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   139087篇
  免费   2361篇
  国内免费   1074篇
测绘学   3448篇
大气科学   9553篇
地球物理   27140篇
地质学   50974篇
海洋学   12312篇
天文学   30641篇
综合类   468篇
自然地理   7986篇
  2022年   789篇
  2021年   1372篇
  2020年   1538篇
  2019年   1661篇
  2018年   4760篇
  2017年   4403篇
  2016年   4663篇
  2015年   2249篇
  2014年   3904篇
  2013年   6923篇
  2012年   4638篇
  2011年   6830篇
  2010年   5955篇
  2009年   7467篇
  2008年   6559篇
  2007年   6825篇
  2006年   5213篇
  2005年   4135篇
  2004年   4015篇
  2003年   3831篇
  2002年   3585篇
  2001年   3135篇
  2000年   3042篇
  1999年   2429篇
  1998年   2547篇
  1997年   2326篇
  1996年   1814篇
  1995年   1979篇
  1994年   1695篇
  1993年   1573篇
  1992年   1489篇
  1991年   1462篇
  1990年   1524篇
  1989年   1296篇
  1988年   1189篇
  1987年   1437篇
  1986年   1233篇
  1985年   1543篇
  1984年   1730篇
  1983年   1655篇
  1982年   1551篇
  1981年   1406篇
  1980年   1298篇
  1979年   1215篇
  1978年   1188篇
  1977年   1041篇
  1976年   1018篇
  1975年   980篇
  1974年   981篇
  1973年   1025篇
排序方式: 共有10000条查询结果,搜索用时 640 毫秒
71.
Izvestiya, Atmospheric and Oceanic Physics - The problem of atmospheric correction for shortwave channels of a multispectral low-resolution scanning radiometer onboard the Meteor-M No. 2 satellite...  相似文献   
72.
Izvestiya, Atmospheric and Oceanic Physics - As a result of studies conducted in the city of Derbent, it is established that its monumental fortification structures erected at the end of the 560s...  相似文献   
73.
Natural Resources Research - Carbon capture and storage is part of Canada’s climate change action plan to reduce greenhouse gas emissions. The Containment and Monitoring Institute Field...  相似文献   
74.
Natural Resources Research - There have been many studies carried out in the past decades attempting to develop strategies for a safe injection of CO2 into storage sites without leakage and...  相似文献   
75.
Wuyep  E. O.  Oluyemi  G. F.  Yates  K.  Akisanya  A. R. 《Natural Resources Research》2020,29(2):1239-1258
Natural Resources Research - Sand failure and production occurs when the formation stress exceeds the strength of the formation, which is derived majorly from the natural material that cements the...  相似文献   
76.
Abstract— Active capture is a new process for the incorporation of large quantities of heavy noble gases into growing surfaces. Adsorption in the conventional sense involves surface bonding by polarization (Van der Waals forces). What is referred to as “anomalous adsorption” of heavy noble gases involves chemical bonds and can occur when other (more chemically active) species are not available to preempt sites with unfilled bonds. Anomalous adsorption has been observed under conditions of fracture, vacuum deposition and ionizing radiation. Active capture depends upon anomalous adsorption to retain noble gases on a surface long enough to be captured in a growing surface film as it is deposited. The fundamental principle may be the impingement onto the growing film with sufficient energy to liberate surface electrons (work function energy of a few electronvolts) so that they are retained by anomalous adsorption long enough to be entrapped in the growing surface. Trapping efficiencies of ?1% have been observed for Kr and Xe in laboratory experiments, implying a fundamentally new mechanism for the incorporation of heavy noble gases onto surfaces. It may play a role in explaining the large concentrations of planetary noble gases contained in phase‐Q.  相似文献   
77.
We present our observations of the galaxy UGS 5600 with a long-slit spectrograph (UAGS) and a multipupil field spectrograph (MPFS) attached to the 6-m Special Astrophysical Observatory telescope. Radial-velocity fields of the stellar and gaseous components were constructed for the central region and inner ring of the galaxy. We proved the existence of two nearly orthogonal kinematic subsystems and conclude that UGC 5600 is a galaxy with an inner polar ring. In the circumnuclear region, we detected noncircular stellar motions and suspected the existence of a minibar. The emission lines are shown to originate in H II regions. We estimated the metallicity from the intensity ratio of the [N II]λ6583 and Hα lines to be nearly solar, which rules out the possibility that the polar ring was produced by the accretion of gas from a dwarf companion.  相似文献   
78.
Abstract— The possibility of volcanism on Mercury has been a topic of discussion since Mariner 10 returned images of half the planet's surface showing widespread plains material. These plains could be volcanic or lobate crater ejecta. An assessment of the mechanics of the ascent and eruption of magma shows that it is possible to have widespread volcanism, no volcanism on the surface whatsoever, or some range in between. It is difficult to distinguish between a lava flow and lobate crater ejecta based on morphology and morphometry. No definite volcanic features have been identified on Mercury. However, known lunar volcanic features cannot be identified in images with similar resolutions and viewing geometries as the Mariner 10 dataset. Examination of high‐resolution, low Sun angle Mariner 10 images reveals several features which are interpreted to be flow fronts; it is unclear if these are volcanic flows or ejecta flows. This analysis implies that a clear assessment of volcanism on Mercury must wait for better data. MESSENGER (MErcury: Surface, Space ENvironment, GEochemistry, Ranging) will take images with viewing geometries and resolutions appropriate for the identification of such features.  相似文献   
79.
80.
We present our spectroscopic observations of the novae V1425, V1493, and V1494 Aql carried out with the 125-cm telescope at the Crimean Station of the Sternberg Astronomical Institute in the wavelength range 4000–11000 Å. We measured the emission-line intensities, determined the nova shell expansion velocities from the line profile FWHMs and components, and estimated the interstellar reddening from the first members of the Balmer series. The chemical composition of the nova shells is analyzed. Nitrogen and oxygen were found to be overabundant in V1425 and V1494 Aql; the helium abundance turned out to be normal in the two stars.  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