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   21275篇
  免费   1568篇
  国内免费   3522篇
安全科学   2649篇
废物处理   199篇
环保管理   3479篇
综合类   11873篇
基础理论   2262篇
环境理论   14篇
污染及防治   1182篇
评价与监测   1285篇
社会与环境   2286篇
灾害及防治   1136篇
  2024年   70篇
  2023年   229篇
  2022年   501篇
  2021年   631篇
  2020年   601篇
  2019年   552篇
  2018年   485篇
  2017年   691篇
  2016年   855篇
  2015年   940篇
  2014年   909篇
  2013年   1225篇
  2012年   1574篇
  2011年   1663篇
  2010年   1234篇
  2009年   1180篇
  2008年   977篇
  2007年   1421篇
  2006年   1499篇
  2005年   1217篇
  2004年   1013篇
  2003年   1112篇
  2002年   902篇
  2001年   727篇
  2000年   689篇
  1999年   648篇
  1998年   469篇
  1997年   399篇
  1996年   319篇
  1995年   278篇
  1994年   279篇
  1993年   238篇
  1992年   192篇
  1991年   139篇
  1990年   96篇
  1989年   64篇
  1988年   50篇
  1987年   31篇
  1986年   22篇
  1985年   32篇
  1984年   25篇
  1983年   26篇
  1982年   20篇
  1981年   20篇
  1980年   18篇
  1979年   20篇
  1977年   18篇
  1974年   13篇
  1973年   12篇
  1971年   12篇
排序方式: 共有10000条查询结果,搜索用时 421 毫秒
101.
The Chesapeake Bay benthic index of biotic integrity (B-IBI) was developed to assess benthic community health and environmental quality in Chesapeake Bay. The B-IBI provides Chesapeake Bay monitoring programs with a uniform tool with which to characterize bay-wide benthic community condition and assess the health of the Bay. A probability-based design permits unbiased annual estimates of areal degradation within the Chesapeake Bay and its tributaries with quantifiable precision. However, of greatest interest to managers is the identification of problem areas most in need of restoration. Here we apply the B-IBI to benthic data collected in the Bay since 1994 to assess benthic community degradation by Chesapeake Bay Program segment and water depth. We used a new B-IBI classification system that improves the reliability of the estimates of degradation. Estimates were produced for 67 Chesapeake Bay Program segments. Greatest degradation was found in areas that are known to experience hypoxia or show toxic contamination, such as the mesohaline portion of the Potomac River, the Patapsco River, and the Maryland mainstem. Logistic regression models revealed increased probability of degraded benthos with depth for the lower Potomac River, Patapsco River, Nanticoke River, lower York River, and the Maryland mainstem. Our assessment of degradation by segment and water depth provided greater resolution of relative condition than previously available, and helped define the extent of degradation in Chesapeake Bay.  相似文献   
102.
Selecting Socio-Economic Metrics for Watershed Management   总被引:1,自引:0,他引:1  
The selection of social and economic metrics to document baseline conditions and analyze the dynamic relationships between ecosystems and human communities are important decisions for scientists, managers, and watershed citizens. A large variety of social and economic data is available but these have limited use without theoretical frameworks. In this paper, several frameworks for reviewing social-ecosystem relations are offered, namely social sanctions, sense of place, civic structure, and cultural differences. Underlying all of these frameworks are attitudes, beliefs, values, and norms that affect which questions are asked and which indicators are chosen. Much work and significant challenges remain in developing a standard set of spatially based socio-economic metrics for watershed management.  相似文献   
103.
固定化微生物处理有机污染物的研究进展   总被引:4,自引:0,他引:4  
胡燕荣  于雪峰 《干旱环境监测》2002,16(4):195-196,F004
综述了近年来固定化微生物技术用于有机污染物治理中的最新进展,这些有机污染物包括难降解有机污染物(酚类、芳香烃类等)及其它化合物(DMP、甲硫醇恶臭气体、制药废水等)。此外,对藻类固定化技术作了简介,并对固定化技术的应用前景及存在问题进行了评述。  相似文献   
104.
The goal of this study was to identify the relative toxicity ofambient areas in the Chesapeake Bay watershed by using a suiteof concurrent water column and sediment toxicity tests at seventy-five ambient stations in 20 Chesapeake Bay rivers from1990 through 1999. Spatial and temporal variability was examinedat selected locations throughout the 10 yr study. Inorganicand organic contaminants were evaluated in ambient water andsediment concurrently with water column and sediment tests toassess possible causes of toxicity although absolute causalitycan not be established. Multivariate statistical analysis wasused to develop a multiple endpoint toxicity index (TOX-INDEX) at each station for both water column and sediment toxicity data. Water column tests from the 10 yr testing period showed that49% of the time, some degree of toxicity was reported. The mosttoxic sites based on water column results were located inurbanized areas such as the Anacostia River, Elizabeth River andthe Middle River. Water quality criteria for copper, lead,mercury, nickel and zinc were exceeded at one or more of thesesites. Water column toxicity was also reported in localizedareas of the South and Chester Rivers. Both spatial and temporalvariability was reported from the suite of water column toxicitytests. Some degree of sediment toxicity was reported from 62% of the tests conducted during the ten year period. The ElizabethRiver and Baltimore Harbor stations were reported as the most toxic areas based on sediment results.Sediment toxicity guidelines were exceeded for one or more of thefollowing metals at these two locations: arsenic, cadmium,chromium, copper, lead, nickel and zinc. At the Elizabeth Riverstations nine of sixteen semi-volatile organics and two of sevenpesticides measured exceeded the ER-M values in 1990. Ambientsediment toxicity tests in the Elizabeth River in 1996 showedreduced toxicity. Various semi-volatile organics exceeded the ER-M values at a number of Baltimore Harbor sites; pyrene anddibenzo(a,h)anthracene were particularly high at one of thestations (Northwest Harbor). Localized sediment toxicity was alsoreported in the Chester, James, Magothy, Rappahannock, andPotomac Rivers but the link with contaminants was not determined.Both spatial and temporal variability was less for sedimenttoxicity data when compared with water column toxicity data. Acomparison of water column and sediment toxicity data for thevarious stations over the 10 yr study showed that approximatelyhalf the time agreement occurred (either both suite of testsshowed toxicity or neither suite of tests showed toxicity).  相似文献   
105.
