全文获取类型
收费全文 | 36826篇 |
免费 | 5708篇 |
国内免费 | 7981篇 |
专业分类
测绘学 | 8984篇 |
大气科学 | 6492篇 |
地球物理 | 7720篇 |
地质学 | 13396篇 |
海洋学 | 4623篇 |
天文学 | 1459篇 |
综合类 | 3163篇 |
自然地理 | 4678篇 |
出版年
2024年 | 236篇 |
2023年 | 596篇 |
2022年 | 1305篇 |
2021年 | 1601篇 |
2020年 | 1767篇 |
2019年 | 1956篇 |
2018年 | 1553篇 |
2017年 | 1964篇 |
2016年 | 2007篇 |
2015年 | 2145篇 |
2014年 | 2326篇 |
2013年 | 2701篇 |
2012年 | 2450篇 |
2011年 | 2390篇 |
2010年 | 1934篇 |
2009年 | 2245篇 |
2008年 | 2256篇 |
2007年 | 2451篇 |
2006年 | 2281篇 |
2005年 | 1956篇 |
2004年 | 1787篇 |
2003年 | 1480篇 |
2002年 | 1326篇 |
2001年 | 1141篇 |
2000年 | 1009篇 |
1999年 | 896篇 |
1998年 | 803篇 |
1997年 | 666篇 |
1996年 | 605篇 |
1995年 | 562篇 |
1994年 | 496篇 |
1993年 | 423篇 |
1992年 | 261篇 |
1991年 | 233篇 |
1990年 | 150篇 |
1989年 | 126篇 |
1988年 | 118篇 |
1987年 | 76篇 |
1986年 | 45篇 |
1985年 | 40篇 |
1984年 | 26篇 |
1982年 | 17篇 |
1981年 | 13篇 |
1980年 | 14篇 |
1979年 | 13篇 |
1978年 | 11篇 |
1977年 | 14篇 |
1976年 | 6篇 |
1971年 | 5篇 |
1954年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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
72.
73.
74.
We present the excitation energies and lifetimes for the 3 s 3 p 3 d 4 F 7/2,9/2 levels for five aluminium-like ions of the iron group. Apart from the wavelengths, this also includes the transition probabilities and branching ratios for the electric-dipole allowed (E1) and forbidden (M1, E2, M2) lines into the energetically lower lying levels of the 3 s 2 3 d , 3 s 3 p 2 and 3 s 3 p 3 d configurations. Applying systematically enlarged multiconfiguration Dirac–Fock (MCDF) wavefunctions, here the effects of relativity and the electron–electron correlation are treated within the same (computational) model. 相似文献
75.
76.
77.
The supraregional GIS-supported stochastical model, WEKU, for the determination of groundwater residence times in the upper
aquifers of large groundwater provinces is presented. Using a two-dimensional analytical model of groundwater flow, groundwater
residence times are determined within two extreme cases. In the first case, maximal groundwater residence times are calculated,
representing the part of groundwater, that is drained by the main surface water of a groundwater catchment area. In the second
case, minimal groundwater residence times for drainage into the nearest surface water are determined. Using explicit distribution
functions of the input parameters, mean values as well as potential ranges of variations of the groundwater residence times
are derived. The WEKU model has been used for the determination of groundwater residence times throughout Germany. The model
results – mean values and deviations of the groundwater velocity and the maximal and minimal groundwater residence times in
the upper aquifers – are presented by general maps and discussed in detail. It is shown that the groundwater residence times
in the upper aquifer vary regionally, differentiated between less than 1 year and more than 2000 years. Using this information,
the time scales can be specified, until measures to remediate polluted groundwater resources may lead to a substantial groundwater
quality improvement in the different groundwater provinces of Germany. With respect to its supraregional scale of application,
the WEKU model may serve as a useful tool for the supraregional groundwater management on a state, federal or international
level.
Received: 15 August 1995 · Accepted: 15 October 1995 相似文献
78.
E. Biémont P. Palmeri P. Quinet G. Paquin Z. G. Zhang G. Somesfalean S. Svanberg 《Monthly notices of the Royal Astronomical Society》2001,328(4):1085-1090
Lifetimes of six levels belonging to the 4f10 6p configuration of Ho iii have been measured for the first time using the time-resolved laser-induced fluorescence method. They are compared with multiconfigurational pseudo-relativistic Hartree–Fock calculations. A very good agreement is found. Using the experimental lifetimes and theoretical branching fractions, a first set of transition probabilities of astrophysical interest has been obtained for this ion. 相似文献
79.
80.
Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination. 相似文献