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   16460篇
  免费   205篇
  国内免费   140篇
安全科学   479篇
废物处理   611篇
环保管理   2329篇
综合类   3134篇
基础理论   4122篇
环境理论   10篇
污染及防治   4040篇
评价与监测   1002篇
社会与环境   950篇
灾害及防治   128篇
  2022年   123篇
  2021年   132篇
  2020年   112篇
  2019年   143篇
  2018年   203篇
  2017年   248篇
  2016年   342篇
  2015年   291篇
  2014年   378篇
  2013年   1401篇
  2012年   492篇
  2011年   656篇
  2010年   533篇
  2009年   595篇
  2008年   654篇
  2007年   686篇
  2006年   656篇
  2005年   518篇
  2004年   504篇
  2003年   519篇
  2002年   449篇
  2001年   555篇
  2000年   435篇
  1999年   256篇
  1998年   212篇
  1997年   195篇
  1996年   223篇
  1995年   225篇
  1994年   220篇
  1993年   212篇
  1992年   219篇
  1991年   209篇
  1990年   208篇
  1989年   181篇
  1988年   156篇
  1987年   135篇
  1986年   160篇
  1985年   161篇
  1984年   167篇
  1983年   166篇
  1982年   163篇
  1981年   167篇
  1980年   158篇
  1979年   151篇
  1978年   112篇
  1977年   124篇
  1974年   111篇
  1973年   93篇
  1972年   108篇
  1971年   88篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
ABSTRACT: Faced with the necessity of meeting growing municipal water requirements in areas where available supplies are completely allocated, numerous cities throughout the West are turning to their eminent domain powers to affect a reallocation of water from less preferred uses to municipal uses, thus bringing about a sharp conflict with agricultural interests. As a basis for discussing these eminent domain powers, this paper begins with a brief review of the development of property rights. The existence of both private and public (social) rights in the “bundle of rights” is noted. In recent years the Public Trust Doctrine has been used to limit private rights in property, and to protect and strengthen social rights. A case study which focuses on a conflict between individual and social interests in water rights is discussed. This case involves the City of Thorton, Colorado which initiated municipal condemnation proceedings to acquire the water rights and structures of two nearby irrigation companies. The case represents an attempt to incorporate the spirit of the Public Trust Doctrine into legislation which sets forth procedures for resolution of similar water rights conflicts that will inevitably become more numerous throughout the West in the future.  相似文献   
982.
ABSTRACT: Artificial and natural marshes were studied to determine changes in quality of polluted water passing through them. Phosphorus removal ranged from zero to 64%. Removals in the 35% range were common, however. Much of the phosphorus went into sediments and unharvestable plant parts. Harvesting vegetation removed 6% of the phosphorus put into the system. Accumulation of phosphorus during the growing season was about 20 g*m?2, much of which was flushed out after the onset of freezing weather. The amount of phosphorus flushed out can be prevented from entering a lake or stream by handling the marsh discharge in one of three ways; irrigate on land, lagoon to recycle later, treat conventionally if facilities are available.  相似文献   
983.
ABSTRACT: Data were developed within a three-year period for indicator bacteria and three species of bacterial pathogens following rural storm event hydrographs. The first flush concept was confirmed in all hydrographs. Bacterial density peaking occurred at or before the hydrograph peaks. FC and FS values were higher in more developed areas than the primary rural test site and their numerical ratios followed similar trends. Chlorine demand of storm waters varied between 8 and 16 mg/l and, the ozone requirement was greater than 32 mg/l in the same waters. Aftergrowth of total coliform bacteria occurred following chlorine and ozone doses of 16 mg/l and 32 mg/l respectively. Fecal coliform, fecal streptococci, Salmonella sp., and Pseudomonas sp. all were reduced to near detectable limits by the disinfectants up to 8 days. Staphylococcus sp. demonstrated a propensity to restablish their populations. Multiple regression analysis of the bacterial groups and species in storm waters suggested the fecal streptococci to have been the most useful group in evaluating bacterial storm water quality, with staphylocci have been closely related insofar as their statistical significance was concerned.  相似文献   
984.
