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71.
Lambert Wanninger 《GPS Solutions》2009,13(2):133-139
Antenna changes at GNSS reference stations frequently produce discontinuities in the coordinate time series. These apparent
position shifts are mainly caused by changes of carrier-phase multipath effects and different errors in the antenna phase
center corrections. A monitoring method was developed and successfully tested, which requires additional GNSS observations
from a local, temporary reference station. Changes of carrier-phase measurement errors due to the antenna change are determined
and stored in L1 and L2 phase maps. These phase maps provide corrections to be applied either to the observation data obtained
before the antenna change or to the observation data obtained after the antenna change. The observation corrections are able
to remove coordinate discontinuities independent of the selected coordinate estimation algorithm.
相似文献
Lambert WanningerEmail: |
72.
Ute C. Herzfeld Craig S. Lingle Cecily Freeman Chris A. Higginson Michael P. Lambert Li-Her Lee Vera A. Voronina 《Mathematical Geology》1997,29(7):859-890
The Antarctic Ice Sheet plays a major role in the global system, and the large ice streams discharging into the circumpolar sea represent its gateways to the world's oceans. Satellite radar altimeter data provide an opportunity for mapping surface elevation at kilometer-resolution with meter-accuracy. Geostatistical methods have been developed for the analysis of these data. Applications to Seasat data and data from the Geosat Exact Repeat Mission indicate that the grounding line of Lambert Glacier/Amery Ice Shelf, the largest ice stream in East Antarctica, has advanced 10–12 km between 1978 and 1987–89. The objectives of this paper are to explore possibilities and limitations of satellite-altimetry-based mapping to capture changes for shorter time windows and for smaller areas, and to investigate some methodological aspects of the data analysis. We establish that one season of radar altimeter data is sufficient for constructing a map. This allows study of interannual variation and is the key for a time-series analysis approach to study changes in ice streams. Maps of the lower Lambert Glacier and the entire Amery Ice Shelf are presented for austral winters 1978, 1987, 1988, and 1989. As a first step toward understanding the dynamics of the ice-stream/ice-shelf system, elevation changes are calculated for grounded ice, the grounding zone, and floating ice. In the absence of (sufficient) surface gravity control for the Lambert Glacier/Amery Ice Shelf area, altimetry-based maps may facilitate improvement of geoid models as they provide constraints on the terrain correction in the inverse gravimetric problem. 相似文献
73.
Hornblendic and felsic groups of Archean age and each of broadly similar geochemical composition across the Malton Gneiss Complex southeast of Valemount, Bristish Columbia, show detailed mineralogical and chemical variations from one geographical district to another. The complex appears to be composed of meta-igneous rocks which were originally developed as petrologically discrete units on a roughly 10-km scale, but which all belonged to one similar petrographic province. Overall they are characterized by rather high immobile trace and alkali element abundances. Their nearest geochemical equivalent appear to be found in the grey gneiss complexes of the North Atlantic Craton rather than in the granite-greenstone complexes of the Canadian Shield, but no other Archean complex possesses their overall characteristics. Some similarities in A-F-M and Q-Ab-Or content of these gneisses and those of the Laramie Range, Wyoming, are noted. 相似文献
74.
D. L. Lambert 《Solar physics》1968,3(1):118-124
A simplified representation of the temperature distribution in the solar photosphere is proposed: (
0) =
0 -
1 log
0. An expression is derived for the emergent continuous spectrum from the simple model. The limitations and applications of the simple model are discussed. 相似文献
75.
