全文获取类型
收费全文 | 3261篇 |
免费 | 656篇 |
国内免费 | 2434篇 |
专业分类
地球物理 | 684篇 |
地质学 | 5224篇 |
海洋学 | 100篇 |
天文学 | 17篇 |
综合类 | 63篇 |
自然地理 | 263篇 |
出版年
2024年 | 30篇 |
2023年 | 121篇 |
2022年 | 224篇 |
2021年 | 210篇 |
2020年 | 196篇 |
2019年 | 258篇 |
2018年 | 263篇 |
2017年 | 317篇 |
2016年 | 318篇 |
2015年 | 343篇 |
2014年 | 352篇 |
2013年 | 408篇 |
2012年 | 436篇 |
2011年 | 299篇 |
2010年 | 287篇 |
2009年 | 301篇 |
2008年 | 278篇 |
2007年 | 296篇 |
2006年 | 284篇 |
2005年 | 202篇 |
2004年 | 192篇 |
2003年 | 115篇 |
2002年 | 71篇 |
2001年 | 69篇 |
2000年 | 83篇 |
1999年 | 52篇 |
1998年 | 39篇 |
1997年 | 73篇 |
1996年 | 41篇 |
1995年 | 29篇 |
1994年 | 28篇 |
1993年 | 27篇 |
1992年 | 23篇 |
1991年 | 21篇 |
1990年 | 14篇 |
1989年 | 12篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 1篇 |
1984年 | 4篇 |
1983年 | 1篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1977年 | 1篇 |
排序方式: 共有6351条查询结果,搜索用时 15 毫秒
761.
762.
763.
764.
吐格尔明背斜核部花岗岩的年代学、地球化学与构造环境及其对塔里木地块北缘古生代伸展聚敛旋回的揭示 总被引:2,自引:0,他引:2
塔里木盆地北缘库车坳陷东部地区吐格尔明背斜核部花岗岩发育,该套花岗岩侵位于以云母石英片岩为主的元古界基底岩系中,上覆的三叠系以角度不整合与其接触。本区花岗岩的研究对揭示库车地区的基底性质与构造演化历史具有重要意义。对吐格尔明花岗岩锆石的U-Pb年代学和岩石地球化学的研究表明, 吐格尔明背斜核部的花岗岩锆石为典型岩浆成因锆石,其锆石SHRIMP U-Pb定年结果分别为626.4±5.2Ma~643.3±4.0Ma,表明它们的形成时代为新元古代晚期埃迪卡拉纪早期。该套花岗岩的SiO2 (67.95%~78.59%)和Al2O3 (11.81%~16.21%) 含量均很高,A/CNK在1.2~1.6,为硅和铝过饱和类型,属典型的过铝质花岗岩;稀土元素总量为106×10-6~207×10-6,稀土元素配分曲线呈右倾型,具有明显的负Eu异常;高场强元素(Ta、Nb、Ti等)具有明显的负异常,大离子亲石元素(Rb、Ba、Sr等) 具有明显的正异常。吐格尔明花岗岩是由地壳物质在底侵热源或构造动力作用下引起的局部熔融形成的,属典型的壳源成因类型,形成于挤压环境向伸展环境转化阶段,推测塔里木北缘在震旦纪已开始伸展,代表了古亚洲洋早期的伸展构造环境。实验测得花岗岩钾长石40Ar/39Ar年龄平均为291.4~255.8Ma,代表了花岗岩的隆升剥蚀年龄,反映出吐格尔明花岗岩在二叠纪受到挤压发生剥露的过程。因而从年代学框架上更好地约束了塔里木地块北缘在古生代由伸展裂解到聚敛隆升的构造旋回。 相似文献
765.
The existence of the Cretaceous-Tertiary (K/T) boundary in the non-marine succession is expected at Jiayin in the Heilongjiang River area, China. Zircons from a tuff sample from the Baishantou Member of Wuyun Formation in Jiayin were analyzed by the laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb dating and fission-track dating methods. Ages of 64.1±0.7 Ma (U-Pb) and 61.7±1.8 Ma (fission-track dating) were obtained, which allow re-evaluation of a previously reported late Maastrichian age for the tuff layer that was in conflict with the paleontological evidence. These results confirm the Danian age of the section in agreement with the paleontological evidence. 相似文献
766.
