全文获取类型
收费全文 | 126篇 |
免费 | 0篇 |
专业分类
测绘学 | 42篇 |
地球物理 | 36篇 |
地质学 | 30篇 |
海洋学 | 9篇 |
天文学 | 1篇 |
自然地理 | 8篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2018年 | 2篇 |
2015年 | 2篇 |
2014年 | 1篇 |
2013年 | 3篇 |
2012年 | 6篇 |
2011年 | 7篇 |
2010年 | 2篇 |
2009年 | 7篇 |
2008年 | 4篇 |
2007年 | 3篇 |
2006年 | 3篇 |
2005年 | 7篇 |
2004年 | 4篇 |
2003年 | 7篇 |
2002年 | 4篇 |
2001年 | 6篇 |
2000年 | 4篇 |
1999年 | 5篇 |
1998年 | 5篇 |
1997年 | 2篇 |
1996年 | 1篇 |
1995年 | 1篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 4篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1988年 | 3篇 |
1985年 | 2篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 1篇 |
1981年 | 3篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1976年 | 1篇 |
排序方式: 共有126条查询结果,搜索用时 15 毫秒
51.
Based on Vening Meinez-Moritz global inverse isostatic problem, the Moho density contrast is formulated as that of finding
a solution of a Fredholm integral equation of the first kind. We present solutions to this equation by combining global models
of gravity (EGM08), topography (DTM2006) and seismic crust (CRUST2.0) to a resolution of 2°×2°. The test computations yielded
Moho density contrasts ranging from 81.5 kg/m3 (in Pacific) to 988 kg/m3 (Tibet), with averages of 678 ± 78 and 334 ± 108 kg/m3 for continental and oceanic regions, respectively, and a global average of 448 ± 187 kg/m3. Estimated Moho depths range from 8 to 75 km with continental and oceanic averages of 36.6 ± 5.3 km and 12.9 ± 5.8 km, respectively,
and a global average of 21 ± 12.5 km. 相似文献
52.
Equilibrium reactions involving Cu(II) and As(V) have been studied with respect to formation of complexes in aqueous solutions as well as formation of solid phases. Potentiometric titrations performed at 25 °C (I = 0.1 M Na(Cl)) and at different Cu to As ratios gave no evidence for the existence of Cu(II) arsenate complexes in solution below the pH of the precipitation boundaries (pH ≈ 4), irrespective of the Cu to As ratio and pH. Mixing of solutions of Cu(II) and As(V) at different proportions and adjusting pH to values ranging from 4 to 9 resulted in precipitation of five different solid phases. The elemental composition of the solids was determined using X-ray Photoelectron Spectroscopy, and Environmental Scanning Microscopy-Field Emission Gun equipped with an energy dispersive spectroscopy detector. The average Cu/As ratio was determined by dissolving the solids. Total soluble concentrations of the components Cu(II) and As(V), as well as the basicity of the solid phases were determined by analysis of aqueous solutions. Based upon these experimental data the stoichiometric composition of the solid phases and their stability were determined. The resulting equilibrium model includes the solid phases Cu3(AsO4)2, Cu3(AsO4)(OH)3, Cu2(AsO4)(OH), Cu5Na(HAsO4)(AsO4)3 and Cu5Na2AsO4)4, where Cu5Na(HAsO4)(AsO4)3 and Cu5Na2(AsO4)4 have not been reported previously. In 0.1 M Na(Cl), Na+ was found to be a significant component in two of the solid phases. The Cu5Na2(AsO4)4 was formed in weakly alkaline conditions with pNa < 2.5. Stability constants for all solid phases have been determined. Distribution diagrams as well as predominance area (pNa-pH) diagrams are presented to illustrate stability fields of the different solid phases. 相似文献
53.
The AlOx1-3 (Ox = oxalate) species were identified in 0.6 M aqueous NaCl by 13C nuclear magnetic resonance (NMR). Rate constants and activation parameters for intramolecular cis/trans isomerization of the Werner-type AlOx2− complex (k(298 K) = 5 s−1, ΔH# = 67 ± 5 kJ mol−1, ΔS# = −6 ± 6 J mol−1 K−1, the rate determining step could be the breaking of the Al-O(C=O) bond) and a very slow intermolecular ligand exchange reaction of AlOx33− complex and the free ligand (k30(298 K) = 6.6 · 10−5 s−1, ΔH# = 164 ± 17 kJ mol−1, ΔS# = 225 ± 51 J mol−1 K−1, D/Id mechanism) were determined by dynamic 1D and 2D 13C NMR measurements. Mixed complexes, AlFOx, AlFOx22-, AlF2Ox−, and AlF2Ox23-, with overall stability (logβ) of 11.53 ± 0.03, 15.67 ± 0.03, 15.74 ± 0.02, and 19.10 ± 0.04 were measured by potentiometry using pH- and fluoride-selective electrodes and confirmed by 13C and19F NMR. The role of these complexes in gibbsite dissolution was modeled. The mixed Al(III)-Ox2--F− complexes have to be considered as the chemical speciation of Al(III) in natural waters is discussed. 相似文献
54.
