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   1283篇
  免费   27篇
  国内免费   9篇
安全科学   55篇
废物处理   48篇
环保管理   331篇
综合类   133篇
基础理论   384篇
污染及防治   197篇
评价与监测   107篇
社会与环境   49篇
灾害及防治   15篇
  2023年   6篇
  2022年   11篇
  2021年   22篇
  2020年   14篇
  2019年   17篇
  2018年   28篇
  2017年   27篇
  2016年   47篇
  2015年   31篇
  2014年   29篇
  2013年   78篇
  2012年   75篇
  2011年   73篇
  2010年   55篇
  2009年   49篇
  2008年   58篇
  2007年   68篇
  2006年   77篇
  2005年   52篇
  2004年   49篇
  2003年   56篇
  2002年   38篇
  2001年   19篇
  2000年   27篇
  1999年   20篇
  1998年   23篇
  1997年   24篇
  1996年   22篇
  1995年   19篇
  1994年   12篇
  1993年   15篇
  1992年   16篇
  1991年   8篇
  1990年   13篇
  1989年   9篇
  1988年   11篇
  1987年   9篇
  1986年   11篇
  1985年   7篇
  1984年   13篇
  1983年   10篇
  1982年   11篇
  1981年   16篇
  1980年   6篇
  1979年   12篇
  1978年   7篇
  1977年   6篇
  1976年   4篇
  1975年   2篇
  1974年   2篇
排序方式: 共有1319条查询结果,搜索用时 31 毫秒
91.
Abstract: Considerable attention has recently been focused on using levels of developmental instability among members of a population to detect environmental or genetic stresses on animals or plants. It is not yet clear, however, that high developmental instability in a sample of individuals always indicates environmental stress or poor genetic quality. We studied 13 fragmented populations of prairie phlox (   Phlox pilosa L.) to test the hypothesis that developmental instability should decrease with increasing population size—as expected if small populations suffer genetic problems associated with inbreeding or are exposed to more environmental stress than larger populations. We used two different measures of developmental instability, each calculated for two different traits: radial asymmetry of flowers (for petal width and petal length) and modular fluctuating asymmetry of leaves (  for leaf widths at two points along the leaf  ). There were weak but significant correlations among individuals for four of six pairwise combinations of these measures. Surprisingly, three of our four measures of developmental instability showed strong population size effects that were opposite to those expected: developmental instability increased with population size. We conclude that measures of developmental instability cannot be applied uncritically for biomonitoring without considerable knowledge of developmental mechanisms, natural history, and population biology of the species in question.  相似文献   
92.
This paper introduces the problems of a market-driven waste management strategy in the UK and the momentum towards developing markets for recycled materials. It focuses on the demand side barriers and principally the need for market stimulation in the end uses for recyclables. The important role, which small- and medium-sized manufacturing enterprises (SMEs) have to play in developing existing markets for recyclate, is discussed. SMEs also have the potential to contribute to the radical new approach of identifying and developing a broad range of new, more diverse and higher value uses for recyclate. If these enterprises are to be engaged effectively then regional action is essential. The paper then reports on research work focusing on SMEs that has taken place as a component of the CWMRE (Creating Welsh Markets for REcyclate) market development initiative in Wales. As a foundation for this, a series of semi-structured interviews with SMEs has been conducted with those operating in sectors that are known to have the potential to provide novel applications for secondary materials or to have the potential for material displacement. Some of the barriers and corresponding needs within the case study companies involved are discussed. The implications of these findings for a regional market development programme are considered and in particular how these case studies support the need to engage SMEs in the use of secondary materials.  相似文献   
93.
Mitigation and Adaptation Strategies for Global Change -  相似文献   
94.
95.
Neanderthals disappeared sometime between 30,000 and 24,000?years ago. Until recently, Neanderthals were understood to have been predominantly meat-eaters; however, a growing body of evidence suggests their diet also included plants. We present the results of a study, in which sequential thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) were combined with morphological analysis of plant microfossils, to identify material entrapped in dental calculus from five Neanderthal individuals from the north Spanish site of El Sidrón. Our results provide the first molecular evidence for inhalation of wood-fire smoke and bitumen or oil shale and ingestion of a range of cooked plant foods. We also offer the first evidence for the use of medicinal plants by a Neanderthal individual. The varied use of plants that we have identified suggests that the Neanderthal occupants of El Sidrón had a sophisticated knowledge of their natural surroundings which included the ability to select and use certain plants.  相似文献   
96.
Variation in vocal behavior among local populations of songbirds may be significant to females in mate choice. In a study of dialect populations of brown-headed cowbirds, estradiol-implanted females from two dialects held the pre-copulatory lordosis posture longer in response to playback of the local flight whistle song than to foreign whistle types from adjacent and more distant dialects. Females were held in captivity for a relatively brief period prior to testing and received no tutoring so discrimination was based solely on experience in the wild. This is the first study to show evidence of discrimination by female cowbirds based on flight whistle type. Evidence is presented from one of the study dialects that the majority of yearling male cowbirds are vocally distinct from resident adults in having either foreign or incomplete local whistles. Although these yearlings are fully mature sexually, they have little or no mating success. The correlation between female whistle preference and male mating success suggests that the ability to give the correct local whistle type may be a characteristic used by females to assess age and quality of a potential mate. A learned female preference for the predominant local song type may be a factor in the stability of these dialects by making it adaptive for males to conform to the local dialect.  相似文献   
97.
The authors carried out an nvestigative mission to San Salvador between 20th October and 3rd November 1986, under the auspices of the Earthquake Engineering Field Investigation Team (EEFIT). The mission was funded by Rendel Palmer & Tritton and the Science and Engineering Research Council.  相似文献   
98.
99.
100.
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