Philippe Lambert John F. McHone Robert S. Dietz Messaoud Houfani 《Meteoritics & planetary science》1980,15(2):157-179
From orbital, aviation and geologic documents, four circular depressions on the Sahara sedimentary platform were selected for field investigation because of their possible impact origin. Our results can be summarized as follows: Amguid Crater (26° 05′N; 004° 23.5′E; 450 m diameter, 30 m deep) is perfectly circular, with a steep wall, a raised rim and an ejecta blanket. The strata are uplifted, outward dipping, dislocated and locally overturned at the rim crest. Large blocks are scattered around the rim. There is petrological evidence of shock by planar elements in quartz. Amguid is a well preserved impact crater probably no older than 100,000 years. Talemzane (33° 19′N; 004° 02′E; 1.7 km diameter, 70 m deep) is also perfectly circular and displays a raised rim. The strata are uplifted, outward dipping, and locally highly fractured. Numerous breccia veins are clearly exposed in the crater wall. Consolidated ejected debris form a continuous blanket more than 500 m outward from the rim. Reworked mixed breccias are exposed at the base of the crater wall. Planar elements are observed in quartz clasts in the mixed breccia. Talemzane is an impact crater on the order of 0.5 to 3 million years old. El Mouilah (33° 51′N; 002° 03′E; 4.5 km diameter, 130 m deep) is almost perfectly circular, the walls are steep and there is a central dome. In spite of a promising morphology, there is no field evidence of impact. El Mouilah is possibly a recent collapse structure due to dissolution in the thick underlying limestone and gypsum formations or purely erosional in origin. Aflou (34° 00′N; 002° 03′E) is not circular (3 × 5 km) but was selected because it appears in the literature as a probable impact crater, the main argument being the existence of fused materials in the center (Marks et al., 1972). We found no evidence of impact, but several occurrences of igneous rocks along an E-W direction suggest a structurally controlled volcanic activity. A volcanic activity is also supported by the existence of a local magnetic anomaly centered on the depression. Aflou is neither an impact structure nor a crater. Located on a probable structural dome, at the intersection of several structural trends, the formation of the depression can be due to erosion and/or dissolution in the thick underlying limestone and gypsum formations. 相似文献
76.
77.
Precise gravity networks and profiles have been established in three locations in Canada for the purpose of measuring possible gravity changes associated with seismic events. All measurements were made using two LaCoste and Romberg model D gravimeters. The standard deviation of a single observed gravity difference ranges from 50 to 120 nm/sec2. The precision of the measurements appears to depend mainly on the amount of exposure to vibration during transportation. A preliminary comparison between results of different instruments reveals unexplained discrepancies, and calibration tests show that the D meter scale factor varies significantly with either dial reading or reset screw position or both. 相似文献
78.
N. Lehner P. L. Dufton D. L. Lambert R. S. I. Ryans F. P. Keenan 《Monthly notices of the Royal Astronomical Society》2000,314(1):199-208
Very-high-resolution ( R ∼160 000) spectroscopic observations are presented for the early B-type star, HD 83206. Because it has very sharp metal lines, this star affords an opportunity to test theories of model atmospheres and line formation. Non-LTE model atmosphere calculations have been used to estimate the atmospheric parameters and absolute metal abundances (C, N, O, Mg and Si); an LTE analysis was also undertaken to investigate the validity of this simpler approach and to estimate an iron abundance. For the non-LTE calculations, there is excellent agreement with observations of the Balmer lines H α and H δ and the lines of Si ii and Si iii for atmospheric parameters of T eff ≃21 700±600 K and log g ≃4.00±0.15 dex. The agreement is less convincing for the LTE calculations, and a higher gravity is deduced. Careful comparison of the metal line profiles with non-LTE calculations implies that the projected rotational and microturbulent velocities have maximum values of ≃5 and ≃2 km s−1 , respectively. The latter value is smaller than has often been adopted in LTE model atmosphere analyses of main-sequence stars. Non-LTE absolute metal abundances are estimated, and a comparison with those for normal B-type stars (deduced using similar non-LTE techniques) shows no significant differences. A comparison of the abundances deduced using non-LTE and LTE calculations implies systematic differences of 0.1–0.2 dex, showing the importance of using a non-LTE approach when accurate absolute abundances are required. Its location in the Hertzsprung–Russell diagram and normal metal abundance lead us to conclude that HD 83206 is probably a main-sequence B-type star. As such, it is among the sharpest-lined young B-type star discovered to date. 相似文献
79.
Abstract A series of fifteen 96‐h forecasts made with a spectral numerical weather prediction model is studied with reference to errors in the planetary wavelengths. The major contributor to the short (less than 48‐h) range forecast error is identified as an external mode. The medium range forecast error (96 h) is internal in character and reflects a deficiency in the simulation of the quasi‐stationary components. 相似文献
80.