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781.
A. Baran R. Oreiro A. Pigulski F. Pérez Hernández A. Ulla M. D. Reed C. Rodríguez-López P. Moskalik S.-L. Kim W.-P. Chen R. Crowe M. Siwak L. Armendarez P. M. Binder K.-J. Choo A. Dye J. R. Eggen R. Garrido J. M. González Pérez S. L. Harms F.-Y. Huang D. Kozie H.-T. Lee J. MacDonald L. Fox Machado T. Monserrat J. Stevick S. Stewart D. Terry A.-Y. Zhou S. Zoa 《Monthly notices of the Royal Astronomical Society》2009,392(3):1092-1105
782.
A 29-year time-series of four-times-daily atmospheric effective angular momentum (EAM) estimates is used to study the atmospheric
influence on nutation. The most important atmospheric contributions are found for the prograde annual (77 μas), retrograde
annual (53 as), prograde semiannual (45 as), and for the constant offset of the pole (δψsinɛ0=−86 as, δɛ=77 as). Among them only the prograde semiannual component is driven mostly by the wind term of the EAM function,
while in all other cases the pressure term is dominant. These are nonnegligible quantities which should be taken into account
in the new theory of nutation. Comparison with the VLBI corrections to the IAU 1980 nutation model taking into account the
ocean tide contribution yields good agreement for the prograde annual and semiannual nutations. We also investigated time
variability of the atmospheric contribution to the nutation amplitudes by performing the sliding-window least-squares analysis
of both the atmospheric excitation and VLBI nutation data. Almost all detected variations of atmospheric origin can be attributed
to the pressure term, the biggest being the in-phase annual prograde component (about 30 as) and the retrograde one (as much
as 100200 as). These variations, if physical, limit the precision of classical modeling of nutation to the level of 0.1 mas.
Comparison with the VLBI data shows significant correlation for the retrograde annual nutation after 1989, while for the prograde
annual term there is a high correlation in shape but the size of the atmospherically driven variations is about three times
less than deduced from the VLBI data. This discrepancy in size can be attributed either to inaccuracy of the theoretical transfer
function or the frequency-dependent ocean response to the pressure variations. Our comparison also yields a considerably better
agreement with the VLBI nutation data when using the EAM function without the IB correction for ocean response, which indicates
that this correction is not adequate for nearly diurnal variations.
Received: 10 September 1997 / Accepted: 5 March 1998 相似文献
783.
A. H. W. Kearsley R. Forsberg A. Olesen L. Bastos K. Hehl U. Meyer A. Gidskehaug 《Journal of Geodesy》1998,72(10):600-605
Two detailed geoids have been computed in the region of North Jutland. The first computation used marine data in the offshore
areas. For the second computation the marine data set was replaced by the sparser airborne gravity data resulting from the
AGMASCO campaign of September 1996. The results of comparisons of the geoid heights at on-shore geometric control showed that
the geoid heights computed from the airborne gravity data matched in precision those computed using the marine data, supporting
the view that airborne techniques have enormous potential for mapping those unsurveyed areas between the land-based data and
the off-shore marine or altimetrically derived data.
Received: 7 July 1997 / Accepted: 22 April 1998 相似文献
784.
A. Dermanis 《Journal of Geodesy》1998,72(2):71-100
Motivated by the existing theory of the geometric characteristics of linear generalized inverses of linear mappings, an attempt
is made to establish a corresponding mathematical theory for nonlinear generalized inverses of nonlinear mappings in finite-
dimensional spaces. The theory relies on the concept of fiberings consisting of disjoint manifolds (fibers) in which the domain
and range spaces of the mappings are partitioned. Fiberings replace the quotient spaces generated by some characteristic subspaces
in the linear case. In addition to the simple generalized inverse, the minimum-distance and the x
0-nearest generalized inverse are introduced and characterized, in analogy with the least-squares and the minimum-norm generalized
inverses of the linear case. The theory is specialized to the geodetic mapping from network coordinates to observables and
the nonlinear transformations (Baarda's S-transformations) between different solutions are defined with the help of transformation parameters obtained from the solution
of nonlinear equations. In particular, the transformations from any solution to an x
0-nearest solution (corresponding to Meissl's inner solution) are given for two- and three-dimensional networks for both the
similarity and the rigid transformation case. Finally the nonlinear theory is specialized to the linear case with the help
of the singular-value decomposition and algebraic expressions with specific geometric meaning are given for all possible types
of generalized inverses.
