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   86714篇
  免费   1261篇
  国内免费   747篇
测绘学   1989篇
大气科学   5801篇
地球物理   17239篇
地质学   31313篇
海洋学   7676篇
天文学   19727篇
综合类   244篇
自然地理   4733篇
  2022年   557篇
  2021年   985篇
  2020年   1030篇
  2019年   1127篇
  2018年   2489篇
  2017年   2322篇
  2016年   2797篇
  2015年   1558篇
  2014年   2682篇
  2013年   4634篇
  2012年   2848篇
  2011年   3836篇
  2010年   3295篇
  2009年   4292篇
  2008年   3921篇
  2007年   3888篇
  2006年   3567篇
  2005年   2695篇
  2004年   2591篇
  2003年   2440篇
  2002年   2310篇
  2001年   2134篇
  2000年   1976篇
  1999年   1596篇
  1998年   1671篇
  1997年   1591篇
  1996年   1292篇
  1995年   1312篇
  1994年   1147篇
  1993年   1008篇
  1992年   1002篇
  1991年   900篇
  1990年   992篇
  1989年   859篇
  1988年   769篇
  1987年   960篇
  1986年   794篇
  1985年   1013篇
  1984年   1086篇
  1983年   1016篇
  1982年   962篇
  1981年   840篇
  1980年   793篇
  1979年   741篇
  1978年   728篇
  1977年   659篇
  1976年   637篇
  1975年   603篇
  1974年   602篇
  1973年   600篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
The paper deals with a numerical integrated procedure to calculate the effects of the interaction between sea waves and a tripod-type steel gravity platform. The main aspects to be taken into account for a reliable wave loading analysis of such a new type of platform are emphasized. Among them, the field perturbation effect due to the large bodies presence is analysed. Finally, some principal results in terms of structure global loads obtained by the numerical integrated procedure are presented.  相似文献   
102.
The fauna composition, ecological groups, and life forms of Harpacticoids of soft littoral grounds from 15 sites off the Karelian coast in Kandalaksha Bay of the White Sea were studied. Six types of harpacticoid taxocens with different sets of dominating species are described. On silty sands with clear signs of desalination, the Stenchelia palustris taxocen is common; medium-grained sands are characterized by the Heterolaophonte minuta, Paraleptastacus kliei — Huntemannia jadensis, and Amphiascoides nanus — Scottopsyllus minor taxocens; while on coarse sands, the Ameira parvula and Ameira scotti — Mesochra lilljeborgi taxocens have developed. The diversity of the taxocens is partly explained by the differences in the grain-size composition and salinity at different sites. In addition, groups of various taxocens dwelling on the same type of the sediments were found in different minor bights of the coastline.  相似文献   
103.
104.
Satellite imagery and offshore magnetic data were analysed to correlate regional tectonic elements on the inner continental shelf off Konkan and the adjacent Deccan plateau. Three statistically important lineament trends—N-S, WNW-ESE and ENE-WSW—that prevail on land are correlatable well with the offshore trends. This positive correlation suggests simultaneous deformation. The major magnetic lineament observed off Jaigad Bay, west coast of India, may be the extension of onshore lineaments. The correlation of both the offshore and onshore trends indicates that the fracture pattern of the crystalline basement has also controlled the offshore structural pattern.  相似文献   
105.
Trends in emigration from Ireland over time are reviewed. "During the eighteenth and nineteenth centuries overseas migration to the United States and seasonal harvest migration to Britain were the main types of movement, but over the past 100 years the Irish have developed a special affinity for settling in British towns. Although the outflow was halted for a time during the 1970s, when return migration took over, the 1980s have seen a renewal of the exodus. This time, however, the character of the flow has changed from predominantly low-skill construction and factory workers to embrace better-educated emigrants, including many graduates. This shift reflects Ireland's changing position in the international market for labour."  相似文献   
106.
M. J. Martres 《Solar physics》1989,119(2):357-384
This paper consists of two parts. We first discuss recent general results on the study of properties of flare homology, and their relevance to the physical interpretation of the flare phenomenon at large. We devote particular attention to the discovery of homologous flares which occur in rapid succession, within a few minutes of each other in many cases. We name these kind of flares rafales. These flares signal the existence of several episodes of energy release within the same magnetic configuration. We also show the existence of particular sites in the solar atmosphere which have peculiar characteristics in terms of solar rotation, and where recurrent flaring may take place over and over again in different solar rotations. This indicates that the disturbance causing the emergence of activity is deep seated, below the solar photosphere. Finally, in the second part, we discuss an extensive set of observations of two homologous flares of a rafale, stressing the dynamic aspects of the observations, particularly the presence of peaks in the vertical component of the velocity field. These results are shown to be in agreement with studies of filament activations and the surging arches which are observed before the flash phase of solar flares.  相似文献   
107.
The author examines circular labor migration in Fiji. "This paper is organized into five sections. The first section provides a brief discussion of two major perspectives of labour circulation in developing countries. The second section presents the state of the Fijian village in the context of the current pattern of uneven development in Fiji. The practice of labour circulation by Fijian villagers is dealt with in the third section. In the last two sections, issues concerning the maintenance of the polarized pattern and the preservation of the village mode of production are discussed."  相似文献   
108.
109.
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