全文获取类型
收费全文 | 14793篇 |
免费 | 1516篇 |
国内免费 | 3224篇 |
专业分类
安全科学 | 2000篇 |
废物处理 | 137篇 |
环保管理 | 2237篇 |
综合类 | 8930篇 |
基础理论 | 1897篇 |
环境理论 | 4篇 |
污染及防治 | 770篇 |
评价与监测 | 855篇 |
社会与环境 | 1960篇 |
灾害及防治 | 743篇 |
出版年
2024年 | 86篇 |
2023年 | 304篇 |
2022年 | 593篇 |
2021年 | 648篇 |
2020年 | 642篇 |
2019年 | 562篇 |
2018年 | 490篇 |
2017年 | 666篇 |
2016年 | 769篇 |
2015年 | 843篇 |
2014年 | 679篇 |
2013年 | 856篇 |
2012年 | 1186篇 |
2011年 | 1267篇 |
2010年 | 924篇 |
2009年 | 950篇 |
2008年 | 762篇 |
2007年 | 992篇 |
2006年 | 996篇 |
2005年 | 780篇 |
2004年 | 608篇 |
2003年 | 574篇 |
2002年 | 526篇 |
2001年 | 393篇 |
2000年 | 397篇 |
1999年 | 327篇 |
1998年 | 256篇 |
1997年 | 234篇 |
1996年 | 200篇 |
1995年 | 177篇 |
1994年 | 162篇 |
1993年 | 128篇 |
1992年 | 103篇 |
1991年 | 71篇 |
1990年 | 57篇 |
1989年 | 37篇 |
1988年 | 40篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 26篇 |
1978年 | 17篇 |
1973年 | 8篇 |
1972年 | 8篇 |
1971年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
951.
减灾效益的获得离不开民众的参与,而其参与意识又与减灾效益的可见度有关。减灾效益越能迅速、明确地被人们见到或预见到,人们的减灾参与意识越高。在客观现实中,减灾效益的显现时间具有各种类型,而人们主观意识中“见”到的类型却又可能有质的差异。本文划分了减灾效益的显现类型并提出与论述了与其有关的一些问题,分析了其与主观意识之间的复杂关系,以及影响人们的减灾参与心理的作用机制。进而探讨了如何通过这些关系、机制的认识与把握,效益意识引导,对减灾见效时间意识的人为控制等途径提高民众的减灾参与意识与减灾效益。 相似文献
952.
Martha W. Gilliland Lee Becker Ralph Cady Joe Gabig James Gilley Richard A. Kern Arley Larson Quang M. Nguyen William Powers Raymond Supalla 《Journal of the American Water Resources Association》1985,21(2):281-290
Substantial conflict exists over water management and allocation in the Platte River Basin of Nebraska. An interdisciplinary computer simulation model, representing the water quantity, water quality, environmental, and economic dimensions of the conflict, was developed in order to analyze the tradeoffs among allocation scenarios. Most importantly, decisionmakers and interest groups were involved in model development. Simulation results for a base case and two scenarios are presented. One scenario favors protection of instream flow for wildlife; the other favors water diversions for agriculture. Impacts of the instream flow scenario, as measured by the amount of land irrigated, groundwater levels, the amount of wildlife habitat for cranes and catfish, and net agricultural benefits did not differ greatly from those of the base case. However, impacts of the diversion scenario were substantial. On the negative side, instream flows and wildlife habitat declined an average of 39 percent; while, on the positive side, groundwater levels and net agricultural benefits each increased 6 percent. The modeling process was successful insofar as it promoted an understanding among the highly diverse interest groups of the systems nature of the Basin. One agreement on a water diversion schedule among three of the parties has been reached, partly as a result of this process. More comprehensive compromises have not yet been forged. Our experience, however, indicates that modeling success at the policymaking level depends more on the extent to which the policymakers understand the model than it does on model sophistication. 相似文献
953.
Levees and floodwalls are used extensively throughout the United States for flood control. Levee projects often lack ecological, recreational, and aesthetic values, except for incidental fish and wildlife benefits derived from borrow pits and recreational facilities found in some urban settings. In recent years increased environmental concern within construction agencies and greater responsiveness to public opinion have resulted in increasing numbers of levee projects designed, built, and maintained with environmental objectives in mind. This paper reviews environmental concepts successfully employed on levee projects constructed in recent years by the US Army Corps of Engineers. Some of the most innovative concepts are described and illustrated and design considerations are discussed. 相似文献
954.
ABSTRACT: A method is presented for determining low discharge periods of rivers based on threshold values defined in terms of MEAN OF MINIMUM SUMMER (WINTER) DISCHARGES. The method is used to determine summer low flow periods in the Vistula River basin in Poland. Analysis is based on daily discharge data for 84 basins of the Upper Vistula River which was collected by the Polish Institute of Meteorology and Water Economy. 相似文献
955.
