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111.
A Bayesian approach to palaeoecological environmental reconstruction deriving from the unimodal responses generally exhibited
by organisms to an environmental gradient is described. The approach uses Bayesian model selection to calculate a collection
of probability-weighted, species-specific response curves (SRCs) for each taxon within a training set, with an explicit treatment
for zero abundances. These SRCs are used to reconstruct the environmental variable from sub-fossilised assemblages. The approach
enables a substantial increase in computational efficiency (several orders of magnitude) over existing Bayesian methodologies.
The model is developed from the Surface Water Acidification Programme (SWAP) training set and is demonstrated to exhibit comparable
predictive power to existing Weighted Averaging and Maximum Likelihood methodologies, though with improvements in bias; the
additional explanatory power of the Bayesian approach lies in an explicit calculation of uncertainty for each individual reconstruction.
The model is applied to reconstruct the Holocene acidification history of the Round Loch of Glenhead, including a reconstruction
of recent recovery derived from sediment trap data.
The Bayesian reconstructions display similar trends to conventional (Weighted Averaging Partial Least Squares) reconstructions
but provide a better reconstruction of extreme pH and are more sensitive to small changes in diatom assemblages. The validity
of the posteriors as an apparently meaningful representation of assemblage-specific uncertainty and the high computational
efficiency of the approach open up the possibility of highly constrained multiproxy reconstructions. 相似文献
112.
Diatom-inferred lake level from near-shore cores in a drainage lake from the Experimental Lakes Area,northwestern Ontario,Canada 总被引:1,自引:0,他引:1
We inferred late Holocene lake-level changes from a suite of near-shore gravity cores collected in Lake 239 (Rawson Lake),
a headwater lake in the Experimental Lakes Area, northwestern Ontario. Results were reproduced across all cores. A gravity
core from the deep central basin was very similar to the near-shore cores with respect to trends in the percent abundance
of the dominant diatom taxon, Cylcotella stelligera. The central basin, however, does not provide a sensitive site for reconstruction of lake-level changes because of the insensitivity
of the diatom model at very high percentages of C. stelligera and other planktonic taxa. Quantitative estimates of lake level are based on a diatom-inferred depth model that was developed
from surficial sediments collected along several depth transects in Lake 239. The lake-level reconstructions during the past
~3,000 years indicate that lake depth varied on average by ±2 m from present-day conditions, with maximum rises of ~3–4 m
and maximum declines of ~3.5–5 m. The diatom-inferred depth record indicates several periods of persistent low levels during
the nineteenth century, from ~900 to 1100 AD, and for extended periods prior to ~1,500 years ago. Periods of inferred high
lake levels occurred from ~500 to 900 AD and ~1100 to 1650 AD. Our findings suggest that near-shore sediments from small drainage
lakes in humid climates can be used to assess long-term fluctuations in lake level and water availability. 相似文献
113.
We examined the relationship between three key environmental variables (water depth, loss-on-ignition, and bottom-water temperature)
and fossil chironomid distributions sampled from within-lake gradients in three small, moderately deep (18–35 m), maar lakes
on St Michael Island, western Alaska. Site-specific (one lake, 29 samples) and local (three lakes, 87 samples) inference models
for reconstructing water depth were developed using partial least squares regression and calibration. These models and a previously
published regional model (136 lakes, one central-lake sample from each) are used to infer water depths from 78 fossil samples
spanning the last ~30,000 14C years B.P. at Zagoskin Lake. Although the site-specific [r
2
boot = 0.90, root mean square error of prediction (RMSEP) = 1.76] and local (r
boot2 = 0.68, RMSEP = 4.36) inference models have better performance statistics than the regional model, few clear trends among
all three models exist in the lake-level reconstruction. We propose that multiple, within-lake sampling of gradients can be
used to improve the performance statistics of water-depth transfer functions and ultimately reconstruct paleohydrology in
regions known to exhibit large fluctuations in moisture balance through time given that: (1) adequate analogs are established
and (2) taphonomic processes important to benthic invertebrate remains are more fully understood. 相似文献
114.
115.
