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   915篇
  免费   8篇
  国内免费   15篇
安全科学   27篇
废物处理   53篇
环保管理   93篇
综合类   142篇
基础理论   204篇
环境理论   2篇
污染及防治   302篇
评价与监测   55篇
社会与环境   58篇
灾害及防治   2篇
  2023年   2篇
  2022年   15篇
  2021年   17篇
  2020年   8篇
  2019年   8篇
  2018年   29篇
  2017年   36篇
  2016年   36篇
  2015年   31篇
  2014年   29篇
  2013年   93篇
  2012年   47篇
  2011年   73篇
  2010年   56篇
  2009年   55篇
  2008年   66篇
  2007年   53篇
  2006年   47篇
  2005年   31篇
  2004年   29篇
  2003年   31篇
  2002年   19篇
  2001年   8篇
  2000年   6篇
  1999年   6篇
  1998年   8篇
  1997年   9篇
  1996年   4篇
  1995年   12篇
  1994年   2篇
  1993年   4篇
  1991年   4篇
  1990年   3篇
  1987年   2篇
  1981年   3篇
  1965年   7篇
  1964年   3篇
  1963年   4篇
  1962年   9篇
  1961年   11篇
  1960年   1篇
  1958年   2篇
  1957年   1篇
  1956年   1篇
  1954年   1篇
  1947年   1篇
  1942年   1篇
  1941年   2篇
  1938年   1篇
  1932年   1篇
排序方式: 共有938条查询结果,搜索用时 15 毫秒
901.
The success of reintroduction programs greatly depends on the amount of mortality and dispersal of the released individuals. Although local environmental pressures are likely to play an important role in these processes, they have rarely been investigated because of the lack of spatial replicates of reintroduction. In the present study, we analyzed a 25-year data set encompassing 272 individuals released in five reintroduction programs of Griffon Vultures (Gyps fulvus) in France to examine the respective roles of survival and dispersal in program successes and failures. We use recent developments in multi-strata capture-recapture models to take into account tag loss in survival estimates and to consider and estimate dispersal among release areas. We also examined the effects of sex, age, time, area, and release status on survival, and we tested whether dispersal patterns among release areas were consistent with habitat selection theories. Results indicated that the survival of released adults was reduced during the first year after release, with no difference between sexes. Taking into account local observations only, we found that early survival rates varied across sites. However when we distinguished dispersal from mortality, early survival rates became equal across release sites. It thus appears that among reintroduction programs difference in failure and success was due to differential dispersal among release sites. We revealed asymmetrical patterns of dispersal due to conspecific attraction: dispersers selected the closest and the largest population. We showed that mortality can be homogeneous from one program to another while, on the contrary, dispersal is highly dependent on the matrix of established populations. Dispersal behavior is thus of major interest for metapopulation restoration and should be taken into account in planning reintroduction designs.  相似文献   
902.
903.
The pH-dependent release of cadmium, copper, and lead from soil materials was studied by use of a stirred flow cell to quantify their release and release rates, and to evaluate the method as a test for the bonding strength and potential mobility of heavy metals in soils. Soil materials from sludge-amended and nonamended A horizons from a Thai coarse-textured Kandiustult and a Danish loamy Hapludalf were characterized and tested. For each soil sample, release experiments with steady state pH values in the range 2.9 to 7.1 and duration of 7 d were performed. The effluent was continuously collected and analyzed. Release rates and total releases were higher for the Hapludalf than the Kandiustult and higher for the sludge-amended soils than the nonamended soils. With two exceptions the relative release rates (release rate/total content of metal in soil) plotted vs. steady state pH followed the same curves for each metal, indicating similar bonding strengths. These curves could be described by a rate expression of the form: relative release rate = k[H+]a, with specific a (empirical constant) and k (rate constant) parameters for each metal demonstrating that metal release in these systems can be explained by proton-induced desorption and dissolution reactions. With decreasing pH, pronounced increases in release rates were observed in the sequence cadmium > lead > copper, which express the order of metal lability in the soils. The flow cell system is useful for comparison of metal releases as a function of soil properties, and can be used as a test to rank soils with respect to heavy metal leaching.  相似文献   
904.
The Oregon Department of Forestry is a designated management agency to provide a forestry program to assist in bringing the Tualatin River into complicance with pH and dissolved oxygen water quality standards. The Oregon Environmental Quality Commission set a total maximum daily load (TMDL) of 70 µg/l total phosphorus to control algae growth and meet these standards. The Department of Forestry has a basin effectiveness monitoring plan to determine that the Oregon Forest Practice Rules' BMPs are maintaining adequate control of phosphorus loadings from forest operations. Three sites monitored during May to October of 1990 were augmented by eight more sites in 1991. As laboratory methods were refined, the results became more accurate. The 1991 monitoring showed lower phosphorus levels that were consistent for each tributary. Mean total phosphorus levels ranged from 17 to 65 µg/l. Preliminary field reconnaissance suggests a correlation between phosphorus levels and underlying geology. Concentrations were lowest at sites underlain by tertiary intrusive basalts, next higher for sites with terrestrial basalt, next higher for one site with a basalt-sandstone bedrock mix, and highest for sites underlain predominately by sandstone. These results may be modified by 1992 monitoring and further analysis.  相似文献   
905.
906.
907.
Two types of northern Adriatic mucous macroaggregates—surface and cloud-like—collected in June 2000 at the sea surface and at the depth of the pycnocline, respectively, were studied by light and cryo-scanning electron microscopy. The combination of both techniques permitted investigation of species/particle composition and particle–organic matrix associations of copious mucous aggregates. Both types of macroaggregates had, on average, heterogeneous composition with diatoms the dominant biotic component, differing by the prevailing species and stage of degradation. Some differences in the organization of the basic fibrillar organic network of macroaggregates were observed. Clouds were characterized by a tighter organization of the polysaccharidic fibrils within the walls of the organic network constituting the cloud. This organization was looser in the organic network within surface aggregates. Plankton remains and inorganic particles could lead to lower porosity and greater rigidity of these aggregates. The more complex organization of the organic matter and the intense growth of Cylindrotheca closterium within the clouds probably reflect a longer physical diagenesis of the polysaccharidic fibrils in comparison to surface aggregates.Communicated by O. Kinne, Oldendorf/Luhe  相似文献   
908.
Research aimed at understanding the response of plants to ozone has been conducted for over four decades but little of it has addressed intact natural systems. Even so, there is sufficient scientific information at this time to support air quality standards that will protect natural terrestrial ecosystems from ozone. What is unknown is the risk associated with continued exposure of natural systems, including both above- and below-ground components, in combination with other stresses including changing temperature and precipitation, elevated carbon dioxide, pests and pathogens, invasive species, and other activities that may fragment the landscape. Research to support an assessment of the ecological risk associated with ozone as it exists, in a milieu of stresses, must include endpoints beyond those addressed in the past, primarily productivity and species composition. To estimate the risk to society of ozone impacts on natural systems, endpoints such as the integrity of soil food webs, the quantity and quality of water supplied from terrestrial ecosystems, wildlife and recreational values, and the transfer and fate of carbon, nutrients, and water within the systems must be quantified. Not only will this research provide the basis for a sound estimate of risk, but also it will improve our understanding of fundamental ecosystem processes.  相似文献   
909.
910.
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