Richard L. Cooley Aldo V. Vecchia 《Journal of the American Water Resources Association》1987,23(4):581-599
ABSTRACT: A method is derived to efficiently compute nonlinear confidence and prediction intervals on any function of parameters derived as output from a mathematical model of a physical system. The method is applied to the problem of obtaining confidence and prediction intervals for manually-calibrated ground-water flow models. To obtain confidence and prediction intervals resulting from uncertainties in parameters, the calibrated model and information on extreme ranges and ordering of the model parameters within one or more independent groups are required. If random errors in the dependent variable are present in addition to uncertainties in parameters, then calculation of prediction intervals also requires information on the extreme range of error expected. A simple Monte Carlo method is used to compute the quantiles necessary to establish probability levels for the confidence and prediction intervals. Application of the method to a hypothetical example showed that includsion of random errors in the dependent variable in addition to uncertainties in parameters can considerably widen the prediction intervals. 相似文献
956.
Daniel H. Hoggan John C. Peters Werner Loehlein 《Journal of the American Water Resources Association》1987,23(6):1141-1147
ABSTRACT: The Pittsburgh District, U.S. Army Corps of Engineers, is responsible for operating two multipurpose reservoirs in the 7384 square mile (19198 square kilometer) Monongahela Basin. A third reservoir, presently under construction, will soon be operating. The real-time forecasting of runoff for operational purposes requires simulation of snow accumulation and snowmelt throughout the Basin during the winter season. This article describes capabilities of SNOSIM, a model being developed for performing such simulation. The application of this model as part of a comprehensive system of water control software, and some initial simulation results are presented. 相似文献
957.
Rochelle L. Rittmaster David K. Mueller 《Journal of the American Water Resources Association》1986,22(1):81-89
ABSTRACT: A study was performed to identify sources of solute loading to the Dirty Devil River and its major tributaries, in southeastern Utah. A primary goal was to determine the contribution of gypsum dissolution to total dissolved solids concentration, and its potential increase in the future if salinity control measures are instituted. Synoptic field data were collected during the low flow period in October 1983. Data were analyzed using the geochemistry models WATEQF and BALANCE to postulate mineral reactions leading to solute loading. Three known sources of solute loading, involving two different geochemical mechanisms, were clearly discernable. Two additional areas of possible gypsum dissolution were located. 相似文献
958.
ABSTRACT: Although evidence of modern recharge in the North African and Arabian sedimentary basin aquifers exists, it is difficult to determine the volume of recharge. Also, from the evidence of regional groundwater gradients, the flow within the aquifers seems to be appreciably greater than one would intuitively expect. A hypotehtical model embodying the characteristics of the aquifers has been used to investigate the likely significance of various possible flow mechanisms. It is shown that while dewatering in the unconfined area can possibly contribute to flows for a considerable period of time, the maintenance of water levels in the unconfined zone must be the result of modern recharge. It is also shown that recharge depths of less than 10 mm per annum are sufficient given suitable aquifer parameters. Results for various combinations of aquifer parameters and configurations are given, including layered aquifers and the effects of restricted oufflows. Comparisons are made using a “bench mark” example. The work indicates that there is little point in carrying out conventional hydrological balance studies in hyper-arid areas and that, instead, more emphasis should be placed upon good groundwater hydrographic data and modeling. 相似文献
959.
Robert G. Bailey 《Environmental management》1988,12(1):11-17
As part of the planning process, maps of natural factors are often superimposed in order to identify areas which are suitable or unsuitable for a particular type of resource management. Overlay maps may also be used to identify analysis areas for predictive modeling of resource productivity and ecological response to management. Current interest in applying computer-assisted mapping technology to making overlay maps is drawing attention to geographic information systems for this purpose. The resultant maps, however, may be so inaccurate or unable to capture significant units of productivity and ecological response that they could lead to imperfect or false conclusions. Recommendations are made on how to proceed in light of these problems. 相似文献
960.
John E. Keith Rangesan Narayanan 《Journal of the American Water Resources Association》1988,24(6):1247-1256
ABSTRACF: Examination of a series of studies of the economically efficient water allocations in the Upper Colorado River, Yellowstone River, and Great Basins indicate that water is not a serious general physical constraint on the development of energy resources, so long as public institutions do not hinder the exchange of water rights in markets. Energy development will cause limited impacts on other water-using sectors, principally agriculture. There appears to be little reason to develop large-scale water storage facilities, even during periods of reduced water production. Water storage developments appear to be necessary only when institutional constraints severely restrict water rights markets and transfers. 相似文献