全文获取类型
收费全文 | 1318篇 |
免费 | 209篇 |
国内免费 | 382篇 |
专业分类
测绘学 | 51篇 |
大气科学 | 77篇 |
地球物理 | 376篇 |
地质学 | 687篇 |
海洋学 | 400篇 |
天文学 | 27篇 |
综合类 | 94篇 |
自然地理 | 197篇 |
出版年
2024年 | 3篇 |
2023年 | 11篇 |
2022年 | 46篇 |
2021年 | 56篇 |
2020年 | 62篇 |
2019年 | 81篇 |
2018年 | 61篇 |
2017年 | 50篇 |
2016年 | 57篇 |
2015年 | 67篇 |
2014年 | 75篇 |
2013年 | 78篇 |
2012年 | 85篇 |
2011年 | 88篇 |
2010年 | 71篇 |
2009年 | 100篇 |
2008年 | 85篇 |
2007年 | 98篇 |
2006年 | 99篇 |
2005年 | 76篇 |
2004年 | 83篇 |
2003年 | 74篇 |
2002年 | 61篇 |
2001年 | 50篇 |
2000年 | 41篇 |
1999年 | 40篇 |
1998年 | 37篇 |
1997年 | 33篇 |
1996年 | 27篇 |
1995年 | 30篇 |
1994年 | 24篇 |
1993年 | 16篇 |
1992年 | 13篇 |
1991年 | 10篇 |
1990年 | 4篇 |
1989年 | 4篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1985年 | 4篇 |
1983年 | 2篇 |
1979年 | 2篇 |
1973年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有1909条查询结果,搜索用时 23 毫秒
61.
The impact of accelerometry on CHAMP orbit determination 总被引:6,自引:0,他引:6
The contribution of the STAR accelerometer to the CHAMP orbit precision is evaluated and quantified by means of the following
results: orbital fit to the satellite laser ranging (SLR) observations, GPS reduced-dynamic vs SLR dynamic orbit comparisons,
and comparison of the measured to the modeled non-gravitational accelerations (atmospheric drag in particular). In each of
the four test periods in 2001, five CHAMP arcs of 2 days' length were analyzed. The mean RMS-of-fit of the SLR observations
of the orbits computed with STAR data or the non-gravitational force model were 11 and 24 cm, respectively. If the accelerometer
calibration parameters are not known at least at the few percent level, the SLR orbit fit deteriorates. This was tested by
applying a 10% error to the along-track scale factor of the accelerometer, which increased the SLR RMS-of-fit on average to
17 cm. Reference orbits were computed employing the reduced-dynamic technique with GPS tracking data. This technique yields
the most accurate orbit positions thanks to the estimation of a large number of empirical accelerations, which compensate
for dynamic modeling errors. Comparison of the SLR orbits, computed with STAR data or the non-gravitational force model, to
the GPS-based orbits showed that the SLR orbits employing accelerometer observations are twice as accurate. Finally, comparison
of measured to modeled accelerations showed that the level of geomagnetic activity is highly correlated with the atmospheric
drag model error, and that the largest errors occur around the geomagnetic poles.
Received: 7 May 2002 / Accepted: 18 November 2002
Correspondence to: S. Bruinsma
Acknowledgments. The TIGCM results were obtained from the CEDAR database. This study was supported by the Centre National d'Etudes Spatiales
(CNES). The referees are thanked for their helpful remarks and suggestions. 相似文献
62.
利用1970~2000年安阳市高温天气资料和实时资料,分析了安阳市2000年6~7月两次区域性连续高温天气的天气形势、地面要素特征、地形影响及高温天气变化周期,揭示了高温天气的成因,找出了预报着眼点。 相似文献
63.
本文通过桩基渗水力工模型试验实例,介绍了一种新的室内土工模型试验方法-渗水力土工模型试验。它利用水在土体中的渗流来提供土工模型试验中必须的体积力,因而克服了常规模型试验和离心模型试验中一些缺陷。该方法在桩基研究及工程实际中具有良好的应用前景。 相似文献
64.
马宗晋认为,岩石圈的西向漂移和地幔东向运动的定向性显示了地球自转变化的导向作用[1]。本文证明,地球自转中的一种惯性力──科里奥利力是产生地球各圈层差异旋转的原因。 相似文献
65.
斜向坡变形破坏机制的数值模拟研究 总被引:3,自引:0,他引:3
本文讨论了斜向坡的旋转式变形和破坏机制,用有限元法计算了此种斜坡中的剩余下滑力的分布方式,并以此来解释在滑动过程中发生一定旋转的原因;论文还运用离散元法,模拟了此种滑坡的滑动过程。 相似文献
66.
67.
Metropolitan growth and labor markets in Mexico 总被引:1,自引:0,他引:1
Adrian Guillermo Aguilar 《GeoJournal》1997,43(4):371-383
The objective of this paper is to examine the main changes in the metropolitan labor markets associated with economic restructuring in Mexico during the late 1980s and beginning of the 1990s. The analysis refers particularly to the four largest metropoles of the country, Mexico City, Guadalajara, Monterrey and Puebla, looking for common characteristics in their emergent employment structures now strongly differentiated in terms of rewards, stability in employment relations and conditions of access to jobs. The analysis reveals that largest metropolitan areas have been the most profoundly affected by the economic restructuring resulting from globalization, through a rapid de-industrialization and the expansion of the tertiary sector. Metropolitan labor markets in Mexico, at the time that show signs of social polarization in the formal sector, put in evidence a general process of precarization – less labor stability, replacement of permanent by part-time jobs, and increasing subcontracting –, segmentation of the labor force, and an increasing informal conditions of economic activities with small businesses and unskilled, temporarly and poorly paid jobs. The labor force segmentation and its more precarious and casual conditions are mostly explained by the impact of recent neoliberal policies, and recurrent economic crisis during the 1980s and 1990s which highly contributes to social inequality. 相似文献
68.
By contrasting and analyzing the characteristics of gravity field nearby some important active faults in the continent of
China, it can be found that the crust blocks where Bouguer anomalies are regionally positive (or relatively positive) are
moving towards the terrestrial poles and the blocks where Bouguer anomalies in a tremendous area are negative (or relatively
negative) are moving towards the equator. By analysis of mechanics and mathematics calculation and based on lots of practical
data, the authors hold that the change in density of a crust block is a decisive factor that causes the horizontal movement
of the continental crust, while magma activity is an important factor that leads to the change in density of a crust block. 相似文献
69.
70.
PDC钻头切削齿受力随布齿密度变化关系研究 总被引:1,自引:0,他引:1
采用不同布齿方式的3个PDC切削齿同步连续切削转动的岩石为模拟井底钻头切削齿实际工作状态,用切削岩石时相同的布齿参数切削砂轮来磨损切削以模拟切削的以模拟切削齿磨状态,试验研究了不同磨损程度的切削齿受力与布齿密度的关系。 相似文献