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   297篇
  免费   2篇
  国内免费   6篇
安全科学   3篇
废物处理   8篇
环保管理   27篇
综合类   45篇
基础理论   65篇
环境理论   1篇
污染及防治   108篇
评价与监测   26篇
社会与环境   22篇
  2023年   2篇
  2022年   10篇
  2021年   21篇
  2020年   6篇
  2019年   5篇
  2018年   7篇
  2017年   11篇
  2016年   24篇
  2015年   10篇
  2014年   10篇
  2013年   31篇
  2012年   12篇
  2011年   27篇
  2010年   15篇
  2009年   20篇
  2008年   9篇
  2007年   16篇
  2006年   13篇
  2005年   11篇
  2004年   13篇
  2003年   5篇
  2002年   7篇
  2001年   2篇
  2000年   5篇
  1999年   1篇
  1998年   1篇
  1996年   3篇
  1995年   1篇
  1994年   1篇
  1990年   1篇
  1988年   1篇
  1986年   1篇
  1984年   1篇
  1981年   2篇
排序方式: 共有305条查询结果,搜索用时 562 毫秒
1.
Selective feticide is the procedure of choice when, in twin binovular pregnancy, only one of the fetuses is shown to be affected. As the probabilities for this condition are almost 1:2 when the genetic disease is due to homozygosity for two autosomal recessive genes, the problem is expected to occur frequently among the ever increasing number of couples seeking prenatal diagnosis of thalassaemia and the haemoglobinopathies. The present report is the first case of this condition and the ninth in the overall medical literature.  相似文献   
2.
3.
High litter inputs in agroforestry systems contribute to soil microbial activity, soil fertility and productivity. Considering that the cycling of organic matter is essential to the maintenance of physical–chemical and microbiological properties of the soil, the aims of this work were to estimate the production, accumulation and decomposition of litter, and assess soil microbial respiration in a complex multistrata agroforestry system located in the north-east of Brazil. This agroforestry system has three strata formed by forest and fruit trees and species of multiple uses. During 3 years (2011–2013), leaf litter was sampled monthly to account for litterfall and quarterly to account for litter accumulation. The rates of litter decomposition were estimated using the ratio produced-to-accumulated litter, and the correlation between litter fall and rainfall was calculated. Precipitation data were provided by the water and climate agency of Pernambuco (APAC). Soil samples (0–15 cm) were also taken quarterly, simultaneously with the litter accumulation samples, and soil microbial respiration was assessed using the capture, by a KOH solution, of the evolved CO2. The annual production of leaf litter was stable in the 3 years of study in this agroforestry system, and the monthly input of litter to the soil was influenced by rainfall, being higher in the dry seasons. The accumulated litter on the ground was constant, as was microbial activity (respiration) through time. The estimated litter decomposition rates were 1.49 (first year), 1.33 (second year) and 1.42 (third year), being considered rapid rates of decomposition. This guarantees (to the farmer) that this system is capable of maintaining soil fertility and eliminates the need for chemical fertilizers.  相似文献   
4.
Consideration is given to changes in the vegetation and climatic conditions on the eastern slope of the Northern Urals in the second half of the Holocene as reconstructed on the basis of integrated palynological, botanical, paleocarpological, and radiocarbon analysis of material from a peat bog section in the floodplain of the Loz’va River. The results show that the northern taiga zone of the study region in the period between approximately 5000 and 700 years BP was occupied by forests of southern taiga facies, as the climate was significantly warmer than it is today.  相似文献   
5.
6.
This article focuses on the optimization of the production of fatty acid ethyl esters from soybean oil using CaO-based heterogeneous catalysts. Three different catalytic promoters were evaluated: Magnesium, zinc, and potassium. The reaction has evaluated the promoter content (promoter to calcium molar ratio), catalyst load, alcohol to oil molar ratio, and temperature. Response surface methodology (RSM) was used to evaluate the influence of each variable on the yield of biodiesel. The addition of K2O or MgO in the catalyst has enhanced the yield in fatty acid ethyl esters, while the use of ZnO as a promoter was not successful.  相似文献   
7.
Environmental Geochemistry and Health - Lake Atamanskoye is one of the most polluted aquatic environments in the South of Russia. This water body was affected by long-term pollution by effluent...  相似文献   
8.
Environmental Science and Pollution Research - In this study, the photocatalytic degradation of four fungicides, myclobutanil, penconazole and difenoconazole (triazole compounds) and boscalid...  相似文献   
9.
Environmental Science and Pollution Research - In this work, the activated persulfate oxidation of ciprofloxacin (CIP) using a low-grade titanium ore under sunlight or simulated sunlight were...  相似文献   
10.
Environmental Science and Pollution Research - Potentially toxic elements (PTEs) are of great concern in steel mill wastes. Therefore, in order to use them as potential fertilizers in soil, risk...  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