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   494篇
  免费   56篇
  国内免费   503篇
测绘学   3篇
大气科学   120篇
地球物理   199篇
地质学   334篇
海洋学   157篇
天文学   91篇
综合类   52篇
自然地理   97篇
  2024年   24篇
  2023年   99篇
  2022年   59篇
  2021年   77篇
  2020年   28篇
  2019年   20篇
  2018年   50篇
  2017年   30篇
  2016年   15篇
  2015年   24篇
  2014年   46篇
  2013年   41篇
  2012年   33篇
  2011年   38篇
  2010年   29篇
  2009年   28篇
  2008年   31篇
  2007年   18篇
  2006年   17篇
  2005年   21篇
  2004年   20篇
  2003年   27篇
  2002年   15篇
  2001年   19篇
  2000年   55篇
  1999年   22篇
  1998年   12篇
  1997年   21篇
  1996年   19篇
  1995年   20篇
  1994年   12篇
  1993年   13篇
  1992年   16篇
  1991年   13篇
  1990年   13篇
  1989年   5篇
  1988年   7篇
  1987年   3篇
  1986年   6篇
  1985年   3篇
  1947年   2篇
  1946年   2篇
排序方式: 共有1053条查询结果,搜索用时 15 毫秒
1.
The structural feature shown on a remote sensing image is a synthetic result ofcombination of the deformations produced during the entire geological history of an area.Therefore, the respective tectonic stress field of each of the different stages in the complexdeformation of an area can be reconstructed in three steps: (1) geological structures formed atdifferent times are distinguished in remote sensing image interpretation; (2) structuraldeformation fields at different stages are determined by analyzing relationships betweenmicrostructures (joints and fractures) and the related structures (folds and faults); and (3)tectonic stress fields at different stages are respectively recovered through a study of the featuresof structural deformation fields in different periods. Circular structures and related circlular and radial joints are correlated in space to con-cealed structural rises. The authors propose a new method for establishing a natural model ofthe concealed structural rises and calculating the tectonic stress field by using quantitative dataof the remote sensing information of circular structures and related linear structures.  相似文献   
2.
Although the CTBT (Comprehensive Nuclear Test-Ban Treaty) was passed in 1996, it is still necessary to develop new and highly efficient methods (Wu Zhongliang, Chen Yuntai, et al.,1993 ; Xu Shaoxie, et al. 1994; Richard L. Garwin, 1994) to monitor possible events. Many discrimination criteria (Xu Shaoxie, et al., 1994 ; Institute of Geophysics, Chinese Academy of Sciences, 1976; Richard L. Garwin, 1994) have been put forward since the 1950s. The results show that each of the existing criteria has its own limitation, but the seismological method is an important and efficient method in the discrimination between nuclear explosion and earthquake. Especially in recent years, because of the little and little equivalent as well as the increasing hiding steps used in the test, a number of more efficient seismological methods have been worked out. In this paper, a new discrimination method, the Wavelet Packet Component Ratio (WPCR) method, is put forward. This method makes full use of the difference in variation with time between the spectra of nuclear explosions and earthquakes. Its discrimination efficiency is rather high.  相似文献   
3.
1 Introduction Soiland waterlossisoneofthe worldwide environm entalissuesthreatening sustainable land use in semiarid areas.However,soiland water loss is highly variable in space and time,and its variability resultsfrom m any factorsoperating ata wide ran…  相似文献   
4.
INTRODUCTION Tunnel typeanchoragehasobviousadvantages inbearingcapacityversusinvestment(LiuandHu,1996).However,itisrarelyusedinapracticalpro jectbecauseofitsrequirementofgoodrockcondi tions.Siduhebridge(Fig.1),whichliesintheBa dongmountainsinthewestplatea…  相似文献   
5.
Natural gas hydrates(NGHs) are a new type of clean energy with great development potential. However, it is urgent to achieve safe and economical NGHs development and utilization. This study established a physical model of the study area using the FLAC3D software based on the key parameters of the NGHs production test area in the South China Sea, including the depressurization method, and mechanical parameters of strata, NGHs occurrence characteristics, and the technological characteri...  相似文献   
6.
