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   591篇
  免费   32篇
  国内免费   39篇
安全科学   40篇
废物处理   31篇
环保管理   130篇
综合类   93篇
基础理论   166篇
环境理论   2篇
污染及防治   129篇
评价与监测   47篇
社会与环境   19篇
灾害及防治   5篇
  2023年   9篇
  2022年   5篇
  2021年   15篇
  2020年   11篇
  2019年   19篇
  2018年   26篇
  2017年   25篇
  2016年   42篇
  2015年   35篇
  2014年   32篇
  2013年   39篇
  2012年   28篇
  2011年   46篇
  2010年   37篇
  2009年   35篇
  2008年   41篇
  2007年   32篇
  2006年   18篇
  2005年   15篇
  2004年   18篇
  2003年   19篇
  2002年   19篇
  2001年   4篇
  2000年   8篇
  1999年   1篇
  1998年   3篇
  1997年   13篇
  1996年   15篇
  1995年   8篇
  1994年   5篇
  1993年   5篇
  1992年   9篇
  1991年   5篇
  1990年   3篇
  1989年   2篇
  1988年   2篇
  1987年   3篇
  1985年   2篇
  1984年   1篇
  1982年   2篇
  1981年   2篇
  1979年   1篇
  1978年   2篇
排序方式: 共有662条查询结果,搜索用时 15 毫秒
41.
42.
43.
This paper develops a methodology for integrating a land-use forecasting model with an event scale, rainfall-runoff model in support of improving land-use policy formulation at the watershed scale. The models selected for integration are loosely coupled, structured upon a common GIS platform that facilitates data exchange. The hydrologic model HEC-HMS is calibrated for a specific storm event that occurred within central Washington State. The land-use forecasting model, What If? is implemented to forecast future spatial distributions of low-density residential land-uses under low and high population growth estimates. Forecasted land-use distribution patterns for the years 2015, 2025, and 2050 are then used as land-use data input for the calibrated hydrologic model, keeping all other parameters constant. Impacts to the stream discharge hydrograph are predicted as the study area becomes increasingly developed as forecasted by What If?. The initial results of this integration process demonstrate the synergy that can be generated through the linkage of the selected models. The ability to quantifiably forecast the potential hydrologic implications of proposed land-use policies before their implementation offers land-use decision-makers a valuable tool for discerning which proposed land-use alternatives will be effective at minimizing storm water runoff.  相似文献   
44.
Multiple paternity was recently observed in a population of the brown smoothhound shark, Mustelus henlei, from Las Barrancas, Baja California Sur, Mexico, with litters demonstrating the greatest percentage of multiple paternity for any shark species (93 % of litters and an average number of sires = 2.3). To determine whether this frequency is consistent elsewhere in the species’ range, 4 polymorphic microsatellite loci were used to determine the frequency of multiple paternity in 18 litters of M. henlei from Santa Catalina Island, CA, sampled in 2004, 2008, and 2012. Multiple paternity varied among sampling years with 2004 demonstrating multiple sires for 40 % of sampled litters (n = 10) with an average of 1.4 sires per litter and 2008/2012 demonstrating a total lack of multiply sired litters (n = 8). Although multiple paternity was detected in this study, the range of frequencies observed is lower than that observed in the Mexican population. Based on these findings, investigators should take location into consideration when assessing the existence of multiple paternity in future studies of elasmobranch species.  相似文献   
45.
