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   333篇
  免费   6篇
  国内免费   3篇
安全科学   26篇
废物处理   18篇
环保管理   90篇
综合类   32篇
基础理论   72篇
污染及防治   79篇
评价与监测   7篇
社会与环境   16篇
灾害及防治   2篇
  2021年   2篇
  2020年   2篇
  2019年   2篇
  2018年   6篇
  2017年   6篇
  2016年   3篇
  2015年   6篇
  2014年   8篇
  2013年   34篇
  2012年   11篇
  2011年   18篇
  2010年   9篇
  2009年   13篇
  2008年   8篇
  2007年   15篇
  2006年   20篇
  2005年   12篇
  2004年   16篇
  2003年   11篇
  2002年   7篇
  2001年   2篇
  2000年   5篇
  1999年   3篇
  1998年   2篇
  1997年   3篇
  1996年   3篇
  1995年   10篇
  1994年   7篇
  1993年   3篇
  1992年   6篇
  1991年   2篇
  1990年   5篇
  1989年   2篇
  1988年   7篇
  1987年   5篇
  1986年   7篇
  1985年   6篇
  1984年   10篇
  1983年   7篇
  1982年   11篇
  1981年   4篇
  1979年   6篇
  1977年   3篇
  1975年   2篇
  1974年   1篇
  1972年   2篇
  1969年   1篇
  1967年   1篇
  1962年   1篇
  1952年   1篇
排序方式: 共有342条查询结果,搜索用时 250 毫秒
141.
Many current wildlife conservation efforts in Africa focus on providing local communities with economic incentives to utilize wildlife as a form of land use in order to achieve the twin goals of ecological preservation as well as sustainable human economic development. Tanzanian Maasailand is home to some of the greatest concentrations of large mammals remaining outside National Parks and reserves, as well as a uniquely traditional human culture in the form of the Maasai themselves. Both are increasingly threatened by a variety of factors; poaching and habitat loss for wildlife, and the increasing marginalization of their pastoralist economy with regards to the Maasai. The fundamental cause of declining wildlife populations and biodiversity loss is that the Maasai have little economic or social interest in wildlife due to centralized management and financial benefits which are directed primarily to the Tanzanian state. Maasai pastoralism is highly compatible with wildlife, and the potential for the local communities to sustainably manage and benefit from this resource is promising. However, implementation of effective community-based natural resource management in the area faces political, cultural, and economic obstacles which will be critical in determining the outcomes of both conservation and community development efforts in Maasailand.  相似文献   
142.
从大鼠低Cot值DNA文库分离到一种类Alu的重复序列,命名为RALRS-1。对RALRS-1克隆并进行了测序,长度为283bp,发现其中含有单一的微卫星(microsatellite)序列AG,AGG和AGGG。RALRS-1DNA序列在大鼠单倍体基因组中的拷贝数为150000~330000。依RALRS-1中的一段序列合成了一28寡核苷酸探针(AGGG)7,对大鼠正常组织和肿瘤组织DNA指数谱  相似文献   
143.
A combination of in-situ PM2.5, sunphotometers, upward pointing lidar and satellite aerosol optical depth (AOD) instruments have been employed to better understand variability in the correlation between AOD and PM2.5 at the surface. Previous studies have shown good correlation between these measures, especially in the US east, and encouraged the use of satellite data for spatially interpolating between ground sensors. This work shows that cases of weak correlation can be better understood with knowledge of whether the aerosol is confined to the surface planetary boundary layer (PBL) or aloft. Lidar apportionment of the fraction of aerosol optical depth that is within the PBL can be scaled to give better agreement with surface PM2.5 than does the total column amount. The study has shown that lidar combined with surface and remotely sensed data might be strategically used to improve our understanding of long-range or regionally transported pollutants in multiple dimensions.  相似文献   
144.
There are two predominant views of organizational commitment: instrumental and affective. The purpose of the paper is to explore the extent to which an adapted version of Etzioni's macro organizational model of involvement may serve as a single model of both affective and instrumental perspectives of organizational commitment. Moral commitment and alienative commitment are treated as affective forms of organizational attachment, and calculative commitment is treated as an instrumental form of organizational attachment. The paper employs five samples for the investigation. It develops scales for measuring each of the three dimensions of commitment. The paper concludes that organizational commitment is multidimensional. It also concludes that employees report a mixture of commitment types. Evidence is offered in support of the affective character of moral and alienative commitment. Although the evidence is equivocal, there is support for the independence of the two dimensions of affective commitment: moral and alienative. Evidence is also offered for the differential association of the three dimensions of organizational commitment with related aspects of organizational behavior. The paper extends our understanding of organizational commitment by providing a place for both instrumental and affective forms of psychological attachment to organizations. It offers scales which may be used for future research, and it suggests research which may extend the adapted model in this paper as well as provide direction for practising managers.  相似文献   
145.
