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   102530篇
  免费   1251篇
  国内免费   1337篇
安全科学   4041篇
废物处理   3954篇
环保管理   15336篇
综合类   21749篇
基础理论   27972篇
环境理论   75篇
污染及防治   20155篇
评价与监测   6217篇
社会与环境   4942篇
灾害及防治   677篇
  2022年   887篇
  2021年   897篇
  2020年   695篇
  2019年   910篇
  2018年   1418篇
  2017年   1442篇
  2016年   2369篇
  2015年   1898篇
  2014年   2625篇
  2013年   9291篇
  2012年   2805篇
  2011年   3575篇
  2010年   3585篇
  2009年   3740篇
  2008年   3198篇
  2007年   3120篇
  2006年   3129篇
  2005年   2973篇
  2004年   3171篇
  2003年   3100篇
  2002年   2590篇
  2001年   3053篇
  2000年   2391篇
  1999年   1696篇
  1998年   1418篇
  1997年   1422篇
  1996年   1557篇
  1995年   1655篇
  1994年   1535篇
  1993年   1383篇
  1992年   1397篇
  1991年   1353篇
  1990年   1321篇
  1989年   1268篇
  1988年   1104篇
  1987年   1041篇
  1986年   1010篇
  1985年   1084篇
  1984年   1179篇
  1983年   1186篇
  1982年   1182篇
  1981年   1108篇
  1980年   960篇
  1979年   956篇
  1978年   840篇
  1977年   726篇
  1976年   646篇
  1974年   633篇
  1973年   665篇
  1972年   674篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
McMurdo Station is the largest research station in Antarctica, with a population that ranges each year from 250 to 1200 people. Because of its size and 40-year history of use, a number of locations around the station have become contaminated with wastes. Soils and sediments in these areas have been shown to contain elevated levels of petroleum-related products, PCBs, other organics, and metals. While some remedial investigations have been conducted, background levels of metals in soils have not been determined. This paper reports on background levels of metals in a natural basalt-derived soil (gray soil) and scoria (soft porous rock used as fill, red soil) near McMurdo Station using two fundamentally different analytical procedures, concentrated acid extraction/analysis and total metals. These data facilitate determining the extent and levels of metal contamination near McMurdo Station and provide reference levels of metals for comparison with existing and future remediation data. There were statistically significant differences between metals concentrations in both gray and red soils, and no correlations between the level of extracted versus total metal. Generally, only a small fraction of a metal was extractable.  相似文献   
122.
Population characteristics, individual life-history variables, feeding and vertical distribution of the mesopelagic fish Müller's pearlside Maurolicus muelleri collected in 1990 in Masfjorden, western Norway, are reported as well as environmental variables from the fjord. Minimum size at maturity was far smaller than reported from previous investigations in the same region. Fecundity was size-dependent and total egg numbers were higher than reported from other investigations of M. muelleri world wide, while the number of maturing eggs was far lower than observed in the same region earlier. Food concentration in the fjord was an order of magnitude lower than previous early summer observations, and several factors indicated that feeding opportunities may have been low for a long period. Daily feeding rate (g prey g-1 fish) decreased with increasing fish size. These observations fit well with a model of maximizing fitness by means of a flexible size at maturity. Minimum age at maturity seems to be achieved at the expense of fecundity. M. muelleri was concentrated in a 20 to 30 m deep sound scattering layer (SSL). The SSL stayed close to the surface during the night and at 100 to 180 m during the daytime. The vertical position of the SSL varied instantaneously with changes in surface light intensity, remaining at 10-3 to 10-4 mol m-1 s-1 at the top of the SSL. Stomach fullness was highest during the night; feeding intensity seems to have been peaked at dusk. Cladocerans were the main prey ranked by number, copepods by biomass. Intake of large copepods increased with fish size.  相似文献   
123.
124.
125.
126.
127.
128.
129.
130.
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