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   40419篇
  免费   288篇
  国内免费   241篇
安全科学   748篇
废物处理   1874篇
环保管理   4981篇
综合类   8334篇
基础理论   10207篇
环境理论   20篇
污染及防治   9271篇
评价与监测   2645篇
社会与环境   2752篇
灾害及防治   116篇
  2021年   204篇
  2019年   206篇
  2018年   1855篇
  2017年   1754篇
  2016年   1711篇
  2015年   565篇
  2014年   638篇
  2013年   2160篇
  2012年   1234篇
  2011年   2466篇
  2010年   1617篇
  2009年   1623篇
  2008年   2113篇
  2007年   2516篇
  2006年   1128篇
  2005年   954篇
  2004年   955篇
  2003年   1054篇
  2002年   1011篇
  2001年   1077篇
  2000年   723篇
  1999年   514篇
  1998年   373篇
  1997年   374篇
  1996年   405篇
  1995年   433篇
  1994年   431篇
  1993年   394篇
  1992年   371篇
  1991年   378篇
  1990年   402篇
  1989年   360篇
  1988年   320篇
  1987年   310篇
  1986年   288篇
  1985年   302篇
  1984年   323篇
  1983年   321篇
  1982年   319篇
  1981年   300篇
  1980年   272篇
  1979年   252篇
  1978年   259篇
  1977年   235篇
  1976年   237篇
  1975年   202篇
  1974年   247篇
  1973年   214篇
  1972年   207篇
  1967年   222篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
The boll weevil (Anthonomus grandis Boheman), generally considered to be native to Mexico or Central America, spread into the southern United States of America in the late 1800s and seriously threatened the cotton industry. As there were no effective alternatives, pest control specialists studied the insect's ecology and advocated cultural practices that would disrupt its environment and maximize the benefits of natural biological and environmental controls. An ecologically orientated pest management scheme founded on cultural practices emerged well before suitable chemical control technology became available and allowed farmers to live with the weevil problem.Despite the ingenuity of the early management scheme, it frequently did not provide satisfactory boll weevil control gauged by present standards. Control of the pest thus shifted largely from an ecological to a chemical approach as effective synthetic organic insecticides became available after World War II. The chemical approach was successful for a number of years, but problems of insecticide-resistant strains of pests, secondary pest outbreaks, environmental quality, and increased costs of the insecticides have forced pest control specialists to re-emphasize the nonchemical techniques used widely against the boll weevil before World War II and to revive the ecological approach to weevil management.This article examines boll weevil ecology as related to management of the insect and reviews the status and prospects of ecologically-based weevil management techniques in the United States.  相似文献   
42.
Plasticity of honeybee castes   总被引:1,自引:0,他引:1  
  相似文献   
43.
44.
45.
46.
47.
Online searching in publically available patent files opens up interesting possibilities to provide a rapid response to critical questions. A computerized analysis of all patents of leading German pharmaceutical companies over the last decade in important indication areas is described. Supported by subsequent manual processing of individual patents it is shown that duplicate experiments on animals practically never occur.  相似文献   
48.
49.
Recent years have shown a rise in mean global temperatures and a shift in the geographical distribution of ectothermic animals. For a cause and effect analysis the present paper discusses those physiological processes limiting thermal tolerance. The lower heat tolerance in metazoa compared with unicellular eukaryotes and bacteria suggests that a complex systemic rather than molecular process is limiting in metazoa. Whole-animal aerobic scope appears as the first process limited at low and high temperatures, linked to the progressively insufficient capacity of circulation and ventilation. Oxygen levels in body fluids may decrease, reflecting excessive oxygen demand at high temperatures or insufficient aerobic capacity of mitochondria at low temperatures. Aerobic scope falls at temperatures beyond the thermal optimum and vanishes at low or high critical temperatures when transition to an anaerobic mitochondrial metabolism occurs. The adjustment of mitochondrial densities on top of parallel molecular or membrane adjustments appears crucial for maintaining aerobic scope and for shifting thermal tolerance. In conclusion, the capacity of oxygen delivery matches full aerobic scope only within the thermal optimum. At temperatures outside this range, only time-limited survival is supported by residual aerobic scope, then anaerobic metabolism and finally molecular protection by heat shock proteins and antioxidative defence. In a cause and effect hierarchy, the progressive increase in oxygen limitation at extreme temperatures may even enhance oxidative and denaturation stress. As a corollary, capacity limitations at a complex level of organisation, the oxygen delivery system, define thermal tolerance limits before molecular functions become disturbed.  相似文献   
50.
IntroductionSiberiaandtheFarEastaretheoldestandtherichestgold miningareasofRussia .Intensivegold miningherestartedinthebeginningofthe 19thcentury(Vyazelshchikov ,1963) .Forthemostpartgold bearingoresandsandswereprocessedwiththeuseofamalgamationmethodforgolde…  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