全文获取类型
收费全文 | 164篇 |
免费 | 25篇 |
国内免费 | 39篇 |
专业分类
测绘学 | 1篇 |
大气科学 | 1篇 |
地球物理 | 26篇 |
地质学 | 156篇 |
海洋学 | 9篇 |
天文学 | 15篇 |
综合类 | 6篇 |
自然地理 | 14篇 |
出版年
2023年 | 4篇 |
2022年 | 4篇 |
2021年 | 5篇 |
2020年 | 11篇 |
2019年 | 6篇 |
2018年 | 6篇 |
2017年 | 6篇 |
2016年 | 8篇 |
2015年 | 5篇 |
2014年 | 8篇 |
2013年 | 7篇 |
2012年 | 6篇 |
2011年 | 13篇 |
2010年 | 8篇 |
2009年 | 10篇 |
2008年 | 9篇 |
2007年 | 15篇 |
2006年 | 6篇 |
2005年 | 5篇 |
2004年 | 9篇 |
2003年 | 12篇 |
2002年 | 8篇 |
2001年 | 5篇 |
2000年 | 10篇 |
1999年 | 7篇 |
1998年 | 2篇 |
1997年 | 7篇 |
1996年 | 7篇 |
1995年 | 9篇 |
1994年 | 1篇 |
1993年 | 3篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 1篇 |
1986年 | 1篇 |
排序方式: 共有228条查询结果,搜索用时 484 毫秒
101.
Proven reserves of liquid hydrocarbons are now assessed at between 950 and 1,000 billion barrels, depending on the source. Their life expectancy at the current rate of world production is about 41 to 45 years. This lifetime is much longer than what was predicted in both 1970 and 1980. However, this wealth of resources does not necessarily mean that the security of oil supplies is guaranteed for all countries. Oil reserves are unequally distributed from a geopolitical standpoint. Reserves and output are mainly due to big fields (with more than 500 million barrels of initial reserves).Though oil supplies seem to be ensured for the coming 30 to 40 years, what does the picture look like beyond 2020–20307 The increased lifetime of proven oil reserves has been apparent only in the last 10 to 20 years. The considerable increase in proven oil reserves reported after 1986 is, in fact, mainly due to revisions and extensions, rather than to new sources of oil: conventional oil (with the price per barrel of oil on the order of $20 and recovery rate around 30 percent) remaining to be discovered today; oil resources stemming from an improvement in recovery rate; oil resources resulting from exploitation of new zones, such as deep sea zones; and unconventional types of oil, such as extra-heavy crudes, tar sands, shale oils, and liquid hydrocarbons from chemical-enhanced oil recovery methods. 相似文献
102.
季节性的降雨及其所引起的地下水状态的变化是促使日本大型结晶片岩滑坡活动和诱发灾害发生的重要原因。基于对一典型结晶片岩滑坡、降雨和地下水位的长期观测,利用Tank模型建立了一种模拟滑坡地下水位变化的方法。通过对滑体内不同观测点地下水位实际观测数据与模拟结果的对比分析,证明所采用的模拟方法能够很好地再现地下水位随降雨的变化形态,从而为预测和评价降雨型滑坡的地下水状态变化提供了依据。 相似文献
103.
104.
105.
106.
Basement interface structural characteristics beneath Jiashi strong earthquake swarm area in Xinjiang, China 总被引:1,自引:0,他引:1
The seismic data obtained from high resolution seismic refraction profile in Jiashi strong earthquake swarm area in Xinjiang, China were further processed with ray hit analysis method and more complete basement interface struc-tural characteristics beneath Jiashi strong earthquake swarm area were determined. The results show that there are two clear basement interfaces at the upper crust in Jiashi strong earthquake swarm area. The first one with buried depth ranging from 2.6 km to 3.3 km presents integral and continuous structure, and it appears an inclined plane interface and smoothly rises up toward Tianshan Mountain. The second basement interface with buried depth from 8.5 km to 11.8 km, is the antiquated crystalline basement of Tarim basin. Near the post number of 37 km, the bur-ied depth of the crystalline basement changed abruptly by 2.5 km, which maybe result from an ultra crystalline basement fault. If taking this fault as a boundary, the crystalline basement could be divided into two parts, i.e. the southwestern segment with buried depth about 11.5 km, and the northeastern segment with buried depth approxi-mately from 8.5 km to 9.0 km. That is to say, in each segment, the buried depth changes not too much. The north-east segment rises up as a whole and upheaves slightly from southwest to northeast, which reflects the upper crustal deformation characteristics under the special tectonic background at the northwestern edge of Tarim basin. 相似文献
107.
Kevin Righter 《Chemie der Erde / Geochemistry》2007,67(3):179-200
A widely accepted model for the origin of the Earth and Moon has been a somewhat specific giant impact scenario involving an impactor to proto-Earth mass ratio of 3:7, occurring 50-60 Ma after T0, when the Earth was only half-accreted, with the majority of Earth's water then accreted after the main stage of growth, perhaps from comets. There have been many changes to this specific scenario, due to advances in isotopic and trace element geochemistry, more detailed, improved, and realistic giant impact and terrestrial planet accretion modeling, and consideration of terrestrial water sources other than high D/H comets. The current scenario is that the Earth accreted faster and differentiated quickly, the Moon-forming impact could have been mid- to late in the accretion process, and water may have been present during accretion. These new developments have broadened the range of conditions required to make an Earth-Moon system, and suggests there may be many new fruitful avenues of research. There are also some classic and unresolved problems such as the significance of the identical O isotopic composition of the Earth and Moon, the depletion of volatiles on the lunar mantle relative to Earth's, the relative contribution of the impactor and proto-Earth to the Moon's mass, and the timing of Earth's possible atmospheric loss relative to the giant impact. 相似文献
108.
