全文获取类型
收费全文 | 958篇 |
免费 | 66篇 |
国内免费 | 2篇 |
专业分类
测绘学 | 36篇 |
大气科学 | 51篇 |
地球物理 | 346篇 |
地质学 | 359篇 |
海洋学 | 32篇 |
天文学 | 142篇 |
综合类 | 12篇 |
自然地理 | 48篇 |
出版年
2024年 | 3篇 |
2023年 | 6篇 |
2022年 | 11篇 |
2021年 | 14篇 |
2020年 | 18篇 |
2019年 | 16篇 |
2018年 | 63篇 |
2017年 | 59篇 |
2016年 | 82篇 |
2015年 | 70篇 |
2014年 | 66篇 |
2013年 | 67篇 |
2012年 | 52篇 |
2011年 | 43篇 |
2010年 | 49篇 |
2009年 | 51篇 |
2008年 | 42篇 |
2007年 | 35篇 |
2006年 | 31篇 |
2005年 | 18篇 |
2004年 | 12篇 |
2003年 | 11篇 |
2002年 | 16篇 |
2001年 | 9篇 |
2000年 | 12篇 |
1999年 | 7篇 |
1998年 | 16篇 |
1997年 | 4篇 |
1996年 | 16篇 |
1995年 | 7篇 |
1994年 | 10篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 8篇 |
1990年 | 5篇 |
1989年 | 8篇 |
1988年 | 5篇 |
1987年 | 4篇 |
1986年 | 6篇 |
1985年 | 5篇 |
1984年 | 5篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1971年 | 3篇 |
排序方式: 共有1026条查询结果,搜索用时 15 毫秒
81.
82.
Tourist farms in Lower Silesia, Poland 总被引:1,自引:0,他引:1
Stanisław Grykień 《GeoJournal》1998,46(3):279-281
In view of the small size of most Polish farms, attempts have been made to encourage diversification into rural tourism. The
paper examines the progress made in Lower Silesia which has good resources for domestic and international tourism. Thanks
to the promotional work of the Agricultural Consultative Centres over a hundred farms are now providing services. They do
not generate a large share of the farm income but business is expanding and some areas are becoming very popular. Thus a base
has been established for future expansion. Further development depends on easier access to credit and government support for
ecological agriculture. Better promotion is also needed to increase interest in rural tourism in Poland and attract more visitors
from abroad.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
83.
84.
Jan Kryński 《Journal of Geodesy》1979,53(1):19-36
Summary The concept of satellite-to-satellite tracking measuring the relative velocity of two orbiting satellites spaced some hundreds
kilometers on a close orbit, provides now possibilities for the investigation of the Earth’s gravity field. In the paper only
medium and short wave length effects affecting the measured relative velocity have been considered. Collocation is used in
such an analysis of local geoid improvement, because this method allows to combine heterogeneous data in a consistent way.
Covariance functions relevant for the particular case of a circular equatorial orbit are given. Two kinds of observation equations
have been formulated. The choice of observation equation with regard to satellites configuration is discussed.
It is found that it is sufficient to have a limited number of satellite-to-satellite observations in a 7o×7o area around the estimation point with distances between profiles of about 1o.5 and between the two satellites forming the pair of 200+350 km; the altitude of satellite-to-satellite observations should
be as low as possible. The accuracy of the geoid determination strongly depends on the degree and order of the reference field
used. An accuracy of about ±1 m can be achieved with an assumed reference field of (40,40).
The influence of measuring errors is discussed and it is shown that only satellite-to-satellite observations with accuracy
better then 0.1 mm/sec will give an improvement of the geoid. Finally, some results on the combination of low-low satellite-to-satellite
tracking and terrestrial gravity data are given.
The proposed method seems to be especially interesting for unsurveyed areas. Furthermore, it has the practical advantage that
only a local coverage data is needed. 相似文献
85.
Summary Satellite gradiometry is studied as a means to improve the geoid in local areas from a limited data coverage. Least-squares
collocation is used for this purpose because it allows to combine heterogeneous data in a consistent way and to estimate the
integrated effect of the attenuated spectrum. In this way accuracy studies can be performed in a general and reliable manner.
It is shown that only three second-order gradients contribute significantly to the estimation of the geoidal undulations and
that it is sufficient to have gradiometer data in a 5°×5° area around the estimation point. The accuracy of the geoid determination
is strongly dependent on the degree and order of the reference field used. An accuracy of about ±1 m can be achieved with
a reference field of (12, 12). There is an optimal satellite altitude for each reference field and this altitude may be higher
than 300 km for a field of low degree and order. The influence of measuring errors is discussed and it is shown that only
gradiometer data with accuracies better than ±0.05 E will give a significant improvement of the geoid. Finally, some results
on the combination of satellite gradiometry and terrestrial gravity measurements are given.
The proposed method seems to be well suited for local geoid determinations down to the meter range. It is especially interesting
for unsurveyed and difficult areas because no terrestrial measurements are necessary. Furthermore, it has the practical advantage
that only a local data coverage is needed. 相似文献
86.
Invasion of mud filtrate from the borehole into the surrounding formation can significantly alter the response of logging tools.In this paper the neutron tool response was calculated for a gas-bearing rock crossed by the borehole.The invaded zone is characterized by variable fluid and gas saturation and is defined by a specific hyperbolic function. The saturation function is based on the characteristics of Polish Carpathian Foredeep Miocene formations reached in gas-bearing rocks. The whole system including neutron tool equipped with Am-Be neutron source and a set of neutron detectors, borehole, invaded zone, and virgin zone, was numerically modeled and used as the input to the Monte-Carlo neutron transport code. The response of each detector was calculated for different combinations of porosity and saturation of invaded zone and virgin zone. 相似文献
87.
M. Ćwiok W. Dominik K. Małek L. Mankiewicz J. Mrowca-Ciułacz K. Nawrocki L. W. Piotrowski P. Sitek M. Sokołowski G. Wrochna A. F. Żarnecki 《Astrophysics and Space Science》2007,309(1-4):531-535
Experiment “Pi of the Sky” is designed to search for prompt optical emission from GRB sources. 32 CCD cameras covering 2 steradians will monitor the sky continuously. The data will be analysed on-line in search for optical flashes. The prototype with 2 cameras operated at Las Campanas (Chile) since 2004 has recognised several outbursts of flaring stars and has given limits for a few GRB. 相似文献
88.
89.
90.
B. Košt’ák S. Cacoń N. D. Dobrev E. Avramova-Tačeva E. Fecker J. Kopecký L. Petro R. Schweitzer A. A. Nikonov 《Izvestiya Physics of the Solid Earth》2007,43(6):503-516
Long-term repeated measurements of microdisplacements in tectonic fault structures of various parts of Central Europe and the Balkan Mountains showed that displacement trends changed significantly at several points in the period from 1997 through 2000; afterward, long-term trends were restored. This phenomenon took place in the periods of strong (M > 7) earthquakes in Iran (1997) and in the North Anatolian fault zone in Turkey (1999). Two strong Izmit earthquakes of 1999 in Turkey at distances of 600 km from the Balkan Peninsula and 1400 km from observation points in Central Europe were the main seismic events of the period studied. Apparently, the crustal deformation due to the sources of the aforementioned earthquakes reaches the central part of the European craton. Anomalous displacements in some areas occurred due to deformation propagating for great distances in the heterogeneous block medium of the West European part of the Eurasian plate. Changes in stresses can be caused by impulsive deformations of various intensities acting on some structural units (fault segments) at various distances. 相似文献