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281.
This study presents a framework for numerical simulations based upon micromechanical parameters in modeling progressive failures
of heterogeneous rock specimens under compression. In our numerical simulations, a Weibull distribution of the strength and
elastic properties of the finite elements is assumed, and the associated Weibull parameters are estimated in terms of microstructural
properties, such as crack size distribution and grain size, through microscopic observations of microcracks. The main uncertainty
in this procedure lies on the fact that various ways can be used to formulate a ``microcrack size distribution' in relating
to the Weibull parameters. As one possible choice, the present study uses the number of counted cracks per unit scanned volume
per grain size to formulate the crack distributions. Finally, as a tool, the Rock Failure Process Analysis code (RFPA2D) is adopted for simulating the progressive failure and microseismicity of heterogeneous rocks by using an elastic-damage
finite-element approach. To verify our framework, compression tests on marble specimens are conducted, and the measured acoustic
emissions (AE) are compared with those predicted by the numerical simulations. The mode of failure, compressive strength and
AE pattern of our simulations basically agree with experimental observations. 相似文献
282.
A GIS-based decision support system, which incorporates local topographic and rainfall effects on debris flow vulnerability
is developed. Rainfall at a scale compatible with the digital elevation model resolution is obtained using a neural network
with a wind-induced topographic effect and rainfall derived from satellite rain estimates and an adaptive inverse distance
weight method (WTNN). The technique is tested using data collected during the passage of typhoon Tori-Ji on July 2001 over
central Taiwan. Numerous debris flows triggered by the typhoon were used as control for the study. Our results show that the
WTNN technique outperforms other interpolation techniques including adaptive inversed distance weight (AIDW), simple kriging
(SK), co-kriging, and multiple linear regression using gauge, and topographic parameters. Multiple remotely-sensed, fuzzy-based
debris-flow susceptibility parameters are used to describe the characteristics of watersheds. Non-linear, multi-variant regressions
using the WTNN derived rainfall and topography factors are derived using self-organizing maps (SOM) for the debris flow vulnerability
assessment. An index of vulnerability representing the degrees of hazard is implemented in a GIS-based decision support system
by which a decision maker can assess debris flow vulnerability. 相似文献
283.
This paper studies the sedimentation–consolidation of a double porosity material, such as lumpy clay. Large displacements and finite strains are accounted for in a multidimensional setting. Fundamental equations are derived using a phenomenological approach and non-equilibrium thermodynamics, as set out by Coussy [Coussy, Poromechanics, Wiley, Chichester, 2004]. These equations particularise to three non-linear partial differential equations in one dimensional context. Numerical implementation in a finite element code is currently being undertaken. 相似文献
284.
285.
Based on a case study in a Thai forest reserve, this article compares two modes of ‘reading’ the forest - official and local forest classification systems - and discusses how they imply different ideas about the forest, and how these competing knowledges interact with the politics of forest governance. Forest classification conventions are shown to slip, as ‘facts’ about the forest, from their origins in extraction-oriented forestry to the realm of conservation. Through a comparison of conventional vegetation classifications used in the state’s governance of the Thung Yai Naresuan Wildlife Sanctuary in Thailand, with the classificatory systems of resident Pwo Karen communities, this paper examines the slippage of conventional classifications through various uses and the emphases placed by competing representations of the forest within the context of conservation politics in Thailand. It was found that conventional classifications continued to prioritise the silvicultural potential of trees within a conservation context, downplaying other notions of forests - such as their importance to livelihoods and as lived spaces - which are present in Karen classifications. 相似文献
286.
Melisa C. Wong 《Estuaries and Coasts》2018,41(2):536-548
In nearshore ecosystems, habitats with emergent structure are often assumed to have higher ecosystem functioning than habitats lacking structure. However, such habitat-specific differences may depend on the surrounding environment. In this study, I examine the robustness of habitat-specific differences in ecosystem functioning for seagrass (Zostera marina) and adjacent bare soft sediments across varying environmental conditions on the Atlantic Coast of Nova Scotia, Canada, using secondary production as a metric. I also examine relationships of community secondary production and faunal structure with measured environmental variables (water depth, temperature, exposure, sediment, and plant properties). Benthic secondary production (invertebrates ≥500 μm) was higher in seagrass compared to bare sediments only at exposed sites with sandy sediments low in organic content, deep and cool water, and high belowground plant biomass. A regression relating community secondary production to the environmental variables explained 56% of the variance, while a constrained ordination explained 16% of the community structure. Important environmental determinants of community production were shoot density, temperature, depth, exposure, sediment organic content, and belowground plant biomass. Community structure was influenced by these variables plus sediment sand content and canopy height. This study shows that habitat-specific differences in secondary production may not be consistent across varying environmental conditions. Furthermore, seagrass beds are not always associated with higher ecosystem functioning than adjacent bare sediment. Both the surrounding environmental conditions and the presence of habitat structure should be considered for optimal management of nearshore ecosystems. 相似文献
287.
Lai Teck Yew Loo Vera Hui Wong Vun Ket Wong Kwong Soon 《Geotechnical and Geological Engineering》2022,40(6):3169-3190
Geotechnical and Geological Engineering - The durability of clay-bearing rocks has been a concern to the construction industry. Extensive research have been conducted to determine the durability of... 相似文献
288.
Natural Hazards - Recent years have seen growing interest in enabling volunteers to play a more pronounced role in disaster response, and yet efforts to systematically analyse this crisis volunteer... 相似文献
289.
摘 要 通过对湘中南龙潭煤系不同煤级煤样的煤岩学和有机地球化学研究概括了湘中南
龙潭煤系煤的有机显微组成和主要有机地球化学特征指出其中的气煤、肥煤和焦煤是具有
较高生烃潜力的烃源岩壳质组和基质镜质体是这一阶段煤中的主要生烃组分。 相似文献
290.
Seasonal changes in imposex and tissue burden of butyltin compounds in Thais clavigera populations along the coastal area of Mirs Bay, China 总被引:1,自引:0,他引:1
We assessed the current status of tributyltin (TBT) contamination of Thais clavigera (Gastropoda) along the coastal area of Mirs Bay, China for the first time. The snail samples were collected from 10 different sites in the summer (June) and winter (December) of 2006, respectively. They were analyzed for imposex status, i.e. relative penis size index (RPSI) and vas deferens sequence index (VDSI), followed by quantification of butyltins in their tissues. Most of the collected females suffered from imposex, but the level of butyltin contamination varied with the distance from Yantian Port, which is currently the fourth busiest container port in the world. The tissue concentration of TBT varied with season. For a particular site, the winter samples in general contained much higher concentration of TBT than the summer samples. RPSI, VDSI and organotin concentrations were higher in T. clavigera collected from sites closer to the Port, such as the Seafood Street and Kat O. Both RPSI and VDSI were positively correlated with the tissue burden of tributyltin. VDSI exhibited little seasonal variability, whereas RPSI showed marked seasonal variability, with lower values in the summer samples. The current results will serve as an important reference for long-term monitoring of butyltin contamination in this area. 相似文献