全文获取类型
收费全文 | 1214篇 |
免费 | 207篇 |
国内免费 | 365篇 |
专业分类
测绘学 | 10篇 |
大气科学 | 181篇 |
地球物理 | 251篇 |
地质学 | 923篇 |
海洋学 | 159篇 |
天文学 | 9篇 |
综合类 | 52篇 |
自然地理 | 201篇 |
出版年
2024年 | 5篇 |
2023年 | 16篇 |
2022年 | 25篇 |
2021年 | 35篇 |
2020年 | 44篇 |
2019年 | 60篇 |
2018年 | 41篇 |
2017年 | 48篇 |
2016年 | 62篇 |
2015年 | 51篇 |
2014年 | 100篇 |
2013年 | 91篇 |
2012年 | 61篇 |
2011年 | 60篇 |
2010年 | 50篇 |
2009年 | 89篇 |
2008年 | 103篇 |
2007年 | 111篇 |
2006年 | 102篇 |
2005年 | 81篇 |
2004年 | 58篇 |
2003年 | 57篇 |
2002年 | 58篇 |
2001年 | 43篇 |
2000年 | 44篇 |
1999年 | 38篇 |
1998年 | 24篇 |
1997年 | 35篇 |
1996年 | 25篇 |
1995年 | 32篇 |
1994年 | 26篇 |
1993年 | 28篇 |
1992年 | 14篇 |
1991年 | 15篇 |
1990年 | 7篇 |
1989年 | 15篇 |
1988年 | 10篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1786条查询结果,搜索用时 46 毫秒
881.
A detailed kinematic study in the Piedras–Girardot area reveals that approximately 32 km of ENE–WSW oblique convergence is accommodated within a northeast-trending transpressional shear zone with a shear strain of 0.8 and a convergence factor of 2. Early Campanian deformation is marked by the incipient propagation of northeast-trending faults that uplifted gentle domes where the accumulation of sandy units did not take place. Maastrichtian unroofing of a metamorphic terrane to the west is documented by a conglomerate that was deformed shortly after deposition developing a conspicuous intragranular fabric of microscopic veins that accommodates less than 5% extension. This extensional fabric, distortion of fossil molds, and a moderate cleavage accommodating less than 5% contraction, developed concurrently, but before large-scale faulting and folding. Paleogene folding and southwestward thrust sheet propagation are recorded by syntectonic strata. Neogene deformation took place only in the western flank of this foldbelt. The amount, direction, and timing of deformation documented here contradict current tectonic models for the Cordillera Oriental and demand a new tectonic framework to approach the study of the structure of the northern Andes. Thus, an alternative model was constructed by defining three continental blocks: the Maracaibo, Cordillera Central, and Cordillera Oriental blocks. Oblique deformation imposed by the relative eastward and northeastward motion of the Caribbean Plate was modeled as rigid-body rotation and translation for rigid blocks (derived from published paleomagnetic and kinematic data), and as internal distortion and dilation for weak blocks (derived from the Piedras–Girardot area). This model explains not only coeval dextral and sinistral transpression and transtension, but also large clockwise rotation documented by paleomagnetic studies in the Caribbean–northern Andean region. 相似文献
882.
Detrital zircon provenance evidence for large-scale extrusion along the Altyn Tagh fault 总被引:12,自引:1,他引:12
Yongjun Yue Stephan A. Graham Bradley D. Ritts Joseph L. Wooden 《Tectonophysics》2005,406(3-4):165-178
The question of whether or not the Altyn Tagh fault is a large-scale extrusion boundary is critical for understanding the role of lateral extrusion in accommodating the Indo-Asian convergence and in building the Tibetan Plateau. Oligocene conglomerate clasts in the eastern Xorkol basin are low-grade slate, phyllite, sandstone, dacite and carbonate, and associated paleocurrent indicators evince sediment derivation from the opposing side of the Altyn Tagh fault. Matching these clasts with similar basement rocks in the North Qilian and Tuolainanshan terranes requires post-Oligocene left-lateral offset of 380 ± 60 km on the eastern segment of the Altyn Tagh fault, suggesting large-scale extrusion along the fault in the Cenozoic (Yue, Y.J., Ritts, B.D., Graham, S.A., 2001b. Initiation and long-term slip history of the Altyn Tagh fault. International Geological Review 43, 1087–1094.). In order to further define this piercing point, the detrital zircon pattern of Oligocene sandstone from the Xorkol basin and the zircon ages of basement on the southern side of the fault were established by ion microprobe dating. Characterized by strong peaks between 850 and 950 Ma and the absence of Paleozoic and Mesozoic ages, the detrital zircon age pattern of the Oligocene sandstone matches the age distribution of zircon-bearing rocks of the Tuolainanshan terrane. This match requires 360 ± 40 km of post-Oligocene left-lateral displacement on the eastern segment of the Altyn Tagh fault, supporting as well as refining the previously reported lithology-based cross-fault match. At least one of the following three extrusion scenarios must have existed to accommodate this large offset: (1) northeastward extrusion along the Altyn Tagh–Alxa–East Mongolia fault, (2) eastward extrusion along the Altyn Tagh–North Qilian–Haiyuan fault, and (3) northeastward extrusion of northern Tibet as a Himalaya-scale thrust sheet along the North Qilian–Haiyuan fault. We prefer the first scenario inasmuch as rapidly growing evidence for Cenozoic strike-slip activity on the Alxa–East Mongolia fault and mid-Miocene exhumation of northern Tibet supports it. 相似文献
883.
