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   25892篇
  免费   466篇
  国内免费   213篇
测绘学   520篇
大气科学   1947篇
地球物理   5199篇
地质学   9056篇
海洋学   2106篇
天文学   6012篇
综合类   47篇
自然地理   1684篇
  2021年   160篇
  2020年   197篇
  2019年   209篇
  2018年   497篇
  2017年   462篇
  2016年   568篇
  2015年   436篇
  2014年   606篇
  2013年   1215篇
  2012年   731篇
  2011年   1015篇
  2010年   875篇
  2009年   1219篇
  2008年   1052篇
  2007年   1053篇
  2006年   979篇
  2005年   819篇
  2004年   837篇
  2003年   800篇
  2002年   739篇
  2001年   688篇
  2000年   636篇
  1999年   571篇
  1998年   576篇
  1997年   576篇
  1996年   440篇
  1995年   419篇
  1994年   380篇
  1993年   335篇
  1992年   311篇
  1991年   276篇
  1990年   304篇
  1989年   281篇
  1988年   235篇
  1987年   311篇
  1986年   257篇
  1985年   346篇
  1984年   384篇
  1983年   371篇
  1982年   335篇
  1981年   310篇
  1980年   312篇
  1979年   282篇
  1978年   311篇
  1977年   263篇
  1976年   267篇
  1975年   275篇
  1974年   234篇
  1973年   238篇
  1972年   158篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
This study continues our investigation of the super-fast variability of line profiles in the spectra of early-type stars. We have investigated the line-profile variability in spectra of OBA-stars with the SCORPIO multi-mode focal reducer mounted at the 6-m SAO RAS telescope. Regular short-period variations of the H and He lines in the spectra of the B1I star ρ Leo were detected with periods ranging from 2 to 90 minutes, as well as irregular line-profile variations on time intervals less than 1 minute. A possible origin of rapid spectral variations is discussed.  相似文献   
992.
With the aid of silt spectrograms gained at the 6 meter telescope Selenchukskaja and at the 2 meter telescope Tautenburg a brightness outburst (the only one so far observed) could be followed up spectroscopically. The spectral behaviour resembles SS Cygni, but the presence of CIII and NIII emission is not typical of dwarf novae. Possibly the object is related to the anomalous recurrent nova WZ Sge. The definite determination of its belonging to a known subclass of cataclysmic variables will be possible only after obtainment of extensive photometric material.  相似文献   
993.
The riebeckite-bearing rhyolite of Winkston Hill, Peebles, is shown to be peralkaline and may be named a pantellerite. Trace element comparison with other more altered members of the Tweeddale lavas from Wrae Hill suggests that the whole suite is peralkaline. It is thought most unlikely that the suite was developed in association with an Upper Ordovician subduction zone, and it was perhaps erupted on an oceanic island.  相似文献   
994.
Für 95 sehr schwache blaue Objekte in der Nähe des Zentrums des Virgo-Galaxienhaufens werden Auffindungskarten, Koordinaten, Schätzungen des (U – B)-Farbenindexes und grobe B-Helligkeiten mitgeteilt. Die Objekte wurden durch Blinken einer Tautenburger U- und B-Schmidtplatte gefunden.  相似文献   
995.
We present a list of 39 dwarf galaxies of the M 81/82 group. Three different methods are applied to determine their apparent integral magnitude: digital processing, equidensitometry, and calculation according to the formulae of FISHER and TULLY . The plates used were obtained with the Tautenburg Schmidt telescope. For a distance of the group of 3.5 Mpc the absolute magnitudes of the dwarf galaxies investigated are -15m < M < -9m.  相似文献   
996.
We present 93 micrometer measurements of 55 double stars observed with the 152 cm telescope at the Spanish observatory at Calar Alto (Almeria, Spain).  相似文献   
997.
998.
We consider current problems connected with the evolution of central dominant (cD) galaxies in clusters. In the second part of this series, internal properties of the cD galaxy — in particular its radio structure — are related to the appropriate ones of the cluster. The observations point to an earlier jet ejection along the major axis of the galaxy and a following change of the jet axis. From the existence of “hot-spot” like regions in different directions it is suggested that the radio engine would have to be intermittent with a relatively short period. Alternatively to the intermittent ejection scenario, the radio morphology of 4C 26.42 can be explained in the frame of the “standard” beam or jet model. The radio structure of 4C 26.42 being an inversion-symmetric configuration, which is probably due to galactic cannibalism, could be interpreted as a transition at the inner hot spots (at about 1 kpc) from supersonic, stable Fanaroff-Riley type II jets to subsonic, unstable FR I type structures (“plumes”). A quantitative investigation of the two scenarios for jet interaction with the surroudning interstellar/intercluster medium in 4C 26.42 gives parameter values in reasonable agreement with the ones discussed in the literature for related objects.  相似文献   
999.
Es wird eine Übersicht gegeben über die im Jahr 1991 auf Tautenburger Schmidtplatten gefundenen Kleinen Planeten. Es wurden 533 Objekte beobachtet und für diese 2066 Positionen gerechnet. Es handelt sich um 456 Planetoiden mit provisorischer Bezeichnung, unter denen 324 neu vergebene Bezeichnungen sind, sowie um 77 numerierte Objekte. Für Tautenburger Objekte wurden 250 Bahnen aus einer Opposition gerechnet. Für 54 im Berichtszeitraum numerierte Planeten, darunter befinden sich auch (4999) MPC und (5000) IAU, haben Tautenburger Positionen einen Beitrag geleistet. Neun Tautenburger Planetoiden wurden numeriert (Tab. 3). A summary is given about the Minor Planet survey performed in 1991 on Tautenburg Schmidt plates. 533 asteroids were observed and 2066 positions are calculated for them. These are 456 asteroids with provisional designations (324 of them have new designations) and 77 numbered objects. One-opposition orbits have been computed for 250 Teutenburg asteroids. Tautenburg observations could give a tribute to 54 planets numbered in the period of this report, among them are (4999) MPC and (5000) IAU, too. Nine Tautenburg asteroids have been numbered (Tab. 3).  相似文献   
1000.
The presence of a dispersed clast fraction in strata near the base of the Cosquer Formation in west Brittany, does not support a glacial origin for this unit. The upper 25 to 30 m of the underlying Kermeur Formation consists of a prograding sequence of very fine to fine sandstones deposited in a mid to distal current swept shelf setting. This sequence shows signs of slope instability, as do the supposed ‘glacial strata’ which overlie it. The upper two thirds of the Cosquer Formation contain spectacular slump-breccias. Smaller clasts within the laminated mudrocks at the base of the formation are associated with thin graded and non-graded sandstone laminae. They show no evidence of active penetration into underlying laminae other than can be explained by compaction. Larger clasts are confined to thicker massive beds, or disrupted units with marked internal contorted lamination. This, along with the abundance of slump features within the sequence suggests lateral emplacement by sediment gravity flows in a distal shelf-slope setting. Surface textures of sand grains within the formation are related to rock disaggregation along fractures developed during post-depositional deformation and are not related to glacial processes. Distinctive mineralogically immature, poorly-sorted aggregate sediment pellets, which have been considered as positive proof of glaciation, are not present.  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