Received: 11 April 1996 / Accepted: 19 April 1997 相似文献
785.
786.
A. Mancini 《Journal of Geodesy》1965,39(2):97-113
The space orientation and geodetic azimuths of lines ranging from 300 km to 1400 km have been determined from simultaneous
optical observations of the ANNA Flashing Satellite. The results of this test prove that the azimuth and the space direction
between two stations can be achieved to an accuracy of 0.5″ and 0.8″ second respectively with only a limited amount of data.
The reason for the high accuracy is attributed to two factors: [1] the metric quality of the PC-1000's stellar cameras, and
[2] the “perfect” simultaneity in the observations provided by the ANNA flashing light.
Much of this work was accomplished by the writer while employed by the Geodesy and Gravity Branch of Cambridge Research Laboratories. 相似文献
787.
Although current navigation services provide significant benefits to people's mobility, the turn‐by‐turn instructions they provide are sometimes ineffective. These instructions require people to maintain a high level of attention and cognitive workload while performing distance or angle measurements on their own mental map. To overcome this problem, landmarks have been identified as playing a major role in turn‐by‐turn instructions. This requires the availability of landmarks in navigation databases. Landmarks are commonly selected manually, which involves time‐consuming and tedious tasks. Automatic selection of landmarks has recently gained the attention of researchers but currently there are only a few techniques that can select appropriate landmarks. In this article, we present a technique based on a neural network model, where both static and dynamic features are used for selecting landmarks automatically. To train and test this model, two labeling approaches, manual labeling and rule‐based labeling, are also discussed. Experiments on the developed technique were conducted and the results show that rule‐based labeling has a precision of approximately 90%, which makes the technique suitable and reliable for automatic selection of landmarks. 相似文献
788.
Towards a Better Understanding of Dynamic Interaction Metrics for Wildlife: a Null Model Approach 总被引:3,自引:0,他引:3 下载免费PDF全文
Jennifer A. Miller 《Transactions in GIS》2015,19(3):342-361
The ability to measure dynamic interactions, such as attraction or avoidance, is crucial to understanding socio‐spatial behaviors related to territoriality and mating as well as for exploring resource use and the potential spread of infectious epizootic diseases. In spite of the importance of measuring dynamic interactions, it has not been a main research focus in movement pattern analysis. With very few exceptions (see Benhamou et al. 2014), no new metrics have been developed in the past 20 years to accommodate the fundamental shift in the type of animal movement data now being collected and there have been few comparison or otherwise critical studies of existing dynamic interaction metrics (but see Long et al. 2014; Miller 2012). This research borrows from the null model approach commonly used in community ecology to compare six currently used dynamic interaction metrics using data on five brown hyena dyads in Northern Botswana. There was disconcerting variation among the dynamic interaction results depending on which metric and which null model was used, and these results highlight the need for more extensive research on measuring and interpreting dynamic interactions in order to avoid making potentially misleading inferences about socio‐spatial behaviors. 相似文献
789.
Population growth worldwide leads to an increasing pressure on the land. Recent studies reported that many areas covered by badlands are decreasing because parts of badlands are being levelled and converted into arable land. It is important to monitor these changes for environmental planning. This paper proposes a remote-sensing-based detection method which allows mapping of badland dynamics based on seasonal vegetation changes in the lower Chambal valley, India. Supervised classification was applied on three Landsat (Thematic Mapper) images, from 3 different seasons; January (winter), April (summer) and October (post-monsoon). Different band selection methods were applied to get the best classification. Validation was done by ground referencing and a GeoEye-1 satellite image. The image from January performed best with overall accuracy of 87% and 0.69 of kappa. This method opens the possibilities of using semi-automatic classification for the Chambal badlands which is so far mapped with manual interpretations only. 相似文献
790.
Oshan Taylor M. Wolf Levi J. Sachdeva Mehak Bardin Sarah Fotheringham A. Stewart 《Journal of Geographical Systems》2022,24(3):293-324
Journal of Geographical Systems - Scale is a central concept in the geographical sciences and is an intrinsic property of many spatial systems. It also serves as an essential thread in the fabric... 相似文献