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   89451篇
  免费   1222篇
  国内免费   1081篇
安全科学   3706篇
废物处理   3268篇
环保管理   13756篇
综合类   21037篇
基础理论   26164篇
环境理论   71篇
污染及防治   14179篇
评价与监测   5378篇
社会与环境   3667篇
灾害及防治   528篇
  2022年   780篇
  2021年   795篇
  2020年   645篇
  2019年   857篇
  2018年   1118篇
  2017年   1164篇
  2016年   2159篇
  2015年   1825篇
  2014年   2575篇
  2013年   9245篇
  2012年   2153篇
  2011年   2382篇
  2010年   3285篇
  2009年   3368篇
  2008年   1901篇
  2007年   1749篇
  2006年   2173篇
  2005年   2184篇
  2004年   2511篇
  2003年   2334篇
  2002年   1893篇
  2001年   2222篇
  2000年   1972篇
  1999年   1488篇
  1998年   1361篇
  1997年   1351篇
  1996年   1477篇
  1995年   1566篇
  1994年   1473篇
  1993年   1330篇
  1992年   1315篇
  1991年   1289篇
  1990年   1221篇
  1989年   1214篇
  1988年   1042篇
  1987年   980篇
  1986年   985篇
  1985年   1055篇
  1984年   1154篇
  1983年   1162篇
  1982年   1170篇
  1981年   1091篇
  1980年   942篇
  1979年   917篇
  1978年   820篇
  1977年   714篇
  1976年   637篇
  1975年   601篇
  1973年   629篇
  1972年   634篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Garden black ants,Lasius niger L., in a laboratory colony, attacked three species of live ladybirds found near their nest, killing the smaller two species. A second colony was offered artificial diets containing crushed ladybirds of two species, and the ants' choice of feeding site noted. Both the diets were aversive compared to control, but that containing 7spot,Coccinella septempunctata L., was more aversive than the diet containing 2spot,Adalia bipunctata L. The implications of this lesser protection for 2spots in terms of the chemical defence of the species are discussed.  相似文献   
182.
183.
184.
185.
The typical parameters of acid precipitation are evaluated in the forest of Vallombrosa (Tuscan Appennines) during the dry period 1988-89. Individual rain events (dry and wet deposition) were sampled in a clearing of the forest and below the canopy of an evergreen tree as well as a deciduous broadleaf tree.

In atmospheric precipitation the pH values usually vary around 4.4, with neutralization in the hot season due to calcareous material from distant sources. Relatively large concentrations of Pb and Cd are found in rain, but only in a small amount in canopy leachate. Aluminium, manganese and iron are more significantly washed off than Pb and Cd.  相似文献   
186.
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   
187.
Sustainable development of the earth's limited water and land resources is of paramount importance because of rising world population and existing conflicting demands for these resources. Enormous capital investment has been made in developing these resources, but now there is irrefutable evidence that such developments have led to major resource degradation. This includes problems of salinisation and damages to ecosystems. The countries predominantly affected by human induced salinisation are located in arid and semi-arid regions of the world and include Australia, China, Egypt, India, Pakistan, USSR, and USA. This paper describes the processes of salinisation, its impacts and the use of quantitative methods in salinity investigation and management. Australia is used as a case study of typical salinity problems and as a demonstration of the fruitful application of quantitative methods. The paper concludes that quantitative methods such as surface water and groundwater models are powerful design, management and predictive tools in salinity investigation. However, application of some models, such as those for unsaturated flow and transport and groundwater solute transport, are not widespread due to uncertainties in describing the complexity of the processes and the lack of hydrodispersive data.  相似文献   
188.
A number of Mn-oxide minerals in soils from a farm in North Devon have been tentatively identified using a combination of advanced analytical techniques: scanning electron microscopy (SEM), scanning electron microprobe (SEMP), X-ray diffraction (XRD) and bulk chemical analysis by wet digestion followed by inductively-coupled plasma spectrometry (ICP). The minerals lithiophorite and hollandite are thought to occur throughout the study area although there is considerable geographical variation in the proportions of minerals present. Bimessite, vernadite, romanechite, todorokite and cryptomelane may also be present, although in smaller amounts. The use of SEMP, together with a simple sorption experiment, has allowed a study of the extent of uptake of Co and Cu by different Mn-oxide minerals. Lithiophorite appears to take up Co and Cu more effectively than hollandite within a pH range of 4–6.  相似文献   
189.
This article reviews the application of environmental impact assessment (EIA) procedures and practices to three watershed modification projects situaled in western Canada. These ventures were justified for accelerating regional economic development, and cover the period during which public concerns for protecting the environment rapidly made their way into the national political agenda. An historical account and analysis of the situation, therefore, seems desirable in order to understand the development of EIA processes, practices, and methodologies since the start of construction of the first project in 1961. This study concludes that there has been good progress in predicting and evaluating environmental and related social impacts of watershed modification proposals. However, a number of obstacles need to be overcome before EIA can firmly establish itself as an effective planning tool. These difficulties include jurisdictional confusions and conflicts, division of authority and responsibility in designing and implementing appropriate mitigative and monitoring measures, lack of tested EIA methodologies, and limited availability of qualified human resources. A number of conclusions and suggestions are offered so that future watershed modification proposals may be planned and implemented in a more environmentally sustainable fashion. These include: (1) EIA processes must be completed before irrevocable decisions are made. (2) Any major intrusion into a watershed is likely to impact on some major components of the ecosystem(s). (3) Mitigation costs must form part of the benefit-cost analysis of any project proposal. (4) Interjurisdictional cooperation is imperative where watersheds cross political boundaries. (5) The EIA process is a public process, hence public concerns must be dealt with fairly. (6) The role of science in the EIA process must be at arms length from project proponents and regulators, and allowed to function in the interest of the protection of the environment and public health and safety. The views expressed here are the authors’ own and do not necessarily reflect those of FEARO and/or other government agencies and officials involved in the review of these projects.  相似文献   
190.
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