In this paper, modal parameters of a layered soil system comprising of a soft clay layer overlying a dense sand layer are identified from accelerometer recordings in a centrifuge test. For the first time, the subspace state space system identification (4SID) method was employed to identify the natural frequencies, damping ratios, and complex valued mode shapes while considering the non-proportional damping in a soil system. A brief review of system identification concepts needed for application of the 4SID techniques to structural modal identification is provided in the paper. The identified natural frequencies were validated against those estimated by transfer function spectra. The computed normal mode shapes were compared with closed-form solutions obtained from the one-dimensional shear wave propagation equation. The identified modal parameters were then employed to synthesize state space prediction models which were subsequently used to simulate the soil response to three successive base motions. The identified models captured acceleration time-histories and corresponding Fourier spectra reasonably well in the small and moderate shaking events. In the stronger third shaking event, the model performed well at greater soil depths, but was less accurate near the surface where nonlinearities dominated. 相似文献
116.
小波超分辨率重建算法及其在SPOT影像中的应用 总被引:1,自引:0,他引:1
影像超分辨率重建就是从一系列质量较差、分辨率较低的图像来重建图像质量更好、空间分辨率更高的影像的算法.在将所有低分辨率影像纳入同一参考格网中考虑的情况下,低分辨率数据相当于一非规则采样的交错采样数据.本文在多分辨率分析的基础上对基于小波的影像超分辨率重建理论进行介绍,并将现有的小波超分辨率重建算法推广到更一般的运动模型,以充分利用交错采样数据的内在规律性和结构特征,同时针对SPOT影像的特点,分析SPOT影像的调制传送函数,对SPOT重建影像进行包括去噪与解卷积的复原后处理.最后给出基于小波的SPOT影像超分辨率重建结果,表明遥感影像的超分辨率重建在应用中取得进展. 相似文献
117.
The Direct Matrix Method Interaction Theory (IT) proposed by Kagemoto and Yue [1] speeds up the computation of hydrodynamic coefficients for large arrays of bodies when compared to direct calculations using standard Boundary Element Method (BEM) solvers. One of the most computationally expensive parts of the matrix method is the calculation of two hydrodynamic operators, known as Diffraction Transfer Matrix (DTM) and Radiation Characteristics (RC), which describe the way an isolated geometry scatters and radiates waves, respectively. A third operator, called Force Transfer Matrix (FTM), was introduced by McNatt et al. [2] to facilitate the calculation of the forces exerted on the bodies. In this paper, a novel set of relations between the FTM and RC components is obtained using the Kochin functions specific to the cylindrical basis solutions. They extend the classical Haskind's relations, valid with incident plane waves, to the cylindrical components of the scattered and radiated fields. Moreover, an alternative demonstration of the identities is given, which does not rely on the far-field asymptotic representation of the potential. Additional expressions are provided that relate the hydrodynamic coefficients and the RC for isolated bodies as well as for arrays, and numerical checking of the derived mathematical expressions is presented. These new relations can be used to speed up calculation of the hydrodynamic operators required for the use of the IT and to test its accuracy. 相似文献
118.
景区周边社区居民对旅游开发的参与度分析——南水北调中线渠首景区实证研究 总被引:2,自引:0,他引:2
采用问卷调查、现场访谈等方法对南水北调中线渠首景区概况、社区居民基本状况、社区发展情况、社区居民对景区旅游开发的态度和社区居民参与景区旅游开发的现状进行深入调查,将调查数据统计分析,结合相关理论,得出南水北调中线渠首景区社区居民参与旅游开发的结果与结论:居民对当地旅游开发的支持程度较高,有一定的主动参与意识,与政府和投资商合作的意愿较强,但居民参与旅游开发处于较低层次,参与程度受到多种因素影响,需要构建合理的参与机制和模式。 相似文献
119.
南水北调中线工程对汉江中下游流域生态环境影响的综合评价 总被引:8,自引:0,他引:8
南水北调中线工程的实施,对汉江中下游流域的生态环境会造成一系列的影响,对其进行综合评价具有重要意义。在探讨评价指标体系建立原则的基础上,构建了南水北调中线工程对汉江中下游流域生态环境影响的综合评价指标体系;对各指标的影响分值进行了计算,并采用层次分析法了计算各指标的权重,在此基础上采用指标加权求和法对生态环境影响进行综合评价。评价结果表明:南水北调中线工程的实施,对汉江中下游流域生态环境的综合影响程度为-37.91%~-64.46%,相比调水前,生态环境处于强烈或明显负影响状态;分变量的影响程度排序依次为水质变量、土壤地质变量、社会生产变量、水生生物变量、水资源变量和气候变量,其中对水质变量、土壤地质变量、社会生产变量和水生生物变量的影响幅度上限均超过了-40%,对水资源变量的影响幅度也超过了-20%,影响较大,而对气象变量的影响幅度几乎为零。 相似文献
120.