全文获取类型
收费全文 | 37272篇 |
免费 | 6308篇 |
国内免费 | 7720篇 |
专业分类
测绘学 | 4085篇 |
大气科学 | 4652篇 |
地球物理 | 6297篇 |
地质学 | 20161篇 |
海洋学 | 4072篇 |
天文学 | 3647篇 |
综合类 | 2545篇 |
自然地理 | 5841篇 |
出版年
2024年 | 173篇 |
2023年 | 462篇 |
2022年 | 1238篇 |
2021年 | 1433篇 |
2020年 | 1338篇 |
2019年 | 1743篇 |
2018年 | 1196篇 |
2017年 | 1449篇 |
2016年 | 1462篇 |
2015年 | 1652篇 |
2014年 | 2119篇 |
2013年 | 2089篇 |
2012年 | 2252篇 |
2011年 | 2394篇 |
2010年 | 2050篇 |
2009年 | 2604篇 |
2008年 | 2477篇 |
2007年 | 2558篇 |
2006年 | 2531篇 |
2005年 | 2409篇 |
2004年 | 2092篇 |
2003年 | 2015篇 |
2002年 | 1699篇 |
2001年 | 1514篇 |
2000年 | 1504篇 |
1999年 | 1298篇 |
1998年 | 1139篇 |
1997年 | 798篇 |
1996年 | 669篇 |
1995年 | 559篇 |
1994年 | 525篇 |
1993年 | 446篇 |
1992年 | 323篇 |
1991年 | 285篇 |
1990年 | 190篇 |
1989年 | 162篇 |
1988年 | 121篇 |
1987年 | 79篇 |
1986年 | 44篇 |
1985年 | 39篇 |
1984年 | 21篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1978年 | 18篇 |
1976年 | 10篇 |
1972年 | 10篇 |
1971年 | 9篇 |
1954年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
201.
John F. Rudge Marian B. Holness Graham C. Smith 《Contributions to Mineralogy and Petrology》2008,156(4):413-429
The spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush, and
in turn is controlled by the rate of crystal growth and accumulation. A predominant non-spherical habit for igneous minerals
brings into question the use of spherical particles in reference packings used for quantification of spatial distribution.
Furthermore, variations of crystal clustering/ordering with length scale require spatial statistics which take into account
the distribution of particles beyond nearest neighbours. Using random close packings of spherocylinders, we demonstrate the
importance of aspect ratio for the aggregation index (usually known as R) and show that packings of spherical particles have more structure than packings of rods. The spatial distribution functions
demonstrate that the plagioclase grains in the colonnade from the Holyoke basalt are clustered on a length scale of 0.5 mm.
Understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques
to well-understood environments. 相似文献
202.
Håkon Austrheim Christine V. Putnis Ane K. Engvik Andrew Putnis 《Contributions to Mineralogy and Petrology》2008,156(4):517-527
Ilmenite in coronitic gabbros from the Bamble and Kongsberg sectors, southern Norway, is surrounded by zircons ranging in
diameters from a fraction of a micrometer to 10 μm across. The zircons are inert during subsequent metamorphism (amphibolite-
to pumpellyite–prehnite facies) and metasomatism (scapolitization and albitization) and can be found as trails in silicates
(phlogopite, talc, chlorite, amphibole, albite, and tourmaline) in the altered rocks. The trails link up to form polygons
outlining the former oxide grain boundary. This 3-dimensional framework of zircons is used to (a) recognize metasomatic origin
of rocks, (b) quantify the mobility of elements during mineral replacement, (c) establish the growth direction of reaction
fronts and to identify the reaction mechanism as dissolution–reprecipitation. Zircon coronas on Fe–Ti oxides have been described
from a number of terrains and appear to be common in mafic rocks (gabbros and granulites) providing a tool for a better understanding
of metasomatic and metamorphic reactions. 相似文献
203.
A strain of thermophilic fungus Aspergillus fumigatus was cultured with K-bearing minerals to determine if microbe-mineral interactions enhance the release of mineralic potassium. Experiments were carried out in two settings, one with the mineral grains and the fungal cells in direct contact, and the other employing a membrane (pore size 0.22 μm) to separate the two. Measurements over a period of 30 days showed that, irrespective of the experimental setup, the concentration of free K in the culture was drastically higher than those in any of the control experiments where no living organism was present. Moreover, the occurrence of mineral-cell physical contact enhanced potassium release by an additional factor of 3 to 4 in comparison to the separation experiments. For contact experiments, Electron Probe Microanalysis revealed the formation of mycelium-mineral aggregates, and Atomic Force Microscopy imaging further indicated the possible ingestion of mineral particles by the fungus cells. Contrasting to what was observed and expected in control experiments, the potassium solubilization rate showed a positive dependence upon pH when fungi and minerals were mixed directly, and exhibited no correlations with solution acidity if cell-rock contact was restrained. These results appear to suggest that A. fumigatus promoted potassium release by means of at least three likely routes, one through the complexation of soluble organic ligands, another appealing to the immobile biopolymers such as the insoluble components of secretion, and the third related to the mechanical forces in association with the direct physical contact between cells and mineral particles. 相似文献
204.