鄂尔多斯盆地地温场与烃源岩演化特点   总被引:9,自引:0,他引:9  
通过对鄂尔多斯盆地地壳结构、岩石热导率和生热率的综合研究,盆地莫霍面现今平均温度为568.5℃。各层面地温场展布可归纳为三种展布形式,分别以莫霍面、中元古界底面和侏罗系底面为代表。对应于生油门限的范围是侏罗系底面(现今平均温度为45.8℃)-寒武系底面(现今平均温度为117.3℃).生油门限的上界,在盆地西北部为1300m左右,在盆地南缘为1700m左右,在盆地东部为1200m左右.  相似文献   
7.
INTRoDUCTIONThe3.8GaBeijiafentrondhjemiticrockwasformedbypartialmeltingofsomeoldercontinentalmaterialintermsofgeochemicalresearches(Waneta1-,l999).Soitisveryim-portanttofindthemoreancientrocksintheAnshanarea.Therecentdiscoveryofthemeta-dioriticrockofEoarchaeanintheDongshanScenicSpotisspecificallyimportantsignifi-canceforit'GEOLOGYANDPETROGRAPHYlntheDongshanScenicSpotoftheAnshancity,thereis.anancientrockbeltbeingmorethanlomwideandstrikingapproximatelyNNW-SSE.Inthebelttherear…  相似文献   
8.
During the period between 18 August and 22 September 2006, an ultraviolet photometric O3 analyzer, a NO-NO2-NOx chemiluminescence analyzer, and a quartz micro-oscillating-scale particle concentration analyzer were simultaneously used for monitoring at three different heights each at Beijing (325-m tower) and Tianjin (255-m tower). These towers belong to the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences (CAS) and to the Tianjin Municipal Meteorological Bureau, respectively. These measurements were used to continuously measure the atmospheric O3 and NOx volume-by-volume concentrations and the PM2.5 mass concentration within a vertical gradient. When combined with meteorological data and information on the variation of vertical characteristics of the various atmospheric pollutants in the two cities, analysis shows that these two cities were seriously polluted by both PM2.5 and O3 during summer and autumn. The highest daily-average concentrations of PM2.5 near the ground in Beijing and Tianjin reached 183 μg m-3 and 165 μg m-3, respectively, while the O3 concentrations reached 52 ppb and 77 ppb, and NOx concentrations reached 48 ppb and 62 ppb for these two cities, respectively. The variations in the daily-average concentrations of PM2.5 between Beijing and Tianjin were demonstrated to be consistent over time. The concentrations of PM2.5 measured in Beijing were found to be higher than those in Tianjin. However, the overall O3 concentrations near the ground in Tianjin were higher than in Beijing. NOx concentrations in Tianjin were consistently lower than in Beijing. It was also found that PM2.5 pollution in Beijings atmosphere may also be affected by the pollutants originating in and delivered from Tianjin, and that Ti  相似文献   
9.
辽宁雾预报区的划分初探   总被引:3,自引:1,他引:3       下载免费PDF全文
分析了1997—2006年辽宁境内能见度小于1000 m雾的时空分布特征。结果表明:就雾发生的频率而言,辽宁存在两个高值区和两个低值区,高值区分别位于黄海北部沿岸至辽宁东部山区和锦州北部至阜新一带,低值区分别位于辽宁中北部平原以及朝阳地区。从雾的日变化上看,近86%的雾出现在夜间,近69%的雾出现在02-08时,且多为辐射雾。地域不同但气候条件相近时,雾的日变化与雾发生的次数存在极其相似的特点。依据相似的地理环境和气候条件、雾的日变化特征以及雾发生次数等,将辽宁划分为5个预报区,对雾采取分区预报,以提高雾预报的准确率。  相似文献   
10.
Drill and blast is a commonly used method for rock slope excavation in hydropower engineering. During blasting excavation of rock slopes, far-field vibration monitoring on the first upper berm for statutory compliance is usually performed to control the blast-induced rock damage to the final slope face. In this study, for the rock slope excavation in the Jinping-I hydropower station, the field vibration monitoring and acoustic testing are presented to investigate the vibration characteristics on...  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