MICHAEL SOFER 《The Geographical journal》2005,171(4):357-368
The Moshav, a family farm-based settlement, has been a prime example of the major changes in the rural space in Israel. The aim of this paper is to present and understand these changes by studying the economic characteristics of second-generation – that is relatively younger – households in the Moshav. This group has shown a higher tendency to either adopt a livelihood strategy of pluriactivity, or to disassociate itself from agriculture in favour of non-agricultural income-generating activities, both inside and outside the settlement. Both trends have emerged in response to the increasing difficulty of deriving income from agriculture. The paper identifies the major patterns of economic activity and income sources among this group and assesses future attitudes towards operating the farm, choosing pluriactivity as a livelihood strategy, and remaining on the farm in the future. 相似文献
884.
In-migration to popular ‘sea change’ and ‘tree change’ regions has produced conflicts between rural land users. In the Northern Rivers region of New South Wales, new residential developments have been built on much of what was previously prime agricultural land, while farmers (in particular, those negatively affected by the deregulation of the dairy industry) have sought to secure retirement incomes by subdividing land for sale. Although developers, local councils and individual farmers sometimes see eye to eye on the mutual benefits of in-migration and population growth, land use has none the less become the subject of a hotly contested local political battle. Conflicts occur at the interface of growing urban developments and surrounding farmland, with new residents finding the sights, sounds and smells of rural production intrusive. More generally, there is considerable concern that the best farmland in the region may be lost to urbanisation and rural residential subdivision. This paper discusses the results of a survey that collected opinions from local residents about the pressures on the region's land uses by in-migration, the future role of farmland as both an economic and cultural landscape, and views on proposed measures to protect prime farmland in the region. Results highlighted a strong and consistent ‘pro-farmland’ and ‘pro-protection’ attitude throughout the region, and across social groups. Yet, variations emerged when respondents were asked about why they attribute value to agricultural landscapes. For some, ‘economic’ values dominated, while for others, value was attributed in ways that reflected an emerging ethos of ‘localism’ and village lifestyle. Although values differed, a clear message from this study is that the population of Australia's pre-eminent ‘sea change’ region strongly support measures to curb urban development and the more destructive consequences of a dynamic property market. 相似文献
885.
Origin of the Gabbro-Peridotite Association from the Northern Apennine Ophiolites (Italy) 总被引:4,自引:0,他引:4
TRIBUZIO RICCARDO; THIRLWALL MATTHEW F.; VANNUCCI RICCARDO 《Journal of Petrology》2004,45(6):1109-1124
The Northern Apennine ophiolites are remnants of the MiddleJurassicEarly Cretaceous lithosphere from the LigurianTethys. New trace element and NdSr isotope investigationswere performed on: (1) the rare gabbros associated with thesubcontinental mantle rocks from the External Liguride ophiolites;(2) the gabbroperidotite association from the poorlyknown ophiolitic bodies from Cecina valley (Southern Tuscany).Clinopyroxenes from the External Liguride and Cecina valleygabbros have similar trace element compositions, which are consistentwith formation from normal mid-ocean ridge basalt (N-MORB) magmas.SmNd mineral isochron ages are 179 ± 9 Ma foran External Liguride gabbro and 170 ± 13 Ma and 173·5± 4·8 Ma for two different gabbroic bodies fromthe Cecina valley ophiolites. These ages are interpreted todate the igneous crystallization of the gabbros and are slightlyolder than the oldest pelagic sediments of the Ligurian Tethys.Initial 相似文献
886.
887.
新疆准北地区铜矿床主要类型控矿条件及找矿前景分析 总被引:5,自引:0,他引:5
准北地区铜矿床已发现有岩浆熔离铜镍硫化物型,海相火山岩型,隐爆角砾岩型和陆相火山岩型,那林卡拉-喀拉通克铜镍矿带受控于海沟岛弧盆地内基性岩带的控制,岩浆分异程度对铜矿形成具有明显的控制作用,海相火山岩铜矿受火山机构制约,常产出于海底火山喷发中心及附近洼地,将准北地区划分冲乎尔-麦兹铜多金属,阿舍勒铜锌,额尔齐斯铜(镍)金-萨吾尔-加波萨尔铜(钼)和谢米斯台-阿尔曼台-北塔山铜等五个具找矿前景的成矿 相似文献
888.
889.
通过对北秦岭丹凤地区早古生代花岗岩的Ph、Sr、Nd同位素地球化学特征的系统研究,结合元素地球化学特征,证明早古生代具成分极性的枣园、黄柏岔、石门花岗岩是由于秦岭群斜长角闪岩和黑云斜长片麻岩部分熔融,近俯冲带以熔体与熔体的混合、远离俯冲带是前者产生的熔体与后者熔融后的残留相以不同比例混合形成的。 相似文献
890.
The abrupt warming of Northern Hemisphere in 1920s has been detected,the simplest model is introduced to ex-plain some deterministic and stochastic nature with this interesting phenomenon,and the implications of our approachto the predictability are discussed. 相似文献