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   46606篇
  免费   866篇
  国内免费   359篇
测绘学   910篇
大气科学   3239篇
地球物理   9398篇
地质学   16801篇
海洋学   4244篇
天文学   9827篇
综合类   124篇
自然地理   3288篇
  2022年   288篇
  2021年   546篇
  2020年   631篇
  2019年   716篇
  2018年   1191篇
  2017年   1195篇
  2016年   1298篇
  2015年   755篇
  2014年   1271篇
  2013年   2277篇
  2012年   1433篇
  2011年   1996篇
  2010年   1785篇
  2009年   2210篇
  2008年   1986篇
  2007年   2060篇
  2006年   1867篇
  2005年   1321篇
  2004年   1320篇
  2003年   1382篇
  2002年   1223篇
  2001年   1055篇
  2000年   1002篇
  1999年   869篇
  1998年   853篇
  1997年   840篇
  1996年   711篇
  1995年   694篇
  1994年   616篇
  1993年   540篇
  1992年   500篇
  1991年   485篇
  1990年   524篇
  1989年   461篇
  1988年   449篇
  1987年   486篇
  1986年   491篇
  1985年   607篇
  1984年   659篇
  1983年   654篇
  1982年   589篇
  1981年   526篇
  1980年   480篇
  1979年   469篇
  1978年   438篇
  1977年   440篇
  1976年   404篇
  1975年   416篇
  1974年   392篇
  1973年   432篇
排序方式: 共有10000条查询结果,搜索用时 11 毫秒
61.
62.
63.
64.
65.
66.
Karst database development in Minnesota: design and data assembly   总被引:1,自引:0,他引:1  
The Karst Feature Database (KFD) of Minnesota is a relational GIS-based Database Management System (DBMS). Previous karst feature datasets used inconsistent attributes to describe karst features in different areas of Minnesota. Existing metadata were modified and standardized to represent a comprehensive metadata for all the karst features in Minnesota. Microsoft Access 2000 and ArcView 3.2 were used to develop this working database. Existing county and sub-county karst feature datasets have been assembled into the KFD, which is capable of visualizing and analyzing the entire data set. By November 17 2002, 11,682 karst features were stored in the KFD of Minnesota. Data tables are stored in a Microsoft Access 2000 DBMS and linked to corresponding ArcView applications. The current KFD of Minnesota has been moved from a Windows NT server to a Windows 2000 Citrix server accessible to researchers and planners through networked interfaces.  相似文献   
67.
68.
A recent article by Beer et al. (1974) in Marine Geology describes an in-situ suspended sediment sampling system which utilizes a pump/motor unit, filter holders, and a lead-acid battery power source. Two aspects of their article may be misleading: the use of certain filter material as X-ray diffraction mounts, and the technique by which an oil-filled battery case may be operated.  相似文献   
69.
Marine molluscan shells from para-type and other loclities of the Holsteinian interglaciation were dated by Th/U and the electron spin resonance (ESR) method to more than 350,000 and 370,000 yr B.P., beyond the limit of Th/U dating. The high age estimate is corroborated by a K/Ar age of 420,000 yr B.P. determined from volcanic ash near the base of the Ariendorf paleosol in the Middle Rhine valley believed to be a pedostratigraphic equivalent of the Holsteinian. Shells from the Herzeele marine unit III, an equivalent of the Wacken (Dömnitz) warm stage in northern France and subsequent to the Holsteinian, revealed ages between 300,000 and 350,000 yr B.P. A correlation of these two warm stages with marine oxygen-isotope stages 11 and 9 on the SPECMAP and CARTUNE time scales is suggested. From the benthic oxygen-isotope record one may infer that no exceptionally high global sea-level rise corresponds to the large transgressions of the Holstein Sea in northern Germany. Therefore, a significant proportion of the transgression was probably the result of an unusually large local glacial-isostatic depression caused by the extreme buildup of ice during the preceding Elster glaciation (stage 12). According to the deep-sea record, it lasted approximately 50% longer than the subsequent cold stage 10. The outstanding soil formation with Braunlehm and the well-developed thermal optimum of the Holsteinian are tentatively related to a phase of minimum sea-ice cover in the Norwegian-Greenland Sea, as deduced from long benthic carbon-isotope records from the central Atlantic.  相似文献   
70.
In this 8th compilation, the following results of observations are given: 207 observed minima of 56 eclipsing binaries, 100 maxima of 21 RR Lyrae- and δ Cephei-stars, 82 results of 32 Mira stars and long period variables, and 47 results of 9 RV Tauri stars, semiregular, and irregular variables, from the years 1966 up to 1968.  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