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   41302篇
  免费   2216篇
  国内免费   3995篇
测绘学   2329篇
大气科学   4489篇
地球物理   7828篇
地质学   20136篇
海洋学   3381篇
天文学   3485篇
综合类   3059篇
自然地理   2806篇
  2024年   121篇
  2023年   327篇
  2022年   765篇
  2021年   990篇
  2020年   878篇
  2019年   919篇
  2018年   5761篇
  2017年   4962篇
  2016年   3523篇
  2015年   1023篇
  2014年   1105篇
  2013年   1088篇
  2012年   2011篇
  2011年   3790篇
  2010年   2983篇
  2009年   3251篇
  2008年   2765篇
  2007年   3248篇
  2006年   880篇
  2005年   635篇
  2004年   767篇
  2003年   834篇
  2002年   757篇
  2001年   503篇
  2000年   398篇
  1999年   398篇
  1998年   326篇
  1997年   330篇
  1996年   276篇
  1995年   267篇
  1994年   243篇
  1993年   192篇
  1992年   168篇
  1991年   113篇
  1990年   108篇
  1989年   118篇
  1988年   82篇
  1987年   67篇
  1986年   63篇
  1985年   47篇
  1984年   43篇
  1983年   41篇
  1982年   41篇
  1981年   48篇
  1980年   43篇
  1979年   31篇
  1977年   19篇
  1976年   24篇
  1975年   24篇
  1973年   18篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
高精度层序地层学已被证明是寻找隐蔽圈闭行之有效的理论方法.运用该理论对南阳凹陷进行了研究,对地震剖面中反射界面的追踪,在古近系中识别出了各级别的层序界面,结合周缘露头、钻井、测井等资料,分析了主要目的层序内体系域的构成及高频单元变化规律,建立了层序地层模式,在此基础上预测南部陡崖式断坡带和北部缓坡式弯折带是低位域砂体和隐蔽岩性油气藏形成的有利区带.  相似文献   
82.
大张坨凝析气藏是在我国发现的高含量凝析气藏之—.开发中据相态特征及流体组份研究结果,适时调整开发方式.1994年开始试采,1995年初实施循环注气开发.该气藏的开发经历了衰竭试采循环注气2个开采过程,开发过程中定期取地层流体样品进行相态特征和流体组份研究,并注重其成果的应用,凝折油采出率29.0%,取得了较好的开发效果.证实了相态研究在凝析气藏循环注气开发全过程应用的重要性.  相似文献   
83.
岫岩-海城5.4级地震前小震震源机制解与记录特征分析   总被引:4,自引:2,他引:4  
采用Pn、Pg初始波初动符号,利用乌尔夫网上半球投影,用作图方法求解了岫岩-海城震区(1999年1月-1999年11月29日)主震前辽宁数字地震台网记录(ML≥2.5)的41个小震的震源机制参数。结合前震记录的某些特征,对主震前应力方向的时空变化,震源错动性质进行分析和讨论。  相似文献   
84.
科技期刊编辑应具备的基本素质   总被引:2,自引:0,他引:2  
李玉亭  刘素英 《山西地震》2003,(4):27-28,35
对科技期刊质量和编辑素质的关系进行了研究,认为编辑是期刊的设计师。一本期刊从总体创意、策划选题、编审稿件到排版设计,无不体现编辑的主体意识。期刊质量的好坏,读者评价的高低都与编辑息息相关。编辑的素质关系到期刊的生存和发展。得出不断提高科技期刊编辑的素质是十分必要的结论。  相似文献   
85.
86.
We use 23298 Pn arrival-time data from Chinese national and provincial earthquake bulletins to invert fine structure of Pn velocity and anisotropy at the top of the mantle beneath the Sichuan-Yunnan and its adjacent region. The results suggest that the Pn velocity in this region shows significant lateral variation; the Pn velocity varies from 7.7 to 8.3 km/s. The Pn-velocity variation correlates well with the tectonic activity and heat flow of the region. Low Pn velocity is observed in southwest Yunnan, Tengchong volcano area, and the Panxi tectonic area. These areas have very active seismicity and tectonic activity with high surface heat flow. On the other hand, high Pn velocity is observed in some stable regions, such as the central region of the Yangtze Platform; the most pronounced high velocity area is located in the Sichuan Basin, south of Chengdu. Pn anisotropy shows a complex pattern of regional deformation. The Pn fast direction shows a prominent clockwise rotation pattern from east of the Tibetan block to the Sichuan-Yunnan diamond block to southwest Yunnan, which may be related to southeastward escape of the Tibetan Plateau material due to the collision of the Indian Plate to the Eurasia Plate. Thus there appears to be strong correlation between the crustal deformation and the upper mantle structure in the region. The delay times of events and stations show that the crust thickness decreases from the Tibetan Plateau to eastern China, which is consistent with the results from deep seismic sounding.  相似文献   
87.
88.
— Seismic responses of weathered and non-weathered ridge models were simulated to study the ridge effects on the ground motion characteristics. The range of ridge slope from 19.98° to 45° was considered to produce a possible set of generalized results. 2.5-D modeling based on parsimonious staggered grid approximation of elastodynamic wave equations was adopted in simulations. Computed results reveal an increase of amplitude of incoming waves with both elevation and the slope of the ridge. Further, the characteristics of surface waves are highly ridge slope dependent. The analysis of responses of weathered and non-weathered ridge models reveals that ridge has caused a strong generation of surface waves near its top. The surface waves are not dominating on the top of the ridge but at some lower elevation. The increase of weathering of ridge further intensified the ridge effect. Analysis in frequency domain, based on spectral ratio method, does not indicate any pattern in the spectral amplification factor and is very much sensitive to slope, source focal mechanism and location. However, on an average there is a continuous decrease of amplification with slope in the vertical component and increase in the transverse component, and it is increasing in the radial component up to slope =38.0° and thereafter decreasing.  相似文献   
89.
Tidal mixing plays an important role in the modification of dense water masses around the Antarctic continent. In addition to the vertical (diapycnal) mixing in the near-bottom layers, lateral mixing can also be of relevance in some areas. A numerical tide simulation shows that lateral tidal mixing is not uniformly distributed along the shelf break. In particular, strong mixing occurs all along the Ross Sea and Southern Weddell Sea shelf breaks, while other regions (e.g., the western Weddell Sea) are relatively quiet. The latter regions correspond surprisingly well to areas where indications for cross-shelf exchange of dense water masses have been found. The results suggest that lateral tidal mixing may account for the relatively small contribution of Ross Sea dense water masses to Antarctic Bottom Water.  相似文献   
90.
A laboratory study was conducted to examine oil biodegradation in the presence of a fouling organism community. It is shown that the majority of fouling species exhibit relatively weak tolerance to oil. Oil degradation in seawater is shown to proceed quicker and more completely in the presence of the fouling organism community than it does without such organisms. The population of specific bacterial groups is shown first to grow and next decrease as a result of accumulation in water of toxic products of their vital activity. Oil biodegradation is found to cause substantial changes in the water hydrochemical characteristics in experimental vessels.  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