全文获取类型
收费全文 | 1910篇 |
免费 | 56篇 |
国内免费 | 5篇 |
专业分类
测绘学 | 71篇 |
大气科学 | 145篇 |
地球物理 | 742篇 |
地质学 | 521篇 |
海洋学 | 86篇 |
天文学 | 345篇 |
综合类 | 6篇 |
自然地理 | 55篇 |
出版年
2020年 | 17篇 |
2018年 | 53篇 |
2017年 | 52篇 |
2016年 | 94篇 |
2015年 | 57篇 |
2014年 | 78篇 |
2013年 | 92篇 |
2012年 | 46篇 |
2011年 | 53篇 |
2010年 | 76篇 |
2009年 | 71篇 |
2008年 | 58篇 |
2007年 | 54篇 |
2006年 | 43篇 |
2005年 | 30篇 |
2004年 | 34篇 |
2003年 | 30篇 |
2002年 | 48篇 |
2001年 | 34篇 |
2000年 | 35篇 |
1999年 | 24篇 |
1998年 | 34篇 |
1997年 | 30篇 |
1996年 | 44篇 |
1995年 | 31篇 |
1994年 | 34篇 |
1993年 | 50篇 |
1992年 | 29篇 |
1991年 | 24篇 |
1990年 | 26篇 |
1989年 | 29篇 |
1988年 | 22篇 |
1987年 | 26篇 |
1986年 | 28篇 |
1985年 | 24篇 |
1984年 | 27篇 |
1983年 | 32篇 |
1982年 | 22篇 |
1981年 | 19篇 |
1980年 | 21篇 |
1979年 | 25篇 |
1978年 | 31篇 |
1977年 | 28篇 |
1976年 | 20篇 |
1975年 | 18篇 |
1974年 | 16篇 |
1973年 | 20篇 |
1972年 | 15篇 |
1971年 | 24篇 |
1969年 | 16篇 |
排序方式: 共有1971条查询结果,搜索用时 296 毫秒
51.
52.
The hydraulic behaviour of the karst aquifer in the Hubelj spring catchment area (SW Slovenia) was studied by using an indirect
research method based on natural tracers. The variations of natural tracers (in precipitation and in groundwater) during the
storm event made possible the separation of the Hubelj spring storm hydrograph by the three-component separation technique.
The results produced information on the aquifer recharge, storage and discharge processes, as well as on the mechanisms that
affected them. They verified the so-called epikarst hypothesis presuming that an important part of a karst aquifer recharge
reaches rapidly and intensively from the epikarst zone. It was demonstrated that epikarst water could occupy up to 50% of
the spring discharge during precipitation events. This phenomenon could have important consequences on protection and management
of the problems of karst aquifers, including engineering problems in karst areas. With this respect the results could give
way to new engineering ideas. 相似文献
53.
The analysis of the time and space distribution of specular (reflecting) points in bistatic altimetry between GPS and CHAMP
satellites or SAC-C (taken as examples) is extended from Wagner and Klokočník (2003 J. Geod 77: 128–138). We demonstrate a
significantly higher number and density of reflecting points in bistatic altimetry in comparison with traditional monostatic
altimetry. After an outline of our older accuracy assessment for the vertical position of the reflecting point, we add a new
independent derivation and compare both approaches. We account for orbit errors of both the transmitters (GPS) and receiver
(CHAMP) satellites, and the measurement (delay) error. We found that the accuracy of the vertical position of the reflecting
point decreases only slowly with increasing off-nadir angle and that the orbit errors must be accounted for if decimeter and
better accuracy is required. In this paper, we do not study errors such as state of the ocean, technical parameters of the
receiving system, and atmospheric corrections. 相似文献
54.
Georg Bergeton Larsen Stig Syndergaard Per Høeg Martin Bjært Sørensen 《GPS Solutions》2005,9(2):144-155
The Global Positioning System (GPS) radio occultation measurements obtained using the TurboRogue GPS receiver on the Danish satellite Ørsted have been processed using the single frequency method. Atmospheric profiles of refractivity and temperature are derived and validated against numerical weather prediction data from the European Centre for Medium-Range Weather Forecast (ECMWF). Results from the Ørsted GPS measurement campaign in February 2000 indicate that the single frequency method can provide retrievals with accuracy comparable to that of using two frequencies. From comparisons between measured dry temperature profiles and corresponding dry temperature profiles derived from ECMWF analysis fields, we find a mean difference of less than 0.5 K and a standard deviation of 2–4 K between 500 and 30 hPa in height. Above 30 hPa the impact of the ionosphere becomes more dominant and more difficult to eliminate using the single frequency method, and the results show degraded accuracy when compared to previous analysis results of occultation data from other missions using the dual frequency method. At latitudes less than 40° (denoted low latitudes), the standard deviation is generally smaller than at latitudes higher than 40° (denoted high latitudes). A small temperature bias is observed centered at 200 hPa for low latitudes and at 300 hPa for high latitudes. This indicates that the ECMWF analyses do not adequately resolve the tropopause temperature minimum. In the lowest part of the troposphere an observed warm bias is thought to be due to erroneous tracking of the GPS signal in cases of atmospheric multipath propagation. 相似文献
55.
