全文获取类型
| 收费全文 | 2768篇 |
| 免费 | 299篇 |
| 国内免费 | 282篇 |
专业分类
| 测绘学 | 1220篇 |
| 大气科学 | 282篇 |
| 地球物理 | 359篇 |
| 地质学 | 514篇 |
| 海洋学 | 368篇 |
| 天文学 | 66篇 |
| 综合类 | 333篇 |
| 自然地理 | 207篇 |
出版年
| 2024年 | 9篇 |
| 2023年 | 20篇 |
| 2022年 | 86篇 |
| 2021年 | 115篇 |
| 2020年 | 119篇 |
| 2019年 | 165篇 |
| 2018年 | 92篇 |
| 2017年 | 171篇 |
| 2016年 | 157篇 |
| 2015年 | 170篇 |
| 2014年 | 191篇 |
| 2013年 | 208篇 |
| 2012年 | 202篇 |
| 2011年 | 155篇 |
| 2010年 | 128篇 |
| 2009年 | 123篇 |
| 2008年 | 140篇 |
| 2007年 | 168篇 |
| 2006年 | 155篇 |
| 2005年 | 113篇 |
| 2004年 | 84篇 |
| 2003年 | 76篇 |
| 2002年 | 71篇 |
| 2001年 | 57篇 |
| 2000年 | 63篇 |
| 1999年 | 43篇 |
| 1998年 | 62篇 |
| 1997年 | 43篇 |
| 1996年 | 35篇 |
| 1995年 | 37篇 |
| 1994年 | 16篇 |
| 1993年 | 15篇 |
| 1992年 | 17篇 |
| 1991年 | 7篇 |
| 1990年 | 15篇 |
| 1989年 | 6篇 |
| 1988年 | 2篇 |
| 1987年 | 5篇 |
| 1986年 | 2篇 |
| 1985年 | 1篇 |
| 1983年 | 3篇 |
| 1977年 | 1篇 |
| 1973年 | 1篇 |
排序方式： 共有3349条查询结果，搜索用时 15 毫秒
1.
Soil salinization, caused by salt migration and accumulation underneath the soil surface, will corrode structures. To analyze the moisture-salt migration and salt precipitation in soil under evaporation conditions, a mathematical model consisting of a series of theoretical equations is briefly presented. The filling effect of precipitated salts on tortuosity factor and evaporation rate are taken into account in relevant equations. Besides, a transition equation to link the solute transport equation before and after salt precipitation is proposed. Meanwhile, a new relative humidity equation deduced from Pitzer ions model is used to modify the vapor transport flux equation. The results show that the calculated values are in good agreement with the published experimental data, especially for the simulation of volume water content and evaporation rate of Toyoura sand, which confirm the reliability and applicability of the proposed model. 相似文献
2.
Summary. Four box cores collected from the Ontong—Java plateau during the Eurydice expedition have been used to make relative geomagnetic palaeo-intensity measurements. Rock magnetic measurements on the sediments show that they are characterized by a uniform magnetic mineralogy, and that they are suitable for relative intensity estimates. These are obtained by normalizing the NRM by an ARM imparted in a low DC bias field. the palaeoceanographic event known as the preservation spike is used to establish a crude time-scale for the record so that it may be compared with other data from the same region, and also with global palaeointensity estimates. the marine sediment data are quite similar to Australian intensity data from lake sediments and archaeomagnetic sources, but as might be expected exhibit some obvious differences from the global record. 相似文献
3.
4.
T. H. BELL S. E. JOHNSON B. DAVIS A. FORDE N. HAYWARD C. WILKINS 《Journal of Metamorphic Geology》1992,10(3):295-307
Extensive examination of large numbers of spatially orientated thin sections of orientated samples from orogens of all ages around the world has demonstrated that porphyroblasts do not rotate relative to geographical coordinates during highly non-coaxial ductile deformation of the matrix subsequent to their growth. This has been demonstrated for all tectonic environments so far investigated. The work also has provided new insights and data on metamorphic, structural and tectonic processes including: (1) the intimate control of deformation partitioning on metamorphic reactions; (2) solutions to the lack of correlation between lineations that indicate the direction of movement within thrusts and shear zones, and relative plate motion; and (3) a possible technique for determining the direction of relative plate motion that caused orogenesis in ancient orogens. 相似文献
5.
6.
严格论证了在对空间或地面目标的定位中,利用伪距测量观测模型的几何因子大于用台站间一次差分观测模型的几何因子.此外,台站间完全差分测量观测的定位精度优于不完全测量情形的定位精度.这些结果给人们在实际工作中采取何种定位方式提供了可靠的理论依据. 相似文献
7.
Galileo系统及其在中国的应用 总被引：9，自引：0，他引：9
较详细地介绍了Galileo系统的全面体系结构、频率设计、服务内容及其广泛的应用范围，指出了它与GPS系统相比的优点，并对开发和增强Galileo系统在我国多层次、全方位的应用提出了建议。 相似文献
8.
A coupled deterministic hydrological and water temperature model, CEQUEAU, was modified to include soil temperature and crown closure in its calculation of local advective terms in the heat budget. The modified model was than tested to verify its sensitivity to these modifications. An analysis of the heat budget of a small forested catchment in eastern Canada revealed that the advective term related to interflow plays a significant role in the daily water heat budget, providing on average 28% of the local advective budget (which also includes advective heat terms from surface runoff and groundwater) and nearly 14% of the total heat budget (which includes all radiative terms at the water surface, convection and evaporation, as well as the local advective terms). Relative sensitivity indices (RSIs) were used to verify the impact of the newly introduced parameters and variables. Among them, parameters related to the forest cover (crown closure and leaf area index) have a maximum RSI of ?0·6; i.e. a 100% increase in value produces a 60% decrease in the local advective term. Parameters with the greatest influence are the volume of water contributing to interflow and the amplitude of the net radiative flux at the soil surface, which, if doubled, would double the contribution of the local interflow advective term to the heat budget. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
9.
利用 2 0 2个太阳附近疏散星团的视向速度和自行观测资料 ,对太阳的运动和银河系的运动学参数进行了研究。其中 ,距离在 0 .5kpc到 2kpc之间的 12 8个疏散星团对平均太阳运动分量的解算结果是 (u0 ,v0 ,w0 ) =(- 13.8± 1.4 ,- 5 .0± 1.6 ,- 11.6± 2 .9)km/s ;Oort常数和银河系径向运动参数的解算结果分别为 (A ,B) =(16 .9± 1.1,- 11.6± 2 .6 )km·s- 1·kpc- 1及 (C ,D) =(2 .5± 1.1,- 2 .1± 0 .9)km·s- 1·kpc- 1。 相似文献
10.