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   33337篇
  免费   358篇
  国内免费   316篇
安全科学   927篇
废物处理   1449篇
环保管理   4291篇
综合类   5323篇
基础理论   8583篇
环境理论   14篇
污染及防治   8642篇
评价与监测   2429篇
社会与环境   2122篇
灾害及防治   231篇
  2022年   300篇
  2021年   312篇
  2020年   224篇
  2019年   280篇
  2018年   488篇
  2017年   519篇
  2016年   787篇
  2015年   584篇
  2014年   862篇
  2013年   2810篇
  2012年   1039篇
  2011年   1367篇
  2010年   1218篇
  2009年   1238篇
  2008年   1409篇
  2007年   1503篇
  2006年   1358篇
  2005年   1118篇
  2004年   1092篇
  2003年   1096篇
  2002年   1008篇
  2001年   1309篇
  2000年   959篇
  1999年   582篇
  1998年   431篇
  1997年   412篇
  1996年   461篇
  1995年   455篇
  1994年   426篇
  1993年   413篇
  1992年   410篇
  1991年   385篇
  1990年   386篇
  1989年   363篇
  1988年   327篇
  1987年   267篇
  1986年   255篇
  1985年   282篇
  1984年   308篇
  1983年   296篇
  1982年   317篇
  1981年   277篇
  1980年   253篇
  1979年   280篇
  1978年   211篇
  1977年   205篇
  1976年   160篇
  1974年   182篇
  1973年   163篇
  1972年   171篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
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   
83.
84.
A method for estimating the current state of plant communities based on the ecological amplitudes of constituent species is proposed. An original program, Fitoindikatsiya, has been developed to compute the indices of disturbance and homogeneity of plant communities from species ecological scale values. The current state of pine forests in the part of Novosibirsk oblast east of the Ob River has been analyzed; slightly, moderately, and severely disturbed zones have been distinguished.  相似文献   
85.
86.
Estimates of animal methane emissions   总被引:2,自引:0,他引:2  
The enteric methane emissions into the atmospheric annually from domestic animals total about 77 Tg. Another 10 to 14 Tg are likely released from animal manure disposal systems. About 95% of global animal enteric methane is from ruminants, a consequence of their large populations, body size and appetites combined with the extensive degree of anaerobic microbial fermentation occurring in their gut. Accurate methane estimates are particularly sensitive to cattle and buffalo census numbers and estimated diet consumption. Since consumption is largely unknown and must be predicted, accuracy is limited often by the information required, i.e., distribution of animals by class, weight and productivity. Fraction of the diet lost as enteric methane mostly falls into the range of 5.5–6.5% of gross energy intake for the world's cattle, sheep and goats. Manure methane emissions are heavily influenced by fraction of disposal by anaerobic lagoon. Non-ruminants, i.e., swine, become major contributors to these emissions.  相似文献   
87.
88.
89.
90.
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   
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