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   263篇
  免费   0篇
  国内免费   2篇
安全科学   6篇
废物处理   23篇
环保管理   27篇
综合类   52篇
基础理论   63篇
污染及防治   66篇
评价与监测   22篇
社会与环境   6篇
  2023年   1篇
  2022年   9篇
  2021年   8篇
  2020年   5篇
  2019年   9篇
  2018年   5篇
  2017年   10篇
  2016年   16篇
  2015年   13篇
  2014年   17篇
  2013年   24篇
  2012年   10篇
  2011年   13篇
  2010年   10篇
  2009年   15篇
  2008年   21篇
  2007年   11篇
  2006年   13篇
  2005年   10篇
  2004年   9篇
  2003年   8篇
  2002年   6篇
  1999年   1篇
  1998年   2篇
  1994年   1篇
  1992年   3篇
  1991年   2篇
  1989年   1篇
  1988年   2篇
  1986年   4篇
  1984年   1篇
  1961年   1篇
  1960年   1篇
  1940年   1篇
  1938年   2篇
排序方式: 共有265条查询结果,搜索用时 15 毫秒
241.
In this work the dynamics of biochemical (enzymatic activities) and chemical (water-soluble fraction) parameters during 100 days of municipal solid wastes composting were studied to evaluate their suitability as tools for compost characterization. The hydrolase (protease, urease, cellulase, beta-glucosidase) and dehydrogenase activities were characterized by significant changes during the first 2 weeks of composting, because of the increase of easily decomposable organic compounds. After the 4th week a "maturation phase" was identified in which the enzymatic activities tended to gently decrease, suggesting the stabilisation of organic matter. Also the water-soluble fractions (water-soluble carbon, nitrogen, carbohydrates and phenols), which are involved in many degradation processes, showed major fluctuations during the first month of composting. The results obtained showed that the hydrolytic activities and the water-soluble fractions did not vary statistically during the last month of composting. Significant correlations between the enzymatic activities, as well as between enzyme activities and water-soluble fractions, were also highlighted. These results highlight the suitability of both enzymatic activities and water soluble fractions as suitable indicators of the state and evolution of the organic matter during composting. However, since in the literature the amount of each activity or fraction at the end of composting depends on the raw material used for composting, single point determinations appear inadequate for compost characterization. This emphasizes the importance of the characterization of the dynamics of enzymatic activities and water-soluble fractions during the process.  相似文献   
242.
Angelman Syndrome (AS), characterized by mental retardation, absence of speech, seizures and motor dysfunction, is caused by genetic defects leading to loss of expression of the maternal copy of the chromosome 15q11–13 imprinted region. Most cases are sporadic, being caused by de novo deletion of maternal chromosome 15q11–13 (75%) or by paternal uniparental disomy (3–4%). Familial cases can occur, due to mutations in the UBE3A gene or in the imprinting center. We describe the case of a pregnant woman having two nephews with AS caused by a UBE3A mutation; lack of communication within the family led the woman to be completely unaware of the risk of disease recurrence until 15 weeks of gestation. UBE3A genetic testing revealed she carried the familial mutation 892–893delCT. Prenatal diagnosis was performed on amniotic fluid and demonstrated that the fetus had inherited the mutation. The unexpected diagnosis and the subsequent termination of the pregnancy caused the woman to undergo acute psychological distress showing relevant psychopathological symptoms. Nevertheless, at 2-year follow-up, adverse consequences were minimized, and the couple was planning a new pregnancy. Factors affecting the psychological outcome of abortion and the role of psychological support in reducing the risk of long-term unfavorable consequences are discussed. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   
243.
244.
245.
Under stressful conditions (e.g. finding themselves on dry or moisture-saturated substrates) littoral talitrids (Crustacea, Amphipoda) demonstrate zonal orientation, in which they must promptly reach the optimal zone of the beach, the wet fringe near the shoreline. A relationship might therefore exist between the use of orientation and the frequency of such stressful conditions in the natural environment. Moreover, the efficiency of orientation toward the sea could be related to the possibility of using strategies other than zonal orientation in order to avoid stress. This study analysed the actual use and efficiency of orientation under natural conditions of four Talitrus saltator (Montagu, 1808) populations from Mediterranean and northern European Atlantic coasts with different ecological features. Orientation tests were carried out on the beach with all natural cues available. Then the same individuals underwent control experiments to study their sun orientation far from the sea in an experimental arena. The following results emerge from the comparison of the circular distributions: (1) marked differences among populations in the precision of zonal recovery under natural conditions; (2) a common solar orientation capacity in the control tests far from the sea; (3) different orientation choices of the same individuals according to the test conditions, natural or controlled. The habitat diversity of the four populations (amount, distribution and kind of detritus and wrack on the beach, degree of coastal erosion, orientation of the shoreline, human use of the beach) provides an ecological interpretation for the differences in orientation observed among populations. Received: 13 October 1997 / Accepted after revision: 26 April 1998  相似文献   
246.
Objectives and Methods Assuming that the rate of fetal loss after amniocentesis may be reduced in patients receiving antibiotic prophylaxis, we conducted a retrospective study on untreated versus treated patients receiving prophylactic antibiotics (amoxicillin/clavulanic-acid or azithromycin) and evaluated the fetal loss rate within the 22nd week of gestation, also with respect to the risk of spontaneous abortion, both preexisting and related to mid-trimester amniocentesis. Results Spontaneous abortion occurred in 22 cases out of 1744 (1.26%). The incidence of spontaneous abortion was 1.3% among patients treated with antibiotic prophylaxis and 1.2% among untreated patients. Between patients with risk factors that predated amniocentesis, the spontaneous fetal loss rate was 9.2% in untreated patients versus 2.3% in patients treated (p = 0.10). In patients with procedure-related risk factors at amniocentesis, the spontaneous abortion rate was, respectively, 2.2 and 1.2% (p = 0.72). Conclusion Our data demonstrate that antibiotic prophylaxis does not reduce the risk of spontaneous abortion within the 22nd week of gestation. Compared with untreated patients, patients treated with amoxicillin showed the lower fetal loss rate (1.16 vs 0.31%), but the difference was not statistically significant (odds ratio (OR) = 3.68, p = 0.32). The same was true for patients with preexisting risks (OR = 4.25, p = 0.10). Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
247.
248.
249.
250.
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