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   1337篇
  免费   188篇
  国内免费   4篇
安全科学   129篇
废物处理   82篇
环保管理   389篇
综合类   95篇
基础理论   466篇
环境理论   1篇
污染及防治   212篇
评价与监测   29篇
社会与环境   57篇
灾害及防治   69篇
  2022年   3篇
  2021年   14篇
  2020年   11篇
  2019年   44篇
  2018年   61篇
  2017年   44篇
  2016年   73篇
  2015年   58篇
  2014年   72篇
  2013年   287篇
  2012年   48篇
  2011年   75篇
  2010年   71篇
  2009年   55篇
  2008年   66篇
  2007年   53篇
  2006年   41篇
  2005年   42篇
  2004年   40篇
  2003年   37篇
  2002年   51篇
  2001年   28篇
  2000年   31篇
  1999年   20篇
  1998年   8篇
  1997年   13篇
  1996年   14篇
  1995年   10篇
  1994年   15篇
  1993年   11篇
  1992年   11篇
  1991年   7篇
  1989年   4篇
  1988年   3篇
  1987年   7篇
  1986年   3篇
  1985年   10篇
  1984年   11篇
  1983年   13篇
  1982年   7篇
  1981年   5篇
  1980年   7篇
  1979年   7篇
  1978年   4篇
  1977年   7篇
  1976年   4篇
  1975年   4篇
  1974年   3篇
  1970年   3篇
  1969年   2篇
排序方式: 共有1529条查询结果,搜索用时 15 毫秒
121.
122.
Fire influences the distribution of fauna in terrestrial biomes throughout the world. Use of fire to achieve a mosaic of vegetation in different stages of succession after burning (i.e., patch‐mosaic burning) is a dominant conservation practice in many regions. Despite this, knowledge of how the spatial attributes of vegetation mosaics created by fire affect fauna is extremely scarce, and it is unclear what kind of mosaic land managers should aim to achieve. We selected 28 landscapes (each 12.6 km2) that varied in the spatial extent and diversity of vegetation succession after fire in a 104,000 km2 area in the semiarid region of southeastern Australia. We surveyed for reptiles at 280 sites nested within the 28 landscapes. The landscape‐level occurrence of 9 of the 22 species modeled was associated with the spatial extent of vegetation age classes created by fire. Biogeographic context and the extent of a vegetation type influenced 7 and 4 species, respectively. No species were associated with the diversity of vegetation ages within a landscape. Negative relations between reptile occurrence and both extent of recently burned vegetation (≤10 years postfire, n = 6) and long unburned vegetation (>35 years postfire, n = 4) suggested that a coarse‐grained mosaic of areas (e.g. >1000 ha) of midsuccessional vegetation (11–35 years postfire) may support the fire‐sensitive reptile species we modeled. This age class coincides with a peak in spinifex cover, a keystone structure for reptiles in semiarid and arid Australia. Maintaining over the long term a coarse‐grained mosaic of large areas of midsuccessional vegetation in mallee ecosystems will need to be balanced against the short‐term negative effects of large fires on many reptile species and a documented preference by species from other taxonomic groups, particularly birds, for older vegetation. Mosaicos de Fuego y la Conservación de Reptiles en una Región Propensa al Fuego  相似文献   
123.
Simultaneous measurements of individual hydrocarbons and individual carbonyls were carried out at a downtown Los Angeles location. Concentrations are presented for 50 compounds in morning air samples. While paraffins (C ≥ 4) were a major hydrocarbon subclass on a ppmC basis, higher aromatics (C ≥ 8) were the major component when taking reactivity considerations into account. Comparison of the results with emission inventory data showed good agreement for many hydrocarbons and for paraffins as a subclass. Measured olefins and aromatics concentrations were substantially lower and higher, respectively, than those expected from inventory data.  相似文献   
124.
125.
Abstract: Conservation researchers are increasingly aware of the need to conduct interdisciplinary research and to engage nonscientists in practical applications of conservation biology. But so far, industrial designers have been left out of such collaboration and outreach efforts. Conservation of wildlife often depends on products such as nest boxes, feeders, barriers, and corridors, all of which have a designed component that is frequently overlooked. Furthermore, many products are adopted without testing on short or long time scales. We argue that the design of products for conservation, and hence their functionality, effectiveness, and value, can be improved through collaboration with industrial designers. We see four key benefits that can arise from interactions with industrial designers: improvement of product quality and value, innovation and improvement in functionality of products, harmonization of conservation products with local values, and development of a psychological biomimesis approach to design. The role of industrial designers in conservation projects would be to improve factors such as product durability, affordability, functionality, and aesthetic appeal to local people. Designers can also help to create multiple product options whose success can be tested in the field. We propose that collaborations with industrial designers can contribute to the development of improvements to existing products and innovations in the practice of animal conservation.  相似文献   
126.
The towns and cities of Saudi Arabia have been subjected to sustained growth pressures since the transformation of the country's economy following the discovery of oil in the Eastern Province of the Kingdom. The rapid growth which has been experienced has created major problems for the central and local government agencies responsible for planning and managing urban growth. The experience of Jeddah, one of the major cities in Saudi Arabia, is described and the problems of planning and managing its growth are analysed. Weaknesses relating to the structure of the planning system are identified, as are major difficulties in relation to the quality and quantity of professional staff. Recent attempts to improve the operation of the planning system are described and evaluated.  相似文献   
127.
128.
Traditionally, identification of the Muskingum routing coefficients has been based on observations of the linearity of a loop formed by graphically plotting a forward and a reverse path. This graphical procedure is time-consuming and may not minimize the error of estimation. A procedure was developed to improve the drawbacks of the graphical method. This procedure calls for (a) the use of least square regression on the forward and reverse paths to determine their respective slopes, and (b) the use of statistical t-test to evaluate the hypothesis that these two slopes are equal. The computational procedure is repeated, using incremental values of the flow weighting coefficient, x. A graph of the computed t-value versus x can be constructed. The optimal value of x, as read from the graph, occurs at the minimum computed t-value. The procedure has been demonstrated superior to the graphical method for three illustrative examples, resulting in a reduction of the error squares by factors ranging from 5 to 6.  相似文献   
129.
130.
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