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   1968篇
  免费   74篇
  国内免费   23篇
测绘学   86篇
大气科学   152篇
地球物理   706篇
地质学   681篇
海洋学   154篇
天文学   137篇
综合类   11篇
自然地理   138篇
  2022年   12篇
  2021年   25篇
  2020年   49篇
  2019年   34篇
  2018年   61篇
  2017年   51篇
  2016年   80篇
  2015年   71篇
  2014年   69篇
  2013年   115篇
  2012年   89篇
  2011年   117篇
  2010年   101篇
  2009年   123篇
  2008年   100篇
  2007年   71篇
  2006年   68篇
  2005年   45篇
  2004年   42篇
  2003年   51篇
  2002年   31篇
  2001年   51篇
  2000年   31篇
  1999年   36篇
  1998年   30篇
  1997年   29篇
  1996年   23篇
  1995年   19篇
  1994年   17篇
  1993年   12篇
  1992年   18篇
  1990年   18篇
  1989年   16篇
  1988年   19篇
  1987年   12篇
  1986年   21篇
  1985年   23篇
  1984年   18篇
  1983年   26篇
  1982年   21篇
  1981年   18篇
  1980年   15篇
  1979年   18篇
  1978年   13篇
  1977年   14篇
  1976年   13篇
  1975年   17篇
  1973年   14篇
  1972年   10篇
  1969年   9篇
排序方式: 共有2065条查询结果,搜索用时 15 毫秒
971.
For the activities of the mining industry land, equipment, material, and energy are used. During operation material and energy flows such as overburden, dead rock, tailings, wastewater, exhaust air, dust, energy, abrasion, coolant and lubricant losses, are released. These released material and energy flows are nearly always without value for the raw material supply chain as they are not production targets. Instead, they have negative effects on the economy and ecology and are, therefore, referred to as ‘non-intended’. The knowledge of the quantities and qualities of these non-intended outputs as a function of the processes and their parameters is the basis for technical and economical measures. A methodology for the acquisition and assessment of the material and energy flows in the mining industry was developed and tested at the Technical University Berlin, Germany. For that purpose and based on a system analysis in different mines, all relevant material and energy flows were assigned to individual processes. Causal relationships, possible interactions, quantities, and qualities were examined as functions of system parameters. Finally, a technical and economic evaluation was performed.  相似文献   
972.
Summary The geopotential scale factor R 0 =GM/W 0 has been determined on the basis of satellite altimetry as R 0=(6 363 672·5±0·3) m and/or the geopotential value on the geoid W 0 =(62 636 256·5±3) m 2 s –2 . It has been stated that R 0 and/or W 0 is independent of the tidal distortion of surface W=W 0 due to the zero frequency tide.
¶rt;a nmu amumuu u ama amnmuaa R 0 =GM/W 0 =(6 363 672,5±0,3) m u/uu aunmuaa a nmuu¶rt;a W 0 =(62 636 256,5±3) m2 s–2. m, m R 0 u/uu W 0 auum m nm amu a a nuu ¶rt;au nmu W=W 0 .
  相似文献   
973.
Far-field tsunami deposits observed in the Kahana Valley, O‘ahu, Hawai‘i (USA), were investigated for their organic-geochemical content. During short high-energy events, (tsunamis and storms) organic and chemical components are transported with sediment from marine to terrestrial areas. This study investigates the use of anthropogenic based organic geochemical compounds (such as polycyclic aromatic hydrocarbons, pesticides and organochlorides) as a means to identify tsunami deposits. Samples were processed by solid–liquid extraction and analyzed using gas chromatography–mass spectrometry. A total of 21 anthropogenic marker compounds were identified, of which 11 compounds were selected for detailed analysis. Although the tsunami deposits pre-date industrial activity in Hawai‘i by several hundred years, distinct changes were found in the concentrations of anthropogenic marker compounds between sandy tsunami deposits and the surrounding mud/peat layers, which may help in identifying tsunami deposits within cores. As expected, low overall concentrations of anthropogenic markers and pollutants were observed due to the lack of industrial input-sources and little anthropogenic environmental impact at the study site. This geochemical characterization of tsunami deposits shows that anthropogenic markers have significant potential as another high-resolution, multi-proxy method for identifying tsunamis in the sedimentary record.  相似文献   
974.
Summary Examination of the relation between electric resistivity, compressional wave velocity and density of Indian Precambrian rocks is presented.
¶rt;m auumu ¶rt; muu nmuu, m n¶rt; uu u nmm ¶rt;uu n¶rt; u ¶rt;uu.
  相似文献   
975.
Observations of the polar magnetic fields were made during the period July 3–August 23, 1968, with the Mt. Wilson magnetograph. The scanning aperture was 5 × 5. The magnetic field was found to be ofS polarity near the heliographic north pole and ofN polarity near the south pole. At lower latitudes the polarity was the opposite. The polarity reversal occurred at a latitude of about +70° in the north and -55° in the south hemisphere. This coincides with the position of the polar prominence zones at that time. The observations indicate that the average field strength at the south pole was well above 5 G.Synoptic charts of the magnetic fields have been plotted in a polar coordinate system for two consecutive solar rotations.  相似文献   
976.
977.
We report the discovery of the nearby  ( d = 24 pc)  HD 75767 as an eight billion year old quadruple system consisting of a distant M dwarf pair, HD 75767 C–D, in orbit around the known short-period   P = 10.25 d  single-lined binary HD 75767 A–B, the primary of which is a solar-like G star. On the reasonable assumption of synchronous orbital rotation as well as rotational and orbital coplanarity for the inner pair, we get   M B= 0.96 M  for the unseen HD 75767 B, that is, the case of a massive white dwarf. Upon future evolution, mass transfer towards HD 75767 B will render the   M A= 0.96 M  G-type primary, now a turnoff star, to become a helium white dwarf of   M A∼ 0.33 M  . Depending on the mass accretion rate, accretion efficiency and composition of the massive white dwarf, this in turn may result in a collapse of HD 75767 B with the formation of a millisecond pulsar, i.e. the creation of a low-mass binary pulsar (LMBP), or, instead, a Type Ia supernova explosion and the complete disruption of HD 75767 B. Irrespective of which scenario applies, we point to the importance of the distant M dwarfs as the likely agents for the formation of the inner, short-period HD 75767 A–B pair, and hence a path that particularly avoids preceding phases of common envelope evolution.  相似文献   
978.
979.
A principle of restoration methods based on multichannel blind deconvolution (MBD) is introduced. The methods assume that for every un-degraded unobservable image several degraded observed images are available. It is better conditioned than classical single channel approach. The first algorithm represents a generalization of iterative deconvolution scheme introduced for single images. The second MBD algorithm is based on so-called subspace technique. The subspace method is not iterative and this possibly implies an implementation that can be computationally more efficient. Both methods are presented in applications to artificial image data (computer-generated multichannel degraded data) with known ideal image to get a comparison with restored one. Performance in a real situation on solar photosphere images is shown.  相似文献   
980.
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