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   86221篇
  免费   1223篇
  国内免费   1072篇
安全科学   3668篇
废物处理   3056篇
环保管理   13533篇
综合类   20940篇
基础理论   25818篇
环境理论   74篇
污染及防治   12383篇
评价与监测   5205篇
社会与环境   3344篇
灾害及防治   495篇
  2022年   717篇
  2021年   790篇
  2020年   648篇
  2019年   861篇
  2018年   1082篇
  2017年   1107篇
  2016年   2116篇
  2015年   1821篇
  2014年   2565篇
  2013年   9230篇
  2012年   2031篇
  2011年   2179篇
  2010年   3180篇
  2009年   3328篇
  2008年   1643篇
  2007年   1466篇
  2006年   1983篇
  2005年   2019篇
  2004年   2361篇
  2003年   2168篇
  2002年   1716篇
  2001年   1877篇
  2000年   1781篇
  1999年   1417篇
  1998年   1349篇
  1997年   1331篇
  1996年   1423篇
  1995年   1546篇
  1994年   1445篇
  1993年   1286篇
  1992年   1277篇
  1991年   1252篇
  1990年   1201篇
  1989年   1170篇
  1988年   1008篇
  1987年   957篇
  1986年   984篇
  1985年   1050篇
  1984年   1148篇
  1983年   1160篇
  1982年   1170篇
  1981年   1089篇
  1980年   935篇
  1979年   908篇
  1978年   814篇
  1977年   707篇
  1976年   638篇
  1975年   592篇
  1973年   615篇
  1972年   619篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
The objective of this paper is to discuss the main barriers for modelling and integrating the environmental performances in the automotive concept design. Incorporating environmental assessment in the early design phase of a vehicle component is known as an important challenge that car makers need to face in order to develop more sustainable design solutions; in this regard, the Life Cycle Assessment is the most widespread methodology for the environmental assessment and comparison of alternatives. The present work illustrates the combination of such methodology with the traditional design procedure at two different levels of the component design phase, material choice and concept design. In particular, the potential benefits originated by a lightweight solution for the automotive component Throttle Body are evaluated by considering environmental and technical implications at the same level. The case study shows that a multi-disciplinary approach for design effectively allows the integration of the environmental issue in the company’s established procedures. However, interpretation of results is still a challenging aspect due to the inevitable contradicting elements which should not discourage to develop comprehensive sustainability assessment within the early design stage.  相似文献   
82.
83.
Current wastewater treatment technologies do not remove many unregulated hydrophilic compounds, and there is growing interest that low levels of these compounds, referred to as emerging contaminants, may impact human health and the environment. A probabilistic-designed monitoring network was employed to infer the extent of Florida’s ambient freshwaters containing the wastewater (Includes reuse water, septic systems leachate, and wastewater treatment effluent.) indicators sucralose, acetaminophen, carbamazepine, and primidone and those containing the widely used pesticide imidacloprid. Extent estimates with 95% confidence bounds are provided for canals, rivers, streams, small and large lakes, and unconfined aquifers containing ultra-trace concentrations of these compounds as based on analyses of 2015 sample surveys utilizing 528 sites. Sucralose is estimated to occur in greater than 50% of the canal, river, stream, and large lake resource extents. The pharmaceuticals acetaminophen, carbamazepine, and primidone are most prevalent in rivers, with approximately 30% of river kilometers estimated to contain at least one of these compounds. Imidacloprid is estimated to occur in 50% or greater of the canal and river resource extents, and it is the only compound found to exceed published toxicity or environmental effects standards. Geospatial analyses show sucralose detection frequencies within Florida’s drainage basins to be significantly related to the percentage of urban land use (R2?=?0.36, p?<?0.001), and imidacloprid detection frequencies to be significantly related to the percentage of urban and agricultural land use (R2?=?0.47, p?<?0.001). The extent of the presence of these compounds highlights the need for additional emerging contaminant studies especially those examining effects on aquatic biota.  相似文献   
84.
The Response of Hydrophytes to Environmental Pollution with Heavy Metals   总被引:3,自引:0,他引:3  
The effects of Cu2+, Cd2+, and Ni2+ at low and high concentrations (0.025 and 0.25 mg/ml) on the accumulation capacity, the state of the pigment complex, and photosynthesis rate have been studied in model experiments with three floating hydrophytes (Hydrocharis morsus-ranae L., Lemna gibba L., and Potamogeton natans L.) and four submerged hydrophytes (Elodea canadensis Michx., Lemna trisulka L., Ceratophyllum demersum L., and Potamogeton lucens L.). Copper and cadmium are especially toxic at the concentrations studied. The effect of Cu2+ was the strongest in hydatophytes, and the effect of Cd2+, in pleustophytes. It is hypothesized that the differences between hydrophytes with respect to accumulation of metals and decrease in photosynthesis rate may cause predominant elimination of submerged species. Therefore, changes in the species structure of hydrophyte communities may be expected in waters polluted with metals.  相似文献   
85.
