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   92619篇
  免费   1230篇
  国内免费   1127篇
安全科学   3745篇
废物处理   3392篇
环保管理   14100篇
综合类   21271篇
基础理论   26677篇
环境理论   78篇
污染及防治   15584篇
评价与监测   5617篇
社会与环境   3955篇
灾害及防治   557篇
  2022年   817篇
  2021年   837篇
  2020年   669篇
  2019年   881篇
  2018年   1221篇
  2017年   1236篇
  2016年   2232篇
  2015年   1859篇
  2014年   2609篇
  2013年   9302篇
  2012年   2265篇
  2011年   2599篇
  2010年   3354篇
  2009年   3456篇
  2008年   2129篇
  2007年   2044篇
  2006年   2413篇
  2005年   2354篇
  2004年   2650篇
  2003年   2513篇
  2002年   2092篇
  2001年   2428篇
  2000年   2075篇
  1999年   1546篇
  1998年   1393篇
  1997年   1375篇
  1996年   1507篇
  1995年   1589篇
  1994年   1495篇
  1993年   1342篇
  1992年   1339篇
  1991年   1306篇
  1990年   1251篇
  1989年   1220篇
  1988年   1060篇
  1987年   993篇
  1986年   1001篇
  1985年   1060篇
  1984年   1161篇
  1983年   1174篇
  1982年   1182篇
  1981年   1098篇
  1980年   946篇
  1979年   933篇
  1978年   823篇
  1977年   720篇
  1976年   638篇
  1974年   605篇
  1973年   634篇
  1972年   632篇
排序方式: 共有10000条查询结果,搜索用时 251 毫秒
361.
Historical records from Ontario's Provincial Water Quality Monitoring Network (PWQMN) for rivers and streams were analyzed to assess the feasibility of mapping regional water quality patterns in southeastern Ontario which spans two major geologic zones, the Precambrian Shield and the St. Lawrence Lowlands, thus serving as a paradigm for much of Ontario. Despite biases toward the populated Lowlands and associated pollution problems, general spatial trends are evident via the analysis of intervariable relations, individual parameter maps and multivariate analysis. Using a robust algorithm designed to identify outliers and abstract underlying bivariate relations, a linear regional hardness-alkalinity relation was derived, where most anomalies proved to be mine drainage impacted sites. Regionally, multivariate ordination reveals that central tendencies of common indicators of ionic strength and nutrient richness correlate positively and that site clusters broadly reflect the transition from oligotrophic Shield waters to eutrophic conditions of heavily agricultural Lowland streams. Results suggest that on the Shield more precisely delineated aquatic regions may be realized by applying GIS to integrate river and synoptic lake survey data. Further synthesis with bedrock and surficial geology, physiography, pedology and other temporally invariant spatial attributes should yield regional patterns of background quality from which locally attainable water objectives might be defined. Additional synoptic surveys of sedimentary Lowland streams may be required as most available sites relflect anthropogenic pollution.  相似文献   
362.
Air pollutants or some chemicals applied to plant foliage can alter the ecology of the rhizosphere. Experiments were conducted to distinguish among possible foliage-mediated versus soil- or root-mediated effects of acid deposition on microorganism in the rhizosphere. Seedlings of a sorghum x sudangrass hybrid in pots of non-sterile soil-sand mix in a greenhouse were exposed to simulated rain solution adjusted with H2SO4 + HNO3 to pH 4.9, 4.2, 3.5 or 2.8. Solutions were applied as simulated rain to foliage and soil, foliage only (soil covered by plastic, and deionized water applied directly to the soil), or soil only (solution applied directly to the soil). Solutions were applied on 16 days during a 6-week period (1.5 cm deposition in 1 h per application). Plant shoot and root dry weights and population densities of selected types of bacteria, filamentous actinomycetes and fungi in the rhizosphere were quantified after exposures were completed. Deposition of simulated acidic rain onto foliage alone had no effect on plant biomass or microbial population densities in the rhizosphere (colony-forming units per gram of rhizosphere soil). However, plant growth was stimulated and all microbial populations in the rhizosphere increased 3- to 8-fold with increased solution acidity (relative to pH 4.9 solution) when solution penetrated the soil. Statistical analyses indicated that the acid dose-population response relationships for soil-only and foliage-and-soil applications were not different. Thus, no foliage-mediated effect of simulated acidic rain on rhizosphere ecology was detected.  相似文献   
363.
Simmonds S  Cuttst F  Dick B 《Disasters》1985,9(1):61-69
Many problems have been encountered in the planning and implementation of health care in refugee camps, and more specifically in the training of refugees as primary health care workers. A review of the published literature and a "survey" of the opinions and experiences of refugee, national and international health personnel regarding training has therefore been undertaken to provide an overview of what has been done and to make recommendations for future work.
The review highlights the need to reallocate resources away from high visibility emergency aid to development activities, such as training, that will create an infrastructure for primary health care and promote self-reliance.  相似文献   
364.
Environment, Development and Sustainability - Environmental deterioration and global warming has created a substantial impact on international companies to incorporate eco-friendly, green supply...  相似文献   
365.
Environment, Development and Sustainability - Land use and land cover change (LULCC) is one of the problems that the world has been facing for the last few decades despite political attention....  相似文献   
366.
Environment, Development and Sustainability - Renewable energy (RE) plays an increasingly important role in the economy of almost every country in the world. In order to examine the state of...  相似文献   
367.
Environment, Development and Sustainability - This study describes the results of groundwater table variation in Thanjavur District before and after the monsoon seasons. Groundwater-level data...  相似文献   
368.
Russian Journal of Ecology - Populations at the border of ranges are considered more vulnerable than those in the center. However, some recent reviews contradict this hypothesis. We have studied...  相似文献   
369.
Russian Journal of Ecology - Abstract—We tested a hypothesis about the different abilities of alien and native plants to form arbuscular mycorrhizae. The studies were carried out in the...  相似文献   
370.
Rate-temperature responses in scyphozoan medusae and polyps   总被引:1,自引:0,他引:1  
The effects of temperature on oxygen consumption and spontaneous rhythmic activity have been investigated in various stages of the life histories of 3 species of jellyfish from the Chesapeake Bay, USA. All 3 species clearly show the ability to acclimate positively to temperature change. Thermal sensitivity of metabolism in the winter medusa Cyanea capillata fulva is fairly low at temperature intervals which are experienced in nature. Polyps of the two summer medusae, Chrysaora quinquecirrha and Aurelia aurita, show reduced metabolic sensitivity at temperatures normally accompanying high developmental activity and the onset of strobilation.  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