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   4976篇
  免费   1098篇
  国内免费   2495篇
测绘学   251篇
大气科学   474篇
地球物理   1439篇
地质学   4777篇
海洋学   601篇
天文学   175篇
综合类   652篇
自然地理   200篇
  2023年   6篇
  2022年   6篇
  2021年   14篇
  2020年   13篇
  2019年   8篇
  2018年   10篇
  2017年   13篇
  2016年   16篇
  2015年   43篇
  2014年   11篇
  2013年   38篇
  2012年   22篇
  2011年   499篇
  2010年   305篇
  2009年   458篇
  2008年   144篇
  2007年   301篇
  2006年   520篇
  2005年   609篇
  2004年   1176篇
  2003年   744篇
  2002年   515篇
  2001年   398篇
  2000年   271篇
  1999年   244篇
  1998年   308篇
  1997年   281篇
  1996年   183篇
  1995年   146篇
  1994年   124篇
  1993年   329篇
  1992年   293篇
  1991年   143篇
  1990年   43篇
  1989年   69篇
  1988年   21篇
  1987年   55篇
  1986年   28篇
  1978年   8篇
  1977年   14篇
  1976年   10篇
  1950年   8篇
  1943年   7篇
  1940年   9篇
  1937年   15篇
  1934年   6篇
  1933年   13篇
  1928年   5篇
  1927年   5篇
  1924年   6篇
排序方式: 共有8569条查询结果,搜索用时 15 毫秒
991.
利用1971~2000年逐月SODA(Simple Ocean Data Assimilation)同化资料(Carton等,2004)、1980~2000年逐月NCEP/NCAR再分析资料(Kalnay等,1996)探讨中部型(暖海水首先出现在120°W以西)和东部型(暖海水首先出现在120°W以东)El Nino事件赤道纬向风应力及洋流的异常变化与暖海水信号的传播特征。研究指出:(1)中部型和东部型El Nio事件发生时,太平洋上赤道海表最大西风应力距平在西太平洋地区都有显著的东传现象,但中部型El Nio事件西风应力距平强度强,造成西太平洋赤道表层的东向流可达东太平洋地区,这类El Nio事件强度偏强。(2)中部型El Nio事件,赤道表层洋流辐合区及其下沉运动由西太平洋向东太平洋传播,辐合下沉运动抑制了深层冷海水上翻,西太平洋暖水能够传到东太平洋与西太平洋赤道表层洋流辐合区及其下沉运动的东移有关。(3)东部型El Nio事件西太平洋赤道表层洋流辐合区及其下沉运动没能直接传到东太平洋地区,东太平洋暖水形成与局地(120°W以东)辐合下沉运动抑制深层冷海水上翻有关;东部型El Nio事件暖池次表层的暖水,不是沿着西太平洋赤道次表层向东传播到东太平洋地区,而是由南太平洋西边界流将暖池海水带到40°S左右的西风漂流区,再由西风漂流平流到东太平洋。  相似文献   
992.
A global two-dimensional chemistry model is developed to study long-term trends of CH_4 sinceindustrial revolution.The sources of CH_4,CO and NO_x are parameterized as functions of latitudeand time.With two long-term emission scenarios,long-term trends of CH_4 are simulated.The resultshave a good agreement with observation from ice cores.The modeled CH_4 increased from 760 ppbvin 1840 to 1611.9 ppbv in 1991, while the modeled number concentration of tropospheric OHdecreased from 7.17×10~5 cm~(-3)in 1840 to 5.79×10~5 cm~(-3) in 1991.The increase of atmosphericCH_4 can be explained by the increase of emission of CH_4 and build-up because of decrease of OHradicals that remove CH_4 from the atmosphere.The model is also used to simulate the distribution of CH_4.Comparisons between the modelresults and observations show that the model can simulate both latitudinal distribution and seasonalvariation of CH_4 well.  相似文献   
993.
