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   581篇
  免费   124篇
  国内免费   221篇
测绘学   33篇
大气科学   173篇
地球物理   141篇
地质学   341篇
海洋学   118篇
天文学   6篇
综合类   67篇
自然地理   47篇
  2024年   3篇
  2023年   15篇
  2022年   49篇
  2021年   36篇
  2020年   39篇
  2019年   39篇
  2018年   35篇
  2017年   44篇
  2016年   38篇
  2015年   20篇
  2014年   34篇
  2013年   33篇
  2012年   29篇
  2011年   29篇
  2010年   30篇
  2009年   29篇
  2008年   32篇
  2007年   20篇
  2006年   26篇
  2005年   21篇
  2004年   9篇
  2003年   21篇
  2002年   17篇
  2001年   17篇
  2000年   24篇
  1999年   41篇
  1998年   31篇
  1997年   21篇
  1996年   21篇
  1995年   16篇
  1994年   23篇
  1993年   15篇
  1992年   14篇
  1991年   9篇
  1990年   8篇
  1989年   5篇
  1988年   9篇
  1987年   1篇
  1986年   3篇
  1985年   4篇
  1984年   5篇
  1983年   2篇
  1981年   2篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1976年   1篇
  1958年   1篇
  1957年   1篇
排序方式: 共有926条查询结果,搜索用时 166 毫秒
881.
大庆长垣北部葡萄花上部油层高分辨率层序地层划分   总被引:2,自引:0,他引:2  
应用高分辨率层序地层学以及沉积学相关理论,依据67口井的岩芯和8000口井的测井资料,将松辽盆地大庆长垣北部喇萨杏地区的葡萄花油组上部油层(PI油层)划分为1个受湖泛面限定的完整中期基准面旋回,并在其内部划分出10~14个短期基准面旋回,指出了PI油层在南北向上存在厚度以及短期旋回个数的差异。通过平行及垂直物源方向上的密井剖面分析并结合前人认识以及构造背景,认为葡I油层存在着三种不同的地层叠覆模式:低可容空间下的主动进积薄层叠覆模式;极低可容空间下的强迫进积过路沉积模式;侵蚀进积的叠合模式。该认知对于指导喇萨杏地区甚至整个长垣地区的高精度地层对比具有指导意义。  相似文献   
882.
阐述了虚拟化技术及其优势,探讨在上海市公众网平台上建立公共虚拟机服务平台,并对上海市地理信息服务系统在公共虚拟服务平台上的应用进行实证分析,有助于为政府各部门提供更有效的基础地理信息服务。  相似文献   
883.
Mafic rocks are widespread on the Liaodong Peninsula and adjacent regions of the North China Craton. The majority of this magmatism was originally thought to have occurred during the Pre-Sinian, although the precise geochronological framework of this magmatism was unclear. Here, we present the results of more than 60 U–Pb analyses of samples performed over the past decade, with the aim of determining the spatial and temporal distribution of mafic magmatism in this area. These data indicate that Paleoproterozoic–Mesoproterozoic mafic rocks are not as widely distributed as previously thought. The combined geochronological data enabled the subdivision of the mafic magmatism into six episodes that occurred during the middle Paleoproterozoic, the late Paleoproterozoic, the Mesoproterozoic, the Late Triassic, the Middle Jurassic, and the Early Cretaceous. The middle Paleoproterozoic (2.1–2.2 Ga) mafic rocks formed in a subduction-related setting and were subsequently metamorphosed during a ca. 1.9 Ga arc–continent collision event. The late Paleoproterozoic (ca. 1.87–1.82 Ga) bimodal igneous rocks mark the end of a Paleoproterozoic tectono-thermal event, whereas Mesoproterozoic mafic dike swarms record global-scale Mesoproterozoic rifting associated with the final breakup of the Columbia supercontinent. The Late Triassic mafic magmatism is part of a Late Triassic magmatic belt that was generated by post-collisional extension. The Middle Jurassic mafic dikes formed in a compressive tectonic setting, and the Early Cretaceous bimodal igneous rocks formed in an extensional setting similar to a back-arc basin. These latter two periods of magmatism were possibly related to subduction of the Paleo-Pacific plate.  相似文献   
884.
