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   1346篇
  免费   30篇
  国内免费   16篇
安全科学   23篇
废物处理   22篇
环保管理   220篇
综合类   368篇
基础理论   355篇
污染及防治   285篇
评价与监测   87篇
社会与环境   26篇
灾害及防治   6篇
  2021年   6篇
  2020年   10篇
  2019年   8篇
  2018年   13篇
  2017年   23篇
  2016年   16篇
  2015年   17篇
  2014年   28篇
  2013年   267篇
  2012年   18篇
  2011年   25篇
  2010年   33篇
  2009年   25篇
  2008年   22篇
  2007年   20篇
  2006年   25篇
  2005年   23篇
  2004年   15篇
  2003年   15篇
  2002年   14篇
  2001年   18篇
  2000年   24篇
  1999年   18篇
  1998年   20篇
  1997年   9篇
  1996年   25篇
  1995年   74篇
  1994年   52篇
  1993年   63篇
  1992年   62篇
  1991年   41篇
  1990年   35篇
  1989年   27篇
  1988年   31篇
  1987年   18篇
  1986年   17篇
  1985年   14篇
  1984年   31篇
  1983年   20篇
  1982年   15篇
  1981年   19篇
  1980年   10篇
  1979年   16篇
  1978年   19篇
  1977年   12篇
  1976年   8篇
  1975年   8篇
  1974年   9篇
  1973年   6篇
  1972年   7篇
排序方式: 共有1392条查询结果,搜索用时 843 毫秒
1.
2.
A case of type III congenital cystic adenomatoid malformation of the lung was successfully diagnosed prenatally by fetal lung biopsy. We performed this procedure at 22 weeks of gestation, using a biopsy gun system under ultrasound guidance. The pregnancy was undisturbed by the procedure but as the condition was incompatible with life, an abortion was performed. The diagnosis was confirmed at post-mortem examination. Fetal lung biopsy appears to be a useful method for prenatal diagnosis of fetal lung disorders.  相似文献   
3.
4.
An active capping demonstration project in Washington, D.C., is testing the ability to place sequestering agents on contaminated sediments using conventional equipment and evaluating their subsequent effectiveness relative to conventional passive sand sediment caps. Selected active capping materials include: (1) AquaBlokTM, a clay material for permeability control; (2) apatite, a phosphate mineral for metals control; (3) coke, an organic sequestration agent; and (4) sand material for a control cap. All of the materials, except coke, were placed in 8,000‐ft test plots by a conventional clamshell method during March and April 2004. Coke was placed as a 1.25‐cm layer in a laminated mat due to concerns related to settling of the material. Postcap sampling and analysis were conducted during the first, sixth, and eighteenth months after placement. Although postcap sampling is expected to continue for at least an additional 24 months, this article summarizes the results of the demonstration project and postcap sampling efforts up to 18 months. Conventional clamshell placement was found to be effective for placing relatively thin (six‐inch) layers of active material. The viability of placing high‐value or difficult‐to‐place material in a controlled manner was successfully demonstrated with the laminated mat. Postcap monitoring indicates that all cap materials effectively isolated contaminants, but it is not yet possible to differentiate between conventional sand and active cap layer performance. Monitoring of the permeability control layer indicated effective reductions in groundwater seepage rates through the cap, but also showed the potential for gas accumulation and irregular release. All of the cap materials show deposition of new contaminated sediment onto the surface of the caps, illustrating the importance of source control in maintaining sediment quality. © 2006 Wiley Periodicals, Inc.  相似文献   
5.
6.
Taking Wonderland—a simple model of demographic, economic and environmental interactions—as our artificial world, we illustrate the use of geometric singular perturbation theory in environmental demoeconomics. The theory of slow-fast dynamics helps us to gain new insights into the system's behaviour and enables one to reduce the inherent unpredictability of a “natural catastrophe” in Wonderland. Though we cannot predict the exact date of such an “environmental crash”, we can state the specific demographic, economic and environmental constellations of our artificial world at which the sustainability of nature becomes endangered.  相似文献   
7.
