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371.
C. Vigny J. Chéry T. Duquesnoy F. Jouanne J. Ammann M. Anzidei J.-P. Avouac F. Barlier R. Bayer P. Briole E. Calais F. Cotton F. Duquenne K. L. Feigl G. Ferhat M. Flouzat J.-F. Gamond A. Geiger A. Harmel M. Kasser M. Laplanche M. Le Pape J. Martinod G. Ménard B. Meyer J.-C. Ruegg J.-M. Scheubel O. Scotti G. Vidal 《Journal of Geodesy》2002,76(2):63-76
The Western Alps are among the best studied collisional belts with both detailed structural mapping and also crustal geophysical
investigations such as the ECORS and EGT seismic profile. By contrast, the present-day kinematics of the belt is still largely
unknown due to small relative motions and the insufficient accuracy of the triangulation data. As a consequence, several tectonic
problems still remain to be solved, such as the amount of N–S convergence in the Occidental Alps, the repartition of the deformation
between the Alpine tectonic units, and the relation between deformation and rotation across the Alpine arc. In order to address
these problems, the GPS ALPES group, made up of French, Swiss and Italian research organizations, has achieved the first large-scale
GPS surveys of the Western Alps. More than 60 sites were surveyed in 1993 and 1998 with a minimum observation of 3 days at
each site. GPS data processing has been done by three independent teams using different software. The different solutions
have horizontal repeatabilities (N–E) of 4–7 mm in 1993 and 2–3 mm in 1998 and compare at the 3–5-mm level in position and
2-mm/yr level in velocity. A comparison of 1993 and 1998 coordinates shows that residual velocities of the GPS marks are generally
smaller than 2 mm/yr, precluding a detailed tectonic interpretation of the differential motions. However, these data seem
to suggest that the N–S compression of the Western Alps is quite mild (less than 2 mm/yr) compared to the global convergence
between the African and Eurasian plate (6 mm/yr). This implies that the shortening must be accomodated elsewhere by the deformation
of the Maghrebids and/or by rotations of Mediterranean microplates. Also, E–W velocity components analysis supports the idea
that E–W extension exists, as already suggested by recent structural and seismotectonic data interpretation.
Received: 27 November 2000 / Accepted: 17 September 2001 相似文献
372.
Progress in Carrier Phase Time Transfer 总被引:1,自引:0,他引:1
Jim Ray Felicitas Arias Gérard Petit Tim Springer Thomas Schildknecht Jon Clarke Jan Johansson 《GPS Solutions》2001,4(4):47-54
The progress of the joint Pilot Project for time transfer, formed by the International GPS Service (IGS) and the Bureal International
des Poids et Mesures (BIPM), was recently reviewed. Three notable milestones were set. (1) The IGS will implement, at least
in a test mode, an internally realized time scale based on an integration of combined frequency standards within the IGS network.
This will eventually become the reference time scale for all IGS clock products (instead of the current GPS broadcast time).
(2) A new procedure for combined receiver and satellite clock products will be implemented officially in November 2000. Receiver
clocks are an entirely new product of the IGS. (3) The BIPM will coordinate an effort to calibrate all Ashtech Z12-T (and
possibly other) receivers suitable for time transfer applications, either differentially or absolutely. Progress reports will
be presented publicly in the spring 2001. ? 2001 John Wiley & Sons, Inc. 相似文献
373.
Station coordinates are combined with velocities estimated by space geodesy techniques to produce the International Terrestrial
Reference System. The input is sets of coordinates and velocities calculated by International Earth Rotation Service analysis
centers using space geodesy techniques. The working reference system of individual analysis centers is generally conventionally
defined. However, the implications of such processing can have an effect on the resulting combined set. The problem of datum
definition as a function of coordinate combinations is reviewed. In particular, the problem of minimum constraints is clearly
emphasized and the reference system effect is defined. The goal is to build a process that could be used generally to remove
uncertainties in the underlying coordinate system without disturbing the underlying information with additional unnecessary
information.
Received: 25 January 1999 / Accepted: 20 September 2000 相似文献
374.
Effects of the spherical terrain on gravity and the geoid 总被引:3,自引:0,他引:3
375.
An approach to generate artificial earthquakeaccelerograms on hard soil sites is presented. Eachtime-history of accelerations is considered as arealization of a non-stationary gaussian stochasticprocess, with statistical parameters depending onmagnitude and source-to-site distance. In order tolink the values of these parameters for each groundmotion record with the corresponding magnitude andsource-to-site distance, semi-empirical functionalrelations called generalized attenuationfunctions are determined. The set of realground-motion time histories used to obtain thesefunctions correspond to shocks generated at differentsources and recorded at different sites in thevicinity of the southern coast of Mexico. The resultsshow significant dispersion in the parameters of themodel adopted, which reflect that associated with thereal earthquakes included in the sample employed.The problem of conditional simulation of artificialacceleration time histories for prescribed intensitiesis briefly presented, but its detailed study is leftfor a companion paper. The criteria and modelsproposed are applied to generate two families ofartificial acceleration records for recurrenceintervals of 100 and 200 years at a specific sitelocated in the region under study. The results shownin this article correspond to acceleration timehistories recorded on firm ground for earthquakesgenerated at the subduction zone that runs along thesouthern coast of Mexico, and cannot be generalized tocases of earthquakes generated at other sources orrecorded at other types of local conditions. Thismeans that the methods and functional forms presentedhere are applicable to these other cases, but thevalues of the parameters that characterize thosefunctions may differ from those presented here. 相似文献
376.
