全文获取类型
收费全文 | 1026篇 |
免费 | 142篇 |
国内免费 | 224篇 |
专业分类
测绘学 | 173篇 |
大气科学 | 137篇 |
地球物理 | 86篇 |
地质学 | 599篇 |
海洋学 | 88篇 |
综合类 | 100篇 |
自然地理 | 209篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 26篇 |
2021年 | 30篇 |
2020年 | 49篇 |
2019年 | 46篇 |
2018年 | 29篇 |
2017年 | 46篇 |
2016年 | 58篇 |
2015年 | 34篇 |
2014年 | 57篇 |
2013年 | 53篇 |
2012年 | 61篇 |
2011年 | 73篇 |
2010年 | 69篇 |
2009年 | 73篇 |
2008年 | 45篇 |
2007年 | 56篇 |
2006年 | 63篇 |
2005年 | 47篇 |
2004年 | 42篇 |
2003年 | 52篇 |
2002年 | 43篇 |
2001年 | 28篇 |
2000年 | 39篇 |
1999年 | 43篇 |
1998年 | 37篇 |
1997年 | 30篇 |
1996年 | 27篇 |
1995年 | 18篇 |
1994年 | 28篇 |
1993年 | 18篇 |
1992年 | 14篇 |
1991年 | 14篇 |
1990年 | 7篇 |
1989年 | 7篇 |
1988年 | 7篇 |
1986年 | 1篇 |
1984年 | 1篇 |
排序方式: 共有1392条查询结果,搜索用时 593 毫秒
31.
急倾斜煤层开采地表沉陷的渐近灰色预测 总被引:5,自引:0,他引:5
煤层开采所引起的地表沉陷是一种严重的矿区地质灾害。煤层的倾角、厚度等物理条件是地表沉陷的主要影响因素。在水平煤层或缓倾斜煤的开采过程中,由于地层倾角小,地表沉陷具有较完整的规律性,其预测效果也比较理想。但是,在急倾斜煤层的开采中,由于地层倾角较大,赋存条件和地质体物理力学性质的差异,增强了地表下沉的非线性特征,使地表沉陷具有不确定的表现规律。文章对重庆市南桐矿区东林矿的地表沉陷非线性特征进行了探讨,得到了东林煤矿地表下沉曲线的分形维数是1.07。在岩层移动这个系统当中,既含有已知的又含有未知的或非确定的信息,可以作为一个灰色系统来研究。岩层控制系统的状态、结构和边界条件难以精确描述,属本征性灰色系统。文章针对东林煤矿地表下沉曲线非线性较弱的性质,提出用一种基于GM(1,1)的渐近预测模型对东林煤矿42个月的地表下沉量时间序列进行探讨。结果表明,这种模型对急倾斜层开采地表沉陷的预测是一种行之有效的方法。通过对其他工程实例的应用分析,进一步证明这种渐近的灰色预测方法具有相对较高的精度,是一种比较实用的地表沉陷预测方法,具有广泛的工程实用空间。 相似文献
32.
33.
基于灰关联分析的GPS高程拟合加权平均函数模型权函数优选 总被引:6,自引:0,他引:6
基于灰色系统理论的灰关联分析方法,提出了权函数的优选方法,实例分析表明其具有较好的实用价值. 相似文献
34.
Introduction In recent years, with the development of earthquake observation technology, increasing ofobservation stations and improvement of observation instruments which are digitalized and con-nected by network, a great deal of data is recorded, to some extend, which brings difficulty for usto manage and store them. It leads to traditional methods, which use the file system to managemass data, could not satisfy our requirement, and it is necessary to find a new method in place oftradit… 相似文献
35.
