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   34843篇
  免费   716篇
  国内免费   5634篇
安全科学   1443篇
废物处理   1922篇
环保管理   3562篇
综合类   10744篇
基础理论   7835篇
环境理论   6篇
污染及防治   10820篇
评价与监测   2182篇
社会与环境   1941篇
灾害及防治   738篇
  2023年   310篇
  2022年   882篇
  2021年   754篇
  2020年   545篇
  2019年   602篇
  2018年   847篇
  2017年   970篇
  2016年   1192篇
  2015年   1207篇
  2014年   1724篇
  2013年   3347篇
  2012年   1919篇
  2011年   2189篇
  2010年   1745篇
  2009年   1728篇
  2008年   1891篇
  2007年   1877篇
  2006年   1681篇
  2005年   1313篇
  2004年   1130篇
  2003年   1242篇
  2002年   1140篇
  2001年   1287篇
  2000年   1043篇
  1999年   859篇
  1998年   692篇
  1997年   594篇
  1996年   621篇
  1995年   553篇
  1994年   484篇
  1993年   420篇
  1992年   390篇
  1991年   295篇
  1990年   281篇
  1989年   273篇
  1988年   240篇
  1987年   188篇
  1986年   151篇
  1985年   150篇
  1984年   184篇
  1983年   171篇
  1982年   204篇
  1981年   146篇
  1980年   120篇
  1979年   154篇
  1978年   121篇
  1977年   108篇
  1976年   101篇
  1975年   87篇
  1974年   90篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
81.
Environmental factors have long been shown to influence species distributions, with range limits often resulting from environmental stressors exceeding organism tolerances. However, these abiotic factors may differentially affect species with multiple life-history stages. Between September 2004 and January 2006, the roles of temperature and nutrient availability in explaining the southern distributions of two understory kelps, Pterygophora californica and Eisenia arborea (Phaeophyceae, Laminariales), were investigated along the coast of California, USA and the Baja California Peninsula, Mexico, by limiting either: (a) tissue nitrogen uptake and storage by adult sporophytes during periods of elevated temperature, and/or (b) production of embryonic sporophytes by microscopic gametophytes. Results suggest that while adult sporophytes of both species are tolerant of high temperatures and low nutrients, reproduction by their microscopic stages is not. Specifically, while E. arborea produced embryonic sporophytes at both 12 and 18°C, temperatures commonly observed throughout the southern portion of its range, P. californica produced sporophytes at 12 but not at 18°C. As a result, it appears that the southern distribution of P. californica, which ends in northern Baja California, Mexico, may be limited by temperature acting on its microscopic stages. In contrast, the ability of E. arborea’s microscopic and adult stages to tolerate elevated temperatures allows it to persist in the warmer southern waters of Baja California, as well as to the north along the California coast where both species co-occur.  相似文献   
82.
83.
84.
85.
86.
Community evacuation following a chlorine release, Mississippi   总被引:1,自引:0,他引:1  
On 7th September 1986, four miles north of Collins, Mississippi, a train transporting chlorine derailed. Two cars ruptured and gas escaped. As a result, 100 families were evacuated. To study the evacuation process, we conducted person-to-person interviews with sixty-two families staying in the evacuation center. Only 52.5% of the families received their first directive to evacuate directly from police or other officials. Delays in evacuating tended to be shorter when people were warned by the police and were told the reason for evacuating. Lack of personal transportation and preexisting health problems resulted in delays in evacuation. Concerns about evacuation included fear of looting, lack of a place to go, lack of transportation, difficulty in moving with children and elderly persons, and the need to take care of pets. One third of the interviewees reported feeling panic. Community evacuation procedures would be improved if: (1) officials contact all households directly; (2) the warning message addresses people's concerns; and (3) transportation is provided.  相似文献   
87.
ABSTRACT: This paper describes the formulation of an Index of Water Quality to evaluate the level of pollution in fresh water. A Four-Round Delphi equation, using a panel of seven nationally recognized water scientists, was performed to ascertain the pollutants to be included in the index, the relationship between the quantity of these pollutants in the water and the resulting quality of the water, and the importance of each pollution variable to each water use as well as to overall pollution. A multiplicative index was used to bring the pollutants together into one system.  相似文献   
88.
详细讨论了卫星遥感技术在长江流域水资源管理方面的应用问题,提出了两种实用的方法:①卫星遥感技术在灌溉水资源管理方面的应用;②长江流域地下水、地表水资源估算。进一步分析了两种方法的特点,介绍了卫星遥感技术的优点及用途,建议在长江流域水资源管理中加以利用。  相似文献   
89.
农业生产地域分工与农产品专业化生产是使农业从自然经济阶段向以市场为导向的商品农产品生产转变的一个标志。本文在分析该区农业布局现状及其存在问题的基础上,提出了农业总体布局的设想与不同类型地域农业开发的主攻方向与对策,并对市场经济体制下粮食、棉花、猪、禽、水产品等农产品生产基地的地域选择、建设规模与技术措施等进行了探讨。  相似文献   
90.
Material suppliers and industrial metabolism   总被引:1,自引:1,他引:0  
Life Cycle Assessment (LCA) is not sufficiently tailored to the analysis of strategic environmental problems of material suppliers. Sustainable development calls for a reduction by a factor of 10 to 20 in the material intensity of the economy, a situation which leads to dramatic shifts in markets for raw materials. Furthermore, a material supplier might have major improvement options in the material’s numerous downstream uses. LCAs, however, can’t cover these two aspects. An adapted form of Substance Flow Analysis (SFA) may be an answer. This approach defines a system in relation to the flow of a specific material through society. All environmental interventions related to the material are inventoried. An emission evaluation indicates the dominant environmental bottlenecks, given the current market volume of each application of the material. This helps to identify improvement options and strategic choices in market portfolios. Scenario analysis on potential measures can further indicate changes of material flows — and thus markets — in the system. The approach is illustrated with a case study on chlorine.  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