Copepods are among the most abundant and successful metazoans in the marine ecosystem. However, genomic resources related to fundamental cellular processes are still limited in this particular group of crustaceans. Ribosomal proteins are the building blocks of ribosomes, the primary site for protein synthesis. In this study, we characterized and analyzed the c DNAs of cytoplasmic ribosomal proteins(c RPs) of two calanoid copepods, P seudodiaptomus poplesia and A cartia pacifi ca. We obtained 79 c RP c DNAs from P. poplesia and 67 from A. pacifi ca by c DNA library construction/sequencing and rapid amplifi cation of c DNA ends. Analysis of the nucleic acid composition showed that the copepod c RP-encoding genes had higher GC content in the protein-coding regions(CDSs) than in the untranslated regions(UTRs), and single nucleotide repeats(3 repeats) were common, with "A" repeats being the most frequent, especially in the CDSs. The 3′-UTRs of the c RP genes were signifi cantly longer than the 5′-UTRs. Codon usage analysis showed that the third positions of the codons were dominated by C or G. The deduced amino acid sequences of the c RPs contained high proportions of positively charged residues and had high p I values. This is the fi rst report of a complete set of c RP-encoding genes from copepods. Our results shed light on the characteristics of c RPs in copepods, and provide fundamental data for further studies of protein synthesis in copepods. The copepod c RP information revealed in this study indicates that additional comparisons and analysis should be performed on different taxonomic categories such as orders and families.  相似文献   
885.
作为蓬勃发展的空间大地测量技术,InSAR和北斗/GNSS在地表形变监测中具有独特优势。应用两种手段开展综合测量,可充分利用其互补性,实现北斗/GNSS高时间分辨率与InSAR高空间分辨率的有机统一。本文首先介绍了InSAR与北斗/GNSS监测地表形变的基本原理,重点探讨了InSAR研究在20余年内的理论发展;其次综述了InSAR与北斗/GNSS技术集成及数据融合研究的最新进展;然后总结分析了当前地表形变监测应用所面临的关键问题及挑战;最后对InSAR与北斗/GNSS综合测量方法的发展趋势进行了展望。  相似文献   
886.
Landslides are increasing since the 1980s in Xi’an, Shaanxi Province, China. This is due to the increase of the frequency and intensity of precipitation caused by complex geological structures, the presence of steep landforms, seasonal heavy rainfall, and the intensifcation of human activities. In this study, we propose a landslide prediction model based on the analysis of intraday rainfall (IR) and antecedent effective rainfall (AER). Primarily, the number of days and degressive index of the antecedent effective rainfall which affected landslide occurrences in the areas around Qin Mountains, Li Mountains and Loess Tableland was established. Secondly, the antecedent effective rainfall and intraday rainfall were calculated from weather data which were used to construct critical thresholds for the 10%, 50% and 90% probabilities for future landslide occurrences in Qin Mountain, Li Mountain and Loess Tableland. Finally, the regions corresponding to different warning levels were identified based on the relationship between precipitation and the threshold, that is; “A” region is safe, “B” region is on watch alert, “C” region is on warning alert and “D” region is on severe warning alert. Using this model, a warning program is proposed which can predict rainfall-induced landslides by means of real-time rain gauge data and real-time geo-hazard alert and disaster response programs. Sixteen rain gauges were installed in the Xi’an region by keeping in accordance with the regional geology and landslide risks. Based on the data from gauges, this model accurately achieves the objectives of conducting real-time monitoring as well as providing early warnings of landslides in the Xi’an region.  相似文献   
887.
