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331.
Andreas Goldschmidt-Rokita Knut J. F. Hansch Hans B. Hirschleber Takaya Iwasaki Toshihiko Kanazawa Hideki Shimamura Markvard A. Sellevoll 《Marine Geophysical Researches》1994,16(3):201-224
The Cenozoic margins of the Norwegian-Greenland Sea offer ideal conditions for passive margin studies. A series of structural elements, first observed on these margins, led to the concept of volcanic passive margins. Questions still remain about the development of such features and the location of the boundary between oceanic and continental crust. Despite the thin sediment cover of the margins, seismic reflection data are not able to image the deeper structures due to the occurrence of igneous rocks at shallow depth.This paper presents a 320-km long profile perpendicular to the strike of the main structural units of the Lofoten Margin in Northern Norway. A geological model is proposed, based on observations made with ocean bottom seismographs, which recorded seismic refraction data and wide angle reflections, along with a seismic reflection profile covering the same area. Ray-tracing was used to calculate a geophysical model from the shelf area into the Lofoten basin. The structures typical of a volcanic passive margin were found, showing that the Lofoten Margin was influenced by increased volcanic activity during its evolution. The ocean/continent transition is located in a 30-km wide zone landwards of the Vøring Plateau escarpment.The whole margin is underlain by a possibly underplated, high velocity layer. Evidence for a pre-rift sediment basin landwards of the escarpment, overlain by basalt flows, was seen. These structural features, related to extensive volcanism on the Lofoten Margin, are not as distinct as further south along the Norwegian Margin. Viewed in the light of the hot-spot theory of White and McKenzie (1989) the Lofoten Margin can be interpreted as a transitional type between volcanic and non-volcanic passive margin. 相似文献
332.
The Kane Fracture Zone probably is better covered by geophysical survey data, acquired both by design and incidentally, than
any other fracture zone in the North Atlantic Ocean. We have used this data to map the basement morphology of the fracture
zone and the adjacent crust for nearly 5700 km, from near Cape Hatteras to the middle of the Mesozoic magnetic anomalies west
of Cap Blanc, northwest Africa. We use the trends of the Kane transform valley and its inactive fracture valley to determine
the record of plate-motion changes, and we interpret the basement structural data to examine how the Kane transform evolved
in response to changes in plate motion. Prior to about 133 Ma the Kane was a small-offset transform and its fracture valley
is structurally expressed only as a shallow ( < 0.5 km) trough. In younger crust, the offset may have increased to as much
as 190 km (present offset 150 km) and the fracture valley typically is up to 1.2 km deep. This part of the fracture valley
records significant changes in direction of relative plate motion (5°–30°) near 102 Ma, 92 Ma, 59 Ma, 22 Ma, and 17 Ma. Each
change corresponds to a major reorganization of plate boundaries in areas around the Atlantic, and the fracture-zone orientation
appears to be a sensitive recorder of these events.
The Kane transform has exhibited characteristic responses to changes in relative plate motion. Counterclockwise plate-motion
changes put the left-lateral transform offset into extension, and the response was for ridge tips at the ridge-transform intersections
to propagate across the transform valley and against the truncating lithosphere. Heating of this lithosphere appears to have
produced uplift and formation of a well developed transverse ridge that bounds the inactive fracture valley on its older side.
The propagating ridge tips also rotated toward the transform fault in response to the local stress field, forming prominent
hooked ridges that now extend into or across the inactive fracture valley. Clockwise (compressional) changes in relative plate
motion produced none of these features, and the resulting fracture valleys typically have a wide-V shape.
The Kane transform experienced severe adaptions to the changes in relative plate motion at about 102 Ma (compressional shift)
and 92 Ma (extensional shift), and new transform faults were formed in crust outside the contemporary transform valley. Subsequently,
the transform offset has been smaller and the rates of change in plate motion have been more gradual, so transform-fault adjustment
has been contained within the transform valley. The fracture-valley structure formed during extensional and compressional
changes in relative plate motion can be decidedly asymmetrical in conjugate limbs of the fracture zone. This asymmetry appears
to be related to the ‘absolute’ motion of the plate boundary with respect to the asthenosphere. 相似文献
333.
