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排序方式: 共有114条查询结果,搜索用时 15 毫秒
51.
H. Y. Liu S. Q. Kou P.-A. Lindqvist C. A. Tang 《Rock Mechanics and Rock Engineering》2007,40(2):107-144
Summary A series of numerical tests including both rock mechanics and fracture mechanics tests are conducted by the rock and tool
(R–T2D) interaction code coupled with a heterogeneous masterial model to obtain the physical–mechanical properties and fracture
toughness, as well as to simulate the crack initiation and propagation, and the fracture progressive process. The simulated
results not only predict relatively accurate physical–mechanical parameters and fracture toughness, but also visually reproduce
the fracture progressive process compared with the experimental and theoretical results. The detailed stress distribution
and redistribution, crack nucleation and initiation, stable and unstable crack propagation, interaction and coalescence, and
corresponding load–displacement curves can be proposed as benchmarks for experimental study and theoretical research on crack
propagation. It is concluded that the heterogeneous material model is reasonable and the R–T2D code is stable, repeatable and a valuable numerical tool for research on the rock fracture process. 相似文献
52.
Christian Azar Kristian Lindgren Michael Obersteiner Keywan Riahi Detlef P. van Vuuren K. Michel G. J. den Elzen Kenneth M?llersten Eric D. Larson 《Climatic change》2010,100(1):195-202
The United Nations Framework Convention on Climate Change (UNFCCC 1992) calls for stabilization of atmospheric greenhouse gas (GHG) concentrations at a level that would prevent dangerous anthropogenic
interference with the climate system. We use three global energy system models to investigate the technological and economic
attainability of meeting CO2 concentration targets below current levels. Our scenario studies reveal that while energy portfolios from a broad range of
energy technologies are needed to attain low concentrations, negative emission technologies—e.g., biomass energy with carbon
capture and storage (BECCS)—significantly enhances the possibility to meet low concentration targets (at around 350 ppm CO2). 相似文献
53.
Kristian Vasskog Øyvind Paasche Atle Nesje John F. Boyle H.J.B. Birks 《Quaternary Research》2012,77(1):192-204
We explore the possibility of building a continuous glacier reconstruction by analyzing the integrated sedimentary response of a large (440 km2) glacierized catchment in western Norway, as recorded in the downstream lake Nerfloen (N61°56’, E6°52’). A multi-proxy numerical analysis demonstrates that it is possible to distinguish a glacier component in the ~ 8000-yr-long record, based on distinct changes in grain size, geochemistry, and magnetic composition. Principal Component Analysis (PCA) reveals a strong common signal in the 15 investigated sedimentary parameters, with the first principal component explaining 77% of the total variability. This signal is interpreted to reflect glacier activity in the upstream catchment, an interpretation that is independently tested through a mineral magnetic provenance analysis of catchment samples. Minimum glacier input is indicated between 6700–5700 cal yr BP, probably reflecting a situation when most glaciers in the catchment had melted away, whereas the highest glacier activity is observed around 600 and 200 cal yr BP. During the local Neoglacial interval (~ 4200 cal yr BP until present), five individual periods of significantly reduced glacier extent are identified at ~ 3400, 3000–2700, 2100–2000, 1700–1500, and ~ 900 cal yr BP. 相似文献
54.
Ben K. Bradley Brandon A. Jones Gregory Beylkin Kristian Sandberg Penina Axelrad 《Celestial Mechanics and Dynamical Astronomy》2014,119(2):143-168
We describe a new method for numerical integration, dubbed bandlimited collocation implicit Runge–Kutta (BLC-IRK), and compare its efficiency in propagating orbits to existing techniques commonly used in Astrodynamics. The BLC-IRK scheme uses generalized Gaussian quadratures for bandlimited functions. This new method allows us to use significantly fewer force function evaluations than explicit Runge–Kutta schemes. In particular, we use a low-fidelity force model for most of the iterations, thus minimizing the number of high-fidelity force model evaluations. We also investigate the dense output capability of the new scheme, quantifying its accuracy for Earth orbits. We demonstrate that this numerical integration technique is faster than explicit methods of Dormand and Prince 5(4) and 8(7), Runge–Kutta–Fehlberg 7(8), and approaches the efficiency of the 8th-order Gauss–Jackson multistep method. We anticipate a significant acceleration of the scheme in a multiprocessor environment. 相似文献
55.
