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   38220篇
  免费   5679篇
  国内免费   10131篇
测绘学   1139篇
大气科学   5879篇
地球物理   6839篇
地质学   17223篇
海洋学   8368篇
天文学   6060篇
综合类   1979篇
自然地理   6543篇
  2024年   147篇
  2023年   453篇
  2022年   1221篇
  2021年   1263篇
  2020年   1397篇
  2019年   1723篇
  2018年   1451篇
  2017年   1446篇
  2016年   1485篇
  2015年   1631篇
  2014年   2320篇
  2013年   2405篇
  2012年   2243篇
  2011年   2614篇
  2010年   2177篇
  2009年   3069篇
  2008年   2915篇
  2007年   2821篇
  2006年   2689篇
  2005年   2414篇
  2004年   2199篇
  2003年   1930篇
  2002年   1765篇
  2001年   1476篇
  2000年   1438篇
  1999年   1273篇
  1998年   1049篇
  1997年   865篇
  1996年   738篇
  1995年   620篇
  1994年   577篇
  1993年   486篇
  1992年   366篇
  1991年   295篇
  1990年   207篇
  1989年   203篇
  1988年   156篇
  1987年   81篇
  1986年   66篇
  1985年   76篇
  1984年   56篇
  1983年   42篇
  1982年   42篇
  1981年   38篇
  1980年   20篇
  1979年   12篇
  1978年   23篇
  1977年   20篇
  1976年   3篇
  1954年   14篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
V838 Mon is the prototype of a new class of objects. Understanding the nature of its multistage outburst and similar systems is challenging. So far, several scenarios have been invoked to explain this group of stars. In this work, the planets-swallowing model for V838 Mon is further investigated, taking into account the findings that the progenitor is most likely a massive B-type star. We find that the super-Eddington luminosity during the eruption can explain the fast rising times of the three peaks in the optical light curve. We used two different methods to estimate the location where the planets were consumed. There is a nice agreement between the values obtained from the luminosities of the peaks and from their rising time-scale. We estimate that the planets were stopped at a typical distance of one solar radius from the centre of the host giant star. The planets-devouring model seems to give a satisfying explanation to the differences in the luminosities and rising times of the three peaks in the optical light curve of V838 Mon. The peaks may be explained by the consumption of three planets or alternatively by three steps in the terminal falling process of a single planet. We argue that only the binary merger and the planets-swallowing models are consistent with the observations of the new type of stars defined by V838 Mon.  相似文献   
152.
153.
154.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM   总被引:1,自引:0,他引:1  
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms.  相似文献   
155.
156.
157.
158.
The island of Lampedusa lies on the northern edge of the African continental shelf, but during some Quaternary marine lowstands it was joined to the African continent. The study and dating of the aeolian, alluvial, detrital sediments, calcareous crusts and speleothems have established that the climatic–environmental variations recorded on the island can be related chronologically to those known for northern Libya, Tunisia and the Italian peninsula. During the Last Glacial Maximum, phases of Saharan dust accumulation on Lampedusa occurred, and were coeval with dust accumulation in crater lakes and on high mountains in central‐southern Italy, and with phases of glacial advance in the Apennines and in the Alps. During the late Holocene, accumulation of Saharan dust on Lampedusa occurred but there was little accumulation of dust on the northern side of the Mediterranean Sea. With the new data from Lampedusa, it is possible to envisage two different scenarios of atmospheric circulation relating to the Last Glacial Maximum and to the late Holocene. During the Last Glacial Maximum, southerly atmospheric circulation brought rainfall to the southern slopes of the Alps and to the Apennines. During the late Holocene, a prevalent westerly atmospheric circulation became established in the northern Mediterranean. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   
159.
Radiocaesium isotopes, discharged into the North-east Irish Sea from the Sellafield (formerly Windscale) nuclear fuel reprocessing plant in Cumbria, have been employed as flow monitors to update and extend the record of coastal water movement from the Irish Sea to the Clyde Sea area and, further north, to Loch Etive. The temporal trends in radiocaesium levels have been used to determine the extent of water mixing en route and to define mean advection rates. Flow conditions from the Irish Sea have changed considerably since the mid-1970s, the residence time of northern Irish Sea waters being ~12 months during 1978–1980 inclusive. Average transport times of four and six months are estimated for the Sellafield to Clyde and Sellafield to Etive transects respectively. Sellafield 137Cs levels in seawater were diluted by factors of 27 and 50 respectively during current movement to the Clyde and Etive areas. The decrease in salinity-corrected 137Cs concentrations between the Clyde and Etive suggests that dilution by Atlantic water occurs, the latter mainly entering the Firth of Lorne from the west. The majority (~94%) of the radiocaesium supply to Loch Etive enters the Firth of Lorne via the portion of the coastal current circulating west of Islay, only ~6% arriving via the Sound of Jura.  相似文献   
160.
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