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   92807篇
  免费   1234篇
  国内免费   1103篇
安全科学   3864篇
废物处理   3372篇
环保管理   14339篇
综合类   21294篇
基础理论   26760篇
环境理论   75篇
污染及防治   15585篇
评价与监测   5595篇
社会与环境   3687篇
灾害及防治   573篇
  2022年   812篇
  2021年   804篇
  2020年   670篇
  2019年   875篇
  2018年   1168篇
  2017年   1217篇
  2016年   2203篇
  2015年   1866篇
  2014年   2595篇
  2013年   9297篇
  2012年   2316篇
  2011年   2623篇
  2010年   3331篇
  2009年   3465篇
  2008年   2177篇
  2007年   2027篇
  2006年   2422篇
  2005年   2375篇
  2004年   2668篇
  2003年   2500篇
  2002年   2092篇
  2001年   2340篇
  2000年   2039篇
  1999年   1519篇
  1998年   1384篇
  1997年   1382篇
  1996年   1505篇
  1995年   1600篇
  1994年   1497篇
  1993年   1354篇
  1992年   1330篇
  1991年   1302篇
  1990年   1255篇
  1989年   1229篇
  1988年   1062篇
  1987年   992篇
  1986年   997篇
  1985年   1080篇
  1984年   1167篇
  1983年   1176篇
  1982年   1180篇
  1981年   1117篇
  1980年   948篇
  1979年   936篇
  1978年   829篇
  1977年   718篇
  1976年   651篇
  1975年   627篇
  1973年   659篇
  1972年   656篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
Stormwater runoff is now a major contributor to the pollution of coastal waters in the United States. Public agencies are responding by requiring stormwater monitoring to satisfy the National Pollutant Discharge Elimination System stormwater permit. However, studies to understand the utility of the current programs or to improve their usefulness have not yet been performed. In this paper, we evaluate the land-use-based program, the industrial stormwater permit program, and beach water-quality monitoring in the County of Los Angeles, California, to determine if the results will be helpful to planners and regulators in abating stormwater pollution. The utility of the program has been assessed based on the programs' ability to accurately estimate the emissions for different classes of land use. The land-use program appears successful, while the industrial monitoring program does not. Beach water-quality monitoring suffers from a lack of real-time monitoring techniques. We also provide suggested improvements, such as sampling method and time, and parameter selection.  相似文献   
132.
133.
Pollution due to persistent pesticides is not a regional but a global problem. Organochlorine pesticides are persistent chemicals, stored and accumulated in the tissues of a wide variety of invertebrates and vertebrates including marine species. In the present study the organochlorine residues HCHs, DDTs and PCBs were measured in different trophic groups of birds (scavengers, inland piscivores, coastal piscivores, insectivores, granivores and omnivores) collected from Tamil Nadu Coast, India. The residue accumulation as a function of sex did not depict distinct variation. However, females had lower residue levels than males in terms of their mean weight and feeding habits. A continuous monitoring programme is recommended to establish the studied organisms as indicator species.  相似文献   
134.
The amount of NO2 and NO produced by the machine smoking of cigarettes was determined for 15 commercial Canadian brands. Average yield of NO was 1.44 μmoles or about 13% of the average reported for American cigarettes. Levels of NO2 were less than 12% of NO and were probably due to the oxidation of NO. In order to assess the contribution of tobacco smoke to levels of NO in ambient air, 5 brands of cigarettes were smoked in 27 cubic meter controlled environment room. Ventilation conditions were either 2.5 or 5.0 air changes per hour (ACH) and each experiment was replicated 3 times for a total of 30 experiments. Ventilation rates of 0.3 and 1.5 ACH were also selected in a second series of experiments in which only one brand of cigarette was smoked. Least squares estimates for the effective ventilation rates were obtained in the usual manner after linearizing the decay portion of the NO time curve. In each of the experiments, the regression explained at least 95% of the variation in the levels of NO with time. Loss of NO due to factors other than ventilation appeared to be constant within experimental error and averaged 2.22 ACH. Equilibrium values for NO were grossly underestimated when results from currently accepted proecedures for smoke analysis were used in modeling the growth and decay of NO. Goodness-of-fit was improved when equilibrium values were estimated based on observed levels in ambient air. This approach may be more suitable for evaluating the potential contribution of cigarette smoke to levels of indoor air pollutants.  相似文献   
135.
136.
137.
138.
139.
The towed undulating vehicle (TUV), named SARAGO, was used for two fine-scale surveys between the Italian and the Sardinian coasts during the Astraea 2 cruise (6-7 and 26-27 September 1995), studying the deep chlorophyll maximum distribution. SARAGO sections identify a sub-surface doming with higher chlorophyll a and primary production concentrations in the upwelling area of a cyclonic gyre region, detected by sea-surface temperature images. In the first section, the cyclone presents a double doming, in density and salinity, with shallower and concentrated patches of chlorophyll a for about 2 miles. Twenty days later, the second section shows that the gyre changes shape and extension, showing a single doming with higher primary production and chlorophyll a concentrations, distributed over a large area of about 40 nautical miles. SARAGO allows analysis of this high-variability phenomenon (cyclonic gyre) and allows concentrated patches (2 nm) to be identified, thus proving the importance of TUVs in the study of mesoscale processes.  相似文献   
140.
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