Kimpo metropolitan landfill has received various kinds of wastessince January 1992. The leachate level was measured to be 10.3 m in May 1995 and the level increased to 12.2 m in August 1996. Therefore, to prove the reason for the increasing leachate level, we calibrated hydraulic conductivity of each waste andintermediate layer using the HELP (Hydrologic Evaluation ofLandfill Performance) model. The leachate generation data measured from February 1993 to October 1995 was used in the model calibration. As a result of a model calibration, we obtained anaverage infiltration ratio and used this in analysis of the total water balance to predict elevation of leachate level. Main causes of the elevation of the leachate level were the high water content of the waste and the degradation of the leachate-drainage system caused by the subsidence of a naturalbarrier layer.  相似文献   
106.
博斯腾湖水质矿化度模型及预测研究   总被引:6,自引:0,他引:6  
刘松 《干旱环境监测》1996,10(3):142-146
根据博斯腾湖1985~1995年水质监测数据和出入湖水量等水文数据观测值,采用水质扩散模型和盐量平衡关系推导出博斯腾湖大湖区(简称博湖)水质矿化度模型,并预测了几种情况下博湖水质矿化度及近几年变化趋势,分析了影响博湖水质矿化度的主要因素,为博湖的近期和远期环境保护规划、环境管理等提供科学依据.  相似文献   
107.
用StrandenE.推荐的测量方法对哈密地区环境空气中220Rn子体α潜能浓度测量结果表明,室内、外平均值分别为56.1和10.2(×10-7J·m-3)。室内外220Rn/222Rn子体α潜能浓度比值分别为0.84和032。220Rn子体所致居民有效剂量当量为228μSv·a-1(集体有效剂量当量为0.9×02man·Sv)。  相似文献   
108.
During the summers of 1991–1994, the Environmental Monitoringand Assessment Program (EMAP) sampled 344 lakes throughout thenortheastern United States using a proportional stratified sampling design based on lake size. Approximately one-quarter ofthe 344 lakes were sampled each year (4 years) for totalphosphorus to determine the proportion (and associated95% confidence intervals) of the northeast lake population 1ha (11,076 ± 1,699 lakes) that was in oligotrophic,mesotrophic, eutrophic, or heupereutropic (4 classes) conditionaccording to the total phosphorus criteria of the North AmericaLake Manegement Society. Estimates for the second, third, andfourth yr were developed as cumulative of the previous yrsamples and the current yr samples for the northeast as a wholeand for each of its three ecoregions (4 regions). New confidence intervals were computed for each cumulative yrcondition estimate. This produced a total (4 years × 4classes × 4 regions) of 64 cumulative yr tropic conditionestimates. Confidence intervals for 21% of these estimates didnot shorten with increased sample size. This phenomena raisedquestions about the accuracy of estimates based on cumulativesampling procedures. We explain why and how the phenomenon comesabout with both straight random and proportional randomsampling. Further, we present an example of the effects thisphenomenon has on lake tropic state condition estimates in thenortheastern United States.  相似文献   
109.
对北京中央电视塔周围25 km2区域电磁环境质量分别进行了射频的网格法手工监测和车载巡测自动监测,通过SPSS软件等对两种监测方法获取的数据进行了统计对比分析,发现两组数据在总体水平及数值分布特征上较为接近,因此车载巡测监测可以替代网格法监测。以车载巡测数据为基础,绘制了实测数据的道路电磁地图,利用插值法绘制了区域电磁地图,对区域电磁环境质量进行了直观表征。从回应公众关注和城市电磁规划出发,建议今后可利用车载巡测监测加强时域和频域的监测。  相似文献   
110.
通过对2014—2016年湖体水质中氮素质量浓度分析,结合出入湖总氮浓度、水量、湖体水生生态等影响因素,发现太湖水体中总氮浓度呈现逐年下降的趋势,各监测点位总氮为0.530 mg/L~5.51 mg/L,时空分布不均,差异明显。时间上,总氮浓度表现为春季最高,夏季和秋季最低,且月均值变化曲线呈现出规律的正弦函数波形。空间上,总氮浓度大致表现出由西部湖区向东部湖区递减的趋势,呈现西部湖区﹥北部湖区﹥南部湖区﹥湖心区﹥东部湖区。要改善湖体水质,不仅要切断污染源,而且要加强水生生态功能修复。  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