全文获取类型
收费全文 | 3193篇 |
免费 | 885篇 |
国内免费 | 536篇 |
专业分类
测绘学 | 441篇 |
大气科学 | 218篇 |
地球物理 | 325篇 |
地质学 | 2927篇 |
海洋学 | 178篇 |
天文学 | 116篇 |
综合类 | 184篇 |
自然地理 | 225篇 |
出版年
2025年 | 1篇 |
2024年 | 85篇 |
2023年 | 62篇 |
2022年 | 78篇 |
2021年 | 127篇 |
2020年 | 159篇 |
2019年 | 136篇 |
2018年 | 140篇 |
2017年 | 187篇 |
2016年 | 235篇 |
2015年 | 159篇 |
2014年 | 184篇 |
2013年 | 213篇 |
2012年 | 247篇 |
2011年 | 212篇 |
2010年 | 156篇 |
2009年 | 167篇 |
2008年 | 221篇 |
2007年 | 239篇 |
2006年 | 226篇 |
2005年 | 202篇 |
2004年 | 132篇 |
2003年 | 155篇 |
2002年 | 138篇 |
2001年 | 110篇 |
2000年 | 101篇 |
1999年 | 105篇 |
1998年 | 71篇 |
1997年 | 50篇 |
1996年 | 64篇 |
1995年 | 43篇 |
1994年 | 52篇 |
1993年 | 29篇 |
1992年 | 29篇 |
1991年 | 21篇 |
1990年 | 17篇 |
1989年 | 11篇 |
1988年 | 11篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 8篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 5篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有4614条查询结果,搜索用时 0 毫秒
11.
12.
Osman Parlak 《International Journal of Earth Sciences》2006,95(4):609-627
In southeast Anatolia, there are number of tectonomagmatic units in the Kahramanmaraş–Malatya–Elazığ region that are important in understanding the geological evolution of the southeast Anatolian orogenic belt during the Late Cretaceous. These are (a) metamorphic massifs, (b) ophiolites, (c) ophiolite-related metamorphics and (d) granitoids. The granitoids (i.e. Göksun–Afşin in Kahramanmaraş, Doğanşehir in Malatya and Baskil in Elazığ) intrude all the former units in a NE–SW trending direction. The granitoid in Göksun–Afşin (Kahramanmaraş) region is mainly composed of granodioritic and granitic in composition. The granodiorite contains a number of amphibole-bearing mafic microgranular enclaves of different sizes, whereas the granite is intruded by numerous aplitic dikes. The granitoid rocks have typical calcalkaline geochemical features. The REE- and Ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, as well as biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The K–Ar geochronology of the granitoid rocks yielded ages ranging from 85.76±3.17 to 77.49±1.91 Ma. The field, geochemical and geochronological data suggest the following Late Cretaceous tectonomagmatic scenario for southeast Anatolia. The ophiolites were formed in a suprasubduction zone tectonic setting whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or late-thrusting (∼90 Ma). These units were then overthrust by the Malatya–Keban platform during the progressive elimination of the southern Neotethys. Thrusting of the Malatya–Keban platform over the ophiolites and related metamorphic rocks was followed by the intrusion of the granitoids (88–85 Ma) along the Tauride active continental margin in the southern Neotethys. 相似文献
13.
A new genus and species, Similinannotanyderus lii gen. et sp. nov., is described from Myanmar amber. It differs from other genera of Tanyderidae based on special characters of wing venation and male genitalia. This new taxon broadens the diversity of Tanyderidae in the Cretaceous, and its morphological characters enhance our understanding of the development and evolution of the primitive crane flies. 相似文献
14.
美国中部伊利诺伊煤田(跨伊利诺伊、印第安纳、肯塔基等三个州)的含煤地层为上石炭统宾夕法尼亚系。美国印第安纳地质研究所2006年编制的印第安纳州基岩综合地层柱状图建立了宾夕法尼亚系含煤地层的岩相层序,现将此岩相层序介绍到国内,对我们了解美国晚古生代煤田地质及阅读国外文献资料颇有帮助。 相似文献
15.
Ar–Ar dating, major and trace element analyses, and Sr–Nd–Pb isotope results of two groups of Lower Cretaceous (erupted at 126 and 119 Ma, respectively) intermediate–felsic lava from the northeastern North China Block (NCB) suggest their derivation from melting of mixtures between the heterogeneous lower crust and underplated basalts. Both groups exhibit high‐K calc‐alkaline to shoshonitic affinities, characterized by light rare earth element (LREE) and large ion lithophile element (LILE) enrichment and variable high field strength element (HFSE, e.g. Nb, Ta and Ti) depletion, and moderately radiogenic Sr and unradiogenic Nd and Pb isotopic compositions. Compared with Group 2, Group 1 rocks have relatively higher K2O and Al2O3/(CaO + K2O + Na2O) in molar ratio, higher HFSE concentrations and lower Nb/Ta ratios, and higher Sr–Nd–Pb isotope ratios. Group 1 rocks were derived from a mixture of an enriched mantle‐derived magma and a lower crust that has developed radiogenic Sr and unradiogenic Nd and Pb isotopic compositions, whereas the Group 2 magmas were melts of another mixture between the same mantle‐derived component and another type of lower crust having even lower Sr, Nd, and Pb isotopic ratios. Shift in source region from Group 1 to Group 2 coincided with a change in melting conditions: hydrous melting of both the underplated basalt and the lower crust produced the earlier high‐Nb and low‐Nb/Ta melts with little or no residual Ti‐rich phases; while the younger low‐Nb and high‐Nb/Ta magmas were melted under a water‐deficient system, in which Ti‐rich phases were retained in the source. Generation of the two groups of intermediate–felsic volcanic rocks was genetically linked with the contemporaneous magma underplating event as a result of lithospheric thinning in the eastern NCB. 相似文献
16.
