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   95867篇
  免费   1239篇
  国内免费   1160篇
安全科学   3806篇
废物处理   3523篇
环保管理   14568篇
综合类   21332篇
基础理论   27049篇
环境理论   75篇
污染及防治   17295篇
评价与监测   5783篇
社会与环境   4226篇
灾害及防治   609篇
  2022年   801篇
  2021年   849篇
  2020年   670篇
  2019年   889篇
  2018年   1263篇
  2017年   1280篇
  2016年   2279篇
  2015年   1848篇
  2014年   2607篇
  2013年   9299篇
  2012年   2406篇
  2011年   2837篇
  2010年   3405篇
  2009年   3499篇
  2008年   2455篇
  2007年   2390篇
  2006年   2675篇
  2005年   2519篇
  2004年   2859篇
  2003年   2683篇
  2002年   2247篇
  2001年   2740篇
  2000年   2222篇
  1999年   1595篇
  1998年   1401篇
  1997年   1392篇
  1996年   1519篇
  1995年   1616篇
  1994年   1508篇
  1993年   1359篇
  1992年   1375篇
  1991年   1334篇
  1990年   1286篇
  1989年   1236篇
  1988年   1093篇
  1987年   1020篇
  1986年   1000篇
  1985年   1073篇
  1984年   1174篇
  1983年   1182篇
  1982年   1186篇
  1981年   1103篇
  1980年   952篇
  1979年   942篇
  1978年   834篇
  1977年   728篇
  1976年   646篇
  1974年   625篇
  1973年   663篇
  1972年   661篇
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
112.
We tested separately the effect of two taxonomically related rotifers (B. patulus and B. macracanthus) on the population dynamics of another species (A. fissa) at low (0.5 ×10 6) and high food levels (1.5 × 106 cells/ml of Chlorella vulgaris) using different inoculation densities (0–100%). We also quantified the impact of A. fissa on the two brachionid species. Regardless of the presence of the competing species, an increase in the availability of food led to increase in the abundances of the three rotifers. The population growth of B. patulus, B. macracanthus, or A. fissa was affected negatively when cultured together with another species. An increase in the initial density of any one of the competing species became advantageous to maintain a certain population size. At a low algal food level, B. patulus was able to suppress A. fissa more strongly than B. macracanthus. On the other hand, at a high food level, B. macracanthus suppressed the population of A. fissa more strongly than B. patulus. Peak population densities for A. fissa varied from about 150 to 1000 ind./ml, depending on food density and the presence of competitors. The rate of population increase (r) of A. fissa, B. patulus, and B. macracanthus increased with an increase in food availability but decreased with increasing initial density of the competitor. Both Brachionus spp. experienced negative growth rates in the presence of A. fissa, especially at a high initial density of the latter. Published in Russian in Ekologiya, 2007, Vol. 38, No. 5, pp. 381–390. The article was submitted by the authors in English.  相似文献   
113.
114.
115.
Male Baladi rabbits were acutely and sub-chronically intoxicated with cyanofenphos and profenophos. The levels of cholesterol, triglycerides, B-lipoproteins and total proteins were determined in the serum, brain, spinal cord and sciatic nerve of rabbits. Moreover, the activities of alkaline phosphatase, acid phosphatase and glutamic-pyruvic transaminase were determined in the liver of the animals. The whole studies revealed that the biochemical constituents were highly affected by the tested insecticides. Also, the liver function suffered from adverse effects of the tested insecticides.  相似文献   
116.
工业革命以来,全球环境发生了前所未有的变化,将可能给地球系统带来灾难性后果,究其原因主要是由于人类活动造成的。人的行为深受意识的影响和制约,环境意识对于环境问题的产生和解决至关重要。本文选取上海、香港两个地区来分析公民对环境的关注度、公民的环保意识、环保行为以及公民对政府环境工作的看法和评价,研究公民对全球环境变化反应的区域差异,为政府制定相关环境保护政策提供理论依据。调查结果显示,上海、香港两地公民在很多环境闷题上具有共识。但是。在对手环境状况好转的期待值、参与环境保护活动的积极性、对人为因素主导力量的认识、环境保护与日常生活的切实关系、为环境保护的支付意愿、对于环境教育内容的认可度等方面存在着一定的差异。  相似文献   
117.
118.
A statistical analysis of interannual variation in a set of vegetative and generative characters over 13 years has been performed to characterize the growth and seed production dynamics of the Siberian stone pine (Pinus sibirica Du Tour) in the southeast of the forest zone in western Siberia. The results have shown that the range of fluctuations in most of vegetative characters is ordinary and their distribution is close to normal. The range of fluctuations in many generative characters is enormous (from 0 to +∞), and the distribution of their values is usually skewed, with low values being recorded several times more frequently than high values. Most variable are the proportion of abortive cones and other characters that are determined mainly in the spring of the pollination year. These characters account for a very high level of variation in the total seed production.  相似文献   
119.
120.
This research investigates whether species are perceived differently based on aesthetic and negativistic attitudes, and whether these and other attitudes, naturalistic activities, and gender predict support for the protection of threatened species. 228 undergraduate students completed a survey in which they rated pictures of 10 endangered species on aesthetic and negativistic attitudes, and support for protection. Findings showed that the two-striped garter snake, Ozark big-eared bat, and dolloff cave spider were conceptualized differently than other species, which may be the result of “irrational” fears linked to animal phobias, culture, and emotional reactions to pictures. The regression results support the common belief that aesthetics is an important determinant in perceptions of endangered species and that the importance of negativistic attitudes may be waning. Moralistic worldviews and attitudes toward landowner rights and the Endangered Species Act were significantly related to support for governmental protection of species. Surprisingly, naturalistic activities and gender were not significantly associated with support for governmental protection of species. In general, the results were consistent across both models. However, the amount of variance explained by aesthetic and negativistic attitudes was 23 percent higher in the other species models than in the bat, snake, and spider models.  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