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   99248篇
  免费   1243篇
  国内免费   1141篇
安全科学   3909篇
废物处理   3684篇
环保管理   15017篇
综合类   21591篇
基础理论   27718篇
环境理论   77篇
污染及防治   18743篇
评价与监测   5947篇
社会与环境   4312篇
灾害及防治   634篇
  2022年   834篇
  2021年   837篇
  2020年   669篇
  2019年   888篇
  2018年   1294篇
  2017年   1348篇
  2016年   2303篇
  2015年   1882篇
  2014年   2640篇
  2013年   9356篇
  2012年   2576篇
  2011年   3200篇
  2010年   3486篇
  2009年   3606篇
  2008年   2758篇
  2007年   2715篇
  2006年   2878篇
  2005年   2709篇
  2004年   3017篇
  2003年   2866篇
  2002年   2410篇
  2001年   2881篇
  2000年   2314篇
  1999年   1657篇
  1998年   1427篇
  1997年   1416篇
  1996年   1546篇
  1995年   1642篇
  1994年   1534篇
  1993年   1381篇
  1992年   1378篇
  1991年   1349篇
  1990年   1285篇
  1989年   1270篇
  1988年   1108篇
  1987年   1027篇
  1986年   1010篇
  1985年   1087篇
  1984年   1181篇
  1983年   1195篇
  1982年   1189篇
  1981年   1109篇
  1980年   959篇
  1979年   950篇
  1978年   837篇
  1977年   737篇
  1976年   664篇
  1974年   644篇
  1973年   668篇
  1972年   686篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
311.
312.
313.
314.
One of the most difficult tasks in conservation biology is identifying populations subject to stress before such stress has a detrimental impact on the population, thus allowing conservation and remedial action to be undertaken. Measuring fitness (fecundity, survival, etc.) changes directly is often difficult, expensive, or impractical. The ability of an organism to buffer its development against disturbances (developmental stability) is often considered an integral component of an individual's fitness. Data are presented from a number of studies that establish a clear relationship between developmental stability and fitness in response to both genetic and environmental stress. Consequently, I suggest that developmental stability may be used as a surrogate for more direct fitness estimation for use in conservation biology and biomonitoring programs and that is has widespread application as an early warning system for monitoring the effect of genetic and environmental stresses on natural populations.  相似文献   
315.
316.
Red pine (Pinus resinosa Ait.) is rare (< 15 000 mature trees) in Newfoundland and is known from only 22 locations in the central region. Red pine occupies 3 major site types in Newfoundland: 1) red pine on medium-textured sands (RP1), 2) red pine on coarse-textured glaciofluvial deposits (RP2), and 3) red pine on Folisols over bedrock (RP3). The succession of red pine site types after cutting is from red pine to Kalmia-black spruce (Picea mariana (Mill.) B.S.P.) for RP1, and to Cladonia-Kalmia-black spruce for types RP2 and RP3. Succession after fire is usually to the pre-fire type, but this depends on the severity of the fire.Although occupying a relatively poor site, red pine at 60–70 years reaches heights in excess of 18 m, dbh in excess of 40 cm, and individual tree volumes greater than 1 m3 were recorded in 75 stemanalyzed fire-killed trees. Black spruce on that same site produces less than one-third that volume in 60 years. Merchantable volume of 140–280 m3 ha-1 were recorded i.e., Canada Land Inventory (CLI) forest capability class 5 and class 4 ratings. This raises the CLI rating two capability classes if red pine were occupying these poor quality sites over black spruce. In terms of nutrition, even the best growing red pine are nitrogen (N) deficient as shown by foliar analysis. All natural stands have foliar N concentrations below 1.3% which is the critically low level shown in the literature. Immediately after fire, foliar concentrations reach this level but are usually about 1% or less. Most other nutrients are low but are within the generally reported adequate levels in testing for P, K, Ca and Mg.Fire influences soil nutrient availability as pH increases in the RP1 type. Burning temperature also affects soil pH and the understory vegetation. The RP2 type loses more N in hotter burns on this site type and more N is tied up in these ortstein hardpan soils. The pattern of regeneration following wildfire is related to slope, density, age and species mixture of the stand as well as the thickness and composition of the duff layer.  相似文献   
317.
318.
Protected areas in developing countries play a vital role in promoting the ideal of sustainable development.But 'people-park'conflicts are commonplace,threatening the future of these areas and the long term well-being of local communities. Surprisingly, little attention has been given to applying lessons learned in conflict studies to people-parkconflicts. In contrast to traditional adversarialresponses, negotiated approaches offer considerable potential for transforming people-park conflicts into mutually beneficial relationships.Experiencesin the Richtersveldregion of South Africa demonstrate the cardinal role negotiation can play in addressing key issues underlying people-park conflicts.  相似文献   
319.
Risk homeostasis theory postulates that people accept a specific level (target level) of risk in a given activity in return for benefits accruing from that activity. It follows that, if people expect a great deal from the future, the less likely they are to jeopardise it by taking risks in respect of their health and safety. One effective method for reducing target level of risk are incentives, and the available literature contains ample evidence of the effectiveness of incentives programmes in accident prevention. As incentives essentially imply an enhanced quality of life in the future, the question arises as to how expectations of the future may be related to health and safety habits. In order to explore the relationship between perceived value of the future and health and safety habits, an analysis of the psychological literature on individual differences in future time orientation/perspective is presented. Four factors are identified: (1) clear ideation of the future, (2) active planning for the future, (3) time pressure, and (4) optimistic expectations about events outside one's own control. It is hypothesised that factors (1) and (2) are associated with positive health and safety habits, while factors (3) and (4) may characterise individuals with relatively high target levels of physical risk. Research questions and procedures for the study of these relationships are discussed.  相似文献   
320.
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