全文获取类型
收费全文 | 1656篇 |
免费 | 76篇 |
国内免费 | 18篇 |
专业分类
测绘学 | 45篇 |
大气科学 | 100篇 |
地球物理 | 469篇 |
地质学 | 724篇 |
海洋学 | 126篇 |
天文学 | 206篇 |
综合类 | 14篇 |
自然地理 | 66篇 |
出版年
2023年 | 7篇 |
2022年 | 26篇 |
2021年 | 32篇 |
2020年 | 27篇 |
2019年 | 34篇 |
2018年 | 85篇 |
2017年 | 78篇 |
2016年 | 83篇 |
2015年 | 73篇 |
2014年 | 92篇 |
2013年 | 130篇 |
2012年 | 64篇 |
2011年 | 114篇 |
2010年 | 107篇 |
2009年 | 102篇 |
2008年 | 68篇 |
2007年 | 59篇 |
2006年 | 52篇 |
2005年 | 32篇 |
2004年 | 43篇 |
2003年 | 41篇 |
2002年 | 50篇 |
2001年 | 38篇 |
2000年 | 27篇 |
1999年 | 12篇 |
1998年 | 13篇 |
1997年 | 18篇 |
1996年 | 20篇 |
1995年 | 11篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 14篇 |
1991年 | 11篇 |
1990年 | 5篇 |
1989年 | 14篇 |
1987年 | 11篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 7篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 7篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1973年 | 8篇 |
1971年 | 9篇 |
1962年 | 5篇 |
排序方式: 共有1750条查询结果,搜索用时 15 毫秒
91.
François Nicot Philippe Gotteland David Bertrand Stéphane Lambert 《国际地质力学数值与分析法杂志》2007,31(13):1477-1515
Geo‐composite cellular structures are an efficient technological solution for various applications in civil engineering. This type of structure is particularly well adapted to resisting rockfalls and can act as a defensive structure. However, the design of such structures is for the most part empirically based; this lack of research‐based design stagnates optimization and advanced development. In this paper, the mechanical behaviour of a geo‐composite cellular structure is investigated using a multi‐scale approach, from the individual cell made up of an assembly of rocky particles contained in a wire netting cage to the entire structure composed of a regular array of cells. Based on discrete modelling of both the cell and structure scales, a computational tool has been developed for design purposes. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
92.
In this paper, the ability of a material rate‐independent system to evolve toward another mechanical state from an equilibrium configuration, with no change in the control parameters, is investigated. From a mechanical point of view, this means that the system can spontaneously develop kinetic energy with no external disturbance from an equilibrium state, which corresponds to a particular case of bifurcation. The existence of both conjugate incremental strain and stress such that the second‐order work vanishes is established as a necessary and sufficient condition for the appearance of this bifurcation phenomenon. It is proved that this fundamental result is independent of the constitutive relation of the rate‐independent material considered. Then the case of homogeneous loading paths is investigated, and, as an illustration, the subsequent results are applied to interpret the well‐known liquefaction observed under isochoric triaxial loading conditions with loose granular materials. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
93.
94.
95.
S. Bilir T. Güver I. Khamitov T. Ak S. Ak K. B. Coşkunoğlu E. Paunzen E. Yaz 《Astrophysics and Space Science》2010,326(1):139-150
We present CCD BV and JHK
s
2MASS photometric data for the open cluster NGC 1513. We observed 609 stars in the direction of the cluster up to a limiting
magnitude of V∼19 mag. The star-count method showed that the centre of the cluster lies at α
2000=04
h
09
m
36
s
, δ
2000=49°28′43″ and its angular size is r=10 arcmin. The optical and near-infrared two-colour diagrams revealed the colour excesses in the direction of the cluster
as E(B−V)=0.68±0.06, E(J−H)=0.21±0.02 and E(J−K
s
)=0.33±0.04 mag. These results are consistent with normal interstellar extinction values. Optical and near-infrared Zero Age
Main-Sequences (ZAMS) provided an average distance modulus of (m−M)0=10.80±0.13 mag, which can be translated into a distance of 1440±80 pc. Finally, using Padova isochrones we determined the
metallicity and age of the cluster as Z=0.015±0.004 ([M/H]=−0.10±0.10 dex) and log (t/yr)=8.40±0.04, respectively. 相似文献
96.