Los Angeles is often described as the epitome of urban fragmentation, a notion which in this context is frequently connected to, or even conflated with urban sprawl. At the same time, the city features integrated water and power networks which have been under public ownership for over 70 years. We thus have an apparent paradox in the context of the debate on ‘splintering urbanism’, between socio-spatial fragmentation and the integration of networks. In discussing the idea that deregulation of infrastructural networks exacerbates urban fragmentation, the authors use the case of Los Angeles in order to highlight the central role of private interests in management decisions concerning infrastructure networks. The authors carry out their analysis in an historical perspective, revealing that network integration and universal access can often serve private interests more than the public good. Urban fragmentation in Los Angeles, they conclude, is the result of a complex process of instrumentalisation of network development and management. 相似文献
205.
A. Wendy Russell 《Geoforum》2008,39(1):213-222
In this paper, I argue that genetically modified organisms (GMOs) have inherent potential to contribute to socially and environmentally sustainable agriculture by virtue of their ‘biological embeddedness’. Their actual ‘performance’ and how this contributes to sustainability depends on the ‘mutual shaping’ of technology and context. While much attention has been given to the design context of GMOs, this paper considers the influence of the application context and of users. A case study investigating the use of insect-resistant and herbicide-tolerant GM cotton in the cotton-growing region of New South Wales in Australia is presented. The study was based on focus groups with farmers and other stakeholders in a cotton-growing community. It demonstrated a range of direct and indirect effects of GM cotton use, both positive and negative for sustainability, and the ways in which these effects were influenced by the local social context. The influences of the biotechnology industry context, in limiting the contributions that gene technologies can make to sustainability, were also considered, and remedies suggested. I argue that the polarity of the GM debate is hindering progress on these issues, and that a more balanced approach to our analysis of GMOs is necessary in order to fully understand, and to influence, their role in the future of rural spaces. 相似文献
206.
This paper is about ‘material politics’. It argues that this may be understood as a material ordering of the world in a way that contrasts this with other and equally possible alternative modes of ordering. It also suggests that while material politics may well involve words, it is not discursive in kind. This argument is made for the mundane and material practice of boiling pigswill that the 2001 UK foot and mouth outbreak showed to have a layered importance. Boiling pigswill was a political technique in at least three different ways. First it made difference, dividing the rich from the poor by separating disease free countries from those in which foot and mouth is endemic. Second, it joined times and places by linking past agricultural practices with those of the contemporary world, and linking Britain with the world. And third, it also showed a way of limiting food scarcity on a world wide scale because it allowed food to be recycled, albeit on a small scale, in a region of plenty. ‘Politics’ is often linked to debate, discussion, or explicit contestation. Alternatively, it is sometimes seen as being embedded in and carried by artefacts. For the case of boiling pigswill neither approach is satisfactory. The first privileges the life of the mind while in the second politics is linked too strongly to a single order. The version of politics presented here foregrounds both materiality and difference. And it involves articulation: the question is not whether something is political all by itself but whether it can be called political as part of the process of analysing it. 相似文献
207.
Christopher A. Airriess Wei Li Karen J. Leong Angela Chia-Chen Chen Verna M. Keith 《Geoforum》2008,39(3):1333-1346
This research examines the role of social capital and networks to explain the evacuation, relocation, and recovery experiences of a Vietnamese American community in New Orleans, Louisiana in the aftermath of Hurricane Katrina. As the single largest community institution, the parish church’s complex bonding and bridging social capital and networks proved particularly critical in part because of its historically based ontological security. The process of evacuation, but especially relocation and recovery, was dependent on deploying co-ethnic social capital and networks at a variety of geographical scales. Beyond the local or community scale, extra-local, regional, and national scales of social capital and networks reproduced a spatially redefined Vietnamese American community. Part of the recovery process included constructing discursive place-based collective-action frames to successfully contest a nearby landfill that in turn engendered social capital and networks crossing ethnic boundaries to include the extra-local African American community. Engaging social capital and networks beyond the local geographical scale cultivated a Vietnamese American community with an emergent post-Katrina cultural and political identity. 相似文献
208.
209.
G. N. Sadovnikov 《Stratigraphy and Geological Correlation》2008,16(1):31-46
A unique succession of volcanogenic deposits with representative paleontological remains characterizing the Permian-Triassic boundary interval in the North Siberian platform and Taimyr is described. The succession is suitable for selecting a standard for the Triassic base in nonmarine deposits. Abundant and diverse fossils occurring in the succession evidence that volcanism responsible for origin of the plateau basalt province in Siberia was not a brief epoch of paroxysmal eruptions, which eliminated everything alive. Throughout the formation history of relevant plateau basalts, the organic world of the plateau and around existed and gradually evolved. 相似文献
210.
P. M. Amaral J. Cruz Fernandes L. Guerra Rosa 《Rock Mechanics and Rock Engineering》2008,41(6):917-928
Summary This paper describes and discusses the adequacy of Weibull statistical analysis to analyse the bending strength of granite.
The experimental results show that strength variability is related with a specific origin of failure. This conclusion is based
on analysing the influence of the surface condition (extrinsic defects) on the bending strength results treated by the Weibull
statistics. The conclusions drawn from this study have been validated by analysing the results of the critical flaw dimension
estimated by applying the linear elastic fracture mechanics (LEFM) formulae. Results obtained from fractographic examination
also have been used to describe the location of the origin of the fracture and understand the distribution of defects; i.e.,
there is a unimodal distribution of defects (intrinsic defects), despite the fact that some outlier values are normally observed
in the fractured surfaces.
Correspndence: P. M. Amaral, Department of Materials Engineering, Instituto Superior Técnico, Technical University of Lisbon,
Av. Rovisco Pais, 1049-001 Lisboa, Portugal 相似文献