ABSTRACT: Alum treatment of a shallow lake, with mean depth 2 m and area 137 ha, curtailed internal loading of P for at least one ear. Mean summer total P and chl a decreased from 76 and 27μg l?1, respectively, in 1978 before treatment. to 29 and 14 μ l?1, while mean summer Sed transparency increased from 1.6 to 2.2 m and blue green algae were no longer dominant. Macrophyte biomass and distribution retuned during the post-alum year, 1980-1981, to previous levels after a 1979 four-month lake level drawdown had reduced biomass by 84 percent The improved transparency, resulting from the decrease in chl a following treatment, could encourage greater biomass of macrophytes in the deeper area of the lake. Recovery of macrophyte biomass to predrawdown levels may restore internal loading of P through enrichment of deep water sediments during winter dieback and decomposition.  相似文献   
985.
ABSTRACT: Data splitting is used to compare methods of determining “homogeneous” hydrologic regions. The methods compared use cluster analysis based on similarity of hydrologic characteristics or similarity of characteristics of a stream's drainage basin. Data for 221 stations in Arizona are used to show that the methods, which are a modification of DeCoursey's scheme for defining regions, improve the fit of estimation data to the model, but that is is necessary to have an independent measure of predictive accuracy, such as that provided by data splitting, to demonstrate improved predictive accuracy. The methods used the complete linkage algorithm for cluster analysis and computed weighted average estimates of hydrologic characteristics at ungaged sites.  相似文献   
986.
987.
ABSTRACT: Water resource development has progressed to the stage where various human factors are now being considered in reservoir design and operation. The introduction of human factor objectives complicates the problem since they are noncommensurate with other objectives and they are difficult to identify quantitatively. Some of the problems that now arise concern the proper methods for consideration of several different, sometimes subjectively identified, objectives in reservoir planning. The classical systems analysis approach to decision making for multiple objective problems is outlined and the inherent difficulties associated with multiple objectives and subjective estimates are identified. Techniques being used in reservoir design and operation are reviewed and discussed. An alternate technique for considering noncommensurate, subjectively identified, objectives, which relates the objectives in terms of real trade-off costs and eliminates the need for a priori estimates of objective worth is then presented. The method is illustrated with three examples, including a reservoir operation problem and a cooling tower design problem.  相似文献   
988.
A set of simulation and optimization tools capable of analyzing the development and operation of a complex, multi-basin, interconnected water resource are explained. These models provide valuable information regarding the important questions: (1) “When should new projects be build?” (2) “How big should they be?” and (3) “How should the system be operated?” Since these tools were developed by and for practicing engineers, their applicability to real-world problems is mandatory. To assure this, testing was done on an actual proposed project, the Texas Water System.  相似文献   
989.
Life cycle inventory (LCI) is becoming more widely used as a tool to evaluate the resource and energy use and the environmental releases associated with various products. The methodology for handling different recycling scenarios is also becoming increasingly important. Several different methods exist for handling recycling in an LCI. The method described in this paper uses mathematical models to show that the same basic equations can be used to handle a variety of recycling options for multi-product systems.  相似文献   
990.
ABSTRACT: We investigated spatial and temporal relationships among surface and subsurface watershed attributes and stream nutrient concentrations in urbanizing Johnson Creek watershed in northern Oregon. We sampled stream water at eight urban and five nonurban locations from March 1998 through December 1999. We sampled eight wells distributed over the two primary aquifers in the watershed. Using a Geographic Information System (GIS), percentages of landuse attributes within a radius of 30, 91, and 152 m from each sample site were quantified. We analyzed relationships between (1) nutrient concentrations and percentage cover of different landuse attributes, and (2) nutrient concentrations and underlying hydrologic units. We did not find a significant relationship between ground water chemistry and stream water chemistry. We found elevated levels of phosphorus (P) concentrations correlated with urban landuse, while higher nitrogen (N) concentrations were correlated with nonurban (primarily agricultural) landuse. We concluded that elevated levels of N in nonurban areas of Johnson Creek watershed were associated with agricultural practices. We further concluded that urban development factors such as increases in storm drains, dry wells, and impermeable surfaces may be responsible for higher input of P to the stream in urbanizing areas of the Johnson Creek watershed.  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