全文获取类型
收费全文 | 5734篇 |
免费 | 574篇 |
国内免费 | 162篇 |
专业分类
测绘学 | 250篇 |
大气科学 | 674篇 |
地球物理 | 2044篇 |
地质学 | 2302篇 |
海洋学 | 296篇 |
天文学 | 420篇 |
综合类 | 201篇 |
自然地理 | 283篇 |
出版年
2023年 | 5篇 |
2022年 | 7篇 |
2021年 | 28篇 |
2020年 | 15篇 |
2019年 | 21篇 |
2018年 | 454篇 |
2017年 | 386篇 |
2016年 | 279篇 |
2015年 | 170篇 |
2014年 | 137篇 |
2013年 | 157篇 |
2012年 | 677篇 |
2011年 | 457篇 |
2010年 | 145篇 |
2009年 | 169篇 |
2008年 | 153篇 |
2007年 | 136篇 |
2006年 | 149篇 |
2005年 | 859篇 |
2004年 | 885篇 |
2003年 | 667篇 |
2002年 | 182篇 |
2001年 | 82篇 |
2000年 | 48篇 |
1999年 | 19篇 |
1998年 | 11篇 |
1997年 | 20篇 |
1996年 | 15篇 |
1995年 | 3篇 |
1994年 | 8篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 11篇 |
1988年 | 8篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1969年 | 4篇 |
1968年 | 3篇 |
1967年 | 3篇 |
1965年 | 3篇 |
1959年 | 2篇 |
1955年 | 3篇 |
1954年 | 3篇 |
1951年 | 2篇 |
1948年 | 2篇 |
排序方式: 共有6470条查询结果,搜索用时 0 毫秒
31.
Metaheuristic techniques, which are based on ideas of Artificial Intelligence, are among the best methods for solving computationally the GPS surveying network problem. In this paper, the ant colony optimization metaheuristic, which is inspired by the behavior of real ant colonies, is developed to efficiently provide a general framework for optimizing GPS surveying networks. In this framework, a set of ants co-operate together using an indirect communication procedure to find good GPS observation schedules. A GPS surveying network can be defined as a set of stations, co-ordinated by a series of sessions formed by placing receivers on the stations. The problem is to search for the best order in which to observe these sessions to give the best schedule at minimum cost. Computational results obtained by applying the proposed technique on several networks, with known and unknown optimal schedules, prove the effectiveness of the proposed metaheuristic technique to solve the GPS surveying network problem. 相似文献
32.
JPL's BlackJack receiver currently represents the most widely used geodetic grade GPS receiver for space applications. Using data from the CHAMP science mission, the in-flight performance of the BlackJack receiver has been assessed and the impact of various software updates performed during the 2.5 years since launch is described. Key aspects of the study comprise the channel allocation, anomalous data points, and the noise level of the code and carrier data. In addition, it has been demonstrated that the code measurements collected onboard the CHAMP satellite are notably affected by multipath errors in the aft-looking hemisphere, which can be attributed to cross-talk between the occultation antenna string and the primary precise orbit determination antenna. For carrier smoothed 10 s normal points, the code noise itself varies between a minimum of 5 cm at high elevations and 0.5 m (C/A) to 1.0 m (P1, P2) at 10° elevation. Carrier-phase data exhibit representative errors of 0.2 to 2.5 mm. The results of the CHAMP GPS data analysis contribute to a better understanding and possible improvement of the BlackJack receiver and support the design of optimal data editing and weighting strategies in precise orbit determination applications. 相似文献
33.
34.
Rigorous equations in compact symbolic matrix notation are introduced to transform coordinates and velocities between ITRF
frames and modern GPS-based geocentric geodetic datums. The theory is general but, after neglecting higher than second-order
terms, it is shown that the equations revert to the formulation currently applied in most major continental datums. We discuss
several examples: the North American Datum of 1983 (NAD83), the European Terrestrial Reference System of 1989 (ETRS89), the Geodetic Datum of Australia of 1994 (GDA94), and the South American Geocentric Reference System (SIRGAS).
Electronic Publication 相似文献
35.
LUO Jia LI Jiancheng CHAO Dingbo 《地球空间信息科学学报》2003,6(1):19-23
1 IntroductionTodeveloptheoceanwidelyanddeeply ,weneedabundantoceaninformation .Asanessentialpartofsuchinformation ,seafloortopographyplaysaveryimportantroleinavarietyofmarineactivities .However,thehighcostforoceanbathymetricsurveyinglimitstheapplicationo… 相似文献
36.
LlPingxiang WANGZhijun 《地球空间信息科学学报》2003,6(2):31-34
On the basis of a thorough understanding of the physical characteristics of remote sensing image,this paper employs the theories of wavelet transform and signal sampling to develop a new image fusion algorithm.The algorithm has been successfully applied to the image fusion of SPOT PAN and TM of Guangdong province, China The experimental results show that a perfect image fusion can be built up by using the image analytical solution and reconstruction in the image frequency domain based on the physical characteristics of the image formation.The method has demonstrated that the results of the image fusion do not change spectral characteristics of the original image. 相似文献
37.
PANHeping ZHANGChunsen 《地球空间信息科学学报》2003,6(2):48-54
This paper describes the structure,geometric model and geo-metric calibration of Photogrammetron I-the first type of photogrammetron which is designed to be a coherent stereo photogrammetric system in which two cameras are mounted on a physical base but driven by an intelligent agent architecture.The system calibration is divided into two parts:the in-lab calibration determines the fixed parameters in advance of system operation,and the insitu calibration keeps tracking the free parameters in real-time during the system operation.In a video surveillance set-up, prepared control points are tracked in stereo image sequences,so that the free parameters of the system can be continuously updated through iterative bundle adjustment and kalman filtering. 相似文献
38.
LIPingxiang FANGShenghui 《地球空间信息科学学报》2003,6(3):16-19
SAR images not only have the characteristics of all-ay, all-eather, but also provide object infor-mation which is different from visible and infrared sensors. However, SAR images have some faults, such as more speckles and fewer bands. The au-thors conducted the experiments of texture statistics analysis on SAR im-age features in order to improve the accuracy of SAR image interpretation.It is found that the texture analysis is an effective method for improving the accuracy of the SAR image interpreta-tion. 相似文献
39.
WEIWenzhan ZHONGYexun PENGYueying ZHENGHongbo 《地球空间信息科学学报》2003,6(3):62-65
40.
YU Xuexiang associate professor Ph.D Department of Resource Environment Engineering Anhui University of Science Technology Huainan China. XU Shaoquan GAO Wei LU Weicai 《地球空间信息科学学报》2003,6(4):51-56
A new similar singledifference mathematical model ( SS-DM) and its corresponding algorithm are advanced to solve the deformation of monitoring point directly in single epoch. The method for building the SSDM is introduced in detail, and the main error sources affecting the accuracy of deformation measurement are analyzed briefly, and the basic algorithm and steps of solving the deformation are discussed. In order to validate the correctness and the accuracy of the similar single-difference model, the test with five dual frequency receivers is carried out on a slideway which moved in plane in Feb. 2001. In the test, five sessions are observed. The numerical results of test data show that the advanced model is correct. 相似文献