全文获取类型
收费全文 | 3076篇 |
免费 | 587篇 |
国内免费 | 1650篇 |
专业分类
测绘学 | 39篇 |
大气科学 | 33篇 |
地球物理 | 810篇 |
地质学 | 3654篇 |
海洋学 | 461篇 |
天文学 | 12篇 |
综合类 | 128篇 |
自然地理 | 176篇 |
出版年
2024年 | 11篇 |
2023年 | 47篇 |
2022年 | 99篇 |
2021年 | 103篇 |
2020年 | 159篇 |
2019年 | 217篇 |
2018年 | 186篇 |
2017年 | 137篇 |
2016年 | 252篇 |
2015年 | 192篇 |
2014年 | 244篇 |
2013年 | 296篇 |
2012年 | 211篇 |
2011年 | 275篇 |
2010年 | 217篇 |
2009年 | 223篇 |
2008年 | 253篇 |
2007年 | 244篇 |
2006年 | 278篇 |
2005年 | 232篇 |
2004年 | 168篇 |
2003年 | 180篇 |
2002年 | 130篇 |
2001年 | 132篇 |
2000年 | 95篇 |
1999年 | 93篇 |
1998年 | 89篇 |
1997年 | 82篇 |
1996年 | 71篇 |
1995年 | 66篇 |
1994年 | 68篇 |
1993年 | 57篇 |
1992年 | 39篇 |
1991年 | 35篇 |
1990年 | 33篇 |
1989年 | 25篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 15篇 |
1985年 | 10篇 |
1984年 | 6篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1978年 | 3篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
排序方式: 共有5313条查询结果,搜索用时 281 毫秒
91.
离散裂隙渗流方法与裂隙化渗透介质建模 总被引:4,自引:1,他引:4
流体渗流模拟的连续介质方法通常适用于多孔地质体,并不一定适用于裂隙岩体,由于裂隙分布及其特征与孔隙差异较大。若流体渗流主要受裂隙的控制,对于一定尺寸的裂隙岩体,多孔介质假设则较难刻划裂隙岩体的渗流特征。离散裂隙渗流方法不但可直接用于模拟裂隙岩体非均质性和各向异性等渗流特征,而且可用其确定所研究的裂隙岩体典型单元体及其水力传导(渗透)张量大小。主要讨论了以下问题:(1)饱和裂隙介质中一般的离散流体渗流模拟;(2)裂隙岩体中的REV(典型单元体)及其水力传导(渗透)张量的确定;(3)利用离散裂隙网络流体渗流模型研究裂隙方向几何参数对水力传导系数和REV的影响;(4)在二维和三维离散裂隙流体渗流模型中对区域大裂隙和局部小裂隙的处理方法。调查结果显示离散裂隙流体渗流数学模型可用来评价不同尺度上的裂隙岩体的水力特征,以及裂隙方向对裂隙化岩体的水力特征有着不可忽视的影响。同时,局部小裂隙、区域大裂隙应当区别对待,以便据其所起的作用及水力特征,建立裂隙化岩体相应的流体渗流模型。 相似文献
92.
为探讨高原牌70kN和进口120,210kN瓷绝缘子的成分和结构性能,中采用原子吸收光谱(AAS)和X射线衍射(XRD)方法,对三类产品进行了检测。结果表明,有效成分除K2O外,70kN和210kN的SiO2,Al2O3,Fe2O3含量接近,主晶相基本相同,有刚玉,莫来石、石英和长石等;结晶相总量:70kN35%,120kN40%,210kN48%,这表明机械强度愈大,结晶相含量愈高,只需调整70kN原样的部分成分,粒度和工艺,即生产出高等级(如210kN)瓷绝缘子。 相似文献
93.
Crack damage stress as a composite function of porosity and elastic matrix stiffness in dolomites and limestones 总被引:4,自引:0,他引:4
Twenty-five uniaxial compression tests were performed to determine stress at onset of dilation, referred to herein as “the crack damage stress,” in heterogeneous dolomites and limestones. A simplified model for crack damage stress (σcd) is developed here using porosity, elastic modulus, Poisson's ratio and three empirical coefficients. The model shows that when porosity decreases and elastic modulus increases, σcd rapidly increases and approaches its maximum value. On the other hand, when porosity increases and elastic modulus decreases, σcd rapidly decreases and approaches its minimum value. The proposed model is validated for six heterogeneous limestone and dolomite formations which are widely distributed in Israel. 相似文献
94.
Abstract. The Hishikari epithermal gold deposit consists of the Honko-Sanjin zone and Yamada zone. On the basis of observed crosscutting relationships of veins, vein system in the Hishikari deposit was classified into the early and late veins. They differ from orientation, width, control by unconformity, the amount of displacement and structural features, but have similarity in gold grade and Au/Ag ratios. K-Ar ages are presented for the classified veins to clarify timing of fracturing and duration of mineralization.
Age determination revealed that the early veins in the Honko-Sanjin zone range from 0.86 to 1.11 Ma and that the late veins range from 0.73 to 0. 84 Ma. The economically most important mineralization in the Hishikari deposit occurred around 0.90 Ma in a very short period (about 0.05 million years).
