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   2300篇
  免费   105篇
  2020年   38篇
  2019年   42篇
  2018年   57篇
  2017年   49篇
  2016年   86篇
  2015年   57篇
  2014年   58篇
  2013年   576篇
  2012年   80篇
  2011年   75篇
  2010年   74篇
  2009年   67篇
  2008年   60篇
  2007年   55篇
  2006年   53篇
  2005年   34篇
  2004年   22篇
  2003年   25篇
  2002年   33篇
  2001年   40篇
  2000年   27篇
  1999年   31篇
  1998年   24篇
  1997年   28篇
  1996年   27篇
  1995年   29篇
  1994年   24篇
  1993年   32篇
  1992年   26篇
  1991年   26篇
  1989年   21篇
  1988年   18篇
  1987年   26篇
  1986年   21篇
  1985年   24篇
  1984年   33篇
  1983年   25篇
  1982年   30篇
  1981年   21篇
  1980年   31篇
  1979年   25篇
  1978年   21篇
  1977年   18篇
  1976年   18篇
  1975年   13篇
  1973年   18篇
  1972年   18篇
  1971年   16篇
  1970年   13篇
  1967年   19篇
排序方式: 共有2405条查询结果,搜索用时 15 毫秒
101.
According to the Act of 1996 on nature protection, mounds (kurgans) are natural monuments protected nationally in Hungary. According to the law, all kurgans in Hungary were to be surveyed by 2002, and 1692 were included in the cadastre. Fewer than half of the kurgans remained intact due to numerous anthropogenic impacts. A high number of disturbing artificial buildings together with soil erosion, soil removal, and afforestation have significantly reduced the landscape value of kurgans. In 2002, 51.5% of the surveyed kurgans still represented some kind of a value and thus their protection became one of the most urgent tasks of nature conservation and archaeology. According to a Hungarian ministerial decree, established on the basis of an EU Council decree, the area of kurgans under cultivation must be removed from cultivation. By 2015, in the area of 90% of the kurgans under cultivation this land use, which caused significant erosion, was terminated.  相似文献   
102.
103.
Bell, P.R., Burns, M.E. & Smith, E.T. October 2017. A probable ankylosaurian (Dinosauria, Thyreophora) from the Early Cretaceous of New South Wales, Australia. Alcheringa 42, 120–124. ISSN 0311-5518.

We describe an isolated osteoderm from the Albian Griman Creek Formation where it is exposed near the town of Lightning Ridge in central-northern New South Wales, Australia. Several lines of evidence allow referral of this element to the Ankylosauria—a group that epitomises body armour and ubiquitous osteodermal coverage among dinosaurs. Despite the abundant record of fossil vertebrates from this interval, ankylosaurians have not been previously reported, although, they have been described from penecontemporaneous deposits in western Queensland and Victoria. This discovery, therefore, provides an important link between the northerly faunas (including the Griman Creek Formation) that flourished at the edge of the epeiric Eromanga Sea, with those from the sub-polar rift-valley system of Victoria during the mid-Cretaceous.

Phil R. Bell [], School of Environmental and Rural Science, University of New England, Armidale 2351, NSW, Australia; Michael E. Burns [], Department of Biology, Jacksonville State University, 700 Pelham Rd N., Jacksonville, AL 36265-2138, USA; Elizabeth T. Smith [], Australian Opal Centre, Lightning Ridge 2834, NSW, Australia.  相似文献   

104.
105.
106.
107.
108.
109.
110.
Capillary trapping is a physical mechanism by which carbon dioxide (CO2) is naturally immobilized in the pore spaces of aquifer rocks during geologic carbon sequestration operations, and thus a key aspect of estimating geologic storage potential. Here, we studied capillary trapping of supercritical carbon dioxide (scCO2), and the effect of initial scCO2 saturation and flow rate on the storage/trapping potential of Berea sandstone. We performed two‐phase, scCO2‐brine displacements in two samples, each subject to four sequential drainage–imbibition core‐flooding cycles to quantify end‐point saturations of scCO2 with the aid of micro‐ and macro‐computed tomography imaging. From these experiments, we found that between 51% and 75% of the initial CO2 injected can be left behind after the brine injection. We also observed that the initial scCO2 saturation influenced the residual scCO2 saturation to a greater extent than the rate of brine injection under the experimental conditions examined. In spite of differences in the experimental conditions tested, as well as those reported in the literature, initial and residual saturations were found to follow a consistent relationship.  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