Per-Arne Lindqvist 《Rock Mechanics and Rock Engineering》1984,17(2):97-112
Summary Indentation stress fields of one- and two-point loads applied on an ideal elastic half-space are presented. Laboratory observations, although few, are in surprisingly good agreement with long median and cone-type tensile cracks predicted by normal principal stresses. Results indicate that simultaneous loading by multiple indenters offers a possibility partly to control the direction and length of such cracks. This suggests the development of new cutter configurations with a possible increase in efficiency, as compared with present rock boring and rock cutting practice. A simple fracture mechanics calculation of the length of subsurface cracks is performed by applying indentation fracture studies of ceramics. Results demonstrate the influence of material parameters such as fracture surface energy, hardness and elastic constants. 相似文献
56.
Ocean Dynamics - A first national analysis of the evolution of sea-level rates along the Norwegian coast for the period 1960–2100 has been accomplished by exploring tide-gauge records,... 相似文献
57.
Coarse-scale data assimilation (DA) with large ensemble size is proposed as a robust alternative to standard DA with localization for reservoir history matching problems. With coarse-scale DA, the unknown property function associated with each ensemble member is upscaled to a grid significantly coarser than the original reservoir simulator grid. The grid coarsening is automatic, ensemble-specific and non-uniform. The selection of regions where the grid can be coarsened without introducing too large modelling errors is performed using a second-generation wavelet transform allowing for seamless handling of non-dyadic grids and inactive grid cells. An inexpensive local-local upscaling is performed on each ensemble member. A DA algorithm that restarts from initial time is utilized, which avoids the need for downscaling. Since the DA computational cost roughly equals the number of ensemble members times the cost of a single forward simulation, coarse-scale DA allows for a significant increase in the number of ensemble members at the same computational cost as standard DA with localization. Fixing the computational cost for both approaches, the quality of coarse-scale DA is compared to that of standard DA with localization (using state-of-the-art localization techniques) on examples spanning a large degree of variability. It is found that coarse-scale DA is more robust with respect to variation in example type than each of the localization techniques considered with standard DA. Although the paper is concerned with two spatial dimensions, coarse-scale DA is easily extendible to three spatial dimensions, where it is expected that its advantage with respect to standard DA with localization will increase. 相似文献
58.
59.
Karl Thomas Hjelmervik Jan Kristian Jensen Petter ?stenstad Atle Ommundsen 《Ocean Dynamics》2012,62(2):253-264
Sonar performance modeling is crucial for submarine and anti–submarine operations. The validity of sonar performance models
is generally limited by environmental uncertainty, and particularly uncertainty in the vertical sound speed profile (SSP).
Rapid environmental assessment (REA) products, such as oceanographic surveys and ocean models may be used to reduce this uncertainty
prior to sonar operations. Empirical orthogonal functions (EOF) applied on the SSPs inherently take into account the vertical
gradients and therefore the acoustic properties. We present a method that employs EOFs and a grouping algorithm to divide
a large group of SSPs from an ocean model simulation into smaller groups with similar SSP characteristics. Such groups are
henceforth called acoustically stable groups. Each group represents a subset in space and time within the ocean model domain.
Regions with low acoustic variability contain large and geographically contiguous acoustically stable groups. In contrast,
small or fragmented acoustically stable groups are found in regions with high acoustic variability. The main output is a map
of the group distribution. This is a REA product in itself, but the map may also be used as a planning aid for REA survey
missions. 相似文献
60.