Organic aerosol is the least understood component of ambient fine particulate matter (PM2.5). In this study, organic and elemental carbon (OC and EC) within ambient PM2.5 over a three-year period at a forested site in the North Carolina Piedmont are presented. EC exhibited significant weekday/weekend effects and less significant seasonal effects, in contrast to OC, which showed strong seasonal differences and smaller weekend/weekday effects. Summer OC concentrations are about twice as high as winter concentrations, while EC was somewhat higher in the winter. OC was highly correlated with EC during cool periods when both were controlled by primary combustion sources. This correlation decreased with increasing temperature, reflecting higher contributions from secondary organic aerosol, likely of biogenic origin. PM2.5 radiocarbon data from the site confirms that a large fraction of the carbon in PM2.5 is indeed of biogenic origin, since modern (non-fossil fuel derived) carbon accounted for 80% of the PM2.5 carbon over the course of a year. OC and EC exhibited distinct diurnal profiles, with summertime OC peaking in late evening and declining until midday. During winter, OC peaked during the early morning hours and again declined until midday. Summertime EC peaked during late morning hours except on weekends. Wintertime EC often peaked in late PM or early AM hours due to local residential wood combustion emissions. The highest short term peaks in OC and EC were associated with wildfire events. These data corroborate recent source apportionment studies conducted within 20 km of our site, where oxidation products of isoprene, α-pinene, and β-caryophyllene were identified as important precursors to organic aerosols. A large fraction of the carbon in rural southeastern ambient PM2.5 appears to be of biogenic origin, which is probably difficult to reduce by anthropogenic controls.  相似文献   
46.
47.
Objectives To validate the use of Real Time PCR, a widely used technique that can detect very low levels of Y chromosomal sequence, and to assess the use of a highly sensitive PCR technique, pyrophosphorolysis-activated polymerisation (PAP), for fetal sex determination using free fetal DNA (ffDNA). Methods The fetal sex was determined by Real Time PCR in 58 pregnancies using ffDNA isolated from maternal plasma. In parallel with the Real Time PCR experiments, the presence of Y chromosome sequence was also determined using PAP on 54 isolated ffDNA samples. Results Both techniques detected Y chromosome sequence at very low levels with 98% specificity and 100% sensitivity (Real Time n = 44, PAP n = 54). Furthermore, the PAP technique was shown to be more robust than the Real Time PCR as none of the samples tested failed to meet the acceptance criteria. Combining the two techniques for male fetal sex detection from maternal blood plasma increases the sensitivity and specificity to 100% in this series. Conclusions This study shows that both Real Time PCR and PAP can be used for Y chromosome detection on ffDNA. Furthermore, by using PAP in combination with Real Time PCR more reliable early prenatal sexing can be performed using ffDNA. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
48.
Over the last decade, New Zealand has implemented innovative reforms in respect of natural resource and environmental management. These include the Resource ManagementAct 1991 (RMA), a notable feature of which is the adoption of 'sustainable management' as the key principle guiding resource allocation and use. This and other features of the new administrative context for resource management strongly suggest a prominent role for geographicinformation systems (GIS) and related spatial information technology. In this paper we present an outline of the Regional Resource Evaluation Project (RREP), a project that has been established to explore and demonstrate the capabilities of GIS and related spatial information technology in the context of resource analysis and decision making. To date, the RREP has achieved important outcomes in terms of database design and development. An extensive information base which incorporates data on the physical and natural environment, patterns of human activity, and on social and demographic characteristics has been assembled. We describe the information systems, as well as some of the technical issues that attend to database design and development.We also provide brief reviews of two applications of the GIS to resource evaluation. One relates to the evaluation of changes in regional land use, with a focus on natural habitats. The other is concerned with land suitability assessment for plantation forestry.  相似文献   
49.
The field of engineering is changing rapidly as the growing global population puts added demands on the earth's resources: engineering decisions must now account for limitations in materials and energy as well as the need to reduce discharges of wastes. This means educators must revise courses and curricula so engineering graduates are prepared for the new challenges as practicing engineers. The Center for Sustainable Engineering has been established to help faculty members accommodate such changes through workshops and new educational materials, including a free access website with peer-reviewed materials.  相似文献   
50.
This article is excerpted from Chapter 1 of Environmental Management Information Systems, which will be published by McGraw-Hill in 1994. A central theme of the book is that all successful implementations of environmental management information systems (EMIS) are based on the appropriate alignment of goals and procedures from three enterprise domains: business processes, environmental management, and information systems. Environmental managers (EM) and information systems (IS) professionals have each been guilty of seeing their functions as primary, domains of specialized scientific expertise inaccessible to outsiders. In fact, however, the enterprise is the customer for both domains; without successful business strategies and systems the enterprise does not require either EM or IS wizards. This article shows why and how essential it is that each of the three domains understands enough of the other two domains to structure good decisions.  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