377.
E. L. Gégo G. S. Johnson M. Hankins 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(1):47-64
Stochastic techniques, such as Monte Carlo experiments, are more and more frequently used for the study of flow and transport
in heterogeneous aquifers. When the aquifer is composed of distinct hydrofacies, a common way to model heterogeneity is to
first generate equally-possible hydrofacies fields, and then convert these hydrofacies fields into hydraulic conductivity
(K) fields by assigning a single K value to each facies. This technique assumes relative homogeneity of K within each facies
but may not be appropriate for the most conductive facies that often exhibits substantial variability. In this paper, we assessed
the impacts of assigning multiple random K, rather than a uniform K value, to the highly conductive facies on the results
of a flow and transport model. A set of fifty stochastic hydrofacies maps depicting an environment similar to the Snake River
Plain aquifer (SRPA) in south-east Idaho were generated. Simulations demonstrated that a uniform K value, if carefully chosen,
can reasonably reproduce the specific discharges and early particle arrival times produced by multiple K values. Yet, the
results obtained with a uniform K value are dramatically less variable than those obtained with multiple K values. It is therefore
concluded that stochastic simulations with uniform K assigned to the most conductive and variable facies do not necessarily
portray the entire uncertainty in the analyses. 相似文献
378.
The spatial distribution and fate of petrogenic and pyrogenic hydrocarbons in coastal sediments following the Aegean Sea oil spill (Galicia, NW Spain) was investigated through a detailed study of chemical markers. Alkanes and acyclic isoprenoid hydrocarbons were degraded within six months of the accident, but triterpane and sterane distributions were still detectable and were useful in monitoring, respectively, the oil source and weathering. Aromatic steranes were also useful source indicators, and oil degradation was clear from the decrease of certain alkyl dibenzothiophene and phenanthrene isomers. The pyrogenic polycyclic aromatic hydrocarbons produced in the tanker wreck were found more persistent than the petrogenic ones. However, the presence of the oil in the sediments was recognized even one year after the accident and was found particularly preserved in the subsurface layers. 相似文献
379.
Heavy metals pollution of aquatic ecosystems in the vicinity of a recently closed underground lead-zinc mine (Basque Country, Spain) 总被引:3,自引:0,他引:3
A presentation is made of the study of an underground polymetallic sulphide mine and the pollution caused by this in the adjoining aquatic ecosystems. Troya Mine is in the Basque Cantabrian region (northern Spain). The annual production of the ore deposit of over 3.7 million tons of Pb (0.9%), Zn (11.2%) and Cu (0.2%) was 300,000 t. It was open and producing from 1986-1993. The mineralization was made up of pyrite, marcasite, sphalerite, galena, chalcopyrite and arsenopyrite. Only the Zn and the Pb were mined. We studied the distribution and behaviour of the heavy metals Zn, Pb, Fe, Mn, Cu, Cr and Cd in the water column, dissolved and suspended fractions, and in the sediments of Estanda Stream and of Gezala Creek. Zn, Cd and Mn tend to be found in the water; Fe, Pb, Cu and Cr appear as an adsorbed fractionin the solid phases. Those of the second group are significantly linked to the fluvial sediments and present very high levels. The concentrations of the metals are conditioned by the waters from the mine galleries, by the leached waste, by the surface runoff, and by overflow from the spillway of the tailings pond. Our observations provide knowledge on the extent of the polluting power of the metals, the physico-chemical effects in play and the subsequent chances of recovering these highly affected environments. 相似文献
380.
The neighbouring towns of Haparanda and Tornio, separated only by a narrow strip of grass and wetland, are divided by the
only inhabited land boundary between Finland and Sweden in the southern part of the Torne River. The population represents
four different groups in relation to linguistic and cultural backgrounds. In the daily lives of the inhabitants, the state
boundary is probably of less significance than linguistic, social and ‘ethnic’ differences. On the local government level
there is a strong will to unite forces to make the total area a viable region in spite of its peripheral location, but state
legislation makes co-ordination difficult. This may be seen as a necessity, but in the daily lives of the populations, the
state boundary defines an area of unequal access, sometimes working in favour of and sometimes barring contacts and co-operation.
The media consumption reflects a clear ‘national’ interest with a strong local bias. In their attitudes, Finnish speakers
and bilinguals show a greater appreciation of ‘the other’ than unilingual Swedes. This may reflect the actual possibility
space (reach) in the local area.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献