福建武平地区桃溪群混合岩U-Pb定年及其Hf同位素组成:对桃溪群时代及郁南运动的约束 总被引:4,自引:2,他引:2
桃溪群混合岩位于南岭东段武夷山褶皱带南段.本文通过采自桃溪附近帽村-田园两个代表性花岗片麻岩样品进行LA-ICP-MS锆石U-Pb 测年获得494~496Ma的结晶年龄,641~657Ma和799Ma两组继承锆石的206Pb/238U 表观年龄.同时对样品FJ-137进行的Hf同位素测定表明其εHf(t)变化于-2.3... 相似文献
767.
768.
769.
本文对比了鞍本地区前寒武纪铅-锌-银矿区和铀矿区的硫化物矿石和花岗岩长石Pb同位素组成,分别用矿石铅二阶段普通铅法、铅构造模式图解和全岩铅同位素组成三阶段拟合法计算了年龄和全岩原始铀含量。结果表明,矿石铅和长石铅模式年龄约为2000 Ma,在铅构造模式图上投影于2000~1600 Ma间,花岗岩和辽河群全岩拟合年龄为2000~1800 Ma;铅同位素组成显示铅-锌-银来自早元古代辽河群地层,连山关地区明显为放射性成因Pb同位素组成,源于富铀花岗岩。连山关矿石铅年龄和全岩三阶段年龄与该区铀矿床沥青铀矿的年龄基本一致;花岗岩原始铀的得失计算表明,该地区不同地质体均经历了约2000~1800 Ma花岗岩重熔改造,花岗质岩石发生了铀的丢失,是连山关地区铀矿的主要来源。 相似文献
770.
The Darongshan granitic suite (~ 10,000 km2) consists of five major units (Taima, Nadong and Jiuzhou plutons, and Pubei and Darongshan batholiths) typical of peraluminous S-type granitoids containing abundant granulite inclusions in the Cathaysia block, South China. Six samples from these plutons and batholiths have been investigated using both LA-ICPMS U–Pb age dating on zircon cores and EMP U–Th–Pb chemical age dating on monazite cores and rims. LA-ICPMS zircon results give similar major age populations ranging between 260 ± 3 and 250 ± 3 Ma for all units, with apparent older age peaks concentrated at 1020, 800, 430 and 330 Ma. On the other hand, EMP monazite results yield younger ages of 231–229 Ma for Nadong, Taima, Pubei and Darongshan and 224 Ma for Jiuzhou samples, with older age groups of 264 Ma for Taima and 256–250 Ma for Pubei units. Since the older monazite ages are similar to the majority of zircon ages, the latter are considered as inherited ages. Further because such zircon ages are similar with the emplacement time of the Emeishan large igneous province in western South China, they likely reflect the timing of metamorphism for the included fragments of granulitic crusts that had been formed by invasion of the Emeishan plume. The younger monazite ages, as present for all plutons and batholiths in the entire Darongshan area, are taken as the formation age of the host granites. Combining U–Pb zircon and EMP monazite ages known for Permo-Triassic high temperature and high pressure metamorphic rocks and granites in the Indochina block (e.g., the Kannack Complex of the Kontum massif), it is suggested that the Indosinian thermal activity had set records over both the Indochina (plus Simao) and South China blocks in two main episodes, one is 260–250 Ma and the other is 231–229 Ma. One plausible explanation is that these two blocks were one united continent before the Emeishan plume activity and an opening was triggered by this plume at ~ 260 Ma. Due to forces of the approaching Sibumasu block, both the South China and Indochina blocks were amalgamated again at ~ 230 Ma. We, therefore, advocate that double subduction of the plume-triggered oceanic crusts in opposite directions is responsible for the generation of the Darongshan granitic suite in the South China block and its counterpart in the Indochina block. 相似文献