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   111821篇
  免费   2286篇
  国内免费   1529篇
测绘学   2966篇
大气科学   8185篇
地球物理   22002篇
地质学   42118篇
海洋学   9610篇
天文学   23780篇
综合类   540篇
自然地理   6435篇
  2022年   608篇
  2021年   1005篇
  2020年   1071篇
  2019年   1160篇
  2018年   4426篇
  2017年   4202篇
  2016年   3941篇
  2015年   1870篇
  2014年   2880篇
  2013年   5162篇
  2012年   3948篇
  2011年   6248篇
  2010年   5453篇
  2009年   6624篇
  2008年   5728篇
  2007年   6056篇
  2006年   4061篇
  2005年   3468篇
  2004年   3289篇
  2003年   3120篇
  2002年   2748篇
  2001年   2400篇
  2000年   2319篇
  1999年   1841篇
  1998年   1963篇
  1997年   1796篇
  1996年   1381篇
  1995年   1510篇
  1994年   1274篇
  1993年   1164篇
  1992年   1135篇
  1991年   1058篇
  1990年   1161篇
  1989年   967篇
  1988年   883篇
  1987年   1101篇
  1986年   905篇
  1985年   1190篇
  1984年   1332篇
  1983年   1205篇
  1982年   1174篇
  1981年   1028篇
  1980年   989篇
  1979年   871篇
  1978年   867篇
  1977年   827篇
  1976年   790篇
  1975年   743篇
  1974年   752篇
  1973年   762篇
排序方式: 共有10000条查询结果,搜索用时 296 毫秒
31.
Oceanology - A new approach has been applied to studying marine sedimentation using dispersed sedimentary material in sediment traps compared to the surface layer of bottom sediments. Based on...  相似文献   
32.
An extraordinary experimental fact is presented and analyzed, namely, a rather intense broadband radio noise detected during the passage of an atmospheric front through the field of view of UHF antennas. Local atmospheric properties and possible sources of the extraordinary noise, including the thermal noise from cloudiness and extra-atmospheric sources, are considered. A conclusion is made about the presence of an additional nonthermal source of radio noise in the frontal cloudiness. According to the proposed hypothesis, these are multiple electric microdicharges on hydrometeors in the convective cloud.  相似文献   
33.
34.
GRB 170817A, associated with the LIGO-Virgo GW170817 neutron-star merger event, lacks the short duration and hard spectrum of a Short gamma-ray burst (GRB) expected from long-standing classification models. Correctly identifying the class to which this burst belongs requires comparison with other GRBs detected by the Fermi GBM. The aim of our analysis is to classify Fermi GRBs and to test whether or not GRB 170817A belongs—as suggested—to the Short GRB class. The Fermi GBM catalog provides a large database with many measured variables that can be used to explore gamma-ray burst classification. We use statistical techniques to look for clustering in a sample of 1298 gamma-ray bursts described by duration and spectral hardness. Classification of the detected bursts shows that GRB 170817A most likely belongs to the Intermediate, rather than the Short GRB class. We discuss this result in light of theoretical neutron-star merger models and existing GRB classification schemes. It appears that GRB classification schemes may not yet be linked to appropriate theoretical models, and that theoretical models may not yet adequately account for known GRB class properties. We conclude that GRB 170817A may not fit into a simple phenomenological classification scheme.  相似文献   
35.
The present study used two mitochondrial markers (16S rRNA and COI) to assess the genetic diversity of a newly founded Lessepsian migrant mussel, Brachidontes pharaonis, in Tunisian waters. The species appears to be restricted to only one population in Rades Harbour, in the northern part of the country. Phylogenetic analyses revealed the monophyly of B. pharaonis in Tunisia. Both molecular markers revealed high genetic variability of the B. pharaonis population. Haplotype networks and demographic analyses confirmed the recent expansion events within this population. Multiple human-mediated introduction events involving several founder populations and intensive population growth rates are probably the main causes of the high polymorphism observed within this invasive mollusc.  相似文献   
36.
Izvestiya, Atmospheric and Oceanic Physics - Gravimetric data obtained by the GOCE spacecraft contributes to the development of global models of the deep structure of the Earth’s crust and...  相似文献   
37.
Solar System Research - The discovery of the first interstellar comet 2I/Borisov confirmed the astronomers’ speculation that the passage through the solar system of relatively large objects...  相似文献   
38.
39.
Analytical solutions for generalizing the Ekman stationary flow of a viscous incompressible fluid in an infinite layer are obtained. The solution of an overdetermined system of the Oberbeck–Boussinesq equations is considered. It is suggested to use a class of exact solutions for this problem. It is shown that the structure of the solutions allows one to preserve the advective derivative in the heat-conductivity equation; this makes it possible to model the stratification of the temperature and pressure fields and describe the oceanic countercurrents.  相似文献   
40.
Izvestiya, Atmospheric and Oceanic Physics - Areas with large gradients and anomalous variations in geomagnetic and radiation fields have been revealed and mapped at the northwestern foot of the...  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