全文获取类型
收费全文 | 79975篇 |
免费 | 883篇 |
国内免费 | 1345篇 |
专业分类
测绘学 | 2545篇 |
大气科学 | 5021篇 |
地球物理 | 15134篇 |
地质学 | 32218篇 |
海洋学 | 6328篇 |
天文学 | 15349篇 |
综合类 | 2315篇 |
自然地理 | 3293篇 |
出版年
2022年 | 604篇 |
2021年 | 909篇 |
2020年 | 1040篇 |
2019年 | 1079篇 |
2018年 | 6745篇 |
2017年 | 5859篇 |
2016年 | 4759篇 |
2015年 | 1203篇 |
2014年 | 2097篇 |
2013年 | 3156篇 |
2012年 | 3179篇 |
2011年 | 5334篇 |
2010年 | 4442篇 |
2009年 | 5169篇 |
2008年 | 4421篇 |
2007年 | 5042篇 |
2006年 | 2591篇 |
2005年 | 1657篇 |
2004年 | 1754篇 |
2003年 | 1671篇 |
2002年 | 1504篇 |
2001年 | 1256篇 |
2000年 | 1120篇 |
1999年 | 816篇 |
1998年 | 868篇 |
1997年 | 836篇 |
1996年 | 668篇 |
1995年 | 654篇 |
1994年 | 656篇 |
1993年 | 528篇 |
1992年 | 525篇 |
1991年 | 530篇 |
1990年 | 602篇 |
1989年 | 455篇 |
1988年 | 443篇 |
1987年 | 497篇 |
1986年 | 374篇 |
1985年 | 570篇 |
1984年 | 547篇 |
1983年 | 506篇 |
1982年 | 519篇 |
1981年 | 444篇 |
1980年 | 480篇 |
1979年 | 375篇 |
1978年 | 425篇 |
1977年 | 341篇 |
1976年 | 329篇 |
1975年 | 336篇 |
1974年 | 314篇 |
1973年 | 341篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
62.
Kieran P. Donaghy 《Journal of Geographical Systems》2011,13(1):17-30
In the literatures of regional science, urban economics, and urban development planning, a working assumption is that individuals
respond to incentives and regulations, given their preferences. Models for planning and policy analyses are used to consider
what might occur if the incentives or regulations were different. In these models, however, preferences are usually assumed
to be given and stable, and agents are usually assumed to be homogeneous. This paper focuses on the implications of making
preferences in models of policy implementation endogenously determined and time varying heterogeneous agents. We consider
first the recent literature on intertemporal choice and preference change, which cuts across many disciplines, and more briefly
the literature on norm-regarding behavior. We then elaborate a simple model of transportation demand—from a static to a dynamic
orientation, from fixed and exogenously given preferences of strictly self-regarding agents to endogenously determined and
policy-induced preferences of heterogeneous agents—and illustrate its characteristics with simple numerical examples. 相似文献
63.
N. I. Bondar’ 《Astronomy Reports》2017,61(2):130-137
Photometric data covering 1994–2009, obtained at the Crimean Astrophysical Observatory or retrieved from the ASAS and SuperWASP catalogs, were used to analyze the brightness variations of the rapidly rotating star V833 Tau, whose activity level is close to saturation. Combined with previously published results, these data represent for the first time all stages in the development of the star’s 19- year activity cycle. The photometric period and rotational-modulation amplitude for different epochs are determined, and the qualitative pattern of the spots is considered. The photometric period is close to the orbital period, but always exceeds it, indicating that surface inhomogeneities are located far from the equatorial plane. With the high spottedness of the star, reaching 28% at the cycle maximum, the rotationalmodulation amplitude is 0.05?0.1 m , and increases during the growth and decline phases of the 19-year cycle. The rotational modulation is due to spots with higher latitudes than in the case of the Sun, and concentrating on active longitudes. 相似文献
64.
