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   39315篇
  免费   641篇
  国内免费   241篇
测绘学   761篇
大气科学   2626篇
地球物理   7720篇
地质学   14246篇
海洋学   3597篇
天文学   8769篇
综合类   88篇
自然地理   2390篇
  2022年   259篇
  2021年   444篇
  2020年   502篇
  2019年   583篇
  2018年   1023篇
  2017年   1024篇
  2016年   1095篇
  2015年   599篇
  2014年   1060篇
  2013年   1885篇
  2012年   1217篇
  2011年   1656篇
  2010年   1477篇
  2009年   1814篇
  2008年   1655篇
  2007年   1709篇
  2006年   1577篇
  2005年   1082篇
  2004年   1089篇
  2003年   1124篇
  2002年   1011篇
  2001年   876篇
  2000年   807篇
  1999年   732篇
  1998年   719篇
  1997年   731篇
  1996年   592篇
  1995年   579篇
  1994年   504篇
  1993年   460篇
  1992年   413篇
  1991年   427篇
  1990年   441篇
  1989年   394篇
  1988年   371篇
  1987年   400篇
  1986年   416篇
  1985年   516篇
  1984年   548篇
  1983年   543篇
  1982年   499篇
  1981年   458篇
  1980年   429篇
  1979年   411篇
  1978年   376篇
  1977年   385篇
  1976年   344篇
  1975年   354篇
  1974年   341篇
  1973年   373篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
A model is proposed that shows the relation of the block structure of the crust and earthquake sources (Sadovskii, 1979; Rodionov, 1979, 1984, 1994; Bugaev, 1999, 2011, 2014, 2015). The model can formalize how to assess the prediction of seismic regime parameters depending on the elastic limit and conditions and rate of deformation of the Earth’s crust. The spent nuclear fuel repository site in Olkiluoto (Finland) and a site in the area of the Krasnoyarsk Mining and Chemical Combine are considered as examples. It is demonstrated that the parameters of the prediction graphs limit the location of the points of magnitude repeatability graphs calculated for a site based on samples of earthquakes in the area according to different authors. This makes it possible to recommend predictive assessment of seismic regime parameters for stability monitoring of the seismic regime and safety analysis of a geological environment’s insulation properties for waste sites from the results of seismological monitoring and high-precision observations of modern movements of the Earth’s crust.  相似文献   
63.
64.
65.
The re-entry phase of a highly eccentric satellite is discussed. Numerical simulations allowing the prediction of the exact date of re-entry of a highly eccentric satellite are exposed.It is shown that under very particular circumstances the life of the satellite can be extended by a few days. The number of final revolutions of the rapidly contracting orbit depends critically on the air density between 70 km and 100 km.Re-entry of the European scientific satellite HEOS-1 predicted for 28 October, 1975 is near such a situation.  相似文献   
66.
Zusammenfassung Der Eisengehalt von Andalusiten und Disthenen aus Quarzknauern im Gebiet des Ötztaler—Stubaier Altkristallins wurde regional untersucht. Der Gehalt and Gesamteisen in primären Disthen liegt zwischen 0,17 und 0,22 Gew.% Fe2O3, während primäre Andalusite zwischen 0,26 und 1,93 Gew.% Fe2O3 schwanken. Dieser Unterschied in den Andalusiten wird auf ein wechselndes Angebot von Fe2O3 aus dem Nachbargestein der Knauern zurückgeführt.Ein Zusammenhang zwischen dem Eisengehalt der Andalusite und den verschiedenen Umwandlungsstadien Andalusit—Disthen konnte nicht nachgewiesen werden.
On the iron content of alumosilicates in quartz nodules
Summary A determination of the regional distribution of the ironcontent of andalusites and kyanites in quartz-segregations of the Oetztal—Stubai crystalline complex gave values of 0.17–0.22% for the total iron in primary kyanite and 0.26–1.93% in andalusite. This difference is probably due to a variation in the Fe2O3-content in the country rocks of the quartz veins. No relationship between the iron-content in andalusite and the different stages of transformation from andalusite to kyanite could be established.
  相似文献   
67.
Long-term observational data (1992?C2009) on heavy metal (Cu, Zn, Pb, Cr, Ni, V, Mo, Co, Fe, and Mn) content of different links in the Ivankovo Reservoir ecosystem are used to consider the regularities in the distribution and behavior of heavy metals in the system anthropogenic pollution sources-reservoir and its drainage area, thus enabling the assessment of the pollution level of the Volga Source of water supply to Moscow.  相似文献   
68.
Inceptisols are developed on silt loam, loam, and sandy loam Indian mounds at the Keller Mound Group and Bluff Top Mound in northeastern Iowa. The mounds date to the Allamakee Phase of the Late Woodland Period (ca. 1650–1250 B.P.) and are built with fill obtained from the A, E, and upper B horizons of pre-existing soils (Alfisols). Differences in the morphologic and chemical characteristics of soils on different mounds are attributed to textural differences of the mounds' fill. Coarse-textured mound fill is pedogenically altered at a faster rate than fine-textured fill, but total carbon percentage of the A horizon attains a steady state faster in fine-textured mound fill. Total phosphorus content is used to determine from which horizons of pre-existing soils the specific layers of mound fill originated. Rates and pathways of pedogenesis in mound fill may not provide good analogues for the early stages of soil development in materials that have not undergone previous weathering and subsequent modification by humans. Nevertheless, mound soils are useful benchmarks for some pedologic studies since they provide time lines for evaluating minimum rates for development of argillic and albic horizons, as well as attainment of the Alfisol order.  相似文献   
69.
The mechanism of concentration on the shaking table is discussed and a fresh attempt is made to obtain the theoretical model describing the velocity of a fluid in depth and time when in contact with a symmetrically reciprocating surface.The significance of the many design and operational variables and their interrelationships are examined. The various areas where the shaking table plays its role are then considered.The relevant features of micropanner, superpanner and the subsequent macropanner and pulsepanner are also treated since they all, like the shaking table, have the differential motion in common.  相似文献   
70.
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