全文获取类型
收费全文 | 12031篇 |
免费 | 2204篇 |
国内免费 | 3661篇 |
专业分类
测绘学 | 643篇 |
大气科学 | 728篇 |
地球物理 | 3208篇 |
地质学 | 8388篇 |
海洋学 | 728篇 |
天文学 | 1013篇 |
综合类 | 577篇 |
自然地理 | 2611篇 |
出版年
2024年 | 52篇 |
2023年 | 138篇 |
2022年 | 397篇 |
2021年 | 499篇 |
2020年 | 610篇 |
2019年 | 675篇 |
2018年 | 598篇 |
2017年 | 491篇 |
2016年 | 650篇 |
2015年 | 683篇 |
2014年 | 848篇 |
2013年 | 915篇 |
2012年 | 789篇 |
2011年 | 867篇 |
2010年 | 762篇 |
2009年 | 904篇 |
2008年 | 866篇 |
2007年 | 932篇 |
2006年 | 1009篇 |
2005年 | 764篇 |
2004年 | 715篇 |
2003年 | 620篇 |
2002年 | 555篇 |
2001年 | 470篇 |
2000年 | 382篇 |
1999年 | 332篇 |
1998年 | 302篇 |
1997年 | 202篇 |
1996年 | 206篇 |
1995年 | 119篇 |
1994年 | 111篇 |
1993年 | 100篇 |
1992年 | 81篇 |
1991年 | 65篇 |
1990年 | 52篇 |
1989年 | 35篇 |
1988年 | 29篇 |
1987年 | 17篇 |
1986年 | 15篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1973年 | 2篇 |
1954年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
42.
Dark energy has a dramatic effect on the dynamics of the Universe, causing the recently discovered acceleration of the expansion. The dynamics are also central to the behaviour of the growth of large-scale structure, offering the possibility that observations of structure formation provide a sensitive probe of the cosmology and dark energy characteristics. In particular, dark energy with a time-varying equation of state can have an influence on structure formation stretching back well into the matter-dominated epoch. We analyse this impact, first calculating the linear perturbation results, including those for weak gravitational lensing. These dynamical models possess definite observable differences from constant equation of state models. Then we present a large-scale numerical simulation of structure formation, including the largest volume to date involving a time-varying equation of state. We find the halo mass function is well described by the Jenkins et al. mass function formula. We also show how to interpret modifications of the Friedmann equation in terms of a time-variable equation of state. The results presented here provide steps toward realistic computation of the effect of dark energy in cosmological probes involving large-scale structure, such as cluster counts, the Sunyaev–Zel'dovich effect or weak gravitational lensing. 相似文献
43.
44.
Wang Yanhui 《水文研究》1992,6(2):241-251
Black locust (Robina pseudoacacia) has become one of the most important shelter species in the loess area of northwest China. This paper summarizes recent research concerning its hydrological influence, including canopy interception, litter absorption capacity, its effect on rainfall kinetic energy, infiltration rates, surface runoff, soil moisture, and evapotranspiration, and its role in soil conservation. Several predictive models are listed. on the basis of existing results, optimum characteristics for an effective plantation are defined, and problems requiring further research are identified. 相似文献
45.
46.
47.
S.W. Allen 《Astrophysics and Space Science》2003,285(1):247-256
Chandra X-ray observations of rich, dynamically relaxed galaxy clusters allow the properties of the X-ray gas and the total
gravitating mass to be determined precisely. Here, we discuss how Chandra observations may be used as a powerful tool for
cosmological studies. By combining Chandra X-ray results on the X-ray gas mass fractions in clusters with independent measurements
of the Hubble constant and the mean baryonic matter density of the universe, we obtain a tight constraint on the mean total
matter density of the universe, Οm, and an interesting constraint on the cosmological constant, ΟΛ. Using these results, together with the observed local X-ray luminosity function of the most X-ray luminous galaxy clusters,
a mass-luminosity relation determined from Chandra and ROSAT X-ray data and weak gravitational lensing observations, and the
mass function predicted by numerical simulations, we obtain a precise constraint on the normalization of the power spectrum
of density fluctuations in the nearby universe,σ8. We compare our results with those obtained from other, independent methods.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
48.
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
49.
50.