Herero communities in northern Namibia recently formed the Ehi-rovipuka Conservancy under a national Community-Based Natural Resource Management Programme (CBNRM) that has received international acclaim for wildlife conservation and poverty alleviation. Nearly a century ago ancestors of the Herero were ousted from Etosha National Park, contiguous to the Ehi-rovipuka Conservancy. The communities have been denied access ever since. Participatory Rural Appraisal (PRA) methods were employed to elucidate relationships of the Herero and their communal conservancy with the Etosha National Park. Memory mapping and villager interviews revealed a profound sense of lost traditional territory inside Etosha and a strong desire to return to the Park, not to harvest wildlife but to restore cultural practices and reap certain benefits from the Park. We term the separation of the communities from their traditional territory as a ‘decoupling’ of people from their local environment. We further suggest that the potential benefits that villagers identify from the Park represent mechanisms for ‘recoupling’ local social-ecological systems, requiring the literal and figurative breakdown of the Park fence. We describe a model to illustrate decoupling and recoupling mechanisms, and argue that recoupled social-ecological systems are necessary for long-term conservation of biodiversity. We further suggest a collaborative landscape model for biodiversity conservation featuring institutional linkages and integration between community-conserved areas, integrated conservation corridors for connectivity, and dynamic, mobile reserves collaboratively integrated with national parks management. This model may have applicability in Namibia and similar regions elsewhere with low population densities, high species endemism and prevailing or emerging threats to biodiversity. 相似文献
97.
Basement lithostratigraphy of the Adula nappe: implications for Palaeozoic evolution and Alpine kinematics 总被引:1,自引:0,他引:1
Mattia Cavargna-Sani Jean-Luc Epard François Bussy Alex Ulianov 《International Journal of Earth Sciences》2014,103(1):61-82
The Adula nappe belongs to the Lower Penninic domain of the Central Swiss Alps. It consists mostly of pre-Triassic basement lithologies occurring as strongly folded and sheared gneisses of various types with mafic boudins. We propose a new lithostratigraphy for the northern Adula nappe basement that is supported by detailed field investigations, U–Pb zircon geochronology, and whole-rock geochemistry. The following units have been identified: Cambrian clastic metasediments with abundant carbonate lenses and minor bimodal magmatism (Salahorn Formation); Ordovician metapelites associated with amphibolite boudins with abundant eclogite relicts representing oceanic metabasalts (Trescolmen Formation); Ordovician peraluminous metagranites of calc-alkaline affinity ascribed to subduction-related magmatism (Garenstock Augengneiss); Ordovician metamorphic volcanic–sedimentary deposits (Heinisch Stafel Formation); Early Permian post-collisional granites recording only Alpine orogenic events (Zervreila orthogneiss). All basement lithologies except the Permian granites record a Variscan + Alpine polyorogenic metamorphic history. They document a complex Paleozoic geotectonic evolution consistent with the broader picture given by the pre-Mesozoic basement framework in the Alps. The internal consistency of the Adula basement lithologies and the stratigraphic coherence of the overlying Triassic sediments suggest that most tectonic contacts within the Adula nappe are pre-Alpine in age. Consequently, mélange models for the Tertiary emplacement of the Adula nappe are not consistent and must be rejected. The present-day structural complexity of the Adula nappe is the result of the intense Alpine ductile deformation of a pre-structured entity. 相似文献
98.
In this study, the relationship between the hourly changes of the ionospheric critic frequency values of F2 layers in low latitudes and geomagnetic activity is examined by using statistical methods. The ionospheric critical frequency data has been taken from the Manila (121.1° E, 14.7° N) ionosonde station. In order to investigate the effect of sun activity on ionospheric critical frequency, the data of 1981 when the sun was active and of 1985 when the sun was less active has been used. According to the Granger causality test results, on 5 % significance level, a causality relationship from disturbance storm time (Dst) index values to ionospheric critical frequency values direction has been observed. However, a causality relationship from ionospheric critical frequency values to Dst values has not been observed. From the results of cause-and-effect analysis, it is evaluated that the effect of a shockwave occurring in geomagnetic activity on ionospheric critical frequency continues along 72 h, that is, geomagnetic activity has a long-term effect on ionospheric critical frequency. The response of ionospheric critical frequency to geomagnetic activity substantially depends on seasons. This response is more observed especially in equinox period when the sun is active and in winter months. The increase in geomagnetic activity causes ionospheric critical frequency to decrease in night hours and increase in day hours. The same relationship has not been observed exactly, though observed very little in winter months, for 1985 when the sun was less active. 相似文献
99.
Complete Tertiary exhumation history of the Menderes massif, western Turkey: an alternative working hypothesis 总被引:1,自引:0,他引:1
The main exhumation of the Menderes massif, western Turkey, occurred along an originally N‐dipping Datça–Kale main breakaway fault that controlled depositions in the Kale and the Gökova basins during the Oligocene – Early Miocene interval. The isostatically controlled upward bending of the main breakaway fault brings the lower plate rocks to the surface. In the Early Miocene, E–W‐trending N‐ and S‐dipping graben‐bounding faults fragmented the exhumed, dome‐shaped massif. The development of half grabens by rolling master fault hinges has allowed further exhumation of the central Menderes massif. After the Pliocene, high‐angle normal faults cut all of the previous structures. This model suggests that the Menderes massif is a single large metamorphic core complex that has experienced a two‐stage exhumation process. 相似文献
100.