全文获取类型
| 收费全文 | 64805篇 |
| 免费 | 701篇 |
| 国内免费 | 363篇 |
专业分类
| 测绘学 | 1682篇 |
| 大气科学 | 4368篇 |
| 地球物理 | 12116篇 |
| 地质学 | 25587篇 |
| 海洋学 | 5043篇 |
| 天文学 | 14042篇 |
| 综合类 | 237篇 |
| 自然地理 | 2794篇 |
出版年
| 2021年 | 413篇 |
| 2020年 | 466篇 |
| 2019年 | 467篇 |
| 2018年 | 3801篇 |
| 2017年 | 3554篇 |
| 2016年 | 2651篇 |
| 2015年 | 791篇 |
| 2014年 | 1209篇 |
| 2013年 | 2240篇 |
| 2012年 | 2311篇 |
| 2011年 | 4193篇 |
| 2010年 | 3791篇 |
| 2009年 | 4470篇 |
| 2008年 | 3618篇 |
| 2007年 | 4173篇 |
| 2006年 | 1749篇 |
| 2005年 | 1717篇 |
| 2004年 | 1624篇 |
| 2003年 | 1588篇 |
| 2002年 | 1378篇 |
| 2001年 | 1043篇 |
| 2000年 | 995篇 |
| 1999年 | 831篇 |
| 1998年 | 854篇 |
| 1997年 | 822篇 |
| 1996年 | 702篇 |
| 1995年 | 716篇 |
| 1994年 | 631篇 |
| 1993年 | 538篇 |
| 1992年 | 500篇 |
| 1991年 | 512篇 |
| 1990年 | 584篇 |
| 1989年 | 501篇 |
| 1988年 | 461篇 |
| 1987年 | 584篇 |
| 1986年 | 485篇 |
| 1985年 | 615篇 |
| 1984年 | 698篇 |
| 1983年 | 666篇 |
| 1982年 | 582篇 |
| 1981年 | 626篇 |
| 1980年 | 519篇 |
| 1979年 | 477篇 |
| 1978年 | 478篇 |
| 1977年 | 430篇 |
| 1976年 | 411篇 |
| 1975年 | 413篇 |
| 1974年 | 388篇 |
| 1973年 | 426篇 |
| 1971年 | 259篇 |
排序方式： 共有10000条查询结果，搜索用时 15 毫秒
931.
Kristine M. Larson Eric E. Small Ethan Gutmann Andria Bilich Penina Axelrad John Braun 《GPS Solutions》2008,12(3):173-177
Measurements of soil moisture are important for studies of climate and weather forecasting, flood prediction, and aquifer
recharge studies. Although soil moisture measurement networks exist, most are sparsely distributed and lack standardized instrumentation.
Measurements of soil moisture from satellites have extremely large spatial footprints (40–60 km). A methodology is described
here that uses existing networks of continuously-operating GPS receivers to measure soil moisture fluctuations. In this technique,
incoming signals are reflected off and attenuated by the ground before reception by the GPS receiver. These multipath reflections
directly affect signal-to-noise ratio (SNR) data routinely collected by GPS receivers, creating amplitude variations that
are a function of ground reflectivity and therefore soil moisture content. After describing this technique, multipath reflection
amplitudes at a GPS site in Tashkent, Uzbekistan are compared to estimates of soil moisture from the Noah land surface model.
Although the GPS multipath amplitudes and the land surface model are uncalibrated, over the 70-day period studied, they both
rise sharply following each rainfall event and slowly decrease over a period of ∼10 days. 相似文献
932.
Ben K. H. Soon Steve Scheding Hyung-Kuen Lee Hung-Kyu Lee Hugh Durrant-Whyte 《GPS Solutions》2008,12(4):261-271
This paper presents a simple and effective approach that incorporates single-frequency, L1 time-differenced GPS carrier phase
(TDCP) measurements without the need of ambiguity resolution techniques and the complexity to accommodate the delayed-state
terms. Static trial results are included to illustrate the stochastic characteristics and effectiveness of the TDCP measurements
in controlling position error growth. The formulation of the TDCP observation model is also described in a 17-state tightly-coupled
GPS/INS iterative, extended Kalman filter (IEKF) approach. Preliminary land vehicle trial results are also presented to illustrate
the effectiveness of the TDCP which provides sub-meter positional accuracies when operating for more than 10 min. 相似文献
933.
Zhengzhao Luo Stephens G.L. Emanuel K.A. Vane D.G. Tourville N.D. Haynes J.M. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(1):13-16
This letter presents preliminary results concerning the use of new observations from the A-Train Constellation for testing a new technique of remotely sensing hurricane intensity from space based on modeling a hurricane as a balanced, convectively neutral vortex. The key observational requirements are simultaneous, accurate measurements of cloud-top height, cloudtop temperature, and cloud profiling information across the center of the storm, although there are ways to bypass the need for cloud-top temperature. In this letter, the Moderate Resolution Imaging Spectroradiometer onboard Aqua provides an estimation of the cloud-top temperature, and the near-simultaneous CloudSat observations provide the essential cloud-top height and cloud profiling information. Initial results indicate that the new technique is a promising method for estimating storm intensity when compared post facto to the best track database. Potential uncertainties and room for further refinement of the technique are discussed. 相似文献
934.
This paper describes the spatial and functional evolution of a central place system as market conditions change with population growth. Utilizing a partial equilibrium optimization model, we examine the spatial response of two economic sectors to increases in market populations resulting from natural increase and migration. Response in both sectors is conditioned by threshold demand, with factor prices also affecting one of the sectors. As the central place system evolves it exhibits spatial and functional characteristics that are initially consistent with a Löschian landscape, then a Christallerian landscape at higher populations, while at even larger populations Krugman’s landscape emerges. 相似文献
935.
This paper presents a continuous version of the model of distribution dynamics to analyse the transition dynamics and implied
long-run behaviour of the EU-27 NUTS-2 regions over the period 1995–2003. It departs from previous research in two respects:
first, by introducing kernel estimation and three-dimensional stacked conditional density plots as well as highest density regions
plots for the visualisation of the transition function, based on Hyndman et al. (J Comput Graph Stat 5(4):315–336, 1996), and second, by combining Getis’ spatial filtering view with kernel estimation to explicitly account for the spatial dimension of the
growth process. The results of the analysis indicate a very slow catching-up of the poorest regions with the richer ones,
a process of shifting away of a small group of very rich regions, and highlight the importance of geography in understanding
regional income distribution dynamics.
相似文献
| Manfred M. FischerEmail: |
936.
937.
938.
939.
940.