松嫩地块西缘前寒武岩浆事件——来自龙江地区古元古代花岗岩锆石LA-ICP-MS U-Pb年代学证据 总被引:2,自引:2,他引:0
松嫩地块位于中亚造山带东段,该陆块是否具有前寒武纪结晶基底以及基底的规模和性质一直存在争议。我们在龙江地区识别出~1.8Ga的岩石,揭示了松嫩地块西缘古元古代结晶基底的存在。本文对其进行了岩石地球化学、锆石LA-ICP-MS U-Pb年代学和Hf同位素研究,为探讨松嫩地块西缘古元古代晚期构造演化提供了重要信息。研究结果表明,马山二长花岗岩中的锆石大多具有清晰的振荡生长环带,结合较高的Th/U比值(1.30~2.64),表明其为岩浆成因,岩浆锆石的~(207)Pb/~(206)Pb加权平均年龄为1808±14Ma,形成于古元古代晚期;马山二长花岗岩具有富硅(Si O_2=69.50%~75.11%)、碱(K_2O+Na_2O=5.30%~8.69%)和铁(Fe O~T=2.86%~4.53%),贫钙(Ca O=0.46%~1.87%)、镁(MgO=0.25%~0.93%)的特征。稀土总量较高(∑REE=357.2×10~(-6)~587.1×10~(-6)),具强轻稀土分异((La/Yb)_N为12.2~17.6)和负Eu异常(δEu为0.27~0.77)的"燕式"稀土分配模式。大离子亲石元素Rb、Ba等富集,亏损HFSEs(Nb、Ta、Ti)和P、Sr等元素。结合岩石的Zr+Nb+Ce+Y(772.1×10~(-6)~911.1×10~(-6))和10000×Ga/Al比值(2.41~3.17)较高,全岩锆石饱和温度为891~940℃,暗示其为A型花岗岩,具造山后A_2型花岗岩的特征。马山二长花岗岩锆石ε_(Hf)(t)值介于-9.2~-2.8之间,t_(DM2)=2992~3520Ma,与华北板块北缘~1.8Ga岩浆岩具有相似的锆石Hf模式年龄。上述结果表明,马山A型花岗岩起源于幔源岩浆底侵作用引起的中-新太古代地壳岩石的部分熔融,证明陆壳已转入伸展拉张构造环境,是Columbia超级大陆裂解事件在松嫩地块西缘的响应。综合资料发现,松嫩地块已经发现的新太古代-中元古代的岩浆事件在华北克拉通都有同期的构造地质事件响应,初步认为松嫩地块与华北克拉通具有一定的亲缘性。 相似文献
109.
以坦桑尼亚纳钦圭阿大型晶质石墨矿南部矿体为研究对象,基于3DMine软件平台,通过垂直断面法、距离幂次反比法进行资源量估算,对比研究2种资源量估算方法在矿体的体积、品位、资源量方面的区别。结果表明:2种估算方法体积相对误差为6.30%,品位相对误差为1.45%,资源量结果相对误差为7.83%,资源量验算结果在误差范围之内;3DMine中的断面法计算过程自动、准确、高效,利用三维模型体积替代传统公式计算体积,计算结果更加精准;采用距离幂次反比法时,运用三维模型计算矿体体积,用全局验证和交叉验证对搜索椭球体参数的合理性进行验证,最终选择最优搜索椭球体参数,是进行资源量准确估算的关键。综上所述,用距离幂次反比法估算的资源量结果更加准确,计算过程高效、便捷,并可为后期矿山数字化建设提供基础,是今后矿山发展的趋势。 相似文献
110.
《China Geology》2023,6(2):303-321
The Cenozoic Himalayan leucogranite-pegmatite belt has been a hotspot for rare metal exploration in recent years. To determine the genesis of the pegmatite in the Himalayan region and its relationship with the Greater Himalayan Crystalline Complex (GHC), the Gyirong pegmatite in southern Tibet was chosen for geochronological and geochemical studies. The dating analyses indicate that the U-Th-Pb ages of zircon, monazite, and xenotime exhibit large variations (38.6–16.1 Ma), with the weighted average value of the four youngest points is 16.5 ± 0.3 Ma, which indicates that the final stage of crystallization of the melt occurred in the Miocene. The age of the muscovite Ar-Ar inverse isochron is 15.2 ± 0.4 Ma, which is slightly later than the intrusion age, showing that a cooling process associated with rapid denudation occurred at 16–15 Ma. The εHf(t) values of the Cenozoic anatectic zircons cluster between −12 and −9 with an average of −11.4. The Gyirong pegmatite shows high contents of Si, Al, and K, a high Al saturation index, and low contents of Na, Ca, Fe, Mn, P, Mg, and Ti. Overall, the Gyirong pegmatite is enriched in Rb, Cs, U, K, Th and Pb and depleted in Nb, Ta, Zr, Ti, Eu, Sr, and Ba. The samples show a high 87Sr/86Sr(16 Ma) ratio of ca. 0.762 and a low εNd(16 Ma) value of −16.0. The calculated average initial values of 208Pb/204Pb(16 Ma), 207Pb/204Pb(16 Ma) and 206Pb/204Pb(16 Ma) of the whole rock are 39.72, 15.79 and 19.56, respectively. The Sr-Nd-Pb-Hf isotopic characteristics of the Gyirong pegmatite are consistent with those of the GHC. This study concludes that the Gyirong pegmatite represents a typical crustal–derived anatectic pegmatite with low metallogenic potential for rare metals. The Gyirong pegmatite records the long–term metamorphism and partial melting process of the GHC, and reflects the crustal thickening caused by thrust compression at 39–29 Ma and the crustal thinning induced by extensional decompression during 28–15 Ma.©2023 China Geology Editorial Office. 相似文献