全文获取类型
收费全文 | 240篇 |
免费 | 60篇 |
国内免费 | 58篇 |
专业分类
测绘学 | 31篇 |
大气科学 | 3篇 |
地球物理 | 101篇 |
地质学 | 166篇 |
海洋学 | 20篇 |
综合类 | 12篇 |
自然地理 | 25篇 |
出版年
2024年 | 1篇 |
2023年 | 2篇 |
2022年 | 8篇 |
2021年 | 5篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 2篇 |
2017年 | 4篇 |
2016年 | 10篇 |
2015年 | 7篇 |
2014年 | 8篇 |
2013年 | 13篇 |
2012年 | 9篇 |
2011年 | 19篇 |
2010年 | 20篇 |
2009年 | 18篇 |
2008年 | 18篇 |
2007年 | 26篇 |
2006年 | 21篇 |
2005年 | 25篇 |
2004年 | 22篇 |
2003年 | 19篇 |
2002年 | 17篇 |
2001年 | 8篇 |
2000年 | 3篇 |
1999年 | 6篇 |
1998年 | 9篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1992年 | 4篇 |
1991年 | 2篇 |
1990年 | 2篇 |
1988年 | 1篇 |
1983年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有358条查询结果,搜索用时 62 毫秒
111.
CHEN Gang SUN JianBo ZHOU LiFa ZHANG HuiRuo LI XiangPing WANG ZhiWei 《中国科学D辑(英文版)》2007,50(Z2):133-143
Based on the analysis of apatite and zircon fission track (FT), the FT age distribution and the peck-ages of the Mesozoic tectonic events in the southwest margin of the Ordos Basin (OB) were discussed. (1) The early event mainly occurred at 213-194 Ma with a peck-age of 205 Ma, and corresponded to the tectonic uplift and the mega-clastic deposit in the southwest OB during the Late Triassic. (2) The middle event included at least two episodes. One was at 165-141 Ma with a peck-age of 150 Ma, and the other was at 115-113 Ma with a peck-age of 114 Ma, corresponding to the over-thrusting and the mega- clastic deposits in the southwest OB during the Late Jurassic to the Early Cretaceous. (3) The late event mainly demonstrated the regional uplifting and included at least two episodes. One was at 100-81 Ma with a peck-age of 90 Ma, and the other was at 66-59 Ma with a peck-age of 63 Ma. Additionally, the relationship analysis of the tectonic event and the mineralizing chronology revealed that the extreme environment of the peck-age event and the subsequent moderate activity could be the key factors of the multiple resources coupling and coexistence in the OB. 相似文献
112.
113.
遗传模拟退火算法在边坡稳定分析中的应用 总被引:15,自引:6,他引:9
利用遗传模拟退火算法结合瑞典圆弧法,寻找最危险滑裂面进行边坡稳定分析。对构造数学模型、确定计算步骤、选取参数等方面作了一定的研究。通过实例计算,结果令人满意。 相似文献
114.
基于模拟退火算法的边坡稳定分析方法 总被引:7,自引:2,他引:5
岩石边坡开挖中存在大量的随机结构面,结构面与岩桥的组合破坏是边坡破坏的一种重要形式。如何确定抗剪强度最小的滑裂面是边坡工程中的重要研究方向。在岩体结构面调查统计基础上,运用随机网络模拟的方法得到边坡的裂隙网络图像,在此基础上应用模拟退火算法,搜索出边坡由结构面与岩桥组合形成的潜在最危险滑裂面的位置,将结构面组合滑动面与Sarma分析方法结合,形成一种改进的分析岩石边坡稳定性的方法--Sarma-SA分析法,通过一工程实例验证了该方法的合理性。 相似文献
115.
Lin Li Yani Najman Guillaume Dupont-Nivet Mauricio Parra Pierrick Roperch Mustafa Kaya Niels Meijer Paul O'Sullivan Gilby Jepson Jovid Aminov 《Basin Research》2023,35(2):530-550
Knowledge of the tectonic history of the Pamir contributes to our understanding of both the evolution of collisional orogenic belts as well as factors controlling Central Asian aridification. It is, however, not easy to decipher the Mesozoic–Cenozoic tectonics of the Pamir due to extensive Neogene deformation in an orogen that remains largely understudied. This study reports detrital apatite and zircon fission-track (FT) ages from both the eastern Tajik Basin sedimentary rocks and Pamir modern river sands. These FT data, supported by vitrinite reflectance and zircon and apatite U–Pb double dating, suggest that the majority of the FT ages are unreset and record exhumation stages of the Pamir, which has served as the source terrane of the Tajik Basin since the Cretaceous. Furthermore, we combine the new data with a compilation of published detrital apatite and zircon FT data from both the Tajik Basin sedimentary rocks and Pamir modern river sands, to explore the Mesozoic–Cenozoic tectonic history of Pamir. Deconvolved FT Peak Ages document two major Mesozoic exhumation events associated with the Late Triassic–Early Jurassic Cimmerian orogeny that reflects accretion of the Pamir terranes, as well as the Early–early Late Cretaceous deformation associated with the northward subduction of the Neo-Tethys Ocean beneath Pamir. The compiled data also show significant Late Eocene–Neogene exhumation associated with the ongoing formation of the Pamir, which peaks at ca. 36, 25, 14 and 7 Ma. 相似文献
116.
117.
