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   26474篇
  免费   268篇
  国内免费   226篇
安全科学   760篇
废物处理   1010篇
环保管理   3717篇
综合类   4406篇
基础理论   7070篇
环境理论   12篇
污染及防治   6791篇
评价与监测   1646篇
社会与环境   1374篇
灾害及防治   182篇
  2022年   231篇
  2021年   224篇
  2020年   177篇
  2019年   235篇
  2018年   373篇
  2017年   360篇
  2016年   546篇
  2015年   402篇
  2014年   610篇
  2013年   2060篇
  2012年   758篇
  2011年   1076篇
  2010年   893篇
  2009年   931篇
  2008年   1117篇
  2007年   1131篇
  2006年   1041篇
  2005年   865篇
  2004年   868篇
  2003年   817篇
  2002年   780篇
  2001年   1065篇
  2000年   750篇
  1999年   452篇
  1998年   348篇
  1997年   336篇
  1996年   370篇
  1995年   405篇
  1994年   423篇
  1993年   349篇
  1992年   350篇
  1991年   359篇
  1990年   375篇
  1989年   358篇
  1988年   292篇
  1987年   269篇
  1986年   259篇
  1985年   239篇
  1984年   277篇
  1983年   273篇
  1982年   292篇
  1981年   270篇
  1980年   217篇
  1979年   244篇
  1978年   190篇
  1977年   182篇
  1975年   181篇
  1974年   165篇
  1973年   168篇
  1972年   182篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
The effect of industrial air pollution on natural small mammal populations has been studied in the northern taiga subzone of the boreal forest zone. The results of long-term monitoring have been used to demonstrate the possibility of predicting changes in the main population and community characteristics of the animal species studied as dependent on the degree of anthropogenic impact.  相似文献   
52.
Peregrine falcons (Falco peregrinus) have been recorded nesting in Big Bend National Park, Texas, USA and other areas of the Chihuahuan Desert since the early 1900s. From 1993 to 1996, peregrine falcon productivity rates were very low and coincided with periods of low rainfall. However, low productivity also was suspected to be caused by environmental contaminants. To evaluate potential impacts of contaminants on peregrine falcon populations, likely avian and bat prey species were collected during 1994 and 1997 breeding seasons in selected regions of western Texas, primarily in Big Bend National Park. Tissues of three peregrine falcons found injured or dead and feathers of one live fledgling also were analyzed. Overall, mean concentrations of DDE [1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene], a metabolite of DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane], were low in all prey species except for northern rough-winged swallows (Stelgidopteryx serripennis, mean = 5.1 microg/g ww). Concentrations of mercury and selenium were elevated in some species, up to 2.5 microg/g dw, and 15 microg/g dw, respectively, which upon consumption could seriously affect reproduction of top predators. DDE levels near 5 microg/g ww were detected in carcass of one peregrine falcon found dead but the cause of death was unknown. Mercury, selenium, and DDE to some extent, may be contributing to low reproductive rates of peregrine falcons in the Big Bend region.  相似文献   
53.
54.
55.
56.
57.
Three monoclonal antibodies (MAbs) against trophoblast (GB17, GB21, and GB25) and flow cytometry were used to sort trophoblast-like cells (TLCs) from peripheral blood of pregnant women. Sorted TLCs were processed for electron microscopy and fetal DNA amplification of the Y-specific sequences from mothers carrying male fetuses. At the ultra-structural level, most of the nucleated cells had the morphology of leucocytes, suggesting maternal contaminants, and we did not find the characteristic features of the free inter-villous trophoblast cells. Nevertheless, polymerase chain reaction (PCR) analysis showed an amplification of Y-specific sequences in two out of three samples of sorted TLCs. These results suggest that besides the maternal leucocytes, sufficient trophoblast nucleated fetal cells can be obtained using cell enrichment by sorting. This sensitive method holds promise for non-invasive prenatal diagnosis of fetal sex and if sufficient Y(positive) nuclei are found, for the diagnosis of selected numerical chromosome abnormalities.  相似文献   
58.
59.
The past two decades have witnessed an increase in the exploration for, and development of, mineral resources at Arctic latitudes. Such effort has resulted in the commencement of production at a number of different localities in close proximity to the ocean. Since proximity to a source of transportation for the conveyance of concentrates to the market is a primary requirement governing the economic decisions for the mine to proceed, it is logical that ore deposits near a coastline are primary targets for development.

Closely tied to coastal mining developments is the need to dispose of tailings and waste rock in the most economical manner. Prior to the advent of heightened public awareness and environmental concern, and the enactment of pollution legislation, disposal practices were largely based upon convenience. Currently, however, proposed disposal and operating practices receive closer scrutiny, with a view to providing adequate protection for aquatic resources and habitat. This paper summarizes some of the features of three Arctic mines, wastes from which enter the marine environment, and compares the disposal practices used at each to measures of environmental change as indicated by metal concentrations in various media.  相似文献   
60.
“Ah, Mr. Cahill, I wonder if you could come back to the auditor's team room. It seems one of your auditors has fallen asleep for the second time this week. I know you had a grueling trip getting here, but this is embarrassing to everyone”. So went an audit I led some time ago. It was not a fun experience, and it has left some scars. There has been much discussion lately in the profession about certifying environmental (health and safety) auditors against certain performance criteria. But how does one evaluate for such important measures as physical stamina?. This article discusses the qualifications that environmental auditors should have if they are to lead or conduct a quality audit. It becomes evident after reviewing these expectations that certifying auditors through a traditional written examination might ignore some of the most important skills an auditor should possess, especially in working with managers throughout an organization. Before certifying organizations progress too far down the restrictive written-exam road, they should determine how these other skills are to be assessed. No amount of book learning can overcome the drawbacks of a poor or combative interviewer or even an exhausted auditor.  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