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   29758篇
  免费   336篇
  国内免费   247篇
安全科学   949篇
废物处理   1453篇
环保管理   3953篇
综合类   4482篇
基础理论   7778篇
环境理论   8篇
污染及防治   7355篇
评价与监测   2133篇
社会与环境   2049篇
灾害及防治   181篇
  2023年   133篇
  2022年   249篇
  2021年   320篇
  2020年   196篇
  2019年   245篇
  2018年   436篇
  2017年   462篇
  2016年   722篇
  2015年   533篇
  2014年   856篇
  2013年   2477篇
  2012年   1019篇
  2011年   1359篇
  2010年   1105篇
  2009年   1148篇
  2008年   1416篇
  2007年   1334篇
  2006年   1211篇
  2005年   1082篇
  2004年   1038篇
  2003年   995篇
  2002年   936篇
  2001年   1093篇
  2000年   753篇
  1999年   469篇
  1998年   360篇
  1997年   369篇
  1996年   395篇
  1995年   465篇
  1994年   395篇
  1993年   344篇
  1992年   379篇
  1991年   357篇
  1990年   326篇
  1989年   323篇
  1988年   296篇
  1987年   241篇
  1986年   247篇
  1985年   250篇
  1984年   267篇
  1983年   255篇
  1982年   269篇
  1981年   221篇
  1980年   165篇
  1979年   181篇
  1978年   163篇
  1977年   133篇
  1975年   138篇
  1973年   167篇
  1972年   142篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Changes in the vegetation and fire regimes in the central East European Plain during the second half of the Holocene have been reconstructed based on the results of paleobotanical analysis and radiocarbon dating of material from a section of peat deposit in the Mordovia State Nature Reserve. It has been shown that birch–pine forests were widespread in the region between 7000 and 5000 yr BP, with the frequency of fires in that period being high (the fire return interval ranged from 10–20 to 100 years). Beginning from 5000 yr BP and to the early 20th century, broadleaf forests were dominant, with the fire return interval increasing to 300–500 years or longer.  相似文献   
42.
43.
Winter manure application elevates nutrient losses and impairment of water quality as compared to manure applications in other seasons. In conjunction with reviewing global distribution of animal densities, we reviewed worldwide mandatory regulations and voluntary guidelines on efforts to reduce off-site nutrient losses associated with winter manure applications. Most of the developed countries implement regulations or guidelines to restrict winter manure application, which range from a regulative ban to guidelines based upon weather and field management conditions. In contrast, developing countries lack such official directives, despite an increasing animal production industry and concern over water quality. An analysis of five case studies reveals that directives are derived from a common rationale to reduce off-site manure nutrient losses, but they are also affected by local socio-economic and biophysical considerations. Successful programs combine site-specific management strategies along with expansion of manure storage to offer farmers greater flexibility in winter manure management.  相似文献   
44.
Nuclear bud (NB) formation was investigated in blood erythrocytes of 1892 flounder Platichthys flesus, herring Clupea harengus, and eelpout Zoarces viviparus specimens that were collected at 82 sites representing different regions of the Baltic Sea in 2009–2011. This is the first attempt to evaluate the baseline levels of NB and rank the genotoxicity risk for native fish species. NB levels were compared to the previously published micronuclei (MN) data from the same individual fish specimens in order to compare the two methods of genotoxicity assessment and investigate the relationship between MN as the cytogenetic measure of genotoxicity and the DNA damage reflecting NB. In 2009–2011, elevated NB levels in 89.4 % of flounder sampling groups indicated high and extremely high genotoxicity risk levels. Herring and eelpout sampling groups showed elevated levels of NB, 74.6 and 45.7 %, respectively. In general, herring and eelpout NB measure was more sensitive as the genotoxicity biomarker than MN.  相似文献   
45.
46.
47.
48.
49.
50.
The present study investigates the use of combined methods of optical and acoustic sensors, in collaboration with direct in situ measurements, for the calibration and validation of a model transforming acoustic backscatter intensity series into suspended particulate matter (SPM) concentration datasets. The model follows previously elaborated techniques, placing particular attention to the parameterization of the acoustic absorption index as a function of water physical properties. Results were obtained from the annual deployment (during 2007–2008) of an upward-facing acoustic Doppler current profiler (ADCP) (307 kHz), equipped with a Wave Array, and an optical backscatter sensor (OBS), at the bottom of Thassos Passage near Nestos River plume (Thracian Sea, Northern Greece). The OBS was calibrated through linear regression, using 2007 and 2012 field sampling data, exhibiting an error of 13–14 % due to chlorophyll presence. The ADCP signal was calibrated through simultaneous measurements of backscatter intensity and turbidity profiles. Harmonic analysis on the model-produced SPM concentrations explained the tidal influence on their variability, especially during the summer. Empirical orthogonal functions analysis revealed the impact of waves and wave-induced currents on SPM variability. Finally, Nestos River sediment load was found uncorrelated to the SPM change in Thassos Passage, due to the dispersal and sediment deposition near the river mouth.  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