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   831篇
  免费   33篇
  国内免费   4篇
测绘学   5篇
大气科学   80篇
地球物理   153篇
地质学   280篇
海洋学   53篇
天文学   236篇
综合类   3篇
自然地理   58篇
  2021年   5篇
  2020年   6篇
  2019年   11篇
  2018年   26篇
  2017年   16篇
  2016年   12篇
  2015年   28篇
  2014年   22篇
  2013年   47篇
  2012年   22篇
  2011年   42篇
  2010年   41篇
  2009年   51篇
  2008年   26篇
  2007年   33篇
  2006年   31篇
  2005年   31篇
  2004年   26篇
  2003年   26篇
  2002年   32篇
  2001年   21篇
  2000年   32篇
  1999年   10篇
  1998年   15篇
  1997年   17篇
  1996年   16篇
  1995年   22篇
  1994年   11篇
  1993年   9篇
  1992年   12篇
  1991年   8篇
  1990年   10篇
  1989年   11篇
  1988年   3篇
  1987年   7篇
  1986年   6篇
  1985年   11篇
  1984年   14篇
  1983年   13篇
  1982年   7篇
  1981年   10篇
  1980年   7篇
  1979年   5篇
  1978年   8篇
  1977年   11篇
  1976年   5篇
  1975年   4篇
  1974年   6篇
  1973年   4篇
  1971年   3篇
排序方式: 共有868条查询结果,搜索用时 859 毫秒
101.
The Four-Dimensional Data Assimilation was performed to evaluate source emission strengths over the United States. The USEPA Models-3 system (CMAQ/MM5/SMOKE) and ridge regression are used as the forward and inverse models, respectively. The continental US is divided into six regions, and data assimilation is performed for each region in July 2001 and January 2002. In addition, two separate scaling factors are calculated for weekdays and weekends. Results show that base emissions for CO and SO2 sources are relatively accurate. Base emissions for PEC source are overestimated 100%, but those for POA source are underestimated up to 70% when compared with the adjusted emissions. Emissions for NH3, NO x , and PMFINE sources are relatively accurate in July 2001, but those in January 2002 are around 100% higher than the adjusted emissions. Base VOC emissions in July 2001 are similar to the adjusted emissions but those in January 2002 are underestimated up to 70% when compared with the adjusted emissions. Though the emission adjustment itself improves the overall air quality model performance, a better improvement is expected with the modification of speciation profiles and temporal allocations in the Models-3 system, as well.  相似文献   
102.
The Heterodyne Instrument for the Far Infrared (HIFI) on board the Herschel Space Observatory is composed of a set of fourteen double sideband mixers. We discuss the general problem of the sideband ratio (SBR) determination and the impact of an imbalanced sideband ratio on the line calibration in double sideband heterodyne receivers. The HIFI SBR is determined from a combination of data taken during pre-launch gas cell tests and in-flight. The results and some of the calibration artefacts discovered in the gas cell test data are presented here along with some examples of how these effects appear in science data taken in orbit.  相似文献   
103.
Abstract— Fabric analysis of the interstitial matrix material in primitive meteorites offers a novel window on asteroid formation and evolution. Electron backscatter diffraction (EBSD) has allowed fabrics in these fine‐grained materials to be visualized in detail for the first time. Our data reveal that Allende, a CV3 chondrite, possesses a uniform, planar, short‐axis alignment fabric that is pervasive on a broad scale and is probably the result of deformational shortening related to impact or gravitational compaction. Interference between this matrix fabric and the larger, more rigid components, such as dark inclusions (DIs) and calcium‐aluminium‐rich inclusions (CAIs), has lead to the development of locally oriented and intensified matrix fabrics. In addition, DIs possess fabrics that are conformable with the broader matrix fabric. These results suggest that DIs were in situ prior to the deformational shortening event responsible for these fabrics, thus providing an argument against dark inclusions being fragments from another lithified part of the asteroid (Kojima and Tomeoka 1996; Fruland et al. 1978). Moreover, both DIs and Allende matrix are highly porous (?25%) (Corrigan et al. 1997). Mobilizing a highly porous DI during impact‐induced brecciation without imposing a fabric and incorporating it into a highly porous matrix without significantly compacting these materials is improbable. We favor a model that involves Allende DIs, CAIs, and matrix accreting together and experiencing the same deformation events.  相似文献   
104.
105.
106.
107.
108.
A preliminary analysis of the data from the UCLA magnetometer on board the Apollo 15 subsatellite indicates that remnant magnetization is a characteristic property of the Moon, that its distribution is such as to produce a rather complex pattern or fine structure, and that a detailed mapping of its distribution is feasible with the present experiment. The analysis also shows that lunar induction fields produced by transients in the interplanetary magnetic field are detectable at the satellite orbit so that in principle the magnetometer data can be used to determine the latitudinal and longitudinal as well as radial dependences of the distribution of electrical conductivity within the Moon. Finally, the analysis indicates that the plasma void or diamagnetic cavity which forms behind the Moon when the Moon is in the solar wind, is detectable at the satellite's orbit and that the flow of the solar wind near the limbs is usually rather strongly disturbed.Publication No. 981. Institute of Geophysics and Planetary Physics.  相似文献   
109.
Many of the major British telescopes are described in this volume by other speakers directly involved with those facilities, so this contribution will concentrate on aspects of the operation of the Anglo-Australian Observatory (AAO) which seem particularly relevant to the JNLT. Some requirements for the success of the new very large optical telescopes are also discussed.Paper presented at the Symposium on the JNLT and Related Engineering Developments, Tokyo, November 29–December 2, 1988.  相似文献   
110.
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