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821.
F.J. Colomer Mendoza A. Ferrer Gisbert A. Gallardo Izquierdo M.D. Bovea 《Engineering Geology》2009,105(3-4):231-238
Homogeneous earth dams that are waterproofed with geomembranes are a suitable option for storing water and other sorts of liquids, like leachates from landfills. Such dams do not require complicated engineering technical calculations, their cost is usually low and they are not difficult to construct. To ensure the geotechnical safety of the dam, the slopes of the embankment must be correctly designed and constructed. This paper provides a set of nomograms which allow the user to get the safety factor of the slopes immediately. In some cases, it is only necessary to know previously the material classification according to the Unified Soil Classifications System. From this information it can be determined whether the material is appropriate or not. If the material classification is not available, geotechnical data of the material used in the construction of the embankment are needed. Examples of the application of nomograms are presented. Secondly, the paper includes a set of equations to calculate quickly the safety factor of a slope of earth upper than 7.5 m height. 相似文献
822.
Bovolo F. Bruzzone L. Capobianco L. Garzelli A. Marchesi S. Nencini S. 《Geoscience and Remote Sensing Letters, IEEE》2010,7(1):53-57
823.
Assessment of the LandStar Real-Time DGPS Service under Several Operational Conditions 总被引:1,自引:0,他引:1
LandStar is a differential global positioning service (DGPS) that provides 24-h real-time positioning for various applications
on land, water, and air in North America, Australia, New Zealand, Europe, and Africa. Its focus is on real-time applications
requiring a submeter positioning capability such as agriculture, forestry, Geospatial Information Systems (GIS), survey/mapping,
and land/vehicular navigation. LandStar uses a Wide Area Network of reference stations to derive DGPS corrections to model
the variation of GPS error sources over a large area. These model parameters are used by the Virtual Reference Station processors
to calculate standard corrections that are available for all predefined locations in the network. The corrections are transmitted
to the user by L-band satellite communication in the standard RTCM SC104 DGPS correction format. This article investigates
the performance of the LandStar Mk III system under various operational conditions and assesses its performance in both static
and kinematic modes. Four field tests were conducted during 12 months that tested the sysem in clear static and kinematic
conditions as well as suboptimal environments associated with low and heavy foliage conditions. Both the accuracy and availability
of the system under these conditions is investigated, with an emphasis on whether the above variables are caused by the LandStar
system differential corrections, the GPS measurements, or a combination of both. ? 1999 John Wiley & Sons, Inc. 相似文献
824.
Accurate estimates of the velocity and acceleration of a platform are often needed in high dynamic positioning, airborne gravimetry,
and geophysics. In turn, differentiation of GPS signals is a crucial process for obtaining these estimates. It is important
in the measurement domain where, for example, the phase measurements are used along with their instantaneous derivative (Doppler)
to estimate position and velocity. It is also important in postprocessing, where acceleration is usually estimated by differentiating
estimates of position and velocity. Various methods of differentiating a signal can have very different effects on the resulting
derivative, and their suitability varies from situation to situation. These comments set the stage for the investigations
in this article. The objective is twofold: (1) to carry out a comprehensive study of possible differentiation methods, characterizing
each in the frequency domain; and (2) to use real data to demonstrate each of these methods in both of the measurement and
position domains, in conditions of variable, high, or unknown dynamics. Examples are given using real GPS data in both the
measurement domain and in the position and velocity domain. The appropriate differentiator is used in several cases of varying
dynamics to derive a Doppler signal from carrier phase measurements (rather than using the raw Doppler generated by the receiver).
In the statistic case, it is seen that the accuracy of velocity estimates can be improved from 4.0 mm/s to 0.7 mm/s by using
the correct filter. In conditions of medium dynamics experienced in an airborne gravity survey, it is demonstrated that accelerations
as the 2–4 mGal level (1 mGal = 0.00001 m/s2) can be obtained at the required filtering periods. Finally, a precision motion table is used to show that when using the
correct filter, velocity estimates under high dynamics can be improved by an order of magnitude to 27.0 mm/s. ? 1999 John
Wiley & Sons, Inc. 相似文献
825.
Contribution of new AAM data source to δLOD excitation 总被引:1,自引:0,他引:1
Data sets of the changes of the length of day (ΔLOD) measured by space geodetic techniques and of the atmospheric angular
momentum (AAM) derived from global meteorological data by the National Meteorological Center (NMC) and the National Centers
for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) are used to reanalyze and study the excitations
of ΔLOD, and to examine and compare the contribution of each AAM series to ΔLOD. The main results are as follows.
