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   98篇
  免费   20篇
  国内免费   104篇
测绘学   7篇
大气科学   22篇
地球物理   26篇
地质学   112篇
海洋学   9篇
天文学   8篇
综合类   27篇
自然地理   11篇
  2024年   4篇
  2023年   12篇
  2022年   8篇
  2021年   13篇
  2020年   4篇
  2019年   26篇
  2018年   21篇
  2017年   7篇
  2016年   18篇
  2015年   13篇
  2014年   16篇
  2013年   7篇
  2012年   8篇
  2011年   4篇
  2010年   21篇
  2009年   5篇
  2008年   6篇
  2007年   5篇
  2006年   2篇
  2005年   1篇
  2004年   1篇
  2003年   4篇
  2002年   1篇
  2001年   1篇
  2000年   2篇
  1995年   1篇
  1994年   1篇
  1985年   2篇
  1983年   1篇
  1981年   1篇
  1980年   1篇
  1979年   5篇
排序方式: 共有222条查询结果,搜索用时 31 毫秒
151.
康滇地轴是我国著名的南北向构造带。沿安宁河-易门、绿汁江等深断裂,分布着一组晋宁一澂江期的重熔花岗岩,在其接触带产有各种类型的锡-钨矿床。这些矿床构成了我国时代最老,以锡、钨为主并伴有铁、铜、铅、锌等的一个成矿带。研究该带各成矿元素之间的内在联系和演化历史,有助于深入认识矿床成因和区域成矿规律,为综合普查找矿提供地质依据。  相似文献   
152.
153.
This study investigates the long-term spatiotemporal variability of diurnal temperature range(DTR) in East Africa(EA). The study carries out non-parametric trend analysis of gridded DTR monthly data sourced from Climatic Research Unit(CRU). The DTR exhibits mixed signals in space and time over EA. The DTR correlates negatively with rainfall over EA. Reduction in DTR coincides with the summer season in the northern and southern hemispheres respectively, suggesting the influence of cloud cover on it. There was a non-uniform pattern of DTR changes across the region with time. Lake Victoria basin recorded the highest warming rates. The Indian Ocean coast recorded the least spatiotemporal variability in DTR. A reduction in DTR is evident in the two seasons: hot and cold. The start of the study period; 1921—1930, was the coolest decade in the study period. Most parts of EA recorded negative DTR anomalies in 1961—1970. The overall reduction in DTR throughout the study period highlights the ongoing warming which is a global phenomenon. There remains need for investigating the causation of the observed DTR variability for effective monitoring of the variability in future.  相似文献   
154.
正Dyke swarms are widespread throughout the Kaapvaal Craton(KC)in South Africa and have been documented in some detail.Up to date,only the~2.9 Ga SE-trending and the~2.7 to~2.66 Ga radiating dyke arrays are recognized  相似文献   
155.
利用人口分布与经济发展的不一致性指数和空间自相关模型,从时空角度出发,对1993,2003,2014年新疆人口分布与经济发展的不一致性现象的空间分布及地域关联性进行分析。结果表明:1 1993—2014年新疆人口分布与经济发展呈现严重的不平衡,二者之间存在错位现象,人口集聚高于经济集聚成为主要特征。人口的空间分布与区域经济之间关系有所协调,但仍具有不均衡性。2新疆人口经济不一致性地域分异明显,各类型区在空间分布上存在集聚性。3新疆人口分布与经济发展的不一致性存在正的、显著的空间自相关性,且这种相关性有增强的趋势。局部空间自相关分析下,全疆人口分布与经济发展的不一致性从东到西形成了"低-低""不显著""高-高"平行分布的集聚格局,且"低-低"与"高-高"的分布格局具有背向性,新疆人口经济不一致性的现状正在逐步改善。  相似文献   
156.