This paper analyzed the water-retention mechanism of feldspathic sandstone(fine-(<1 mm diam.)and gravel-sized(2-3 cm diam.)in Mu Us Sandy Land,Northwest China.The objective of this study is to study the effect of feldspathic sandstone amendment on water retention in sandy land.The results showed that as the proportion of fine feldspathic sandstone in the sandy land soil increased,the soil texture changed from sand to silt loam,the capillary porosity gradually increased from 26.3%to 44.9%,and the soil saturated hydraulic conductivity decreased from 7.10 mm/min to 0.07 mm/min.Feldspathic sandstone gravel formed micro-reservoirs in the sandy land soil,playing the role of a′water absorbent′and′water retaining agent′in sandy land.Amendment with feldspathic sandstone can increase water retention in the arable layer of sandy land by 67%.This study provides a theoretical basis for the amelioration of sandy land on a large scale.It can be concluded that amendment with feldspathic sandstone can improve the physical properties of sandy land soil and increase soil water retention.  相似文献   
888.
本文依托2010夏季中国第四次北极科学考察,通过对高纬度极地冰下水和冰芯的营养盐的连续观测及表层水颗粒物的藻类色素分析,获取了夏季快速融冰下冰水界面营养盐和光合色素的分布信息。结果表明调查期间表层水磷酸盐和硅酸盐相对于无机氮更丰富(依据Redfield比值),表现为显著的氮限制。而冰芯无机氮浓度相对更高,融冰释放对水体无机氮有一定的补充。色素分析显示岩藻黄素(Fuco)和叶绿素a(Chl a)是水体颗粒物的主要光合色素。在8/15至8/18期间,叶绿素c(Chl c)、硅藻黄素(Diato)、硅甲藻黄素(Diadino)和岩藻黄素(Fuco)分别达到6,22,73和922μg/m3,体现了硅藻在群落中的优势地位。岩藻黄素(Fuco)的浓度在融冰快速期间有巨大的提升,主要来源于冰芯底部释放的衰老的冰生硅藻和浮游硅藻的生长。此外,青绿黄素(Prasino)和叶黄素(Lut)与岩藻黄素(Fuco)分布模式有明显的差异,暗示青绿藻和绿藻与硅藻对海冰融化的不同响应。  相似文献   
889.
牛杏  何云龙  庄新国 《地球科学》2021,46(10):3549-3559
基于丽水凹陷钻井和地震资料,综合天然气地球化学参数、基底断裂和岩浆底辟发育特征等,研究丽水凹陷CO2的分布特征及其成藏主控因素.研究结果表明,丽水凹陷CO2纵向上主要分布在灵峰组、明月峰组下段及元古界基底片麻岩中,不同层位CO2的含量差别很大;平面上,温州13-1、丽水35-7和南平5-2 CO2气藏均位于岩浆底辟体之上或者附近,同时周围亦发育断层,而丽水36-1高含CO2气藏和LF-1井含CO2气藏周围底辟不发育,均紧邻灵峰凸起西侧的控洼断裂.丽水凹陷幔源CO2成藏主要受早中新世和晚中新世两期火山岩浆活动的影响,这两期火山活动将幔源CO2带到地壳浅层,通过砂体侧向输导进入有利圈闭聚集成藏.   相似文献   
890.
伊舒地堑构造演化的沉积充填响应   总被引:17,自引:1,他引:17       下载免费PDF全文
任建业  陆永潮 《地质科学》1999,34(2):196-203
伊舒地堑是一典型的转换伸展型盆地,它以构造上和沉积上的不对称结构,沉降中心的明显迁移和快速沉降充填为主要特征。本文应用盆地充填记录、盆地构造格架和盆地沉降史分析论证了伊舒地堑构造演化过程中不同级别的幕式裂陷作用,确定了幕式裂陷作用的沉积响应。此外,文章还总结了3种类型的沉积体系域构成样式和沉积特征。  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