全文获取类型
收费全文 | 58974篇 |
免费 | 9575篇 |
国内免费 | 14348篇 |
专业分类
测绘学 | 4960篇 |
大气科学 | 6144篇 |
地球物理 | 12378篇 |
地质学 | 36338篇 |
海洋学 | 6009篇 |
天文学 | 3499篇 |
综合类 | 3806篇 |
自然地理 | 9763篇 |
出版年
2024年 | 320篇 |
2023年 | 871篇 |
2022年 | 1785篇 |
2021年 | 2039篇 |
2020年 | 2195篇 |
2019年 | 2433篇 |
2018年 | 2020篇 |
2017年 | 2171篇 |
2016年 | 2516篇 |
2015年 | 2684篇 |
2014年 | 3265篇 |
2013年 | 3278篇 |
2012年 | 3497篇 |
2011年 | 3722篇 |
2010年 | 3222篇 |
2009年 | 3883篇 |
2008年 | 3831篇 |
2007年 | 4190篇 |
2006年 | 4131篇 |
2005年 | 3521篇 |
2004年 | 3283篇 |
2003年 | 3121篇 |
2002年 | 2791篇 |
2001年 | 2418篇 |
2000年 | 2200篇 |
1999年 | 2034篇 |
1998年 | 1781篇 |
1997年 | 1573篇 |
1996年 | 1432篇 |
1995年 | 1156篇 |
1994年 | 1191篇 |
1993年 | 1017篇 |
1992年 | 804篇 |
1991年 | 585篇 |
1990年 | 506篇 |
1989年 | 398篇 |
1988年 | 312篇 |
1987年 | 202篇 |
1986年 | 131篇 |
1985年 | 94篇 |
1984年 | 41篇 |
1983年 | 35篇 |
1982年 | 33篇 |
1981年 | 27篇 |
1980年 | 26篇 |
1979年 | 30篇 |
1978年 | 37篇 |
1977年 | 25篇 |
1973年 | 4篇 |
1954年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Aimed at promoting regional coalitions and expanding the approach to economic links, this paper puts forward some new concepts
such as link intensity and receiving coefficient, expounds the indexes of quantitative analysis of economic links and establishes
the quantitative-analysis model of economic links. With help of the model, this paper calculates the values of the link intensities
between Su-Xi-Chang (Suzhou-Wuxi-Changzhou) region and Shanghai, and analyzes the regional difference of the economic links. 相似文献
22.
23.
Erosion of man-made, forestry drainage channels occurs when the plough cuts through the surface peat layer into the underlying erodible mineral soil. A procedure is developed, based on hydraulic considerations, which will allow the drainage engineer to design stable drainage networks in upland forestry plantations. An example design chart is given for an erodible sandy loam type soil. 相似文献
24.
25.
Fabio Fontanot Pierluigi Monaco Stefano Borgani 《Monthly notices of the Royal Astronomical Society》2003,341(2):692-706
We apply the ztrace algorithm to the optical NOG and infrared PSC z galaxy catalogues to reconstruct the pattern of primordial fluctuations that have generated our local Universe. We check that the density fields traced by the two catalogues are well correlated, and consistent with a linear relation [either in δ or in log (1 +δ) ] with relative bias (of NOG with respect to PSC z ) b rel = 1.1 ± 0.1 . The relative bias relation is used to fill the optical zone of avoidance at | b | < 20° using the PSC z galaxy density field.
We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber klim ≃ 0.4 h Mpc−1 beyond which all information is lost. We find that the improvement arising from the denser sampling of the optical catalogue is compensated by the uncertainties connected to the larger zone of avoidance.
The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSC z ) to be consistent with a Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe. 相似文献
We perform extensive testing on simulated galaxy catalogues to optimize the reconstruction. The quality of the reconstruction is predicted to be good at large scales, up to a limiting wavenumber k
The initial conditions reconstructed from the NOG catalogue are found (analogously to those from the PSC z ) to be consistent with a Gaussian paradigm. We use the reconstructions to produce sets of initial conditions ready to be used for constrained simulations of our local Universe. 相似文献
26.
Nikolay Sidorenkov 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):27-38
Spectral analysis of the components of the relative atmospheric angular momentum vector is performed based on the series of these components for the 6 h intervals within the period of 1958–2000. These series have been computed in the Subbureau of the Atmospheric Angular Momentum of the International Earth Rotation Service using the NCEP/NCAR reanalysis of atmospheric observations. The basic harmonics of diurnal tides are determined. New results on the fortnight's and week's duration oscillations of the equatorial components of the atmospheric angular momentum are obtained. The zonal tides transformation mechanisms in the atmosphere are discussed. It is shown that the main mechanism of the zonal tides effect on the atmospheric variability is the amplitude modulation of daily oscillations of the relative atmospheric angular momentum. The effects of the atmospheric tides on the Earth rotation are discussed. 相似文献
27.
本文论述了保安地区火山岩的地质、岩石、副矿物、岩石化学、微量元素、稀土元素、稳定同位素、火山岩相及火山机构等特征。并对其演化规律、形成机制与成矿作用的关系,作了初步探讨。 相似文献
28.
For ecosystem modelling of the Boreal forest it is important to include processes associated with low soil temperature during spring‐early summer, as these affect the tree water uptake. The COUP model, a physically based SVAT model, was tested with 2 years of soil and snow physical measurements and sap flow measurements in a 70‐year‐old Scots pine stand in the boreal zone of northern Sweden. During the first year the extent and duration of soil frost was manipulated in the field. The model was successful in reproducing the timing of the soil warming after the snowmelt and frost thaw. A delayed soil warming, into the growing season, severely reduced the transpiration. We demonstrated the potential for considerable overestimation of transpiration by the model if the reduction of the trees' capacity to transpire due to low soil temperatures is not taken into account. We also demonstrated that the accumulated effect of aboveground conditions could be included when simulating the relationship between soil temperature and tree water uptake. This improved the estimated transpiration for the control plot and when soil warming was delayed into the growing season. The study illustrates the need of including antecedent conditions on root growth in the model in order to catch these effects on transpiration. The COUP model is a promising tool for predicting transpiration in high‐latitude stands. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
29.
30.