The marine sediments of the area of Verde Peninsula-Jabali Island(39°28′S/62°19′W-40°28′S/62°11′W) Holocene in age(3-2 ky),and modern beaches contain a significant amount of bioeroded mollusc shells.Fifteen sites were analyzed,in which 20.11%of the mollusc shells(2168 valves) presented bioerosion traces,in 54 species(30 bivalves and 24 gastropods).Fourteen ichnogenera were reported:Entobia,Maeandropoiydora,Iramena,Caulostrepsis,Pennatichnus,Pinaceocladichnus,Trypanites,and Gastrochaenolites(Domichnia),Gnathichnus and Radulichnus(Pascichnia),Finichnus and Centrichnus(Fixichnia),Oichnus(Praedicnia)(macrobioerosion),y Semidendrina(microbioerosion),the latter is first reported in mollusc shells in Argentina.Eleven ichnospecies were identified Finichnus peristroma,Maeandropoiydora sulcans,Gnathichnus pentax,Pinaceocladichnus onubensis,Caulostrepsis taeniola,Centrichnus eccentricus,Radulichnus inopinatus,Oichnus simplex,Oichnus paraboloides,Oichnus gradatus,and Gastrochaenolites torpedo(lithic remains).The dominant ichnogenera in the Holocene deposits are Iramena,Entobia and Oichnus.The same ichnogenera are constant with different abundance in the modern beaches,and increasing representation of Pinaceocladichnus and Pennatichnus.The dominant ichnofacies in the Holocene deposits is Trypanites,revealing a benthonic marine community composed of cheilostome bryzoans,clionaid sponges,predator gastropods,regular echinoids,polychaete annelids,bivalves,thallophytas and fungi.Generally,the area was described as a sublittoral,low-energy,stable environment with high rate of oxygenation,and sandy bottoms,with rocky bottoms at Villalonga locality.  相似文献   
157.
A total of 97 surface sediment samples were collected from the continental shelf and slope of the western Bay of Bengal to assess the potential application of Asterorotalia trispinosa as a paleomonsoon proxy. The relative abundance of living as well as total (living and dead) A. trispinosa ranges from being absent to a maximum of ~31%. The highest abundance of A. trispinosa is close to the outfall region of the Ganga-Brahmaputra Rivers and decreases away from the river mouths. Contrary to that, A. trispinosa is rare in front of both the Cauvery and Pennar river outfall regions, in the central part of the western Bay of Bengal. The living A. trispinosa abundance is the lowest in between two major river systems, viz. Ganga-Brahmaputra-Mahanadi and Krishna-Godavari. The relative abundance of both the total and living A. trispinosa is strongly positively correlated with ambient seawater temperature, and negatively correlated with %Corg and salinity. Based on the spatial distribution, we conclude that A. trispinosa is stenohaline in nature, rather than euryhaline, and further that the increased relative abundance of A. trispinosa indicates warmer and only marginally hyposaline environment. Even though the ecological preference of A. trispinosa suggests it as a potential paleomonsoon proxy, the restricted distribution implies limited application.  相似文献   
158.
This study is aimed at developing statistical equations to estimate the inelastic displacement ratio of singledegree- of-freedom systems subjected to far fault repeated earthquakes. In the study, peak ground motion parameters are used to define the scatter of the original data. The ratio of peak ground acceleration to peak ground velocity, and peak ground velocity of the ground motion records and structural parameters such as period of vibration and lateral strength ratio are used in the proposed equations. For the development of the equations, nonlinear time history analyses of single-degree-offreedom systems are conducted. Then, the results are used in a multivariate regression procedure. The equations are verified by comparing the estimated results with the calculated results. The average error and coefficient of variation of the proposed equations are presented. The analyses results revealed that the direct use of peak ground motion parameters for the estimation of inelastic displacement ratio significantly reduced the scatter in the original data and yielded accurate results. From the comparative results it is also observed that results obtained using equations specific to peak ground velocity or peak ground acceleration to peak ground velocity ratio are similar.  相似文献   
159.
160.
目前的研究已证实能谱CT成像技术可用于评价病灶性质的判断。对于肺结节,能谱CT成像技术有助于肺结节良恶性的鉴别;对于肺癌患者,能谱CT成像技术也可以提供有关定性、分期及疗效监测的信息。本文对目前肺结节的能谱CT成像技术的临床应用进行综述;包括肺结节的能谱CT成像扫描技术、肺结节的鉴别诊断、肺癌分期、与临床指标的相关性以及其在疗效监测等方面的应用。   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