In order to investigate the effect of the factors in tower latitudes on Meiyu/Baiu front,adiagnostic analysis for the two cases during June to July of 1985 and 1986 was examined.We foundthat (1)when the tropical convective activity moves westward to 10.5-15.5′N/140°E from eastside of 10.5-15.5°N/160°E,the northward shifts of the Meiyu/Baiu rain belt occurs;(2)themain factor which results in the northward and southward shifts of Meiyu/Baiu rain belt is thoughtas the 8,18 and 30 day oscillations of the tropical convective activity around West Pacific.Meanwhile,the wave train propagating from Lake Baikal via Okhotsk Sea to the tropics couldsometimes shift Baiu rain belt southward;(3)the onsets of Meiyu in China of both cases tend totake place just when the convective activity around lower latitudes moves westward through about140°E with the 8,18 and 30 day oscillation periods firstly coming to June.  相似文献   
994.
亚洲季风环流在20世纪70年代末之后的减弱(英文)   总被引:73,自引:0,他引:73  
全球大气环流自20世纪70年代末之后的转变可以很清楚地在大气温度、风场等的变化上得到发现。子波分析的结果证实这次转变的时间尺度在20年以上。本文的研究着重揭示:在对流层中层,亚洲中纬度区域的转变趋势同全球平均的转变趋势相反;更重要的是,在这次转变之后亚洲和非洲的季风环流变弱了,同时热带东太平洋区的贸易风环流也变弱了。而在降水的变化中也可以发现这次转变。  相似文献   
995.
Introduction The rock medium shows mainly elastic character under low-temperature, low-pressure and external force for short duration, yet it shows rheologic property under high-temperature, high-pressure and long-time external force. It is reasonable that the rapid earthquake generating process lasted for tens seconds is analyzed by the elastic theory. As for the earthquake generating process for hundreds or thousand years, nevertheless, the rheologic property of rock must be taken into accou…  相似文献   
996.
The northern boundary fault of Huailai-Zhuolu basin,Hebei Province,has a total length of 58 km and a general strike of NE.The geometry and feature of activity of the 5 segments of the fault greatly differ from each other.17 paleoseismic events have been recognized within 11 trenches excavated along the different segments of the fault.It is found that each segment is characterized by its distinct recurrence of paleoearthquakes.The recurrence intervals of strong earthquakes for each segment are 3500-7000 a for the shortest and 17,000-20,500 a for the longest.However,the recurrence interval of strong earthquakes for whole fault ranges between 750-8500 a.The boundary of the segments can be recognized as the junction,gap,bending,jog and salient of the fault.The length of the segment ranges between 7.5-14 km.  相似文献   
997.
In this paper,the theory for applying remote sensing to earthquake prediction has been elucidated and an experiment has been made.Through the experiment,it has been found that the characteristics and temperature of infrared radiant of rocks vary as a function of rock stress,the order of magnitude of radiance variation is 10-5(W/cm2 sr um),the amount of variation of the radiant temperature is 0.2℃~0.8℃ and some significant precursor information has been discovered.The experiment has verified preliminarily that the advanced technology of remote sensing can be applied to earthquake prediction.  相似文献   
998.
V B 编程语言提供了图形环境,能可视化的设计窗体和控件。本文介绍了应用该设计语言的特性如何实现地震资料的动态显示过程。  相似文献   
999.
Traditionally, when creating 4-D models of elastic offsets in the Earth's crust, the data from geodesic and GPS monitoring of offsets on the ground surface, earthquake catalogs, monitoring of the water level and radon content in wells, sea level fluctuations, as well as gravitational and magnetic fields, etc., can be taken as bases for information. In essence, the reason for creating a 4-D model of slow elastic deformations is to approximate the process by a set of plane deformation solitons (solitary waves). The parameters of a set of deformation solitons are obtained by a two-stage inversion. First, the parameters of the model are determined in a kinematic way by the use of a modified simplification of the method. Then, a calibration of the amplitude characteristics of the model is carried out in terms of elastic dynamic offsets. Taking Ural, Northern Tianshan, Greece, and China as examples, models for these regions are created on the basis of seismological, geodesic, deformation, hydrogeological, and  相似文献   
1000.
The regional seismotectonic environment for the Zhangbei- Shangyi earthquake is described, and in combination with the distribution of macroscopic seismic intensity, source mechanism solution, and interpretation of lineaments on satellite images, the seismogenic structure for the earthquake and possible seismogenic fault are discussed in this paper. It is suggested that the Zhangbei-Shangyi earthquake is a result of the latest movement along the northwestern termination of the Zhangjiakou-Penglai fault zone and we should pay serious attention to the future trend of seismic activity along this fault zone.  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