全文获取类型
收费全文 | 20573篇 |
免费 | 534篇 |
国内免费 | 199篇 |
专业分类
测绘学 | 449篇 |
大气科学 | 202篇 |
地球物理 | 538篇 |
地质学 | 1883篇 |
海洋学 | 256篇 |
天文学 | 17363篇 |
综合类 | 95篇 |
自然地理 | 520篇 |
出版年
2024年 | 45篇 |
2023年 | 76篇 |
2022年 | 157篇 |
2021年 | 96篇 |
2020年 | 95篇 |
2019年 | 164篇 |
2018年 | 58篇 |
2017年 | 44篇 |
2016年 | 74篇 |
2015年 | 178篇 |
2014年 | 161篇 |
2013年 | 156篇 |
2012年 | 242篇 |
2011年 | 235篇 |
2010年 | 298篇 |
2009年 | 1617篇 |
2008年 | 1558篇 |
2007年 | 1841篇 |
2006年 | 1840篇 |
2005年 | 1715篇 |
2004年 | 1787篇 |
2003年 | 1539篇 |
2002年 | 1344篇 |
2001年 | 1162篇 |
2000年 | 946篇 |
1999年 | 891篇 |
1998年 | 1060篇 |
1997年 | 240篇 |
1996年 | 108篇 |
1995年 | 295篇 |
1994年 | 307篇 |
1993年 | 129篇 |
1992年 | 77篇 |
1991年 | 93篇 |
1990年 | 91篇 |
1989年 | 146篇 |
1988年 | 97篇 |
1987年 | 96篇 |
1986年 | 79篇 |
1985年 | 45篇 |
1984年 | 30篇 |
1983年 | 28篇 |
1982年 | 13篇 |
1981年 | 9篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1977年 | 6篇 |
1905年 | 3篇 |
1900年 | 3篇 |
1897年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The standard analytical approach which is applied for constructing geopotential models OSU86 and earlier ones, is based on
reducing the boundary value equation to a sphere enveloping the Earth and then solving it directly with respect to the potential
coefficients
n,m
. In an alternative procedure, developed by Jekeli and used for constructing the models OSU91 and EGM96, at first an ellipsoidal
harmonic series is developed for the geopotential and then its coefficients
n,m
e
are transformed to the unknown
n,m
. The second solution is more exact, but much more complicated. The standard procedure is modified and a new simple integral
formula is derived for evaluating the potential coefficients. The efficiency of the standard and new procedures is studied
numerically. In these solutions the same input data are used as for constructing high-degree parts of the EGM96 models. From
two sets of
n,m
(n≤360,|m|≤n), derived by the standard and new approaches, different spectral characteristics of the gravity anomaly and the geoid undulation
are estimated and then compared with similar characteristics evaluated by Jekeli's approach (`etalon' solution). The new solution
appears to be very close to Jekeli's, as opposed to the standard solution. The discrepancies between all the characteristics
of the new and `etalon' solutions are smaller than the corresponding discrepancies between two versions of the final geopotential
model EGM96, one of them (HDM190) constructed by the block-diagonal least squares (LS) adjustment and the other one (V068)
by using Jekeli's approach. On the basis of the derived analytical solution a new simple mathematical model is developed to
apply the LS technique for evaluating geopotential coefficients.
Received: 12 December 2000 / Accepted: 21 June 2001 相似文献
992.
Robustness analysis of geodetic horizontal networks 总被引:2,自引:1,他引:2
993.
Developing a bivariate spatial association measure: An integration of Pearson's r and Moran's I 总被引:1,自引:0,他引:1
Sang-Il Lee 《Journal of Geographical Systems》2001,3(4):369-385
This research is concerned with developing a bivariate spatial association measure or spatial correlation coefficient, which
is intended to capture spatial association among observations in terms of their point-to-point relationships across two spatial
patterns. The need for parameterization of the bivariate spatial dependence is precipitated by the realization that aspatial bivariate association measures, such as Pearson's correlation coefficient,
do not recognize spatial distributional aspects of data sets. This study devises an L statistic by integrating Pearson's r as an aspatial bivariate association measure and Moran's I as a univariate spatial association measure. The concept of a spatial smoothing scalar (SSS) plays a pivotal role in this task.
Received: 07 November 2000 / Accepted: 02 August 2001 相似文献
994.
L. E. Sjöberg 《Journal of Geodesy》2001,75(5-6):283-290
The topographic and atmospheric effects of gravimetric geoid determination by the modified Stokes formula, which combines
terrestrial gravity and a global geopotential model, are presented. Special emphasis is given to the zero- and first-degree
effects. The normal potential is defined in the traditional way, such that the disturbing potential in the exterior of the
masses contains no zero- and first-degree harmonics. In contrast, it is shown that, as a result of the topographic masses,
the gravimetric geoid includes such harmonics of the order of several centimetres. In addition, the atmosphere contributes
with a zero-degree harmonic of magnitude within 1 cm.
