全文获取类型
收费全文 | 77篇 |
免费 | 2篇 |
专业分类
测绘学 | 9篇 |
大气科学 | 1篇 |
地球物理 | 12篇 |
地质学 | 40篇 |
天文学 | 12篇 |
自然地理 | 5篇 |
出版年
2018年 | 1篇 |
2017年 | 1篇 |
2016年 | 2篇 |
2015年 | 1篇 |
2014年 | 2篇 |
2013年 | 1篇 |
2012年 | 1篇 |
2011年 | 5篇 |
2010年 | 3篇 |
2009年 | 2篇 |
2008年 | 9篇 |
2007年 | 4篇 |
2006年 | 6篇 |
2005年 | 2篇 |
2004年 | 8篇 |
2003年 | 5篇 |
2002年 | 4篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1999年 | 1篇 |
1998年 | 1篇 |
1997年 | 1篇 |
1995年 | 1篇 |
1992年 | 1篇 |
1989年 | 2篇 |
1988年 | 3篇 |
1987年 | 1篇 |
1986年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1974年 | 2篇 |
1973年 | 2篇 |
1971年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有79条查询结果,搜索用时 15 毫秒
1.
Burkhard Fuchs 《Astrophysics and Space Science》2003,284(2):719-722
An update of the set of low surface brightness galaxies is presented which can be used to set constraints on the otherwise
ambiguous decompositions of their rotation curves into contributions due to the various components of the galaxies. The selected
galaxies show all clear spiral structure and arguments of density wave theory of galactic spiral arms are used to estimate
the masses of the galactic disks. Again these estimates seem to indicate that the disks of low surface brightness galaxies
might be much more massive than currently thought. This puzzling result contradicts stellar population synthesis models. This
would mean also that low surface brightness galaxies are not dominated by dark matter in their inner parts.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
2.
On the multivariate total least-squares approach to empirical coordinate transformations. Three algorithms 总被引:2,自引:1,他引:1
The multivariate total least-squares (MTLS) approach aims at estimating a matrix of parameters, Ξ, from a linear model (Y−E
Y
= (X−E
X
) · Ξ) that includes an observation matrix, Y, another observation matrix, X, and matrices of randomly distributed errors, E
Y
and E
X
. Two special cases of the MTLS approach include the standard multivariate least-squares approach where only the observation
matrix, Y, is perturbed by random errors and, on the other hand, the data least-squares approach where only the coefficient matrix
X is affected by random errors. In a previous contribution, the authors derived an iterative algorithm to solve the MTLS problem
by using the nonlinear Euler–Lagrange conditions. In this contribution, new lemmas are developed to analyze the iterative
algorithm, modify it, and compare it with a new ‘closed form’ solution that is based on the singular-value decomposition.
For an application, the total least-squares approach is used to estimate the affine transformation parameters that convert
cadastral data from the old to the new Israeli datum. Technical aspects of this approach, such as scaling the data and fixing
the columns in the coefficient matrix are investigated. This case study illuminates the issue of “symmetry” in the treatment
of two sets of coordinates for identical point fields, a topic that had already been emphasized by Teunissen (1989, Festschrift
to Torben Krarup, Geodetic Institute Bull no. 58, Copenhagen, Denmark, pp 335–342). The differences between the standard least-squares
and the TLS approach are analyzed in terms of the estimated variance component and a first-order approximation of the dispersion
matrix of the estimated parameters. 相似文献
3.
4.
Sven O. Franz Lorenz Schwark Cathrin Brüchmann Burkhard Scharf Ralf Klingel Jon D. Van Alstine Namık Çagatay Umut B. Ülgen 《Journal of Paleolimnology》2006,35(4):715-736
A limnogeological reconnaissance study was carried out on Lake Iznik, located in the southeast of the Marmara region of Turkey,
involving a seismic survey and collection of short sediment cores. This lake is located on the middle branch of the North
Anatolian Fault Zone (NAFZ), a transform plate boundary between the Eurasian and Anatolian Plates. It is, therefore, tectonically
active and offers an opportunity to investigate the interplay of sedimentary and seismo-tectonic processes, as well as climate
change and human impact in the region. Short cores of the three sub-basins, maximum length of 35.5 cm, recovered non-laminated,
blackish clays and silts with varying amounts of biogenic and minerogenic (allochthonous, autochthonous) material, which documented
almost the last 80 years of deposition and environmental history. High sedimentation rates in the deeper core sections are
accompanied by changes in land use (conversion of woodland to farmland) in the northern areas of Lake Iznik, which caused
the deposition of more weathered material (high K/Na ratios) and higher contents of Mn in the lake. A tendency towards eutrophic
conditions within the last 20 years is indicated by high nutrient content (N, TOC, P), decreasing C/N-ratios, and characteristic
diatom and cladoceran associations. Also increased pollution is revealed by higher Pb, Cu, and Zn contents and increased supply
of human and animal faeces (high coprostanol content) during the last two decades. But simultaneous lower sedimentation rates
towards the core tops complicate the reconstruction of recent and past eutrophication and pollution states of Lake Iznik.
