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   727篇
  免费   9篇
  国内免费   6篇
安全科学   33篇
废物处理   20篇
环保管理   173篇
综合类   68篇
基础理论   214篇
环境理论   1篇
污染及防治   113篇
评价与监测   60篇
社会与环境   48篇
灾害及防治   12篇
  2022年   4篇
  2021年   3篇
  2020年   7篇
  2019年   8篇
  2018年   19篇
  2017年   13篇
  2016年   24篇
  2015年   12篇
  2014年   18篇
  2013年   37篇
  2012年   24篇
  2011年   44篇
  2010年   23篇
  2009年   37篇
  2008年   35篇
  2007年   32篇
  2006年   31篇
  2005年   27篇
  2004年   20篇
  2003年   22篇
  2002年   28篇
  2001年   17篇
  2000年   23篇
  1999年   14篇
  1998年   13篇
  1997年   9篇
  1996年   14篇
  1995年   18篇
  1994年   16篇
  1993年   13篇
  1992年   9篇
  1991年   8篇
  1990年   10篇
  1989年   6篇
  1988年   11篇
  1987年   7篇
  1985年   11篇
  1984年   9篇
  1983年   14篇
  1982年   8篇
  1981年   5篇
  1980年   4篇
  1979年   8篇
  1977年   3篇
  1976年   2篇
  1975年   3篇
  1974年   3篇
  1972年   4篇
  1968年   2篇
  1967年   2篇
排序方式: 共有742条查询结果,搜索用时 15 毫秒
141.
Adaptive, or 'learning by doing', approaches are often advocated as a means of providing increased understanding within natural resource management. However, a number of organisational and social issues need to be resolved if these approaches are to be used successfully. A case study in the South Island high country of New Zealand is used to review what is needed to support an ongoing community-based monitoring and adaptive management programme. First, the case study is described, paying attention to the social context of the resource management problem. The results of a workshop that explored this problem are then outlined, along with a proposed information flow suggested by participants. Requirements for future steps to resolve these problems (such as information protocols and a multi-stakeholder information system) are discussed. Finally, some broad lessons are drawn from this exercise that could help others developing similar approaches.  相似文献   
142.
Currently, the U.S. Environmental Protection Agency has established air standards for relatively few chemicals. As a result, state agencies are faced with controlling air contaminants for a large number of chemicals posing potential public health threats. Use of occupational standards as a basis for deriving ambient air guidelines is a method used by states to control air toxics. This standard development approach is reviewed by considering the differences in the health basis and numerical values which often occur among the occupational standards set by OSHA, NIOSH and ACGIH. This study indicated that careful selection should be made of the most appropriate occupational standard to use to protect public health. A comparison is made of chemicals regulated by various state air toxic programs using occupational standards lowered by a safety factor to concentrations established by the U.S. EPA. It was found that the air guidelines vary, but the degree of stringency can be comparable.  相似文献   
143.
144.
Summary Parental exclusion analyses based on allozyme data were performed on 105 families of cliff swallows (Hirundo pyrrhonota) from southwestern Nebraska, USA. The protein products of seve polymorphic loci were resolved from blood, and at least one parental exclusion occurred at six of these loci. One or both putative parents were excluded for 35 nestlings from 22 different families. The mean number of non-kin nestlings in these families was 1.59. Non-kin nestlings were found in families with brood sizes ranging from two to five. A greater percentage of families in an 1100-nest colony had non-kin offspring than in two smaller colonics, although the difference was not statistically significant. Application of genetic models to these data and the observed distribution of parental exclusions suggested that multiple parentage in cliff swallows results more often from intraspecific brood parasitism than from forced extra-pair copulations. Based on the calculated probabilities of detecting non-kin, we estimate that 23.7% of all nestlings in our population are not the offspring of one or both of their putative parents. We estimate that about 43% of all cliff swallow nests in Nebraska contain at least one offspring resulting from intraspecific brood parasitism, and that about 6% of nests might contain offspring resulting from extra-pair copulations.  相似文献   
145.
The newly instituted management plan for the Pemigewasset Wilderness area of New Hampshire, USA, which relies principally on providing information to visitors, represents a departure from traditional plans. Logit analysis of survey data indicates limited evidence of the plan having much direct impact on visitor behavior. There is evidence of success in information dissemination to area users; however, the type of information that is being relayed to backcountry users does not appear to be that which the management plan is attempting to promote.  相似文献   
146.
Burning fossil fuel in the North American continent contributes more to the CO2 global warming problem than in any other continent. The resulting climate changes are expected to alter food production. The overall changes in temperature, moisture, carbon dioxide, insect pests, plant pathogens, and weeds associated with global warming are projected to reduce food production in North America. However, in Africa, the projected slight rise in rainfall is encouraging, especially since Africa already suffers from severe shortages of rainfall. For all regions, a reduction in fossil fuel burning is vital. Adoption of sound ecological resource management, especially soil and water conservation and the prevention of deforestation, is important. Together, these steps will benefit agriculture, the environment, farmers, and society as a whole.  相似文献   
147.
On August 1, 1987, a change in Alabama laws went into effect raising the speed limit on the rural interstates to 65 mph. Two accident data sets (one year before and one year after the law change) were compared to assess the impact of the 65 mph speed limit on severity and frequency of accidents. Although accident severity appeared to remain the same from before to after time periods, the frequency of accidents on the rural interstates increased significantly, by 18.88%. However, the significant increase on the rural interstates was accompanied by a nonsignificant decrease of 456 accidents in the entire state of Alabama. This confounding result made it difficult to isolate the cause of various significant changes, but the overall evidence is not favorable to the recent increases in driving speeds.  相似文献   
148.
对环境监测布点采样中的QC/QA以及由采样引起的误差来源做了简要分析,并对监测采样过程中QC/QA的操作提出了一些设想。  相似文献   
149.
The study of the fetal platelet count and size can, according to the literature, be used for the prenatal diagnosis of the Wiskott-Aldrich syndrome (WAS). So far, no affected fetuses have been identified by this method. All pregnancies in which this method had been applied to resulted, as correctly predicted, in the birth of normal children. Here we report on a familial case of WAS where the haematological parameters failed to reveal the affected second child. Hence we assume that the platelet count and size of platelets remain normal in fetuses with WAS to the gestational age of 22 weeks and cannot be used for prenatal diagnosis.  相似文献   
150.
Pyruvate dehydrogenase (PDH) E1α subunit deficiency is an X-linked inborn error of metabolism affecting males and females with equal frequency. The diagnosis is usually based on determination of enzyme activity, although this may present difficulties in some females because of X-inactivation patterns favouring expression of the normal X chromosome. This is a particular problem for prenatal diagnosis using chorionic villus cells where normal enzyme assay results do not necessarily exclude the diagnosis and confirmatory X-inactivation analysis may be complicated by variable methylation of active and inactive X chromosomes. We describe prenatal diagnosis in two pregnancies in a family following diagnosis of a PDH E1α deficient male. The first prenatal diagnosis was performed by enzyme assay, but by the time of the subsequent pregnancy, the underlying mutation in the affected male had been identified and direct gene analysis was possible. This study highlights the limitations of diagnosis of PDH E1α deficiency based on measurement of the gene product and illustrates the need for mutation analysis in affected individuals.  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