planner, from having been a pure technician who does not question the nature of problems faced, must become actively engaged in, and committed to the problems and conflicts of the area, and to the specific proposals put forward. 相似文献
626.
SIMULATION OF REGIONAL GROUND WATER FLOW IN BEDROCK,SOUTHWESTERN NEW YORK-NORTHWESTERN PENNSYLVANIA1
ABSTRACT: This paper presents the results of steady-state three-dimensional computer simulations to determine the hydrogeologic setting of formation water in the hydrocarbon producing formations of southwestern New York and northwestern Pennsylvania. Recharge areas for the regional ground water flow systems in the study area are the Valley Heads Moraine and Allegheny uplands; discharge areas are Lakes Erie and Ontario to the north and the northern margin of the Appalachian basin to the south. Simulated ground water flow in all model layers moves north from the ground water divide on the Valley Heads Moraine towards Lake Erie at a rate from 10?-6 to 10?-3 ft/day. South of the divide intermediate-scale and local-scale flow systems occur in the upper 4000 feet of the stratigraphic section and the directions of ground water flow diverge towards major rivers and other topographically low areas. 相似文献
627.
Jamshid Sadeghipour John A. Dracup 《Journal of the American Water Resources Association》1985,21(3):481-487
This paper is concerned with regional frequency analysis of hydrologic multiyear droughts. A drought event is defined by three parameters: severity, duration, and magnitude. A method is proposed here to standardize drought severities with a duration adjustment to enable comparison among drought events. For purposes of a regional study, the index drought method is selected and applied to standardized droughts to give a regional frequency curve. However, the recurrence intervals of the drought events obtained from index drought method are limited to the historic period of record. Therefore, by taking advantage of random variations of droughts in both time and space, a multivariate simulation model is used to estimate exceedence probabilities associated with regional drought maxima. This method, named the regional extreme drought method, is capable of generating a series of drought events which, although they have not occurred historically, are more severe than historic events. By combining the results of the index drought method and regional extreme drought analysis, a regional drought probability graph is constructed which ranges from severe droughts to more frequent droughts. This procedure is applied to the mean annual flow records of streams located in the San Joaquin Valley of California, and drought-severity-frequency plots are prepared for 1-year, 2-year, and 3-year durations. 相似文献
628.
本文分析评价了温州市农业资源,农业开发条件与潜力,提出了农业区域开发的指导思想,总体目标与主要任务,确定了农业商品生产基地,划分了农业开发区,阐述了农业区域开发的对策与措施。 相似文献
629.
Thomas R. Harris Matthew L. Rea 《Journal of the American Water Resources Association》1984,20(2):193-201
ABSTRACT: Recent growth in irrigated agriculture and metropolitan areas of the Western United States suggests that if growth continues, there will be a potential shortage in future water resources. Compound the expansion of agriculture and municipal demands with possible enaction of instream flow requirements, a method to allocate water among alternative economic sectors in the West is needed. In this study, an interindustry-linear programming model based on the 1972 national model format is used to allocate scarce water supplies among competing regional economic sectors. The shadow price of water and the sectorial value of water at different availabilities for each competing sector is derived. Also, economic sectors are ranked by value of water at different water availabilities. 相似文献
630.
William J. Ashton M.B. Bayer 《Journal of the American Water Resources Association》1983,19(5):779-783
ABSTRACT As urban expansion outstrips water supplies, the usual solution is to build pipelines to bring in water from sources farther afield. Such water supplies may act as either a leader of urban development or as a follower. In either case, this engineering approach to the provision of water has fostered less than optimal utilization of regional water and land resources for urban growth. More efficient utilization of these resources is achieved when water supply development and urban growth planning are conjoint activities. Water supply planners and land use planners, working together, are able to generate and evaluate the full range of urban development options, including water demand management through conservation. Preferred regional growth plans are achieved using the best mix of water supply and urban growth. The result is a reduced rate of water supply development and a reduction of urban expansion on prime lands. This partnership approach is demonstrated for the Calgary Region under two levels of water conservation. 相似文献