This requires an extension of the pilot study and deeper sediment cores, to recover non-anthropogenic influenced sediment
levels. 相似文献
5.
Biocrusts abound in southern Israel, covering the Hallamish dune field near Nizzana (NIZ) in the Negev (mean annual precipitation of 95 mm) and the coast of Nizzanim (NIM) near Ashdod (mean annual precipitation of 500 mm). While the hydrological response of the NIZ crust to natural rain events was thoroughly investigated, no data is available on the hydrological response of the NIM crust. Runoff was monitored in runoff plots during the years 2005–2008, and in addition, sprinkling experiments were carried out on NIM and NIZ crusts. For the evaluation of the possible factors that may control runoff initiation, fine content of the parent material, crust thickness, compressional strength, hydrophobicity, surface microrelief, organic matter, biomass (chlorophyll a and total carbohydrates) and the crust's species composition of NIM were studied and compared to that of NIZ. The data showed that in comparison to the NIZ crust that readily generated runoff, no runoff was produced by the NIM crust. This was so despite the fact that (1) Microculeus vaginatus predominated in both crusts, (2) the substantially higher rain intensities in NIM, (3) the greater thickness and higher chlorophyll content and (4) the lower microrelief at NIM in comparison to NIZ. The lack of runoff in NIM was explained by its low amounts of exopolysaccharides that did not suffice to affectively clog the surface and in turn to facilitate runoff initiation. The absence of runoff and its consequences on the NIM ecosystem are discussed. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
6.
Burkhard Schaffrin 《Journal of Geodesy》1989,63(4):395-404
The now classical collocation method in geodesy has been derived byH. Moritz (1970; 1973) within an appropriate Mixed Linear Model. According toB. Schaffrin (1985; 1986) even a generalized form of the collocation solution can be proved to represent a combined estimation/prediction
procedure of typeBLUUE (Best Linear Uniformly Unbiased Estimation) for the fixed parameters, and of type inhomBLIP (Best inhomogeneously LInear Prediction) for the random effects with not necessarily zero expectation. Moreover, “robust collocation” has been introduced by means of homBLUP (Best homogeneously Linear weakly Unbiased Prediction) for the random effects together with a suitableLUUE for the fixed parameters. Here we present anequivalence theorem which states that the robust collocation solution in theoriginal Mixed Linear Model can identically be derived as traditionalLESS (LEast Squares Solution) in amodified Mixed Linear Model without using artifacts like “pseudo-observations”. This allows us a nice interpretation of “robust collocation”
as an adjustment technique in the presence of “weak prior information”. 相似文献
7.
Burkhard Schaffrin 《Journal of Geodesy》1987,61(3):276-280
The Bayesian estimates
b of the standard deviation σ in a linear model—as needed for the evaluation of reliability—is well known to be proportional
to the square root of the Bayesian estimate (s
2)
b
of the variance component σ2 by a proportionality factor
involving the ratio of Gamma functions. However, in analogy to the case of the respective unbiased estimates, the troublesome
exact computation ofa
b may be avoided by a simple approximation which turns out to be good enough for most applications even if the degree of freedom
ν is rather small.
Paper presented to the Int. Conf. on “Practical Bayesian Statistics”, Cambridge (U.K.), 8.–11. July 1986. 相似文献
8.
