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   20596篇
  免费   234篇
  国内免费   121篇
安全科学   520篇
废物处理   888篇
环保管理   2758篇
综合类   3384篇
基础理论   5814篇
环境理论   10篇
污染及防治   5306篇
评价与监测   1280篇
社会与环境   859篇
灾害及防治   132篇
  2021年   136篇
  2019年   127篇
  2018年   234篇
  2017年   251篇
  2016年   401篇
  2015年   306篇
  2014年   467篇
  2013年   1598篇
  2012年   573篇
  2011年   815篇
  2010年   666篇
  2009年   661篇
  2008年   829篇
  2007年   863篇
  2006年   765篇
  2005年   663篇
  2004年   649篇
  2003年   628篇
  2002年   609篇
  2001年   763篇
  2000年   574篇
  1999年   325篇
  1998年   261篇
  1997年   280篇
  1996年   280篇
  1995年   331篇
  1994年   302篇
  1993年   284篇
  1992年   277篇
  1991年   278篇
  1990年   294篇
  1989年   277篇
  1988年   249篇
  1987年   240篇
  1986年   223篇
  1985年   200篇
  1984年   255篇
  1983年   210篇
  1982年   271篇
  1981年   219篇
  1980年   184篇
  1979年   201篇
  1978年   184篇
  1977年   153篇
  1976年   138篇
  1975年   143篇
  1974年   159篇
  1973年   162篇
  1972年   148篇
  1971年   146篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
791.
The restoration of surface mining landscapes requires the (re)creation of ecosystems. In Lusatia (eastern Germany), large-scale open-cast lignite mining operations generated spoil dumps widely consisting of acidified, phytotoxic substrates. Amelioration and rehabilitation measures have been developed and applied to these substrates since the 1950s. However, it is still not clear whether these approaches are sustainable. This paper reports on collaborative research work into the ecological potential of forest ecosystem development on typical minesites in the Lusatian lignite district. At first sight, pine stands on minesites along a chronosequence comprising about 35 years did not show differences when compared with stands on non-mined sites of the general region. Furthermore, with some modification, conceptual models for flora and fauna succession in forest stands on non-mined sites seem to be applicable, at least for the early stages of forest ecosystem development. For example, soil organism abundance and activity at minesites had already reached levels typical of non-mined sites after about 20-30 years. In contrast, mine soils are very different from non-mined soils of the test region. Chemically, mine soil development is dominated by processes originating from pyrite oxidation. Geogenic, i.e. lignitic, soil organic carbon was shown to substitute for some functions of pedogenic soil organic matter. Rooting was hampered but not completely impeded in strongly acidified soil compartments. Roots and mycorrhizae are apparently able to make use of the characteristic heterogeneity of young mine soils. Considering these recent results and the knowledge accumulated during more than 30 years of research on minesite rehabilitation internationally, it can be stated that minesite restoration might be used as an ideal case study for forest ecosystem development starting at "point zero" on "terra nova".  相似文献   
792.
793.
Behavioural ecologists attempt to predict fitness in birds from estimates of body condition and immune capacity. We investigated how the stresses associated with capture, confinement and captive-rearing of wild zebra finches (Taeniopygia guttata) affected different elements of the immune system and body condition. Wild birds had higher heterophil:lymphocyte ratios and total leucocyte counts than aviary birds, presumably an outcome of mounting specific resistance to pathogens, but this response diminished significantly within 10 days of confinement. Wild birds had lower phytohaemagglutinin-A (PHA) responses than their aviary-bred counterparts possibly because energetic costs limited a general resistance response. Wild birds were heavier and had higher haematocrits than their aviary counterparts, but had less fat, although just 10 days of captivity significantly increased fat levels. Measures of body condition were of limited use for predicting immune responsiveness. We conclude that the different elements of the immune system and body condition respond independently, and often unpredictably, to many ecological and behavioural stressors.  相似文献   
794.
IntroductionFertilizationisessentialforagriculturalproduction ,butunreasonablyapplyingfertilizerscouldresultinseriesofproblemssuchascropqualitydecline,fertilizeruseefficiencydecrease,residualfertilizerspollution groundwaterandriversandnitrogencontented …  相似文献   
795.
种植杂交稻对甲烷排放的影响及评价   总被引:8,自引:0,他引:8  
早、中、晚稻三季24h稻田甲烷监测结果表明,种植杂交稻没有明显增进福田甲烷排放的作用.甲烷释放总量在3个种植季节中,除连作晚稻的杂交稻田比常规稻田高11.6%外,早稻、单季稻杂交稻田分别低于常规稻田6.4%和8.9%.稻田甲烷每周日平均释放量在水稻生长前期(移栽后5~7周)杂交稻高于常规稻,孕穗至收获期杂交稻低于常规稻.温度对甲烷释放影响十分明显.在不同水稻种植季节,稻田甲烷释放模式各不相同.经测定,杂交稻田的土壤产甲烷细菌数量及土壤产甲烷潜力明显高于常规稻田,其中产甲烷细菌数可相差数倍至2个数量级.试验结果还表明,种植水稻明显增加了稻田甲烷排放量,与侵水稻田相比.植稻田甲烷排放量增加了41.4%.  相似文献   
796.
This paper investigates the current treatment of environmental issues by two companies within the large made-to-order sector. Fifty questionnaires were issued to the design team of each company to assess current practice in the integration of environmental issues with design activities, awareness of environmental issues, awareness of existing environmental design tools and the preferred format for a potential clean design tool.  相似文献   
797.
 Ants have a well developed olfactory sense, which they need both for the perception of environmental chemicals, and for a highly sophisticated intraspecific communication system based on pheromones. The question arises therefore as to how different odors are coded in the antennal lobe, the first central neuropil to process olfactory information. We measured odor-evoked activity patterns using in vivo neuropil calcium recording in the antennal lobe of the ant Camponotus rufipes. We found that (a) odors elicit focal activity spots (diameter ca. 20 μm) which most probably represent the olfactory glomeruli; (b) different odors are coded in odor specific patterns of such activated spots, and a particular spot can participate in the pattern for different odors; (c) calcium increased in the activated spots within the 2-s stimulation period and slowly declined thereafter. Received: 10 March 1999 / Accepted in revised form: 5 July 1999  相似文献   
798.
799.
800.
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