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   107926篇
  免费   1601篇
  国内免费   1110篇
测绘学   2763篇
大气科学   7689篇
地球物理   21219篇
地质学   38471篇
海洋学   9559篇
天文学   24578篇
综合类   352篇
自然地理   6006篇
  2022年   630篇
  2021年   1109篇
  2020年   1208篇
  2019年   1268篇
  2018年   2898篇
  2017年   2734篇
  2016年   3451篇
  2015年   1962篇
  2014年   3300篇
  2013年   5760篇
  2012年   3484篇
  2011年   4693篇
  2010年   3982篇
  2009年   5225篇
  2008年   4707篇
  2007年   4535篇
  2006年   4305篇
  2005年   3350篇
  2004年   3301篇
  2003年   3111篇
  2002年   2929篇
  2001年   2637篇
  2000年   2520篇
  1999年   2028篇
  1998年   2160篇
  1997年   2010篇
  1996年   1725篇
  1995年   1690篇
  1994年   1451篇
  1993年   1318篇
  1992年   1295篇
  1991年   1192篇
  1990年   1335篇
  1989年   1095篇
  1988年   1053篇
  1987年   1215篇
  1986年   1059篇
  1985年   1307篇
  1984年   1453篇
  1983年   1315篇
  1982年   1279篇
  1981年   1120篇
  1980年   1033篇
  1979年   978篇
  1978年   973篇
  1977年   849篇
  1976年   817篇
  1975年   796篇
  1974年   764篇
  1973年   750篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
It is proposed that the solar flare phenomenon can be understood as a manifestation of the electrodynamic coupling process of the photosphere-chromosphere-corona system as a whole. The system is coupled by electric currents, flowing along (both upward and downward) and across the magnetic field lines, powered by the dynamo process driven by the neutral wind in the photosphere and the lower chromosphere. A self-consistent formulation of the proposed coupling system is given. It is shown in particular that the coupling system can generate and dissipate the power of 1029 erg s#X2212;1 and the total energy of 1032 erg during a typical life time (103 s) of solar flares. The energy consumptions include Joule heat production, acceleration of current-carrying particles along field lines, magnetic energy storage and kinetic energy of plasma convection. The particle acceleration arises from the development of field-aligned potential drops of 10–150 kV due to the loss-cone constriction effect along the upward field-aligned currents, causing optical, X-ray and radio emissions. The total number of precipitating electrons during a flare is shown to be of order 1037–1038.  相似文献   
182.
Methods of iteration are discussed in relation to Kepler's equation, and various initial guesses are considered, with possible strategies for choosing them. Several of these are compared; the method of iteration used in the comparisons has local convergence of the fourth order.WANG Laboratories, Inc.  相似文献   
183.
184.
185.
186.
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   
187.
188.
A spatial statistical method has been developed from the well-known Kriging technique in geostatistics, as a way of providing quantitative comparison between a pair of spatial data sets, and a measure for such a comparison. This residual analysis method is applied to oceanographic data in order to compare Iceland-Faeroes Front (IFF) model predictions against appropriate field observations, with an aim to assess the IFF model performance and its prediction accuracy. The method is also used to evaluate the model-generated dynamical variability within the model predictions, as well as the natural variability within the frontal observations. From the results, it has been found that the IFF model is highly robust, and gives better predictions at depth 150–350 m than elsewhere. Within such a depth (i.e. 250–350 m), there is also evidence to suggest that the main frontal region is most active above the IF Ridge. The natural variability obtained from the observations appears to be comparable to the model-generated dynamical variability after 20 days of integration, indicating a certain degree of accuracy in the model predictions. The method reported in this paper could also be extended for further use in model data assimilation. Thus, the work not only demonstrates how spatial statistics can be applied to oceanographic data, but also opens up new statistical tools for data handling in ocean modelling.  相似文献   
189.
190.
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   
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