The effect of downward continuation of gravity anomaly to sea level in Stokes' formula 总被引:1,自引:0,他引:1
L. E. Sjöberg 《Journal of Geodesy》2001,74(11-12):796-804
55.
56.
57.
L. E. Sjöberg 《Journal of Geodesy》1999,73(3):118-124
With access to dual-frequency pseudorange and phase Global Positioning System (GPS) data, the wide-lane ambiguity can easily
be fixed. Advantage is taken of this information in the linear combination of the above four observables for base ambiguity
estimation (i.e. of N
1 and N
2). Starting points for our analysis are the Best Linear Unbiased Estimators BLUE1 and BLUE2. BLUE1 is the best one (with minimum mean square error, MSE) if the ionosphere effect is negligible. If this is not the case, BLUE2 has the smallest variance, but not necessarily the least mean square error. Hence, both estimators may suffer from a non-optimal
treatment of the ionosphere bias. BLUE1 ignores possible ionosphere bias, while BLUE2 compensates for this bias in a less favourable way by eliminating it at the price of increased noise. As an alternative,
linear estimators are derived, which make a compromise between the ionosphere bias and the random observation errors. This
leads to the derivation of the Best Linear Estimator (BLE) and the Restricted Best Linear Estimator (RBLE) with minimum MSE.
The former is generally not very useful, while the RBLE is recommended for practical use. It is shown that the MSE of the
RBLE is limited by the variances of BLUE1 and BLUE2, i.e.
However, as is always the case with a BLE, it cannot be used strictly: some parameter (in this case the ionosphere bias) must
be approximately known.
Received: 25 June 1997 / Accepted: 16 November 1998 相似文献
58.
L. E. Sjöberg 《Journal of Geodesy》2002,76(2):115-120
The problems of intersection on the sphere and ellipsoid are studied. On the sphere, the problem of intersection along great
circles is explicitly solved. On the ellipsoid, each of the problems of intersection along arcs of constant azimuth, normal
sections and geodesic lines is solved without any limitation on arc length. In the last case the solution is based on the
Newton–Raphson method of iteration including numerical integration.
Received: 11 April 2001 / Accepted: 3 September 2001 相似文献
59.
New views of the spherical Bouguer gravity anomaly 总被引:7,自引:0,他引:7
P. Vaníek R. Tenzer L. E. Sjöberg Z. Martinec W. E. Featherstone 《Geophysical Journal International》2004,159(2):460-472
60.
Any errors in digital elevation models (DEMs) will introduce errors directly in gravity anomalies and geoid models when used
in interpolating Bouguer gravity anomalies. Errors are also propagated into the geoid model by the topographic and downward
continuation (DWC) corrections in the application of Stokes’s formula. The effects of these errors are assessed by the evaluation
of the absolute accuracy of nine independent DEMs for the Iran region. It is shown that the improvement in using the high-resolution
Shuttle Radar Topography Mission (SRTM) data versus previously available DEMs in gridding of gravity anomalies, terrain corrections
and DWC effects for the geoid model are significant. Based on the Iranian GPS/levelling network data, we estimate the absolute
vertical accuracy of the SRTM in Iran to be 6.5 m, which is much better than the estimated global accuracy of the SRTM (say
16 m). Hence, this DEM has a comparable accuracy to a current photogrammetric high-resolution DEM of Iran under development.
We also found very large differences between the GLOBE and SRTM models on the range of −750 to 550 m. This difference causes
an error in the range of −160 to 140 mGal in interpolating surface gravity anomalies and −60 to 60 mGal in simple Bouguer
anomaly correction terms. In the view of geoid heights, we found large differences between the use of GLOBE and SRTM DEMs,
in the range of −1.1 to 1 m for the study area. The terrain correction of the geoid model at selected GPS/levelling points
only differs by 3 cm for these two DEMs. 相似文献