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   6700篇
  免费   1437篇
  国内免费   1168篇
测绘学   1389篇
大气科学   704篇
地球物理   2808篇
地质学   2388篇
海洋学   872篇
天文学   137篇
综合类   522篇
自然地理   485篇
  2024年   42篇
  2023年   106篇
  2022年   208篇
  2021年   260篇
  2020年   251篇
  2019年   360篇
  2018年   272篇
  2017年   343篇
  2016年   347篇
  2015年   383篇
  2014年   394篇
  2013年   396篇
  2012年   408篇
  2011年   427篇
  2010年   357篇
  2009年   425篇
  2008年   398篇
  2007年   464篇
  2006年   420篇
  2005年   342篇
  2004年   342篇
  2003年   290篇
  2002年   267篇
  2001年   189篇
  2000年   218篇
  1999年   195篇
  1998年   153篇
  1997年   156篇
  1996年   142篇
  1995年   113篇
  1994年   120篇
  1993年   112篇
  1992年   86篇
  1991年   72篇
  1990年   51篇
  1989年   38篇
  1988年   45篇
  1987年   41篇
  1986年   17篇
  1985年   11篇
  1984年   3篇
  1983年   6篇
  1982年   5篇
  1981年   3篇
  1980年   5篇
  1979年   4篇
  1978年   9篇
  1977年   4篇
  1954年   5篇
排序方式: 共有9305条查询结果,搜索用时 0 毫秒
91.
本文研究了以cHCl=8mol·L-1盐酸为移动相,以聚四氟乙烯负载的钽试剂-CHCl3为固定相反相萃取层析钛(Ⅳ)的新体系,柱上层析的钛用cHCl=3mol·L-1盐酸洗脱后经二安替比林甲烷光度法测定,不仅钛回收率可达100%,并可使钛(Ⅳ)与多种离子分离。能用于矿物岩石类复杂样品及其他物质中钛的分离富集与测定,方法简便快速。  相似文献   
92.
93.
The colloidal borescope consists of a set of lenses and miniature video cameras capable of observing natural particles in monitoring wells. Based on field observations of these particles, it appears possible to measure in situ groundwater velocity in a well bore. Field observations have shown that directional measurements using the colloidal borescope are generally in good agreement with expected flow directions. However, the magnitude of flow velocity is higher compared with values based on conventional test methods. High relative flow velocities, even after correction factors have been applied to compensate for well bore effects, are believed to be due to preferential flow zones in the surrounding aquifer. Low flow zones exhibit swirling multidirectional flow that does not allow for a linear velocity measurement. Consequently, groundwater flow velocities measured by the colloidal borescope in heterogeneous aquifers will be biased toward the maximum velocity values present in the aquifer. A series of laboratory experiments was conducted to assess the reliability of the instrument. Based on this work, a seepage velocity correction factor ( ) of 1–4 was found for quantifying groundwater seepage velocity in the adjacent aquifer from observations in a well bore. Laboratory measurements also indicate that preferential flow in the surrounding aquifer dominates flow in the well. Results of this work suggest the possibility of quantifying higher-flow velocities associated with preferential flow zones in the subsurface.  相似文献   
94.
95.
The wave velocity for two types of granitoids was measured using the analytic method of full-wave vibration at high pressure and high temperature. The laws of velocity changes for them differ with the pressure boost and temperature rise, and the velocity change of S-type is more violent than that of I-type. The “softening point” of compressional wave velocity (V μ) is also revealed during the measurement for two types of granitoids imitating the pressure and temperature at a certain depth. But the depth of “softening”, Vp after “softening” and the percentage of Vp’s drop around the “sofrening point” for two types of granitoids are obviously different. The depth of “softening” is 15 km approximately and Vp after “softening” is 5.62 km/s for S-type granitoid. But for I-type granitoid the depth of “softening” is 26 km approximately and Vp after “softening” is 6. 08 km/s. Through careful analysis of rock slices after the experiment, it was found that the “softening” of elastic-wave velocity is caused by the partial melting of granite. Combined with the results of geophysical prospecting, these results suggest that the low-velocity layers developing in the interior of Earth crust are related to thc partial melting of different types of granitoids. The formation of the low-velocity layer in the upper-middle Earth crust is closely related to the development of S-type granitoid, but that in the lower Earth crust is closely related to the development of I-type granitoid.  相似文献   
96.
连续两届国际深部地震讨论会成果累累。对深部地震的资料采集、处理、解释技术以及几类专门地质地球物理问题的研究进行了综述。研究成果在理论、方法方面是该领域的世界先进水平:在地震学应用于陆缘、陆壳与壳幔过渡带等地质问题方面有明显的提高。提出了值得讨论的问题,最后探讨了发展趋势  相似文献   
97.
简要总结了青藏高原地区Pn波速度结构、各向异性研究进展;介绍了Pn波速度结构、各向异性等在岩石圈结构、构造背景反映等方面的应用研究进展。分析了目前青藏高原Pn波研究中存在的一些问题。  相似文献   
98.
采用中国中西部地区(21~36N, 98~112E)193个地震台在1992~1999年间记录到的9 988次地震的Pg和Sg震相走时的读数资料,用Roecker的SPHYPIT90程序,反演了该地区三维地壳P波速度结构,并用SPHREL3D90程序进行了地震的重新定位.反演结果揭示了中国中西部地区地震P波速度结构明显的横向不均匀性,这些不同深度上波速的横向变化多以该地区的活动断裂为分界线.可以看出活动断裂两侧存在明显的速度反差.通过重新定位,得到了6 459次地震的震源参数,这些精确定位的地震震中明显沿该区活动断裂呈现条带状分布,其范围和尺度清晰地表示了这一地区地震活动与活动断裂的紧密关系.其中,82%重新精确定位的事件的震源深度在20 km以内. 这一结果与笔者用双差地震定位法得到的重新定位的震源深度分布相一致.   相似文献   
99.
山地煤矿采区地形条件复杂,正确进行大时差静校正是处理好二维地震勘探资料的重要一环。大时差静校正会改变煤层反射波时间(t0)及双曲线特征,为减小校正误差,需设立一个CMP面,将校正量分为高频分量和CMP校正量。在地形高差变化剧烈的山地,不能用高于地表面的统一基准面为零线进行时深转换,须进行充填层时差(△t)校正,将统一基准面校正到地表面,再以地表面为零线进行时深转换成图。以便准确无误的展示煤层赋存形态,提高构造图精度。  相似文献   
100.
Evaluation of soil liquefaction in the Chi-Chi, Taiwan earthquake using CPT   总被引:1,自引:0,他引:1  
During the 1999 Chi-Chi, Taiwan earthquake, many sand boiling phenomena were observed in central Taiwan, which caused severe ground settlement and structure damages. According to the installed accelerograms, the peak ground surface horizontal accelerations in the liquefaction-affected areas range from 774.42 to 121.3 gal. The writers carried out an extensive investigation of soil liquefaction in this earthquake. In this paper, we present results of the CPT exploration and post-earthquake liquefaction analysis. Two hundred and seventy five (275) cone penetration test data were collected from the liquefaction-affected areas, and 46 liquefaction case histories and 88 non-liquefaction case histories were derived that can be used to evaluate the accuracy of existing liquefaction evaluation models. In addition, the strength of the liquefied soils after earthquake and the implication of its liquefaction potential in the future event are discussed.  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