The middle–late Campanian was marked by an increase in the bioprovinciality of calcareous microfossil assemblages into distinct Tethyan, Transitional, and Austral Provinces that persisted to the end of the Maastrichtian. The northwestern Australian margin belonged to the Transitional Province and the absence of key Tethyan marker species such as Radotruncana calcarata and Gansserina gansseri has led petroleum companies operating in the area to use the locally developed KCCM integrated calcareous microfossil zonation scheme. The KCCM zonation is a composite scheme comprising calcareous nannofossil (KCN), planktonic foraminiferal (KPF) and benthonic foraminiferal (KBF) zones. This paper presents the definitions and revisions of Zones KCCM8–19, from the highest occurrence (HO) of Aspidolithus parcus constrictus to the lowest occurrence (LO) of Ceratolithoides aculeus, and builds on our previous early–late Maastrichtian study. The presence of a middle–upper Campanian disconformity is confirmed by microfossil evidence from the Vulcan Sub-basin, Exmouth and Wombat plateaus, and the Southern Carnarvon Platform. In the Vulcan Sub-basin and on the Exmouth Plateau (ODP Hole 762C) the hiatus extends from slightly above the LO of common Rugoglobigerina rugosa to above the LO of Quadrum gothicum. On the Wombat Plateau (ODP Hole 761B) it spans from above the LO of Heterohelix semicostata to above the LO of Quadrum gothicum; and in the Southern Carnarvon Platform the disconformity has its longest duration from above the HO of Heterohelix semicostata to above the LO of Quadrum sissinghii. A significant revision of the events which define Zones KCCM18 and 19 was necessary owing to the observation that the LO of Ceratolithoides aculeus occurs below the HOs of Archaeoglobigerina cretacea and Stensioeina granulata incondita and the LO of common Rugoglobigerina rugosa. In the original zonation these events were considered to be coincident. 相似文献
17.
移动式测绘系统(MMS)已在交通管理、城市规划、地图更新、工程勘测、精准农业、战场测绘等领域广泛应用。本文在简要叙述MMS基本概念和主要功能的基础上,探讨了MMS的发展现状和应用方向,进而提出了当前发展MMS需要解决的关键技术,仅供参考。 相似文献
18.
19.
塔里木盆地库车坳陷盐下深部储层是天然气勘探的重要领域,白垩系储层岩盐广泛发育,储层含盐特征的精细表征和评价对该区勘探区带优选具有重要意义.以库车坳陷大北克深井区白垩系砂岩储层72件岩心样品为研究对象,通过薄片、扫描电镜、能谱分析与QEMSCAN(岩石矿物定量分析)等技术手段,对研究区白垩系砂岩储层的含盐特征、分布规律、形成条件及来源等进行研究.结果表明:岩盐晶体主要赋存在碎屑颗粒间、碎屑颗粒表面和溶蚀孔与裂缝中,呈格架状、晶粒状和团块状集合体等3种赋存状态,不同状态岩盐晶体Na和Cl等元素的原子分数存在差异;岩盐分布规律为,平面上表现出西高东低的特点,垂向上距上覆膏盐岩层越近,岩盐体积分数越高;不同的盐源供给条件、储层埋藏深度、砂岩粒级、分选性等制约岩盐晶体的集合体形态;岩盐来源主要为古近系膏盐类沉积物的溶蚀渗流,也可能与含盐流体沿构造断裂的侧向渗入有关. 相似文献
20.
现代水资源评价及水资源学学科体系研究 总被引:37,自引:0,他引:37
在追溯水资源界定和内涵历史沿革的基础上,根据水资源评价的有效性、可控性和可再生性准则,按不同评价口径将水资源划分为广义水资源、狭义水资源、国民经济可利用量和生态环境需水量。从水资源承载的双重客体出发,一定程度上澄清了历史上关于水资源评价和定义的争论。而后从水资源科学的发展入手,刻划了水资源学研究的对象和三个层面上的内容,即基础研究、应用研究和综合研究,根据学科研究的内容,构建了包括基础学科、应用学科和综合学科的水资源学学科体系,并分别就三大组成部分作了剖析,这对于水资源学科建设具有积极的意义。 相似文献