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   94805篇
  免费   1225篇
  国内免费   1135篇
安全科学   3825篇
废物处理   3554篇
环保管理   14400篇
综合类   21316篇
基础理论   26777篇
环境理论   72篇
污染及防治   17033篇
评价与监测   5716篇
社会与环境   3902篇
灾害及防治   570篇
  2022年   812篇
  2021年   829篇
  2020年   656篇
  2019年   872篇
  2018年   1193篇
  2017年   1235篇
  2016年   2240篇
  2015年   1855篇
  2014年   2617篇
  2013年   9293篇
  2012年   2373篇
  2011年   2760篇
  2010年   3344篇
  2009年   3512篇
  2008年   2369篇
  2007年   2252篇
  2006年   2587篇
  2005年   2501篇
  2004年   2833篇
  2003年   2666篇
  2002年   2206篇
  2001年   2635篇
  2000年   2188篇
  1999年   1592篇
  1998年   1394篇
  1997年   1377篇
  1996年   1506篇
  1995年   1603篇
  1994年   1501篇
  1993年   1350篇
  1992年   1335篇
  1991年   1314篇
  1990年   1272篇
  1989年   1211篇
  1988年   1066篇
  1987年   1003篇
  1986年   996篇
  1985年   1072篇
  1984年   1169篇
  1983年   1171篇
  1982年   1176篇
  1981年   1107篇
  1980年   948篇
  1979年   944篇
  1978年   823篇
  1977年   724篇
  1976年   648篇
  1974年   622篇
  1973年   654篇
  1972年   657篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
211.
212.
213.
Observations of air temperature changes in a steppe marmot burrow were performed from late July to mid-October. Until early September, temperature in the burrow remained relatively constant, but then it began to decrease rapidly. This occurred after air temperature above the ground became equal to the temperature in the burrow. Supposedly, it is in this particular period that marmots begin to plug the entrance to the burrow with earth, thus reducing heat exchange between the increasingly cold aboveground air and the air in the burrow.  相似文献   
214.
In the periods of summer and autumn bloom of the Stephanodiscus hantzschii Crun. in recreational water bodies, studies on the vertical distribution of chlorophyll a, its contents per unit biomass, efficiency in using photosynthetically active radiation (EPhAR), and assimilative activity of microalgae were performed. The results confirmed the existence of two ecophysiological forms of St. hantzschii and provided evidence that both forms are typically autotrophic and can efficiently use low-intensity PhAR for photosynthesis.  相似文献   
215.
On-going population growth and resulting domestic demand for water require rapid and effective decision-making as regards groundwater management and control of the various sources of salinization and pollution in Coastal aquifers. Sustainability of water resources for utilization by future generations must therefore be a high priority, not only for the purpose of fulfilling needs for water usage but also for bringing people into harmony with their ambient natural environment.The objective of this paper is to propose an empirical approach for prioritization of the needs involved for sustainable aquifer management. The approach involves a schematic format to:(1) develop a global understanding of an aquifer's hydrological and environmental properties in order to delineate appropriate eco-hydrological scenarios and recommend corresponding operational management activities; and(2) emphasize the importance of educating and increasing the awareness of the population involved as to the need for and viability of socially acceptable measures for sustainable management of groundwater and other resources.The psychologist Abraham Maslow utilized a pyramid to illustrate that until people's most basic needs were fulfilled, higher levels of needs would remain irrelevant. This paper postulates a comparable pyramid prioritizing hydrological needs required for progressing towards sustainable groundwater resources. Two sub-regions of Israel's Coastal aquifer in the Sharon region have been presented as representative areas, each characterized by different stress of exploitation. In assessing these sub-regions situation, specific measures have been recommended for achieving and/or maintaining sustainable groundwater resources in light of the ambient environment, and the level of the population on the pyramidal hierarchy of groundwater needs.  相似文献   
216.
217.
218.
Benthic organisms can significantly alter the physical properties of marine sediments, but it has hitherto been difficult to assess and quantify the effects of bioturbation. In situ geophysical techniques offer new methods for measuring these effects: measurement of acoustic shear-wave velocity and electrical resistivity allows nondestructive assessment of the properties of the grain framework and pore-fluid matrix, respectively, of the seabed sediment. The influence of burrowing invertebrates on the structural properties of sandy sediments at intertidal locations on the coast of Wales (UK) was investigated during the periol 1986–1987 using these techniques. Three species (Arenicola marina, Corophium arenarium and Lanice conchilega) were selected on the basis of their contrasting styles of burrow construction. All three species produced measurable and significant, although different, changes in bed properties. They modified shear-wave propagation through the bed by changing bed rigidity: while A. marina and C. arenarium decreased rigidity by creating open burrows, L. conchilega increased rigidity by building shell-lined tubes. All produced a decrease in electrical resistivity by altering porosity and/or tortuosity, which implies an increase in permeability; these changes were attributable not only to the presence of the burrows but also to modification of the between-burrow sediment texture and bed properties.  相似文献   
219.
220.
Study on Assessing Economic Vulnerability of Small Island Regions   总被引:2,自引:0,他引:2  
The main purpose of this study is to assess economic vulnerability of small island development regions as part of their sustainability constraints. By combining economic and environmental time series data, we assessed a composite index of economic vulnerability which is constructed from three exogenous variables, namely economic exposure, economic remoteness, and economic impact of environmental and natural disasters. We used the Amami Islands, Kagoshima Prefecture, Japan as the case studies for this paper.The results indicated that using a gross island products based valuation index, Kikaijima is the most vulnerable island in the Amami Islands with a composite economic vulnerability index (CEVI) value of 0.678, while by using a per capita based index, Okinoerabujima is considered the most vulnerable island with a CEVI value of 0.680. From the results we also revealed that smaller islands have relative higher vulnerability than the bigger one, which also confirms some previous country-level vulnerability studies.However, it is matter of fact that some islands that have relatively high vulnerability also have good economic performance as shown by their per capita income. In this regard, it can be argued that the success of these small islands could have been achieved in spite of and not because of their inherent vulnerability conditions as an indicator of sustainability constraint. Regarding these findings, we also examined a comparison between vulnerability results and the preliminary concept of an island's resilience in order to capture another perspective on sustainability assessment in a small island region.  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