L. Vočadlo K. S. Knight G. D. Price I. G. Wood 《Physics and Chemistry of Minerals》2002,29(2):132-139
The thermal expansion and crystal structure of FeSi has been determined by neutron powder diffraction between 4 and 1173?K. No evidence was seen of any structural or magnetic transitions at low temperatures. The average volumetric thermal expansion coefficient above room temperature was found to be 4.85(5)?×?10?5?K?1. The cell volume was fitted over the complete temperature range using Grüneisen approximations to the zero pressure equation of state, with the internal energy calculated via a Debye model; a Grüneisen second-order approximation gave the following parameters: θD=445(11)?K, V 0=89.596(8)?Å3, K 0′=4.4(4) and γ′=2.33(3), where θD is the Debye temperature, V 0 is V at T=0?K, K 0′ is the first derivative with respect to pressure of the incompressibility and γ′ is a Grüneisen parameter. The thermodynamic Grüneisen parameter, γth, has been calculated from experimental data in the range 4–400?K. The crystal structure was found to be almost invariant with temperature. The thermal vibrations of the Fe atoms are almost isotropic at all temperatures; those of the Si atoms become more anisotropic as the temperature increases. 相似文献
56.
Smoothing the Marmousi Model 总被引:1,自引:0,他引:1
K. Žáček 《Pure and Applied Geophysics》2002,159(7-8):1507-1526
57.
Methodology for construction, calibration and validation of a national hydrological model for Denmark 总被引:13,自引:0,他引:13
Hans Jrgen Henriksen Lars Troldborg Per Nyegaard Torben Obel Sonnenborg Jens Christian Refsgaard Bjarne Madsen 《Journal of Hydrology》2003,280(1-4):52-71
An integrated groundwater/surface water hydrological model with a 1 km2 grid has been constructed for Denmark covering 43,000 km2. The model is composed of a relatively simple root zone component for estimating the net precipitation, a comprehensive three-dimensional groundwater component for estimating recharge to and hydraulic heads in different geological layers, and a river component for streamflow routing and calculating stream–aquifer interaction. The model was constructed on the basis of the MIKE SHE code and by utilising comprehensive national databases on geology, soil, topography, river systems, climate and hydrology. The present paper describes the modelling process for the 7330 km2 island of Sjælland with emphasis on the problems experienced in combining the classical paradigms of groundwater modelling, such as inverse modelling of steady-state conditions, and catchment modelling, focussing on dynamic conditions and discharge simulation. Three model versions with different assumptions on input data and parameter values were required until the performance of the final, according to pre-defined accuracy criteria, model was evaluated as being satisfactory. The paper highlights the methodological issues related to establishment of performance criteria, parameterisation and assessment of parameter values from field data, calibration and validation test schemes. Most of the parameter values were assessed directly from field data, while about 10 ‘free’ parameters were subject to calibration using a combination of inverse steady-state groundwater modelling and manual trial-and-error dynamic groundwater/surface water modelling. Emphasising the importance of tests against independent data, the validation schemes included combinations of split-sample tests (another period) and proxy-basin tests (another area). 相似文献
58.
A new method is presented for the computation of the gravitational attraction of topographic masses when their height information is given on a regular grid. It is shown that the representation of the terrain relief by means of a bilinear surface not only offers a serious alternative to the polyhedra modeling, but also approaches even more smoothly the continuous reality. Inserting a bilinear approximation into the known scheme of deriving closed analytical expressions for the potential and its first-order derivatives for an arbitrarily shaped polyhedron leads to a one-dimensional integration with – apparently – no analytical solution. However, due to the high degree of smoothness of the integrand function, the numerical computation of this integral is very efficient. Numerical tests using synthetic data and a densely sampled digital terrain model in the Bavarian Alps prove that the new method is comparable to or even faster than a terrain modeling using polyhedra. 相似文献
59.
The preparation of the preliminary seismic hazard maps of the territory of Slovenia has been based on an expansion of the basic approach laid out by Cornell in 1968. Three seismic source models were prepared. Two of them are based mainly on the earthquake catalogue using the Poissonian probability model. A map of seismic energy release and a map of earthquake epicenter density are used to delineate seismic sources in these models. The geometry of the third model which is based on a rough estimate of seismotectonic setting is taken from the probabilistic seismic hazard analysis of a nuclear power plant in Slovenia. Published ground motion attenuation models based on strong motion records of recent strong earthquakes in Italy are used. Test maps for variable and uniform b-values are presented. The computer program, Seisrisk III, developed by the U.S. Geological Survey is used. 相似文献
60.