334.
Andreas?BeyerEmail author Rike?Rathlau Hans?Werner?Schenke 《Marine Geophysical Researches》2005,26(1):61-75
The Håkon Mosby Mud Volcano is a natural laboratory to study geological, geochemical, and ecological processes related to deep-water mud volcanism. High resolution bathymetry of the Håkon Mosby Mud Volcano was recorded during RV Polarstern expedition ARK XIX/3 utilizing the multibeam system Hydrosweep DS-2. Dense spacing of the survey lines and slow ship speed (5 knots) provided necessary point density to generate a regular 10 m grid. Generalization was applied to preserve and represent morphological structures appropriately. Contour lines were derived showing detailed topography at the centre of the Håkon Mosby Mud Volcano and generalized contours in the vicinity. We provide a brief introduction to the Håkon Mosby Mud Volcano area and describe in detail data recording and processing methods, as well as the morphology of the area. Accuracy assessment was made to evaluate the reliability of a 10 m resolution terrain model. Multibeam sidescan data were recorded along with depth measurements and show reflectivity variations from light grey values at the centre of the Håkon Mosby Mud Volcano to dark grey values (less reflective) at the surrounding moat. 相似文献
335.
Markus Stoeppler Mechthild Burow Friedrich Backhaus Winfried Schramm Hans Wolfgang Nürnberg 《Marine Chemistry》1986,18(2-4)
A long-term study within the pilot environmental specimen bank programme of the Federal Republic of Germany on arsenic levels in coastal and open seawater and their reflection in the brown seaweed (Fucus vesiculosus) has been performed. Dissolved arsenic was on average 0.76 (range 0.45–1.11) μgl−1 for 17 sampling stations in the Baltic Sea, whereas contents of dissolved arsenic are somewhat higher in shallow waters of the coastal zone of the North Sea. Total arsenic levels in algae ranged up to 40 mg kg−1 (dry weight) and showed for the four locations studied obvious seasonal variations for comparatively nonpolluted or nondisturbed locations only. However, probably due to biological influences, the results obtained so far indicate that composite samples integrating a one year period are supposed to be the best strategy for future environmental specimen banking. Using a new efficient speciation technique the percentage of chemically stable organoarsenic compounds in the investigated algae has been found to be 95% of the total arsenic content and thus somewhat lower than in teleost fish. For comparison, typical data for a few other algae species from the Baltic and the Mediterranean Sea are also shown. 相似文献
336.
337.
Ann-Sofi Smedman Knut Lundin Hans Bergström Ulf Högström 《Boundary-Layer Meteorology》1991,56(3):295-307
A highly mobile system for accurate measurements of wind speed and horizontal turbulence in the lowest few hundred meters of the atmosphere is presented. It consists of a light-weight sonde (only 50 g, including batteries that permit 12 h of continuous operation) which can be easily lifted by a small kite in winds below 5 m/s and up to at least 25 m/s. In winds below 5 m/s, a small kytoon may be used instead. The signals from the sonde are received by a standard FM-radio equipped with a frequency converter, and data are recorded on ordinary cassette tapes. Field tests against towermounted precision instruments were performed at two sites during neutral and unstable conditions with the sonde suspended 25 m below a small kite, the measuring heights being 11 and 18 m respectively during the two test series. Mean wind speeds are found to be accurate to within ±0.2 m/s. Wind speed spectra obtained with the flying sonde can be evaluated up to 0.5 Hz and are found to agree closely with the spectra of the longitudinal component recorded simultaneously by the tower-mounted instrument at the same height. After correction for high frequency loss, which amounted to 5% at this low height (it is expected to decrease rapidly with height), the standard deviation of the wind recorded by the sonde agreed to within 2% with that obtained by the reference instrument. A notable result of the field tests is that there was no sign of degradation of the performance of the sonde in strong turbulence conditions. 相似文献
338.
