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   4874篇
  免费   1096篇
  国内免费   1177篇
测绘学   425篇
大气科学   830篇
地球物理   1321篇
地质学   2647篇
海洋学   631篇
天文学   294篇
综合类   409篇
自然地理   590篇
  2024年   20篇
  2023年   70篇
  2022年   207篇
  2021年   259篇
  2020年   192篇
  2019年   267篇
  2018年   289篇
  2017年   264篇
  2016年   266篇
  2015年   253篇
  2014年   291篇
  2013年   315篇
  2012年   321篇
  2011年   340篇
  2010年   321篇
  2009年   302篇
  2008年   276篇
  2007年   243篇
  2006年   220篇
  2005年   220篇
  2004年   188篇
  2003年   188篇
  2002年   220篇
  2001年   211篇
  2000年   186篇
  1999年   191篇
  1998年   165篇
  1997年   147篇
  1996年   123篇
  1995年   86篇
  1994年   94篇
  1993年   88篇
  1992年   67篇
  1991年   52篇
  1990年   42篇
  1989年   30篇
  1988年   30篇
  1987年   22篇
  1986年   20篇
  1985年   16篇
  1984年   14篇
  1983年   8篇
  1982年   6篇
  1981年   5篇
  1980年   3篇
  1977年   1篇
  1975年   1篇
  1974年   1篇
  1958年   1篇
  1954年   3篇
排序方式: 共有7147条查询结果,搜索用时 203 毫秒
881.
Diapycnal Mixing (DM) within the upper 2000m of the global ocean is calculated by a fine-scale parameterization using the multiyear-mean density gridded product that created by employing all the Argo float observations to date through the recently published equation of seawater TEOS-10. The geographic distribution of Argo-derived DM derived in this study is spatial-dependent and varies with latitude and depth. The magnitude and pattern of DM is favorably validated by comparisons with previous studies. Furthermore, the mixing coefficient tensor K is calculated and analyzed. Components of the tensor fitting for the geopotential coordinate models are also presented. It is found that the tensor components in horizontal direction, Kxx and Kyy, have similar magnitude and distribution pattern. In the vertical, Kzz is enhanced over regions with rough topography and strong wind (e.g., Westerly region), suggesting agreement with previous estimates. This work presents a scheme to estimate the DM and mixing coefficient tensor using Argo observations, and offers a useful Argo-based mixing product for the purpose of promoting the study and modeling of ocean circulation and other processes.  相似文献   
882.
The studies on environmental effects of foreign trade and its spatial variations are helpful to design and implement environmental protection countermeasures.In order to eliminate the adverse effects of insufficient observation values on the accuracy of regression results and dynamic information quantity of fitting equation during empirical study,panel data of the mid-eastern provinces and cities of China from 1985 to 2007 were selected based on the adjustment of classical regression model in this paper.Panel unit root test and panel cointegration analysis method were applied to investigating the environmental effects of foreign trade and its spatial variations in the mid-eastern provinces and cities of China and its three groups divided by foreign trade dependence.The results show that all scale effects are positive,while all technical effects are negative and unable to counteract positive scale effects.Foreign trade development is regarded as an important cause for outstanding eco-environmental problems in the mid-eastern provinces and cities of China.Total effects and structural effects are significantly different among different groups because of spatial variations in environmental policies,export destinations,source of FDI,etc.Following the principle of′coordinating generality and considering differences comprehensively′,it is essential to issue a series of policies and countermeasures corresponding to differences in regional environmental effect of foreign trade,in order to coordinate the relationship between foreign trade development and eco-environment in each region.  相似文献   
883.
研究区内的中元古代魏家沟岩群原岩为一套碳酸盐岩、陆缘碎屑岩及火山岩建造,形成于大陆裂谷-活动大陆边缘阶段,并于1036 Ma左右遭受变质变形.通过岩浆岩形成构造环境的判别,研究区中元古代岩浆活动贯穿于板块碰撞前、同碰撞及碰撞后.伴随着造山带的演化,本区中元古代经历了3期韧性变形,分别形成于大陆裂谷、活动大陆边缘及碰撞造山阶段.通过上述研究,确定了本区中元古代造山带的存在,并经历了大陆裂谷-被动大陆边缘-活动大陆边缘-碰撞造山的地质演化过程,证实了格林维尔造山运动在华北板块北缘的存在和对中元古代末期Rodinia超大陆拼合的响应.  相似文献   
884.
典型滑坡监测点优化布置   总被引:1,自引:0,他引:1  
利用数值模拟技术与模糊模式识别算法提出了滑坡监测点优化布置的基本方法。以链子崖危岩体为例,以Ⅳ-Ⅳ′剖面作为滑坡监测点优化布置的典型剖面,根据监测变量(位移)对外界干扰因素作用下的灵敏度大小与监测信息量获取大小之间的关系,对该危岩体的监测变量(位移)进行了灵敏度分区研究,进而对该典型剖面的监测点进行了优化设计。研究结果表明,链子崖危岩体地表位移监测点宜布置在位移量明显和状态变化灵敏度较高的部位,深部位移监测钻孔宜穿越所有水平位移变化的灵敏区域。  相似文献   
885.