The distribution of mineralization age in the whole Hishikari deposit, occurrences of slickensides and ground water temperatures imply that mineralization lasted longer in the southern part of the deposit. As compared the early veins with late veins, structural changes including width, strike, dip and vein characteristics occurred at around 0.85 Ma. 相似文献
Age determination revealed that the early veins in the Honko-Sanjin zone range from 0.86 to 1.11 Ma and that the late veins range from 0.73 to 0. 84 Ma. The economically most important mineralization in the Hishikari deposit occurred around 0.90 Ma in a very short period (about 0.05 million years).
The distribution of mineralization age in the whole Hishikari deposit, occurrences of slickensides and ground water temperatures imply that mineralization lasted longer in the southern part of the deposit. As compared the early veins with late veins, structural changes including width, strike, dip and vein characteristics occurred at around 0.85 Ma. 相似文献
95.
黄凯音 《CT理论与应用研究》2002,11(2):32-35
目的 讨论CT及X线检查在外伤性骨质疏松中的应用。方法 1998-2000年200例外伤复查病人行CT及X光检查。结果 2-3个月后出现骨疏松的病人113例,3-4个月后出现骨疏松的66例,未见骨疏松的21例。结论 骨折2-3个月后复查病人,应适量降低CT的窗宽,窗位和X线的照射剂量。 相似文献
96.
岩石圈流变机制的确定及影响岩石圈流变强度的因素 总被引:20,自引:2,他引:20
讨论了确定岩石圈流变强度中存在的问题,根据Byerlee定律,给出了在Anderson断层系统下三种断层的摩擦滑动强度公式,利用小标本实验结果外推,用大标本实验结果作约束,得到岩石圈几种典型岩石的脆性破裂规律,利用上述结果和传统的方法,分别得到了鄂尔多斯和山西裂谷两个典型地区的流变强度随深度的变化。结果表明,以往的计算对岩石圈流变强度的估计过高,对脆性形变区估计不足,流变机制估计不对;岩石圈有力学分层的特性,但各地分层的深度范围不同,使得成层和力学作用变得复杂,讨论了水、应变率以及多相矿物对流变强度的影响。 相似文献
97.
T. J. Reston W. Weinrebe I. Grevemeyer E. R. Flueh N. C. Mitchell L. Kirstein C. Kopp H. Kopp participants of Meteor / 《Earth and Planetary Science Letters》2002,200(3-4):255-269
The structure of the Mid-Atlantic Ridge at 5°S was investigated during a recent cruise with the FS Meteor. A major dextral transform fault (hereafter the 5°S FZ) offsets the ridge left-laterally by 80 km. Just south of the transform and to the west of the median valley, the inside corner (IC – the region bounded by the ridge and the active transform) is marked by a major massif, characterized by a corrugated upper surface. Fossil IC massifs can also be identified further to the west. Unusually, a massif almost as high as the IC massif also characterizes the outside corner (OC) south of the inactive fracture zone and to the east of the median valley. This OC massif has axis-parallel dimensions identical to the IC massif and both are bounded on their sides closest to the spreading axis by abrupt, steep slopes. An axial volcanic ridge is well developed in the median valley both south of the IC/OC massifs and in an abandoned rift valley to the east of the OC massif, but is absent along the new ridge-axis segment between the IC and OC massifs. Wide-angle seismic data show that between the massifs, the crust of the median valley thins markedly towards the FZ. These observations are consistent with the formation of the OC massif by the rifting of an IC core complex and the development of a new spreading centre between the IC and OC massifs. The split IC massif presents an opportunity to study the internal structure of the footwall of a detachment fault, from the corrugated fault surface to deeper beneath the fault, without recourse to drilling. Preliminary dredging recovered gabbros from the scarp slope of the rifted IC massif, and serpentinites and gabbros from the intersection of this scarp with the corrugated surface. This is compatible with a concentration of serpentinites along the detachment surface, even where the massif internally is largely plutonic in nature. 相似文献
98.
多矿物岩石流变规律的研究进展及存在问题 总被引:4,自引:2,他引:4
总结了近年来由多种矿物组成的岩石的流变规律的研究,阐述了多矿物岩石流变性质研究的意义和进展,再从实验和理论两个方面,详细论述了目前最具代表性的三种理论模型,算术平均方法、几何平均方法和能量极小方法,最后,指出这方面研究仍然存在的问题和进一步研究的方向。 相似文献
99.
依据高温高压岩石破裂实验结果并结合理论分析,对 附近区域不同深度温压条件下岩石变形破坏性质及破坏失稳的力学行为进行了研究,在一次应力加载循环中,发生破坏的部位随时间具有向深部下迁的趋势。考虑到深度温压条件下岩石的渐进式破坏行为及突发失稳,对主震前震中附近区域小地震活动的增强、平静、活化等现象,以及b值等时间序列参数变化的可能机理进行初步探讨,并简单讨论了两类平静和两类b值变化的可能原因。 相似文献
100.