1. The AAM reanalyzed with the assimilated global meteorological data by NCEP/NCAR are more accurate and have lower noise
than the original AAM derived by NMC. The NCEP/NCAR-based AAM is more consistent with the changes of the length-of-day series.
2. The NCEP reanalysed AAM data may better explain the non-tidal LOD variations on intraseasonal to interannual time scales,
especially on the quasi-biennial time scale. The atmosphere cannot, however, explain all LOD variations; other excitation
sources are possible.
3. The effects of atmosphere on the estimated values of tides for ΔLOD components up to a month are weak. The preliminary
results of the annual and semiannual tides can be estimated after removing the effects of atmosphere from ΔLOD.
Received: 27 May 1998 / Accepted: 22 March 1999 相似文献
826.
827.
V. K. Srivastava A. M. Rai R. K. Dixit M. P. Oza A. Narayana 《International Journal of Applied Earth Observation and Geoinformation》1999,1(3-4)
Sal (Shorea robusta) is an important forest tree species in north and north-eastern India. Large-scale plantations of this species have been raised there under taungya and coppice system of management. The conventional volume table prepared for high sal forest is referred to infer the volume of production of this species. Earlier workers have used aerial remote sensing data to develop volume tables of this species. In the present study a volume table for sal is developed based on remotely sensed satellite data using a regression technique. A two-step method was developed to estimate mean tree volume from satellite data. In step 1, mean crown diameter — an intermediate variable - was estimated from satellite data. In step 2, the estimated mean crown diameter was used to estimate the mean tree volume. Addition of age of the crop as an independent variable improved the predictive ability of the regression equation. 相似文献
828.
Summary
The standard Mollweide projection of the sphere S
R
2
which is of type pseudocylindrical — equiareal is generalized to the biaxial ellipsoid
E
A,B
2
.Within the class of pseudocylindrical mapping equations (1.8) of
E
A,B
2
(semimajor axis A, semiminor axis B) it is shown by solving the general eigenvalue problem (Tissot analysis) that only equiareal mappings, no conformal mappings exist. The mapping equations (2.1) which generalize those from S
R
2
to
E
A,B
2
lead under the equiareal postulate to a generalized Kepler equation (2.21) which is solved by Newton iteration, for instance (Table 1). Two variants of the ellipsoidal Mollweide projection in particular (2.16), (2.17) versus (2.19), (2.20) are presented which guarantee that parallel circles (coordinate lines of constant ellipsoidal latitude) are mapped onto straight lines in the plane while meridians (coordinate lines of constant ellipsoidal longitude) are mapped onto ellipses of variable axes. The theorem collects the basic results. Six computer graphical examples illustrate the first pseudocylindrical map projection of
E
A,B
2
of generalized Mollweide type. 相似文献
829.
Ju Bing Gu Defeng Herring Thomas A. Allende-Alba Gerardo Montenbruck Oliver Wang Zhengming 《GPS Solutions》2017,21(1):53-64
GPS Solutions - Orbital maneuvers are usually performed as needed for low earth orbiters to maintain a predefined trajectory or formation-flying configuration. To avoid unexpected discontinuities... 相似文献
830.
Daniel A. Griffith 《Transactions in GIS》2021,25(1):291-310
Space‐time data are becoming more abundant as time goes by, with hands‐on interest in them becoming more prevalent. These data have a very sensitive ordering in space and time, one that the simplest of recording errors can scramble. These data are also complex, containing both spatial and temporal autocorrelation coupled with their interaction. One goal of many researchers is to disentangle and account for these autocorrelation components in a parsimonious way. This article presents three competing model specifications to achieve this end. In addition, it outlines seven best practices for vetting space‐time datasets. This article cites a publicly available corrupt (containing at least errors of omission) rabies dataset to illustrate how a large volume of potentially valuable data can be rendered meaningless. In addition, it exemplifies postulated contentions about the United States National Cancer Institute Surveillance, Epidemiology, and End Results Program’s 1969–2018 population‐by‐county dataset, a collection of population counts held in high esteem. One major empirical finding is that this particular dataset exhibits traits that may merit remedial revisions action. A key conceptual finding is a suggested set of best practices for space‐time data proofreading. These two findings contribute to an ultimate goal of a large collection of certified open access space‐time datasets supporting repeatable and replicable scientific analyses. 相似文献