Quantitative methods have been applied to the study of floristic structure and diversity in Samarskaya Luka. The results show that Samarskaya Luka is a floristically heterogeneous area in which six elementary floras can be distinguished. This area has been assessed as a floristically autonomous formation, and its floristic representativeness was estimated.  相似文献   
86.
Dust Storms are an Indication of an Unhealthy Environment in East Asia   总被引:1,自引:0,他引:1  
Dust storms frequently occur in Mongolia and in northern China. Each year there are 30 to 120 dusty days in source regions of Mongolia and 14–20 dusty days on the Korean Peninsula. Intense sand storms and associated dust falls produce environmental impacts in East Asia. This paper discusses the environmental degradation in Mongolia and the social, economic and atmospheric impacts of dust storms in the sink area. The impact of dust storms on environmental compartments as well as their direct and indirect consequences to basic resources like water and energy demand and supply is explained. Governments are encouraged to take appropriate action in specified regions. For monitoring dust storms there is a need for international cooperation to combat growing environmental and human security concerns.  相似文献   
87.
Abstact The present study was designed to evaluate indirect, non-invasive, on-line measurement of biofilm thickness using an electrical capacitance technique. Several assays were carried out and the results showed that, at a frequency of 1 kHz, electrical capacitance could be used to measure biofilm thickness indirectly (with a correlation coefficient of 0.9495). The reproducibility revealed by the assays was also highly satisfactory.However, in contrast to what was expected, there was an inverse relationship between electrical capacitance and biofilm thickness, i.e. electrical capacitance diminished with the increase in the biofilm thickness.The tests were also carried out at different frequencies (1 kHz, 10 kHz and 100 kHz)  相似文献   
88.
In the present study, the distribution patterns of various metals were analyzed and compared using PM samples collected concurrently from three monitoring sites located in Korea (Seoul, Busan, and Jeju island) in December 2002. As these sites can represent metal pollution with different degrees of anthropogenic activities, their concentration levels were distinguished in a systematic manner in the order of Jeju, Busan, and Seoul. By comparing the present data sets with those measured previously from other locations in Korea and around the world, we attempted to diagnose the general status of elemental pollution on the Korean peninsula. Through an application of different statistical approaches, the major processes controlling elemental levels were assessed for each of the three study sites. The results indicated the importance of both crustal and anthropogenic sources in all sites with their relative roles varying significantly from each other. The results of the metal analysis data, when examined in relation to back trajectory analysis, confirmed that their concentration changes are affected quite sensitively with air mass movement patterns. The overall results of this study consistently indicated the contribution of a strong anthropogenic source area (e.g., China) to the observed metal concentration levels in the study area, but the strengths of such signals vary considerably across the Korean peninsula.  相似文献   
89.
Statistical analyses were applied at the Hanford Site, USA, to assess groundwater contamination problems that included (1) determining local backgrounds to ascertain whether a facility is affecting the groundwater quality and (2) determining a ‘pre-Hanford' groundwater background to allow formulation of background-based cleanup standards. The primary purpose of this paper is to extend the random effects models for (1) assessing the spatial, temporal, and analytical variability of groundwater background measurements; (2) demonstrating that the usual variance estimate s 2, which ignores the variance components, is a biased estimator; (3) providing formulas for calculating the amount of bias; and (4) recommending monitoring strategies to reduce the uncertainty in estimating the average background concentrations. A case study is provided. Results indicate that (1) without considering spatial and temporal variability, there is a high probability of false positives, resulting in unnecessary remediation and/or monitoring expenses; (2) the most effective way to reduce the uncertainty in estimating the average background, and enhance the power of the statistical tests in general, is to increase the number of background wells; and (3) background for a specific constituent should be considered as a statistical distribution, not as a single value or threshold. The methods and the related analysis of variance tables discussed in this paper can be used as diagnostic tools in documenting the extent of inherent spatial and/or temporal variation and to help select an appropriate statistical method for testing purposes.  相似文献   
90.
Anupgarh is the most fertile area of Rajasthan state where a variety of seasonal crops are grown. The availability of three manmade canals has enhanced the agricultural activities in this area. The farmers use huge amounts of pesticides to increase the crop productivity. Exposure of humans to these hazardous chemicals occurs directly in the fields and indirectly due to consumption of contaminated diet, or by inhalation or by dermal contact. The organochlorine pesticides are reported to be lipophilic and their presence in human milk and blood has been documented in different parts of the world. Blood and milk samples were collected from lactating women who were divided into four groups on the basis of different living standards viz residence area, dietary habits, working conditions and addiction to tobacco. The level of total organochlorine pesticides in blood ranged from 3.319mg/L—6.253mg/L while in milk samples it ranged from 3.209Mdash;4.608 mg/L. The results are in concurrence with the reports from other countries.  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