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   53213篇
  免费   574篇
  国内免费   1138篇
测绘学   2086篇
大气科学   4159篇
地球物理   10150篇
地质学   21973篇
海洋学   3551篇
天文学   7857篇
综合类   2214篇
自然地理   2935篇
  2021年   275篇
  2020年   299篇
  2019年   302篇
  2018年   5354篇
  2017年   4638篇
  2016年   3346篇
  2015年   696篇
  2014年   881篇
  2013年   1580篇
  2012年   1868篇
  2011年   3834篇
  2010年   3001篇
  2009年   3580篇
  2008年   3001篇
  2007年   3463篇
  2006年   1212篇
  2005年   1029篇
  2004年   1230篇
  2003年   1159篇
  2002年   1006篇
  2001年   759篇
  2000年   753篇
  1999年   563篇
  1998年   540篇
  1997年   599篇
  1996年   468篇
  1995年   474篇
  1994年   471篇
  1993年   381篇
  1992年   387篇
  1991年   358篇
  1990年   373篇
  1989年   342篇
  1988年   344篇
  1987年   368篇
  1986年   325篇
  1985年   425篇
  1984年   414篇
  1983年   446篇
  1982年   415篇
  1981年   384篇
  1980年   420篇
  1979年   324篇
  1978年   302篇
  1977年   294篇
  1976年   272篇
  1975年   264篇
  1974年   269篇
  1973年   254篇
  1971年   173篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
201.
The article attempts to test the aluminum consumption–economic growth nexus for 20 rich economies for the period 1970–2009. Various panel data unit root and cointegration tests are applied. The series are found to be integrated of order one and cointegrated, especially after controlling for cross-sectional dependence. Moreover, the Blundell–Bond system generalized methods-of-moments is employed to conduct a panel causality test in a vector error-correction mechanism setting. Unidirectional causality running from aluminum consumption to real GDP is uncovered in the short-run, while real GDP is found to Granger-cause aluminum consumption in the long-run. Moreover, a 1% increase in real GDP generates an increase of 0.44% in aluminum consumption in the long-run for the whole panel.  相似文献   
202.
Developing approaches to automate the analysis of the massive amounts of data sent back from the Moon will generate significant benefits for the field of lunar geomorphology. In this paper, we outline an automated method for mapping lunar landforms that is based on digital terrain analysis. An iterative self-organizing (ISO) cluster unsupervised classification enables the automatic mapping of landforms via a series of input raster bands that utilize six geomorphometric parameters. These parameters divide landforms into a number of spatially extended, topographically homogeneous segments that exhibit similar terrain attributes and neighborhood properties. To illustrate the applicability of our approach, we apply it to three representative test sites on the Moon, automatically presenting our results as a thematic landform map. We also quantitatively evaluated this approach using a series of confusion matrices, achieving overall accuracies as high as 83.34% and Kappa coefficients (K) as high as 0.77. An immediate version of our algorithm can also be applied for automatically mapping large-scale lunar landforms and for the quantitative comparison of lunar surface morphologies.  相似文献   
203.
Neolithic culture series in the Yishu River Basin developed in the order of Beixin culture-Dawenkou culture-Longshan culture-Yueshi culture. During the early and middle stage of Longshan culture (4600-4300 cal. yr BP), the climate in the Yishu River Basin was warm and wet. Paddy-oriented agriculture planted paddy was very developed. The society was flourishing with great amount of archaeological sites. The cooling starting in 4200 cal. yr BP made the paddies shortfall in output or even no seeds were gathered. This situation intensified the discrepancy between population and resource. The scarcity in natural resource led to substantial decrease in population and subsequent drop in archaeological sites. About 4000 cal. yr BP Longshan culture was displaced by Yueshi culture which was relatively un- derdeveloped, simple and unsophisticated.  相似文献   
204.
Summary A formula is derived for the spatial attenuation of the two possible modes of oscilation of a two-layer, rotating system. If the long-wave approximation is made, it is found with reference to the internal mode that this formula disagrees with an earlier result obtained byRattray [8]2).  相似文献   
205.
This work briefly discusses the main features of probabilistic seismic hazard analysis (PSHA). Special attention is paid to the identification and quantification of uncertainties related to seismic source characteristics and seismic engineering models for prediction of strong ground motions. The principal seismic models and the results of PSHA application for detailed seismic zoning of urban territories in Sakhalin Island are presented.  相似文献   
206.
The complex variables boundary element method (CVBEM) is used to study interaction between a circular opening and fractures originating from its boundary in a piecewise homogeneous plane. A new complex hypersingular equation for piecewise homogeneous media with a circular opening is obtained. The equation is solved using the CVBEM technique with circular and straight boundary elements and polynomial approximations (with square root asymptotics for crack tip elements) for the unknown functions. The algorithm is verified through comparison with known semi‐analytical and numerical solutions that involve interaction between a circular opening and specific systems of cracks or other openings. New numerical results concerning the interaction of the circular opening with the cracks and circular inclusions are presented. The method is applied to an important problem in the petroleum industry: modelling propagation of hydraulic fractures in the vicinity of a borehole. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   
207.
We examine the various types of mineral waters occurring on the projected specially protected transboundary natural territory “Istoki Amura”, on the Hentei-Dauria neotectonic high. We suggest the pattern of rational utilization of the mineral springs according to the nature conservation status of the terrain (nature reserves, national parks, and public access areas).  相似文献   
208.
Doklady Earth Sciences - Analysis of observations of the Earth’s rotational velocity and volcanic activity of the planet from 1720 until 2015 suggests that higher volcanic activity temporally...  相似文献   
209.
210.
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