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   589篇
  免费   35篇
  国内免费   2篇
测绘学   13篇
大气科学   100篇
地球物理   124篇
地质学   227篇
海洋学   33篇
天文学   112篇
综合类   2篇
自然地理   15篇
  2021年   5篇
  2020年   7篇
  2019年   6篇
  2018年   25篇
  2017年   28篇
  2016年   56篇
  2015年   31篇
  2014年   43篇
  2013年   42篇
  2012年   18篇
  2011年   27篇
  2010年   33篇
  2009年   30篇
  2008年   20篇
  2007年   23篇
  2006年   14篇
  2005年   8篇
  2004年   9篇
  2003年   9篇
  2002年   9篇
  2001年   6篇
  2000年   7篇
  1999年   2篇
  1998年   12篇
  1997年   8篇
  1996年   13篇
  1995年   5篇
  1994年   4篇
  1993年   14篇
  1992年   7篇
  1991年   7篇
  1990年   11篇
  1989年   8篇
  1988年   3篇
  1986年   6篇
  1985年   6篇
  1984年   7篇
  1983年   4篇
  1981年   4篇
  1978年   3篇
  1977年   4篇
  1976年   2篇
  1974年   2篇
  1973年   4篇
  1972年   3篇
  1971年   5篇
  1970年   3篇
  1969年   5篇
  1965年   4篇
  1963年   2篇
排序方式: 共有626条查询结果,搜索用时 62 毫秒
531.
This paper discusses the possibility of immobilization of TiO2 nanoparticles onto recycled wool‐based nonwoven material, which can be utilized for removal of dyes from wastewater. The photocatalytic activity of TiO2 nanoparticles deposited on the nonwoven material was evaluated in the aqueous solution of direct dye C.I. Direct Blue 78 under the UV illumination. Nonwoven material modified with TiO2 nanoparticles provides complete removal of dye from the solution already after 4–6 h of UV illumination. However, photodegradation of the dye adsorbed on the nonwoven material was obtained within 24 h of UV illumination. The rate of dye adsorption and photodegradation depends on the amount of deposited TiO2 nanoparticles. The increase of initial dye concentration induced decrease in photocatalytic efficiency of immobilized TiO2 nanoparticles. The highest photodegradation rate was achieved in acidic conditions. Elevated temperatures positively affected the removal of dye from solution. Photocatalytic activity of TiO2 nanoparticles deposited on nonwoven material was preserved after three photodegradation cycles.  相似文献   
532.
A. Anđić 《Solar physics》2007,242(1-2):9-20
High-frequency acoustic waves have been suggested as a source of mechanical heating in the chromosphere. In this work the radial component of waves in the frequency interval 22 to 1 mHz are investigated. Observations were performed using 2D spectroscopy in the spectral lines of Fe i 543.45 nm and Fe i 543.29 nm at the Vacuum Tower Telescope, Tenerife, Spain. Speckle reconstruction has been applied to the observations. We have used Fourier and wavelet techniques to identify oscillatory power. The energy flux is estimated by assuming that all observed oscillations are acoustic running waves. We find that the estimated energy flux is not sufficient to cover the chromospheric radiative losses.  相似文献   
533.
Wildfires are an important factor of landscape dynamics in fire-prone environments of the world. In the Mediterranean, one of the most fire-susceptible environments globally, between 45,000 and 50,000 wildfires are recorded every year, causing disturbances in forest and grassland ecosystems. As a Mediterranean country, Croatia faces these problems, averaging over 1000 registered wildfires annually, with the coastal areas dominated by forest fires and continental Croatia by fires on agricultural lands. This research combines various landscape and socio-economic factors in the analysis of fire occurrence in Croatia’s southernmost region of Dalmatia. Around 275 of the largest fires (encompassing 98% of the total burnt area) registered in 2013 were investigated using OLS, and different spatial indices were employed to analyse regional variability in fire distribution. The results revealed that areas more prone to fires are the northern inland areas of Dalmatia and its entire coastal zone. Altitude and vegetation type demonstrated a correlation with fire occurrence, but an increase in population in the study area was also correlated with wildfire occurrence. Regarding vegetation, the grasslands and Mediterranean shrubland (maquis) were found to be the most fire-prone vegetation types in the study region, the distribution of which can be linked to different socio-economic and demographic processes occurring in the Eastern Adriatic.  相似文献   
534.
535.
536.
537.
538.
539.
540.
Recurrent climate‐induced mass mortality episodes have been recorded in the Mediterranean Sea over the past 15 years, affecting rocky benthic communities. In this study, we provide for the first time a report on the annual mortality events of benthic sessile invertebrates occurring in the eastern part of the Adriatic Sea. Over the course of 14 consecutive years, we studied the sea temperature gradient to a depth of 40 m and found an abnormal summer warming trend and an increased frequency of above‐average temperatures. Mortality events were recorded in the summers of 10 observed years, in particular in 2009, when the highest mortality rates were recorded. Late in summer 2009, extensive mass mortality of sessile invertebrates was observed in the entire Eastern Adriatic Sea. We performed an analysis of selected target benthic species associated with mass mortality events with inter‐regional differences in hydrological and temperature conditions. We were able to characterize the mortality event by studying five areas covering the northern, central and southern regions of the Eastern Adriatic Sea. The degree of impact on each study area was quantified at 28 sites by estimating the proportion of affected target species. According to the obtained data, the northern sites (Cres area) were the least affected, whereas sites in the Central and Southern Adriatic [Tela??ica and Lastovo Nature Parks, Mljet National Park (NP)] displayed the highest impact. In summer 2009, sea surface temperatures reached values of 28 °C in the Cres area and 30 °C in Mljet NP. These thermal conditions were concomitant with moderate to severe mass mortalities of benthic populations. Mass mortality events reached depths of 45 m in most parts of the affected areas. Amongst studied species, the scleractinian coral and gorgonian populations suffered the most extensive damage during the mass mortality events.  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