The problem of equivalence in direct current (DC) resistivity and electromagnetic methods for a thin resistive and conducting layer is well‐known. Attempts have been made in the past to resolve this problem through joint inversion. However, equivalence still remains an unresolved problem. In the present study, an effort is made to reduce non‐uniqueness due to equivalence using global optimization and joint inversion by successive refinement of the model space. A number of solutions derived for DC resistivity data using very fast simulated annealing global inversion that fits the observations equally well, follow the equivalence principle and show a definite trend. For a thin conductive layer, the quotient between resistivity and thickness is constant, while for a resistive one, the product between these magnitudes is constant. Three approaches to obtain very fast simulated annealing solutions are tested. In the first one, layer resistivities and thicknesses are optimized in a linear domain. In the second, layer resistivities are optimized in the logarithmic domain and thicknesses in the linear domain. Lastly, both layer resistivities and thicknesses are optimized in the logarithmic domain. Only model data from the mean models, corresponding to very fast simulated annealing solutions obtained for approach three, always fit the observations. The mean model defined by multiple very fast simulated annealing solutions shows extremely large uncertainty (almost 100%) in the final solution after inversion of individual DC resistivity or electromagnetic (EM) data sets. Uncertainty associated with the intermediate resistive and conducting layers after global optimization and joint inversion is still large. In order to reduce the large uncertainty associated with the intermediate layer, global optimization is performed over several iterations by reducing and redefining the search limits of model parameters according to the uncertainty in the solution. The new minimum and maximum limits are obtained from the uncertainty in the previous iteration. Though the misfit error reduces in the solution after successive refinement of the model space in individual inversion, it is observed that the mean model drifts away from the actual model. However, successive refinement of the model space using global optimization and joint inversion reduces uncertainty to a very low level in 4–5 iterations. This approach works very well in resolving the problem of equivalence for resistive as well as for conducting layers. The efficacy of the approach has been demonstrated using DC resistivity and EM data, however, it can be applied to any geophysical data to solve the inherent ambiguities in the interpretations. 相似文献
118.
提出了一种新的射线追踪方法——模拟退火法.新方法不仅较好地解决了传统射线追踪方法过分依赖初始模型的问题,而且对于复杂速度场模型也能保证在固定的发射与接收点之间构建令人满意的射线路径及其相应的走时,搜索到满足旅行时全局最小的射线路径.此外,新方法还可计算局部最小旅行时,并可方便地通过指定射线经过固定点来对射线路径进行限制... 相似文献
119.
JOHN H.KALIVAS 《地理学报(英文版)》1991,(1)
ealibrared.The diseussion in this PaPer foeuses on near一infrared(NIR)sPeetroseoPy as the examPle instrument.However,the Proeedures Presented are aPPlieable tomost methods of instrumental analysis.Essentially,ealibration eonsists of assembling a seriesof samPles eontaining the analyte or analytes at 相似文献
120.
David M. Chew Ray A. Donelick Margaret B. Donelick Balz S. Kamber Michael J. Stock 《Geostandards and Geoanalytical Research》2014,38(1):23-35
Apatite incorporates variable and significant amounts of halogens (mainly F and Cl) in its crystal structure, which can be used to determine the initial F and Cl concentrations of magmas. The amount of chlorine in the apatite lattice also exerts an important compositional control on the degree of fission‐track annealing. Chlorine measurements in apatite have conventionally required electron probe microanalysis (EPMA). Laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) is increasingly used in apatite fission‐track dating to determine U concentrations and also in simultaneous U‐Pb dating and trace element measurements of apatite. Apatite Cl measurements by ICP‐MS would remove the need for EPMA but the high (12.97 eV) first ionisation potential makes analysis challenging. Apatite Cl data were acquired using two analytical set‐ups: a Resonetics M‐50 193 nm ArF Excimer laser coupled to an Agilent 7700× quadrupole ICP‐MS (using a 26 μm spot with an 8 Hz repetition rate) and a Photon Machines Analyte Excite 193 nm ArF Excimer laser coupled to a Thermo Scientific iCAP Qc (using a 30 μm spot with a 4 Hz repetition rate). Chlorine concentrations were determined by LA‐ICP‐MS (1140 analyses in total) for nineteen apatite occurrences, and there is a comprehensive EPMA Cl and F data set for 13 of the apatite samples. The apatite sample suite includes different compositions representative of the range likely to be encountered in natural apatites, along with extreme variants including two end‐member chlorapatites. Between twenty‐six and thirty‐nine isotopes were determined in each apatite sample corresponding to a typical analytical protocol for integrated apatite fission track (U and Cl contents) and U‐Pb dating, along with REE and trace element measurements. 35Cl backgrounds (present mainly in the argon gas) were ~ 45–65 kcps in the first set‐up and ~ 4 kcps in the second set‐up. 35Cl background‐corrected signals ranged from ~ 0 cps in end‐member fluorapatite to up to ~ 90 kcps in end‐member chlorapatite. Use of a collision cell in both analytical set‐ups decreased the low mass sensitivity by approximately an order of magnitude without improving the 35Cl signal‐to‐background ratio. A minor Ca isotope was used as the internal standard to correct for drift in instrument sensitivity and variations in ablation volume during sessions. The 35Cl/43Ca values for each apatite (10–20 analyses each) when plotted against the EPMA Cl concentrations yield excellently constrained calibration relationships, demonstrating the suitability of the analytical protocol and that routine apatite Cl measurements by ICP‐MS are achievable. 相似文献