146.
The US Environmental Protection Agency's Office of Research and Development has initiated the Environmental Monitoring and Assessment Program (EMAP) to monitor status and trends in the condition of the nation's near coastal waters, forests, wetlands, agro-ecosystems, surface waters, deserts and rangelands. the programme is also intended to evaluate the effectiveness of Agency policies at protecting ecological resources occurring in these systems. Monitoring data collected for all ecosystems will be integrated for regional and national status and trends assessments. the near coastal component of EMAP consists of estuaries, coastal waters, and the Great Lakes. Near coastal ecosystems have been regionalized and classified, and an integrated sampling strategy has been developed. EPA and NOAA have agreed to coordinate and, to the extent possible, integrate the near coastal component of EMAP with the NOAA National Status and Trends Program. A demonstration project was conducted in estuaries of the mid-Atlantic region (Chesapeake Bay to Cape Cod) in the summer of 1990. in 1991, monitoring continued in mid-Atlantic estuaries and was initiated in estuaries of a portion of the Gulf of Mexico. Preliminary results indicate: there are no insurmountable logistical problems with sampling on a regional scale; several of the selected indicators are practical and sensitive on the regional scale; and an efficient effort in future years will provide valuable information on condition of estuarine resources at regional scales.  相似文献   
147.
148.
A case of multiple intestinal atresia is described. Dilatation of the bowel was observed at 17 weeks' gestation during routine ultrasound scan of a healthy Caucasian primigravida from a non-consanguineous marriage. Amniocentesis was performed. The karyotype was normal male and cystic fibrosis screening was negative. Regular scans were performed throughout the pregnancy and a simple bowel obstruction was suspected. The baby was delivered at 37 weeks' gestation in good condition. Initial clinical examination was normal but abdominal distension developed during the first day. At laparotomy, prepyloric septal atresia, a distal duodenal membrane, and multiple intestinal atresia were found. The baby died aged 4 days. Post-mortem examination of the abdomen confirmed the absence of lumen from long segments of the small intestine together with areas of colonic atresia. Histology and distribution were consistent with those reported in familial multiple intestinal atresia. The pitfalls in the interpretation of prenatal ultrasound scans and the possibility of prenatal diagnosis in future pregnancies are discussed.  相似文献   
149.
The C-Lock system was developed to address the need for an improved method of quantifying and certifying project-level carbon emission reduction credits (CERC). It was designed to enable individual landowners to efficiently quantify, certify, pool, market and trade CERCs generated by agricultural management practices. We provide a general overview of the C-Lock system as it has been implemented for the USA State of South Dakota. C-Lock is comprised of four linked components: a web interface, a client database, a Geographic Information System (GIS) database of soil, climate and generalized land use history parameters, and the CENTURY soil carbon model. The user-friendly interface elicits generalized land-use and crop history information from the client from 1900 through 1989, then explicit annual information from 1990 onward. A climate-zone level landuse and crop management database is used to fill in gaps in the client-provided data. These data are used to drive the CENTURY model, which estimates annual changes in soil carbon stocks. Monte Carlo simulation is used to estimate uncertainty bounds, and these are applied to the CENTURY outputs in order to provide probabilistic estimates of accrued CERCs in a manner that is transparent and verifiable. In a demonstration application, CERCs are estimated for three different land-use scenarios on a representative field in eastern South Dakota: reduced tillage or conservation (no-till) management of a corn (maize)/wheat/soybean rotation, and enrollment in the Conservation Reserve Program, which entails establishing permanent grass cover. The credits are based on a business-asusual scenario of conventional tillage.  相似文献   
150.
Diluted exhaust from selected military aircraft ground-support equipment (AGE) was analyzed for particulate mass, elemental carbon (EC) and organic carbon (OC), SO4(2-), and size distributions. The experiments occurred at idle and load conditions and utilized a chassis dynamometer. The selected AGE vehicles operated on gasoline, diesel, and JP-8. These military vehicles exhibited concentrations, size distributions, and emission factors in the same range as those reported for nonmilitary vehicles. The diesel and JP-8 emission rates for PM ranged from 0.092 to 1.1 g/kg fuel. The EC contributed less and the OC contributed more to the particulate mass than reported in recent studies of vehicle emissions. Overall, the particle size distribution varied significantly with engine condition, with the number of accumulation mode particles and the count median diameter (CMD) increasing as engine load increased. The SO4(2-) analyses showed that the distribution of SO4(2-) mass mirrored the distribution of particle mass.  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