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   133474篇
  免费   1730篇
  国内免费   1700篇
测绘学   3790篇
大气科学   9296篇
地球物理   25756篇
地质学   49785篇
海洋学   11228篇
天文学   26985篇
综合类   2393篇
自然地理   7671篇
  2022年   679篇
  2021年   1227篇
  2020年   1305篇
  2019年   1474篇
  2018年   7294篇
  2017年   6398篇
  2016年   5648篇
  2015年   1941篇
  2014年   3233篇
  2013年   5800篇
  2012年   4341篇
  2011年   6978篇
  2010年   6004篇
  2009年   7467篇
  2008年   6381篇
  2007年   6888篇
  2006年   4533篇
  2005年   3526篇
  2004年   3641篇
  2003年   3437篇
  2002年   3260篇
  2001年   2707篇
  2000年   2610篇
  1999年   2085篇
  1998年   2152篇
  1997年   2011篇
  1996年   1700篇
  1995年   1691篇
  1994年   1467篇
  1993年   1429篇
  1992年   1317篇
  1991年   1314篇
  1990年   1295篇
  1989年   1194篇
  1988年   1110篇
  1987年   1291篇
  1986年   1135篇
  1985年   1387篇
  1984年   1563篇
  1983年   1478篇
  1982年   1351篇
  1981年   1333篇
  1980年   1143篇
  1979年   1096篇
  1978年   1052篇
  1977年   967篇
  1976年   926篇
  1975年   903篇
  1974年   887篇
  1973年   961篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
141.
Changes in the spatial distribution of the population of the Ukraine between 1959 and 1984 are analyzed. Attention is given to changes in the rural and urban population composition over time as well as to regional variations in population dynamics.  相似文献   
142.
143.
Quasi-steady high-temperature current sheets are an energy source during the main or hot phase of solar flares. Such sheets are shown to be stabilized with respect to the tearing instability by a small transverse component of magnetic field existing in the sheets.  相似文献   
144.
The librational motion of the Ideal Resonance Problem (Garfinkel, 1966, Jupp, 1969) is treated through an initialnon-canonical transformation which, however, leaves the equations of motion in a quasi-canonical form, with Hamiltonian expressed in standard trigonometric functions amenable to traditional averaging techniques. The perturbed solutions, similarly expressed intrigonometric near-identity transformations, and their frequencies can be found to arbitrary order, with the elliptic integrals expected of the system introduced only in a final explicit quadrature for a Kepler-type equation in the angular variable. The specific transformations and resulting equations of motion are introduced, and explicit solutions for the original variables are found to second order, with mean motion accurate to fifth. Limitation of the present solution to the librational region, the extension of that solution to higher order, and observations on the form of the associated Hamiltonian are also discussed.  相似文献   
145.
An analytical relative orientation of a stereo-pair of photographs was computed in an unusual system of co-ordinates. The disparity in the widely mismatched photographs, their tilts and narrow angles subtended resulted in a rather weak solution from which sections of the lunar surface have been plotted. The results were not good but were better than expected. The main outcome of the work is a, probably unique, demonstration of the versatility of analytical photogrammetry.  相似文献   
146.
147.
Summary The geometry of the principal Upper High (near the Indian Occean) in the 300–100 mb layer appears to account for the Southern Oscillation (S.O.), and models of its behaviour are presented. Significant features of these models include the equatorial points of upper convergence (C) and divergence (D), a pressure discontinuity (CNDS) forming «arcs» and an «enclosure» around the high, and, lastly, encircling «crescents» both outside and inside the enclosure. The geography of the seasonal sucession can thus—in a qualitative manner—be interpreted in the light of known wind and contour patterns near the tropopause. With a few general principles, the established empirical rules of long-range forecasting then follow by deduction. The models and the terminology are useful likewise in the interpretation of solar-terrestrial relations and of climatic fluctuations.  相似文献   
148.
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   
149.
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   
150.
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