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   86604篇
  免费   854篇
  国内免费   1037篇
测绘学   2465篇
大气科学   5964篇
地球物理   16463篇
地质学   32792篇
海洋学   7047篇
天文学   17176篇
综合类   1922篇
自然地理   4666篇
  2022年   495篇
  2021年   888篇
  2020年   935篇
  2019年   1036篇
  2018年   5579篇
  2017年   4856篇
  2016年   4104篇
  2015年   1263篇
  2014年   2144篇
  2013年   3603篇
  2012年   3011篇
  2011年   4902篇
  2010年   4125篇
  2009年   5058篇
  2008年   4366篇
  2007年   4787篇
  2006年   2869篇
  2005年   2144篇
  2004年   2249篇
  2003年   2142篇
  2002年   2010篇
  2001年   1635篇
  2000年   1609篇
  1999年   1262篇
  1998年   1268篇
  1997年   1162篇
  1996年   984篇
  1995年   1027篇
  1994年   822篇
  1993年   805篇
  1992年   727篇
  1991年   785篇
  1990年   730篇
  1989年   633篇
  1988年   589篇
  1987年   706篇
  1986年   626篇
  1985年   749篇
  1984年   852篇
  1983年   826篇
  1982年   742篇
  1981年   717篇
  1980年   645篇
  1979年   592篇
  1978年   596篇
  1977年   499篇
  1976年   513篇
  1975年   506篇
  1974年   463篇
  1973年   521篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
291.
Summary Sets of virtual poles corresponding to sets of geomagnetic field values at equidistant points, lying along circles of latitude, were defined on the basis of the 1980 IGRF extending to degree and order 8. Certain places on the Earth's surface yield virtual poles lying very close together. The segments of the virtual pole paths, corresponding to these places, have a large curvature. The mentioned places of the Earth's surface are supposed to be areas with a low rate of the westward drift. They form continuous zones that show a certain relation to global-tectonics features.
uum ¶rt; 8- n¶rt;a ¶rt;a¶rt; aaumu n 1980 u u nmu uma n, mmmu nm uu n ma, a u¶rt;umam ¶rt; naa m ma nmu nua¶rt;am uma n, m uu ¶rt; ¶rt;. amu u, mmmu mu ma, um uu. ¶rt;naam, m nm ma nmu m amu, m m ana¶rt; ¶rt;a ua. u am n na, m naam a m uua mmuu.
  相似文献   
292.
Sixteen foraminiferid assemblages have been studied from the London Clay succession at Lower Swanwick brickyard. These are divided into three faunules which are interpreted as indicating a shallow shelf regime with strong deltaic influences.  相似文献   
293.
A method for comparative estimation of reliability in detection of gravity anomaly sources in indicated fragments of studied geological space is given. The possibility of creation of this estimation is connected with disparate ideas on different peculiarities of the structure of studied geological space and noise characteristics in observed fields. The model example and results of practical problem solution are viewed.  相似文献   
294.
Book reviews     
  相似文献   
295.
A thick (200 m) rock salt mass covering Late Archean granitoids was exposed for the first time in the Early Proterozoic volcanogenic-sedimentary formations in the Onega trough of the east Baltic Shield by the Onega parametric well. The mineral composition of salts, their geochemical features, and the isotopic composition of carbonate carbon and oxygen have been studied. After fluid inclusions present in salts, their metamorphism temperature and isotopic composition of helium and argon were determined. The obtained results give evidence of the fact that rock salts and magnesites associated with them were formed in an evaporate basin with participation of deep crustal processes. The age of the underlying granitoids (2.716 ± 9 Ma) is determined using the Pb—Pb method.  相似文献   
296.
297.
298.

The results of multicolor photometric and polarization observations of the blazar 4C 38.41 (Q 1633+382) performed at St. Petersburg State University, the Pulkovo Astronomical Observatory of the Russian Academy of Sciences, Boston University, and Steward Observatory in 2006–2017 are analyzed. Separate variable sources responsible for the observed activity are distinguished, whose power-lawspectra and high degree of polarization confirm their synchrotron nature. The observed color variability of the object (redder when brighter) can be explained by an increase in the contribution to the total emission of a red component with variable flux and a constant relative spectral energy distribution. A close correlation between the optical and gamma-ray light curves is identified, suggesting the same location of the variable sources responsible for the radiation in these bands.

  相似文献   
299.
It was found as a result of detailed study of ferromanganese stromatolites that columnar formations, i.e., fossilized stratified bacterial tufts with rhythmically alternating layers of glycocalyx, accumulations of filamentous bacteria, and lens-shaped two-layered (alternation of homogeneous microlayers with porous ones containing filamentous bacteria trichomes) packages, serve as the basis for stromatolite buildup.  相似文献   
300.
The melting curve of corundum is calculated by using two approaches: the first one is conventional and the second one is two-phase molecular dynamics method both utilizing the same pairwise interatomic potential developed earlier on. The melting curve obtained by the two-phase simulation method is in agreement with the existing experimental data up to 25 GPa. A comparison of melting curves obtained by a two-phase simulation method and a conventional molecular dynamic method in NPT ensemble demonstrates a substantial overestimation of melting temperatures when applying conventional molecular dynamic technique. The inaccuracy of the conventional method increases with increasing pressure and, in the case of corundum, changes from about 300 K at 1 bar to about 1000 K at 1 Mbar. Received: 25 November 1996 / Revised, accepted: 11 March 1997  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