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   22724篇
  免费   3344篇
  国内免费   5062篇
测绘学   1839篇
大气科学   3602篇
地球物理   4586篇
地质学   11772篇
海洋学   3286篇
天文学   2043篇
综合类   1614篇
自然地理   2388篇
  2024年   145篇
  2023年   395篇
  2022年   1172篇
  2021年   1454篇
  2020年   1197篇
  2019年   1414篇
  2018年   1567篇
  2017年   1463篇
  2016年   1490篇
  2015年   1262篇
  2014年   1462篇
  2013年   1569篇
  2012年   1617篇
  2011年   1646篇
  2010年   1530篇
  2009年   1392篇
  2008年   1285篇
  2007年   1288篇
  2006年   1106篇
  2005年   643篇
  2004年   516篇
  2003年   521篇
  2002年   566篇
  2001年   541篇
  2000年   426篇
  1999年   449篇
  1998年   347篇
  1997年   363篇
  1996年   296篇
  1995年   309篇
  1994年   263篇
  1993年   217篇
  1992年   202篇
  1991年   130篇
  1990年   108篇
  1989年   120篇
  1988年   94篇
  1987年   69篇
  1986年   60篇
  1985年   48篇
  1984年   45篇
  1983年   43篇
  1982年   41篇
  1981年   26篇
  1980年   25篇
  1979年   29篇
  1978年   18篇
  1977年   17篇
  1975年   22篇
  1973年   17篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
241.
242.
In order to provide new data on the neotectonics and geodynamic properties of western Syria, studies of marine terraces have been carried out. The most attention was paid to the lower terraces in the range of 3–5 to 30–35 m above sea level, because they have more complete distributions along the shore. The lower terraces were examined along the coastal area from Tartus to Latakia, and along the carbonate cliff on Arwad Island. Seven 230Th/U dates for these terraces are in the range of 85–130 ka, suggesting the age interval of the last interglacial (MIS 5). New dates on the lower terraces provide a basis for stratigraphical and geomorphological interpretation as well as neotectonic reconstruction. According to the geomorphological data and lithological composition of those terraces, two main uplifted blocks can be established. One coincides with the Latakia block, and another corresponds to the western margin of the Banias volcanic plateau. These blocks are divided by a subsided structure corresponding to the Nahr el Kebir graben. The amplitude of neotectonic uplifting in the Latakia and Banias blocks reaches 15–20 m for the Late Pleistocene.  相似文献   
243.
244.
245.
246.
Elpasolite, K2NaAlF6, has been found for the first time in a pegmatite related to peralkaline foid syenite at Mt. Koashva, Khibiny alkaline pluton, Kola Peninsula, Russia, as pale pink octahedral crystals up to 2 mm in size within cavities in the natrolite core of pegmatite in association with amicite, sodalite, aegirine, pectolite, catapleiite, sitinakite, lemmleinite-K, and vinogradovite. The chemical composition determined with an electron microprobe is as follows, wt %: 31.53 K; 9.22 Na; 11.20 Al; 47.21 F; total is 99.16. The empirical formula is K1.96Na0.98Al1.01F6.05. The infrared spectrum is given. The crystal structure has been refined to R = 0.030, space group Fm $ \bar 3 Elpasolite, K2NaAlF6, has been found for the first time in a pegmatite related to peralkaline foid syenite at Mt. Koashva, Khibiny alkaline pluton, Kola Peninsula, Russia, as pale pink octahedral crystals up to 2 mm in size within cavities in the natrolite core of pegmatite in association with amicite, sodalite, aegirine, pectolite, catapleiite, sitinakite, lemmleinite-K, and vinogradovite. The chemical composition determined with an electron microprobe is as follows, wt %: 31.53 K; 9.22 Na; 11.20 Al; 47.21 F; total is 99.16. The empirical formula is K1.96Na0.98Al1.01F6.05. The infrared spectrum is given. The crystal structure has been refined to R = 0.030, space group Fm m, a = 8.092 ?. The result of a special X-ray powder diffraction study confirmed the suggestion made by Morss (1974) that reflections violating space group Fm m in some published X-ray powder patterns of natural elpasolite are Kβ-lines. Original Russian Text ? I.V. Pekov, N.V. Chukanov, N.N. Kononkova, N.V. Zubkova, M.Kh. Rabadanov, D.Yu. Pushcharovsky, 2007, published in Zapiski Rossiiskogo Mineralogicheskogo Obshchestva, 2007, No. 6, pp. 76–84.  相似文献   
247.
Climatic changes in southeastern Transbaikalia in the Middle and Late Holocene and their influence on alluvial sedimentation environments are reconstructed from the results of study of the Ilya floodplain sediments (Alkhanai National Park). At the beginning of the Subboreal period, the regional climate became more arid, which led to a significant increase in steppe species communities in the landscapes. Intense climate aridization also took place at the beginning and at the end of the Subatlantic period of the Holocene. The alluvial-sedimentation rate increased during the weakening of aridization and decreased during cooling and the intensification of aridization. The obtained regional data are compared with data on the adjacent areas and the global climatic changes in the Northern Hemisphere.  相似文献   
248.
The methods of celestial mechanics can be used to construct a mathematical model for the perturbed rotational motions of the deformable Earth that can adequately describe the astrometric measurements of the International Earth Rotation Service (IERS). This model describes the gravitational and tidal influences of the Sun and Moon. Fine resonant interactions of long-period zonal tides (annual, semiannual, monthly, and biweekly) with the diurnal and semidiurnal tides are revealed. These interactions can be reliably confirmed via a spectral analysis of the IERS data. Numerical modeling of tidal irregularities of the Earth’s axial rotation was carried out, focusing on the analysis and forecasting of variations of the day length occurring within short time intervals of a year or shorter (intrayear variations).  相似文献   
249.
DLG数据任意范围接边算法及实现   总被引:4,自引:0,他引:4  
DLG数据接边在数据入库和数据更新中都有着非常重要的作用,当前在DLG数据接边方面研究的成果主要是基于图幅的接边,这种接边算法不够灵活,局限明显,难以满足接边范围不规则时数据接边的需要。提出一种任意范围接边的算法,并基于ArcEngine实现了相应的功能,该算法也适用于GIS数据入库时的批量图幅接边。  相似文献   
250.
地籍管理数据库特色研究   总被引:1,自引:0,他引:1  
在总结目前地籍管理工作的基础上,较为详细地研究地籍管理工作中的基本管理特点,即城乡一体化地籍管理、地籍数据检查、时空地籍数据管理和基于Web Service的目录数据库管理.并利用ArcEngine组件,在.NET平台基础上,以广东省地籍管理数据库系统建设为例.实现了这些特色管理,它将对我国城乡一体化地籍数据库的建设具有一定的借鉴意义.  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