Giada Iacono Marziano Burkhard C. Schmidt Daniela Dolfi 《Journal of Volcanology and Geothermal Research》2007
Equilibrium and disequilibrium degassing of a volatile phase from a magma of K-phonolitic composition was investigated to assess its behavior upon ascent. Decompression experiments were conducted in Ar-pressurized externally heated pressure vessels at superliquidus temperature (1050 °C), in the pressure range 10–200 MPa using pure water as fluid phase. All experiments were equilibrated at 200 MPa and then decompressed to lower pressures with rates varying from 0.0028 to 4.8 MPa/s. Isobaric saturation experiments were performed at the same temperature and at 900–950 °C to determine the equilibrium water solubility in the pressure range 30–250 MPa. The glasses obtained from decompression experiments were analyzed for their dissolved water content, vesicularity and bubble size distribution. All decompressed samples presented a first event of bubble nucleation at the capsule–melt interface. Homogeneous bubble nucleation in the melt only occurred in fast-decompressed experiments (4.8 and 1.7 MPa/s), for ΔP ≅ 100 MPa. For these decompression rates high water over-saturations were maintained until a rapid exsolution was triggered at ΔP > 150 MPa. For slower rates (0.0028, 0.024, 0.17 MPa/s) the degassing of the melt took place by diffusive growth of the bubbles nucleating at the capsule–melt interface. This process sensibly reduced water over-saturation in the melt, preventing homogeneous nucleation to occur. For decompression rates of 0.024 and 0.17 MPa/s low water over-saturations were attained in the melt, gradually declining toward equilibrium concentrations at low pressures. A near-equilibrium degassing path was observed for a decompression rate of 0.0028 MPa/s. Experimental data combined with natural pumice textures suggest that both homogeneous and heterogeneous bubble nucleations occurred in the phonolitic magma during the AD 79 Vesuvius plinian event. Homogeneous bubble nucleation probably occurred at a depth of ∼ 3 km, in response to a fast decompression of the magma during the ascent. 相似文献
9.
Doreen E. AMES Ingrid M. KJARSGAARD Kevin O. POPE Burkhard DRESSLER Mark PILKINGTON 《Meteoritics & planetary science》2004,39(7):1145-1167
Abstract The 65 Ma Chicxulub impact crater formed in the shallow coastal marine shelf of the Yucatán Platform in Mexico. Impacts into water‐rich environments provide heat and geological structures that generate and focus sub‐seafloor convective hydrothermal systems. Core from the Yaxcopoil‐1 (Yax‐1) hole, drilled by the Chicxulub Scientific Drilling Project (CSDP), allowed testing for the presence of an impact‐induced hydrothermal system by: a) characterizing the secondary alteration of the 100 m‐thick impactite sequence; and b) testing for a chemical input into the lower Tertiary sediments that would reflect aquagene hydrothermal plume deposition. Interaction of the Yax‐1 impactites with seawater is evident through redeposition of the suevites (unit 1), secondary alteration mineral assemblages, and the subaqueous depositional environment for the lower Tertiary carbonates immediately overlying the impactites. The least‐altered silicate melt composition intersected in Yax‐1 is that of a calc‐alkaline basaltic andesite with 53.4–56 wt% SiO2(volatile‐free). The primary mineralogy consists of fine microlites of diopside, plagioclase (mainly Ab 47), ternary feldspar (Ab 37 to 77), and trace apatite, titanite, and zircon. The overprinting alteration mineral assemblage is characterized by Mg‐saponite, K‐montmorillonite, celadonite, K‐feldspar, albite, Fe‐oxides, and late Ca and Mg carbonates. Mg and K metasomatism resulted from seawater interaction with the suevitic rocks producing smectite‐K‐feldspar assemblages in the absence of any mixed layer clay minerals, illite, or chlorite. Rare pyrite, sphalerite, galena, and chalcopyrite occur near the base of the impactites. These secondary alteration minerals formed by low temperature (0–150°C) oxidation and fixation of alkalis due to the interaction of glass‐rich suevite with down‐welling seawater in the outer annular trough intersected at Yax‐1. The alteration represents a cold, Mg‐K‐rich seawater recharge zone, possibly recharging higher temperature hydrothermal activity proposed in the central impact basin. Hydrothermal metal input into the Tertiary ocean is shown by elevated Ni, Ag, Au, Bi, and Te concentrations in marcasite and Cd and Ga in sphalerite in the basal 25 m of the Tertiary carbonates in Yax‐1. The lower Tertiary trace element signature reflects hydrothermal metal remobilization from a mafic source rock and is indicative of hydrothermal venting of evolved seawater into the Tertiary ocean from an impact‐generated hydrothermal convective system. 相似文献
10.