Received: 5 November 1999 / Accepted: 22 January 2001 相似文献
995.
In October 1998 the IGEX field campaign, the first coordinated international effort to monitor GLONASS satellites on global
basis, was started. Currently about 40 institutions worldwide support this effort either by providing GLONASS tracking data
or in operating related data and analysis centers. The increasing quality and consistency of the calculated GLONASS orbits
(about 25 cm early in 2000), even after the end of the official IGEX field campaign, are shown. Particular attention is drawn
to the combination of precise ephemerides in order to generate a robust, reliable and complete IGEX orbits product. Some problems
in modeling the effect of solar radiation pressure on GLONASS satellites are demonstrated. Finally, the expected benefits
and prospects of the upcoming International GLOnass Service-Pilot Project (IGLOS-PP) of the International GPS Service (IGS)
are discussed in more detail.
Received: 17 August 2000 / Accepted: 12 April 2001 相似文献
996.
Laser-based validation of GLONASS orbits by short-arc technique 总被引:1,自引:0,他引:1
F. Barlier C. Berger P. Bonnefond P. Exertier O. Laurain J. F. Mangin J. M. Torre 《Journal of Geodesy》2001,75(11):600-612
The International GLONASS Experiment (IGEX-98) was carried out between 19 October 1998 and 19 April 1999. Among several objectives
was the precise orbit determination of GPS and GLONASS satellites and its validation by laser ranging observations. Local
laser-based orbit corrections (radial, tangential and normal components in a rotating orbital local reference frame) are computed
using a geometrical short-arc technique. The order of magnitude of these corrections is at the level of few decimeters, depending
on the considered components. The orbit corrections are analyzed as a function of several parameters (date, orbital plane,
geographical area). The mean corrections are at the level of several centimeters. However, when averaging over the entire
campaign and for all the satellites, no mean radial, tangential and normal orbit corrections are found. The origin of the
observed corrections is considered (errors due to the geocentric gravitational constant, the non-gravitational forces, the
thermal equilibrium of on-board equipment, the reference systems, the location and the signature of the retroreflector array,
and the precision of the satellite laser ranges). Some features are also due to errors in the radio-tracking GLONASS orbits.
Further investigations will be needed to better understand the origin of various biases.
Received: 17 February 2000 / Accepted: 31 January 2001 相似文献
997.
Geoid, topography, and the Bouguer plate or shell 总被引:1,自引:1,他引:1
Topography plays an important role in solving many geodetic and geophysical problems. In the evaluation of a topographical
effect, a planar model, a spherical model or an even more sophisticated model can be used. In most applications, the planar
model is considered appropriate: recall the evaluation of gravity reductions of the free-air, Poincaré–Prey or Bouguer kind.
For some applications, such as the evaluation of topographical effects in gravimetric geoid computations, it is preferable
or even necessary to use at least the spherical model of topography. In modelling the topographical effect, the bulk of the
effect comes from the Bouguer plate, in the case of the planar model, or from the Bouguer shell, in the case of the spherical
model. The difference between the effects of the Bouguer plate and the Bouguer shell is studied, while the effect of the rest
of topography, the terrain, is discussed elsewhere. It is argued that the classical Bouguer plate gravity reduction should
be considered as a mathematical construction with unclear physical meaning. It is shown that if the reduction is understood
to be reducing observed gravity onto the geoid through the Bouguer plate/shell then both models give practically identical
answers, as associated with Poincaré's and Prey's work. It is shown why only the spherical model should be used in the evaluation
of topographical effects in the Stokes–Helmert solution of Stokes' boundary-value problem. The reason for this is that the
Bouguer plate model does not allow for a physically acceptable condensation scheme for the topography.
Received: 24 December 1999 / Accepted: 11 December 2000 相似文献
998.
In this paper an intervening opportunities model with spatial dominance is developed. The usual assumption in spatial theory
is that decision makers are influenced not just by the size of a destination or distance but by these two factors in combination, that is, spatial dominance. Decision-makers will have more knowledge about, and clearly perceive destinations that exert
the greatest amount of spatial dominance on their origins, just as they would primate cities. Thus destinations are ranked
in terms of the spatial dominance calculated for each destination. Empirical verification of the model utilizes state-to-state
migration flow data for the US. Calibration results compare favourably with the traditional intervening opportunities model
and the production constrained gravity model.
Received: 7 October 1999/Accepted: 15 June 2000 相似文献
999.
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
1000.
Kieran P. Donaghy 《Journal of Geographical Systems》2001,3(3):257-270
This paper presents and demonstrates a general approach to solving spatial dynamic models in continuous space and continuous
time that characterize the behaviour of intertemporally and interspatially optimizing agents and estimating from discrete
data the parameters of such models. The approach involves the use of a projection method to solve the models and a quasi-Newton
algorithm to update quasi-FIML parameter estimates.
Received: 26 July 2000 / Accepted: 31 January 2001 相似文献