In this paper we report on the MEM power spectrum analysis of brightness temperature fluctuations observed at 2.8 GHz during the total solar eclipse of 16 February 1980. The observed periodicities range from 3.5 min to 64 min. These periodicities may arise due to spatial and/or temporal variations in the solar radio emission. The observed periodicities imply presence of scale sizes ranging from 70,000 to 600,000 km assuming that the brightness fluctuations arise because of spatial variation only. On the other hand, if these fluctuations are due to temporal variation, the observed periodicities correspond well to predicted modes of solar global oscillations. 相似文献
65.
E. K. Semenov N. N. Sokolikhina E. V. Sokolikhina 《Russian Meteorology and Hydrology》2013,38(10):661-668
The genetic and synoptic classifications of the Novorossiysk Bora are created using the data of daily observations at the Novorossiysk meteorological station and other available synoptic information. Obtained are the quantitative criteria of these classifications, and on this base worked out are the basic scenarios of the generation and evolution of this dangerous phenomenon on the Black Sea coast of Russia. According to the genetic classification, the Bora was divided into four types: frontal, air-mass, monsoon, and gravity. Quantitative criteria worked out for each type can be used for the more accurate forecast of this destructive phenomenon near Novorossiysk. According to the synoptic classification, four classes were distinguished: Azores, North Atlantic, Siberian, and Arctic. 相似文献
66.
基于交互多模型的水下目标跟踪方法 总被引:1,自引:0,他引:1
According to the requirements of real-time performance and reliability in underwater maneuvering target tracking as well as clarifying motion features of the underwater target, an interacting multiple model algorithm based on fuzzy logic inference (FIMM) is proposed. Maneuvering patterns of the target are represented by model sets, including the constant velocity model (CA), the Singer mode~, and the nearly constant speed horizontal-turn model (HT) in FIMM technology. The simulation results show that compared to conventional IMM, the reliability and real-time performance of underwater target tracking can be improved by FIMM algorithm. 相似文献
67.
68.
The space–time prism demarcates all locations in space–time that a mobile object or person can occupy during an episode of
potential or unobserved movement. The prism is central to time geography as a measure of potential mobility and to mobile
object databases as a measure of location possibilities given sampling error. This paper develops an analytical approach to
assessing error propagation in space–time prisms and prism–prism intersections. We analyze the geometry of the prisms to derive
a core set of geometric problems involving the intersection of circles and ellipses. Analytical error propagation techniques
such as the Taylor linearization method based on the first-order partial derivatives are not available since explicit functions
describing the intersections and their derivatives are unwieldy. However, since we have implicit functions describing prism
geometry, we modify this approach using an implicit function theorem that provides the required first-order partials without
the explicit expressions. We describe the general method as well as details for the two spatial dimensions case and provide
example calculations. 相似文献
69.
H. Got A. Monaco J. Vittori A. Brambati G. Catani M. Masoli N. Pugliese M. Zucchi-Stolfa A. Belfiore F. Gallo G. Mezzadri L. Vernia A. Vinci G. Bonaduce 《Sedimentary Geology》1981,28(4):243-272
Lithological, sedimentological, mineralogical and faunal analyses of twenty cores from the western Peloponnesus margin and adjacent Matapan Trench permit the origin of the sediments and the processes of sedimentation to be defined in some detail.Except for the ash layers derived from the Ischian Province, the major part of the sediment is local in origin (Peloponnesus). Analyses of heavy, light and clay minerals enable three main provinces to be distinguished. Each of these provinces includes one or more slope basins and a portion of trench, without lateral connection between them and mixing of inputs.The diversity and complexity of sedimentary structures, the granulometric characters, the mixed fauna (molluscs and ostracods) and the variability of rates of sedimentation all testify to the prevalence of reworking phenomena and gravitative processes.These data confirm and elaborate on the model of sedimentation deduced from seismic studies in which sediments are successively trapped, released by the slope basins and transferred via channels and canyons towards the underlying trench basins. This “cascade feeding” appears characteristics of this subductive sedimentary environment. 相似文献
70.