In Part I (Storch and Xu 1990) the principal oscillation pattern (POP) analysis of 200 mb equatorial velocity potential leads to the definition of a bivariate (POP-) index of the tropical 30- to 60-day oscillation. Using the POP prediction scheme this index is predictable for a few days in advance. In Part 11, the prediction of the equatorial velocity potential field, made by the POP method and made by two GCMs, is investigated. The POP index forecast can incorporate skillful forecasts of the equatorial velocity potential () field. Its ensemble correlation skill score passes the 0.50 level at 7 days, whereas persistence passes after 3 days. If there is a strong 30- to 60-day oscillation signal in the initial state, useful forecasts of more than 20 days are sometimes possible; if the initial signal is weak, the POP forecast fails. Also, the forecast skill of two GCMs is considered. The NCAR T31 GCM appears to be quite skillful in predicting the equatorial -field, and in particular the 30- to 60-day oscillation. Its skill, however, is less than that of the POP scheme. The CNRM T42 GCM seems not to be able to predict the regular development associated with the tropical 30- to 60-day oscillation. The power of the POP index in explaining the equatorial x-field is a measure of the strength and dominance of the 30- to 60-day oscillation. This measure at day 0 is an a priori indicator of the NCAR T31 GCM's skill in predicting the equatorial velocity potential field.The National Center for Atmospheric Research is sponsored by the National Science Foundation 相似文献
339.
First initial-Hf isotopic compositions for samples from the Alpine domain are presented and discussed. The results are mainly based on zircons and a few whole rocks with ages between 30 and 450 Ma. Of those so far analyzed, the present-day Hf isotopic compositions of zircons from non-metamorphic and metamorphic granitoid rocks vary between 0.2824 and 0.2829. Zircon populations with concordant U-Pb ages have much higher initial 176Hf/177Hf than inversely discordant populations which have been contaminated with older zircons containing less radiogenic Hf. Correlated Nd-Hf crustal-residence ages have been found involving model parameters of Hf/Nd=f(Lu/Hf)/f(Sm/Nd) 1.6 for the depleted mantle and f(Lu/Hf)/f(Sm/Nd) 1.2 for elemental fractionations in the crust. The model implies 176Lu/177Hf of 0.017 for the bulk crust. It is suggested that the granitoid rocks are the result of mixing of subcontinental mantle-derived magmas with 1.7 Ga old recycled and partially molten crustal material. The continental/mantle component mass-ratio values for the granitoids range between 0.3 and 2. 相似文献
340.
Jarle W. Bjerke Arve Elvebakk Hans Tømmervik 《Norsk geografisk tidsskrift. Norwegian journal of geography》2018,72(1):57-64
Icy surfaces impose challenges for northern societies, wildlife and agriculture. However, there have been relatively few studies of the impacts of anoxic ground ice on non-agricultural plants. During the winter of 2009–2010, an extreme winter warming event led to thick ground-ice layer development in the world’s northernmost botanical garden in Tromsø, in subarctic Norway, due to much rain on warm days interspersed with cold dry days. After ice melt in late spring, the authors assessed plant mortality and tested whether certain growth forms, geographical origins, or terrain features were more vulnerable to stress. They found that mortality was negatively correlated with terrain slope, that cryptophytes were most vulnerable, and that good soil drainage improved all plants’ survival. Vegetation greenness (measured by the Normalized Difference Vegetation Index, NDVI) reached an unprecedented minimum in the summer of 2010 and remained low for two more years. The results suggest that more investigations of the impacts of ground ice are needed to understand better how alpine ecosystems might change with increasing climate change. In conclusion, the study revealed that botanical garden studies may be a valuable supplement to field studies, as plants of different origins could be studied under similar climatic conditions. 相似文献