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   1854篇
  免费   156篇
  国内免费   13篇
测绘学   54篇
大气科学   199篇
地球物理   604篇
地质学   690篇
海洋学   130篇
天文学   236篇
综合类   11篇
自然地理   99篇
  2023年   6篇
  2022年   15篇
  2021年   46篇
  2020年   51篇
  2019年   35篇
  2018年   59篇
  2017年   81篇
  2016年   120篇
  2015年   104篇
  2014年   126篇
  2013年   195篇
  2012年   155篇
  2011年   108篇
  2010年   109篇
  2009年   80篇
  2008年   65篇
  2007年   38篇
  2006年   68篇
  2005年   43篇
  2004年   38篇
  2003年   32篇
  2002年   49篇
  2001年   32篇
  2000年   13篇
  1999年   13篇
  1998年   18篇
  1997年   16篇
  1996年   11篇
  1995年   22篇
  1994年   14篇
  1993年   10篇
  1992年   7篇
  1991年   22篇
  1990年   11篇
  1989年   9篇
  1987年   10篇
  1986年   7篇
  1985年   13篇
  1984年   14篇
  1983年   14篇
  1982年   9篇
  1981年   8篇
  1980年   5篇
  1979年   13篇
  1978年   5篇
  1976年   8篇
  1975年   9篇
  1974年   7篇
  1973年   10篇
  1969年   7篇
排序方式: 共有2023条查询结果,搜索用时 15 毫秒
81.
82.
83.
84.
85.
86.
International Journal of Earth Sciences - The geometry and emplacement of the ~ 96 km2, Late Cretaceous Sintra Igneous complex (SIC, ca. 80 Ma) into the West Iberian passive...  相似文献   
87.
International Journal of Earth Sciences - The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated...  相似文献   
88.
Benthic microalgae are key contributors to near-shore food webs and sediment stabilization. Temporal variability in microalgal biomass and production throughout the tidal cycle has been well documented; however, due to limitations of traditional methods of analysis patterns of community composition and diversity over such time scales have not been revealed. To explore the latter and better understand how short-term changes throughout the tidal cycle may affect community functioning, we compared benthic diatom composition and diversity over tidal stage shifts. We employed two disparate molecular techniques (denaturing gel gradient electrophoresis with Sanger DNA sequencing of excised bands and high-throughput community metagenome sequencing) to characterize diatom assemblages in representative muddy and sandy intertidal sites in Charleston Harbor, SC, USA. In support of prior studies, we found higher diatom diversity in sandbar as compared to mudflat sediments. Spatial differences were stronger relative to tidal temporal differences, although diversity metrics generally were highest after prolonged tidal immersion as compared to low-tide emersion or just after immersion at flood tide. Composition of the diatom assemblage differed markedly between sites, with species in genera Halamphora, Amphora, and Navicula dominating the sandbar, whereas Cyclotella, Skeletonema, and Thalassiosira were the most prevalent genera on the mudflat. Diatom composition differed by tidal stage, with assemblages during low-tide exposure distinct from samples taken after immersion. Both sandbar and mudflat sediments exhibited increases in relative proportion of epipelic diatoms and decreases in planktonic taxa during low-tide exposure. Our findings of short-term changes in species composition and dominance could inform primary productivity models to better estimate understudied diatom contributions in heterogeneous and highly variable tidal systems.  相似文献   
89.
An unsupervised machine-learning workflow is proposed for estimating fractional landscape soils and vegetation components from remotely sensed hyperspectral imagery. The workflow is applied to EO-1 Hyperion satellite imagery collected near Ibirací, Minas Gerais, Brazil. The proposed workflow includes subset feature selection, learning, and estimation algorithms. Network training with landscape feature class realizations provide a hypersurface from which to estimate mixtures of soil (e.g. 0.5 exceedance for pixels: 75% clay-rich Nitisols, 15% iron-rich Latosols, and 1% quartz-rich Arenosols) and vegetation (e.g. 0.5 exceedance for pixels: 4% Aspen-like trees, 7% Blackberry-like trees, 0% live grass, and 2% dead grass). The process correctly maps forests and iron-rich Latosols as being coincident with existing drainages, and correctly classifies the clay-rich Nitisols and grasses on the intervening hills. These classifications are independently corroborated visually (Google Earth) and quantitatively (random soil samples and crossplots of field spectra). Some mapping challenges are the underestimation of forest fractions and overestimation of soil fractions where steep valley shadows exist, and the under representation of classified grass in some dry areas of the Hyperion image. These preliminary results provide impetus for future hyperspectral studies involving airborne and satellite sensors with higher signal-to-noise and smaller footprints.  相似文献   
90.
Geotechnical and Geological Engineering - Dispersive soils are susceptible to phenomena of internal and external erosion when in contact with relatively pure water due to its particle’s...  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