The tectono‐metamorphic evolution of the very low‐grade hangingwall constrains two‐stage gneiss dome formation in the Montagne Noire (Southern France)
下载免费PDF全文
![点击此处可从《Journal of Metamorphic Geology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The Montagne Noire in the southernmost French Massif Central is made of an ENE‐elongated gneiss dome flanked by Palaeozoic sedimentary rocks. The tectonic evolution of the gneiss dome has generated controversy for more than half a century. As a result, a multitude of models have been proposed that invoke various tectonic regimes and exhumation mechanisms. Most of these models are based on data from the gneiss dome itself. Here, new constraints on the dome evolution are provided based on a combination of very low‐grade petrology, K–Ar geochronology, field mapping and structural analysis of the Palaeozoic western Mont Peyroux and Faugères units, which constitute part of the southern hangingwall of the dome. It is shown that southward‐directed Variscan nappe‐thrusting (D1) and a related medium‐P metamorphism (M1) are only preserved in the area furthest away from the gneiss dome. The regionally dominant pervasive tectono‐metamorphic event D2/M2 largely transposes D1 structures, comprises a higher metamorphic thermal gradient than M1 (transition low‐P and medium‐P metamorphic facies series) and affected the rocks between c. 309 and 300 Ma, post‐dating D1/M1 by more than 20 Ma. D2‐related fabrics are refolded by D3, which in its turn, is followed by dextral‐normal shearing along the basal shear zone of both units at c. 297 Ma. In the western Mont Peyroux and Faugères units, D2/M2 is largely synchronous with shearing along the southern dome margin between c. 311 and 303 Ma, facilitating the emplacement of the gneiss dome into the upper crust. D2/M2 also overlaps in time with granitic magmatism and migmatization in the Zone Axiale between c. 314 and 306 Ma, and a related low‐P/high‐T metamorphism at c. 308 Ma. The shearing that accompanied the exhumation of the dome therefore was synchronous with a peak in temperature expressed by migmatization and intrusion of melts within the dome, and also with the peak of metamorphism in the hangingwall. Both, the intensity of D2 fabrics and the M2 metamorphic grade within the hangingwall, decrease away from the gneiss dome, with grades ranging from the anchizone–epizone boundary to the diagenetic zone. The related zonation of the pre‐D3 metamorphic field gradients paralleled the dome. These observations indicate that D2/M2 is controlled by the exhumation of the Zone Axiale, and suggest a coherent kinematic between the different crustal levels at some time during D2/M2. Based on integration of these findings with regional geological constraints, a two‐stage exhumation of the gneiss dome is proposed: during a first stage between c. 316 and 300 Ma dome emplacement into the upper crust was controlled by dextral shear zones arranged in a pull‐apart‐like geometry. The second stage from 300 Ma onwards was characterized by northeast to northward extension, with exhumation accommodated by north‐dipping detachments and hangingwall basin formation along the northeastern dome margin. 相似文献
36.
Temporal stability of soil moisture has been widely used in hydrological monitoring since it emerged. However, the spatial analysis of temporal stability at the landscape scale is often limited because of insufficient sampling numbers. This work made an effort to investigate the spatial variations of temporal stability of soil moisture in an oasis landscape. The specific objectives of the study were to explore the spatial patterns of temporal stability and to determine the controlling factors of temporal stability in the desert oasis. A time series of soil moisture measurements were gathered on 23 occasions at 118 locations over 3 years in a rectangular transect of approximately 100 km2. The nonparametric Spearman's rank correlation coefficient, standard deviation of relative difference (SDRD), and mean absolute bias error (MABE) were used to quantify the temporal stability of soil moisture. Results showed that the temporal stability of soil moisture was depth dependent and season dependent. The spatial pattern of soil moisture in a deep soil layer and between two same seasons generally had a high temporal stability. SDRD and MABE were spatially autocorrelated and exhibited strong spatial structures in the geographic space. The concept of temporal stability can be extended to describe the time‐stable areas of soil moisture with geostatistics. There were great differences between SDRD and MABE in describing the temporal stability of soil moisture and in identifying the controlling factors of temporal stability. In this case, MABE was a better alternative to estimate the areal mean soil moisture using representative locations than SDRD. Land use type, soil moisture condition, and soil particle composition were the dominant controls of temporal stability in the oasis. These insights could help to better understand the essence of temporal stability of soil moisture in arid regions. 相似文献
37.
在短期基坑沉降监测中,由于数据量少且呈非线性变化,沉降模型很难准确建立。灰色GM(1,1)对数据少、趋势性强、波动小的数据有较高的预测精度,但不能模拟复杂的非线性函数;BP神经网络可以对非线性数据进行学习训练,具有自学习、自适应能力;通过将GM(1,1)与BP神经网络组合,并优化网络部分的学习率、权值和阈值等,建立一种改进的灰色神经网络模型,该模型具有对非线性数据自学习、自适应能力和预测精度更高等优点。通过某基坑沉降监测分析,验证改进的灰色神经网络模型预测精度更高,适合短期建模,具有很好的实用性。 相似文献
38.
针对GM(1,1)建模过程存在背景值、时间因素和初始条件3方面的不足,该文提出三重加权TPGM(1,1)预测模型。通过对背景值进行加权生成新的背景值,建立PGM(1,1)模型;在PGM(1,1)基础上考虑到时间因素,在求解灰参数时进行第2次加权建立DPGM(1,1)模型;最后考虑到初始条件对预测模型的影响,在DPGM(1,1)基础上进行第3次加权,建立TPGM(1,1)模型。通过实例分析,比较GM(1,1)、PGM(1,1)、DPGM(1,1)、TPGM(1,1)4种模型在变形监测数据处理中的拟合和预测结果,表明三重加权TPGM(1,1)模型拟合效果更好、预测精度更高;该模型具有前3种模型的优点,同时弥补了传统GM(1,1)存在的不足。 相似文献
39.
40.
地热勘查孔(探采结合孔)是在矿山钻探施工工艺的基础上进行的探索性施工。着重介绍了福建省泉州市聚龙小镇DZK1地热勘查孔在钻探施工过程中遇到的施工难题以及新技术、新工艺的应用。如大口径单管取心、空压机洗井和活塞洗井相结合的洗井方法、套管的隔级使用、深孔测试钻杆密闭性、深孔磨钻头、在涌水量大的地层钻进等。 相似文献