延吉盆地是一个后期改造较为强烈的断陷盆地。应用地震、地质、测井资料识别出延吉盆地中存在6个较大的不整合面,它们以角度不整合和超覆不整合2种类型为主。分析认为,燕山Ⅰ、Ⅱ幕运动形成了盆地雏形,燕山Ⅳ幕运动则使盆地回返,此期出现大量高岭石(40%),表明其与大气水淋滤等有关。短暂沉降后(龙井组),燕山运动晚期(Ⅴ幕)发生的又一次大规模以南北挤压为主的构造运动,导致南北两翼抬起幅度巨大,剥蚀厚度超过700 m,盆地中部剥蚀厚度大约为300 m。不整合面是划分三大构造层(前断陷期、断陷期、坳陷期)的依据。其早白垩世铜佛寺组和大砬子组间的整合关系利于油气的生成。不整合面既可改善储集体的渗透性,又是形成油气二次运移的良好通道。初步预测与不整合有关的油气藏(侵蚀残丘、地层超覆不整合、断层坡折)可作为下一步勘探的目标。  相似文献   
886.
泥石流排导结构对于减轻泥石流对周围建筑物的损毁起到了显著作用,但目前大多数排导结构难以抵御泥石流的强烈侵蚀磨损和周围环境恶劣时伴随产生的腐蚀磨损。首先,通过分析泥石流排导结构侵蚀和腐蚀磨损机理,应用相关磨损量计算公式,提出了考虑侵蚀和腐蚀的泥石流排导结构耦合磨损计算公式。然后,以此为基础,针对磨损过程的动态性和随机性,建立了泥石流排导结构耦合磨损随机过程模型,推导了任意时刻磨损量的分布函数,实现了评估泥石流排导结构的动态可靠性和概率失效时间。最后,通过具体算例分析验证了模型的实用性,可为今后泥石流排导结构的磨损定量评估提供理论参考。  相似文献   
887.
This article presents an application of a procedure to modify the intensity distribution by assessing the reliability. There are two potential possibilities that may influence the intensity distribution: (1) For the interpolation error, we generate a measured grid across the calculation region. When the point to station spacing is <5 km, we consider the results precise; however, some points have less precision because these are farther from the corresponding stations. When the spacing is between 5 and 50 km, we consider the results imprecise and define a reliability factor that correlates with the distance. (2) Some records may have errors that result from local site conditions, equipment problems, or some disturbance such as lightning stroke, which will lead to some grid points having an incorrect intensity. We regress the attenuation relation for sites with abnormal intensities and consider the results to be accurate when the standard deviation (STD) is <σ and inaccurate when the STD is > 2σ. We then define a reliability factor to correlate with STD between σ and 2σ, such that the intensity distribution is in accord with both wave propagation theory and the investigation intensity.  相似文献   
888.
In the past several years, from May 12, 2008 Wenchuan MW8.0 earthquake in China to March 11, 2011 off the Pacific coast of Northeastern MW9.0 earthquake in Japan,the world witnessed catastrophic disasters caused by destructive earthquakes. The earthquake posed a great threat to the development of society and economy, especially in the developing countries such as China. In order to reduce the losses in peoples life and properties in maximum possibilities, there were a lots of technologies had been researched and developed, among them the earthquake early warning system(EEWS) and rapid seismic instrumental intensity report(RSIIP) are the two of the state-of-the-art technologies for the purpose. They may be used to minimize property damage and loss of life and to aid emergency response after a destructive earthquake.  相似文献   
889.
大型地下洞室对穿预应力锚索失效形式与耦合模型   总被引:1,自引:0,他引:1  
江权  陈建林  冯夏庭  陈静  崔洁  万祥兵  侯靖 《岩土力学》2013,34(8):2271-2279
以锦屏二级水电站地下厂房与主变室之间中隔墙的多根对穿预应力锚索失效实例为背景,首先总结对穿预应力锚索失效的多种现场表现形式,采用现场取证和室内试验再现的方式论证锚索钢绞线断裂的拉破坏模式。将对穿锚索视为弹脆性体,被锚固围岩视为黏弹性体,提出描述对穿预应力锚索与被锚固围岩之间相互作用关系的锚索-围岩耦合元件模型,并据此分别阐明在洞室开挖卸荷阶段和围岩时效变形阶段中预应力锚索的力学响应机制和荷载变化规律。最后,在现场调研、室内试验和机制分析基础上,综合分析导致锦屏二级水电站地下厂房与主变室之间对穿锚索失效的主要原因,并探讨对穿预应力锚索与被锚固围岩之间对立统一的矛盾关系以及大型洞室群预应力锚索支护时机问题。  相似文献   
890.
�봨����ǰ��ɽ�����ݴ��ĵؿ��˶�   总被引:3,自引:0,他引:3  
????GPS?????????“???????”?????????????????????????????????????????????????????????????????????NW???????????????????????????????????????????????5~6????????????????????2???????????????????????NW????NEE????Щ????????????????????GPS?????????????????????£????????????????????????????????????????????????????????????????α???????????仯?????  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