The intense interest in desertification and climate change has stimulated detailed studies of temperature records in many areas of the world. In this investigation, the temperature records from the Middle East region are analyzed over the period 1950–1990. Results reveal a linear, statistically significant temperature increase of 0.07 °C/decade over the 41-year period. An analysis of spatial controls on these temperature changes reveals a warming effect associated with both overgrazing and the degree of human-induced desertification. The results of this study are consistent with theoretical and empirical studies predicting and demonstrating a warming signal associated with these land surface changes in the world's dryland areas.  相似文献   
8.
Difficulties in making accurate, ecosystem-level predictions of environmental effects of chemicals, mixtures, and effluents based solely on the results of tests on single species have necessitated the development of more environmentally realistic, predictive testing methods. This paper describes a multispecies, community-level toxicity test based on the colonization of artificial substrates by microbial species. Tests examined the colonization of initially barren polyurethane foam artificial substrates by Protozoa from a species source colonized in a natural system. Differences in colonization were examined in microecosystems amended with low levels of cadmium, a very toxic heavy metal, and TFM, an organic biocide used against larval sea lamprey. Tests examined differences in colonization over 28 days. For cadmium, effect levels were estimated to be near 1 g 1–1, in the low range of effect levels determined from chronic single species tests. For TFM, effect levels were estimated to be between 1 and 10 ppm, overlapping the concentrations used in environmental applications. The colonization response, which depends on naked microbial cells reproducing and migrating through toxicant amended water to new substrates, is very sensitive. Tests based on colonization can be adapted to use species from a target receiving system or can use species from a designated natural source. Field validation of these tests can employ nearly identical methods to those used in laboratory studies to assess the accuracy of predictions based on test system data.  相似文献   
9.
Swine Concentrated Animal Feeding Operations (CAFOs) have received much attention in recent years. As a result, a watershed-based screening tool, the Cumulative Risk Index Analysis (CRIA), was developed to assess the cumulative impacts of multiple CAFO facilities in a watershedsubunit. The CRIA formula calculates an index number based on: 1) the area of one or more facilities compared to the area of the watershed subunit, 2) the average of the environmental vulnerability criteria, and 3) the average of the industry-specific impact criteria. Each vulnerability or impact criterion is ranked on a 1 to 5 scale, with a low rank indicating low environmental vulnerability or impact and a high rank indicating high environmental vulnerability or impact. The individual criterion ranks, as well as the total CRIA score, can be used to focus the environmental analysis and facilitate discussions with industry, public, and other stakeholders in the Agency decision-making process.  相似文献   
10.
Methane emissions from natural wetlands   总被引:3,自引:0,他引:3  
Methane is considered one of the most important greenhouse gases in the atmosphere. Because of the strict anaerobic conditions required by CH4-generating microorganisms, natural wetland ecosystems are one of the main sources of biogenic CH4. The total natural wetland area is estimated to be 5.3 to 5.7 × 1012 m2, making up less than 5% of the Earth's land surface. However, natural wetland plays a disproportionately large role in CH4 emissions. Wetlands are likely the largest natural sources of CH4 to the atmosphere, accounting for about 20% of the current global annual emission. Out of the total amount of CH4 emitted, northern wetlands contribute 34%, temperate wetlands 5%, and tropical systems about 60%.Because of the unique characteristics and high productivity, wetland ecosystems are important in the global carbon cycle. Natural wetlands are permanently or temporarily saturated. Strict anaerobic conditions consequently develop, which allows methanogenesis to occur. But the thin oxic layer and the oxic plant rhizophere promote activity of CH4-oxidizing bacteria or methanotrophs. Thus, both CH4 formation and consumption in wetland systems are microbiological processes and are controlled by many factors. Eight of the controlling factors, including carbon supply, soil oxidation-reduction status, pH, temperature, vegetation, salinity and sulfate content, soil hydrological conditions and CH4 oxidation are discussed in this paper.  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