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   51408篇
  免费   562篇
  国内免费   426篇
安全科学   1659篇
废物处理   2208篇
环保管理   7006篇
综合类   8015篇
基础理论   14086篇
环境理论   29篇
污染及防治   12853篇
评价与监测   3309篇
社会与环境   2881篇
灾害及防治   350篇
  2022年   403篇
  2021年   447篇
  2020年   308篇
  2019年   406篇
  2018年   747篇
  2017年   760篇
  2016年   1115篇
  2015年   893篇
  2014年   1328篇
  2013年   4049篇
  2012年   1624篇
  2011年   2223篇
  2010年   1833篇
  2009年   1900篇
  2008年   2255篇
  2007年   2276篇
  2006年   2077篇
  2005年   1780篇
  2004年   1745篇
  2003年   1644篇
  2002年   1613篇
  2001年   1959篇
  2000年   1386篇
  1999年   874篇
  1998年   688篇
  1997年   685篇
  1996年   729篇
  1995年   806篇
  1994年   696篇
  1993年   641篇
  1992年   656篇
  1991年   632篇
  1990年   596篇
  1989年   636篇
  1988年   546篇
  1987年   470篇
  1986年   451篇
  1985年   469篇
  1984年   488篇
  1983年   505篇
  1982年   530篇
  1981年   433篇
  1980年   368篇
  1979年   408篇
  1978年   344篇
  1977年   288篇
  1976年   286篇
  1975年   293篇
  1973年   301篇
  1972年   300篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
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   
103.
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   
104.
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   
105.
106.
107.
Critical loads offer a unique way of evaluating impacts of acid deposition by quantifying environmental sensitivity. The critical loads of acidity for UK peat soils have been based upon an arbitrary reduction in pH of 0.2 units. This chemical shift needs to be better related to adverse effects on sensitive biological receptors. It is known that effective precipitation pH equates closely to soil solution pH, and the latter is directly linkable to biotic effects of pH change. On continuation of a long-term experiment assessing impacts of simulated acid rain on peat microcosms in a realistic outdoor environment, Calluna vulgaris continued to flourish at acid deposition loads well above the existing critical load. Calluna plants were harvested and analysed, and acid deposition treatments to the microcosms continued to allow natural vegetation to regenerate. A diverse mixture of moorland plants and bryophytes established at acidity treatments well above the existing critical load, and only a very high acid load resulted in no natural regeneration. A critical effective rain pH value of 3.6 is suggested as a basis for setting critical loads. At this pH, Calluna grows well, and a healthy diverse vegetation community re-establishes when harvested. It is suggested that the peat critical load should be set at the acid load that, at any specific site, would result in a mean effective precipitation pH of 3.6.  相似文献   
108.
New experimental data on biological productivity of plant communities in oligotrophic and mesotrophic bogs of the middle taiga subzone over the past five years are presented. The relationship between net primary production and the stock of live phytomass is estimated. The stock of necromass in oligotrophic bog ecosystems increases from west to east, while the stock of live phytomass and net primary production decrease.  相似文献   
109.
Studies on paleosols under an archaeological landmark of a rare type (a complex of kurgans with “whiskers”) dating from the Early Iron Age (the fourth century AD) have been performed in the steppe zone of the Transural Plateau. The size and shape of third-order soil polygons under stony ridges (“whiskers”) between the kurgans have been described in detail. The results have shown that the paleosol under the kurgans erected at the turn of the Late Sarmatian and Hun times (1600 years ago) is characterized by a higher humus content and deeper location of the carbonate horizon, compared to the recent soil. This indicates that an increase in atmospheric humidity took place in the fourth century AD.  相似文献   
110.
要保护公园的生态、社会、经济和文化价值 ,游客管理具有根本的重要性 . 政府要求公园进一 步在财政上自给自足 . 正在制定一个更加完善的管理方法代替单纯地限制游客的数量 . 这种 方法鼓励公众参与公园的目标设定和游客满意度评价 ,并奖励胜任的财务管理 .  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