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   29321篇
  免费   391篇
  国内免费   320篇
测绘学   616篇
大气科学   1817篇
地球物理   5246篇
地质学   11265篇
海洋学   2963篇
天文学   6859篇
综合类   68篇
自然地理   1198篇
  2022年   297篇
  2021年   455篇
  2020年   509篇
  2019年   556篇
  2018年   1091篇
  2017年   1040篇
  2016年   1146篇
  2015年   545篇
  2014年   1041篇
  2013年   1686篇
  2012年   1152篇
  2011年   1433篇
  2010年   1282篇
  2009年   1557篇
  2008年   1329篇
  2007年   1395篇
  2006年   1301篇
  2005年   755篇
  2004年   705篇
  2003年   659篇
  2002年   687篇
  2001年   619篇
  2000年   568篇
  1999年   461篇
  1998年   479篇
  1997年   453篇
  1996年   391篇
  1995年   350篇
  1994年   378篇
  1993年   294篇
  1992年   297篇
  1991年   286篇
  1990年   322篇
  1989年   220篇
  1988年   225篇
  1987年   268篇
  1986年   209篇
  1985年   314篇
  1984年   276篇
  1983年   258篇
  1982年   275篇
  1981年   203篇
  1980年   243篇
  1979年   195篇
  1978年   211篇
  1977年   165篇
  1976年   163篇
  1975年   172篇
  1974年   167篇
  1973年   166篇
排序方式: 共有10000条查询结果,搜索用时 13 毫秒
61.
62.
63.
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   
64.
Photometric data covering 1994–2009, obtained at the Crimean Astrophysical Observatory or retrieved from the ASAS and SuperWASP catalogs, were used to analyze the brightness variations of the rapidly rotating star V833 Tau, whose activity level is close to saturation. Combined with previously published results, these data represent for the first time all stages in the development of the star’s 19- year activity cycle. The photometric period and rotational-modulation amplitude for different epochs are determined, and the qualitative pattern of the spots is considered. The photometric period is close to the orbital period, but always exceeds it, indicating that surface inhomogeneities are located far from the equatorial plane. With the high spottedness of the star, reaching 28% at the cycle maximum, the rotationalmodulation amplitude is 0.05?0.1 m , and increases during the growth and decline phases of the 19-year cycle. The rotational modulation is due to spots with higher latitudes than in the case of the Sun, and concentrating on active longitudes.  相似文献   
65.
Lithofacies zoning is described for the first time for the Neo- and Eopleistocene of the Bering Sea. Four lithofacies sedimentation zones are distinguished: (I) terrigenous; (II) siliceous–terrigenous; (III) siliceous, and (IV) volcanoterrigenous ones. Corresponding maps were treated using Ronov volumetric method to quantify sedimentation parameters for distinguished lithofacies zones (subzones) and types of Pleistocene sediments. It was revealed that terrigenous sediments predominate over other sediments. Accumulation of the terrigenous sediments was more intense (by 1.4 times) in the Neopleistocene than in the Eopleistocene. The sedimentation rate of siliceous sediments of the Bowers Ridge in the Eopleistocene was two times higher than in the Neopleistocene.  相似文献   
66.
Investigations on OH maser lines in comets have been performed with the RT-22 at CrAO. The results of observations of 9P/Temper1 and Lulin C/2007 N3 comets in the OH molecule line at a wavelength of 18 cm are presented. An original technique for observation data analysis has been developed. The gas production rate of OH molecules in these comets is estimated.  相似文献   
67.
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   
68.
Doklady Earth Sciences - Distribution density functions for the sensitivity of a three-coil sounder are constructed as the weighted mean rock volume between the in-phase surfaces of running...  相似文献   
69.
70.
The composition and nature of high-Cr minerals in lithic clasts from the carbonatites of the Veseloe occurrence, northern Transbaikalia, were considered. In order to determine their source, the Cr-bearing phases were compared with chromite, magnetite, and rutile from ultrabasic rocks, mantle xenoliths, and eclogites. It was suggested that the xenoclasts studied were formed at great depths, whereas the carbonatites were directly derived from the mantle rather than formed by the crustal differentiation of a silicate-carbonate melt.  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