全文获取类型
收费全文 | 1965篇 |
免费 | 470篇 |
国内免费 | 590篇 |
专业分类
测绘学 | 170篇 |
大气科学 | 677篇 |
地球物理 | 490篇 |
地质学 | 883篇 |
海洋学 | 413篇 |
天文学 | 69篇 |
综合类 | 111篇 |
自然地理 | 212篇 |
出版年
2024年 | 13篇 |
2023年 | 33篇 |
2022年 | 49篇 |
2021年 | 84篇 |
2020年 | 90篇 |
2019年 | 128篇 |
2018年 | 102篇 |
2017年 | 130篇 |
2016年 | 104篇 |
2015年 | 102篇 |
2014年 | 155篇 |
2013年 | 159篇 |
2012年 | 140篇 |
2011年 | 136篇 |
2010年 | 114篇 |
2009年 | 143篇 |
2008年 | 138篇 |
2007年 | 138篇 |
2006年 | 125篇 |
2005年 | 108篇 |
2004年 | 98篇 |
2003年 | 85篇 |
2002年 | 100篇 |
2001年 | 70篇 |
2000年 | 65篇 |
1999年 | 67篇 |
1998年 | 57篇 |
1997年 | 35篇 |
1996年 | 59篇 |
1995年 | 37篇 |
1994年 | 36篇 |
1993年 | 29篇 |
1992年 | 22篇 |
1991年 | 20篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 3篇 |
1985年 | 3篇 |
1984年 | 1篇 |
1978年 | 1篇 |
1954年 | 4篇 |
排序方式: 共有3025条查询结果,搜索用时 515 毫秒
1.
A recently developed near infrared high speed photometer intended for lunar oc-cultation studies is described. The primary scientific objective is to reach milli arc second levels of angular resolution so that circumstellar structure of the occulted sources can be resolved. Near infrared sky brightness close to the lunar limb is also studied. Angular diameter derived from the observed occultation of IRC +20169 is presented and system performance discussed. 相似文献
2.
Andrew J. L. Harris Anna L. Butterworth Richard W. Carlton Ian Downey Peter Miller Pedro Navarro David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64
Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations
where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced
very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large
(3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion
rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at
Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated
near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement
to conventional monitoring methods.
Received: 21 January 1997 / Accepted: 3 April 1997 相似文献
3.
本文报告一种用半导体激光器作光源,用子脉冲宽度100ns,长度为511的周期伪随机码对半导体激光器的输出作幅度调制;APD作光电检测器,高速数字信号处理器TMS320C25作信号处理的激光雷达组成方案和试作样机的实验结果。 相似文献
4.
Water management and engineering in the karstic High Atlas of Morocco are difficult tasks under the prevailing geological, hydrogeological, geomorphological, vegetational and climatic conditions. It is important to be able to understand and predict the characteristics and availability of water for future water planning in the region under changing climatic and agricultural conditions. An interdisciplinary analysis of problems and adequate hydrological modelling tools developed by geologists, hydrologists and biologists are necessary. The karst areas of the High Atlas Mountains are characterised by impermeable triassic basalt underlying substantial subsurface reservoirs with high potential discharge rates. The karst groundwater aquifers are extensive but largely unknown in dimension, probably with a hierarchical network of groundwater flow paths. It is estimated that approximately 70% of the surface water is directly lost to groundwater. Steep landslide- and debris flow prone slopes exist next to coarse-grained, highly porous river beds. Infrequent, high intensity rainfall or snowmelt causes a particularly high flood risk to these karst areas. In addition, agriculture and land use changes have degraded the karst areas. The most important driving forces for degradation include permanent overgrazing even during droughts and the use of firewood by a continually growing population. Large scale degradation of vegetation has occurred in the oro-mediterranean (mountainous Mediterranean) zone, between 2600 and 3400 m which coincides with the most important zone for karstic groundwater creation. The combination of high amounts of groundwater flow and rapid surface flow due to sparse vegetation has increased the problems of flood flow. 相似文献
5.
Serena C. Tarantino Michele Zema Tiziana Boffa Ballaran Paolo Ghigna 《Physics and Chemistry of Minerals》2008,35(2):71-76
High-pressure single-crystal X-ray diffraction measurements of lattice parameters of the compound Li2VOSiO4, which crystallises with a natisite-type structure, has been carried out to a pressure of 8.54(5) GPa at room temperature.
Unit-cell volume data were fitted with a second-order Birch-Murnaghan EoS (BM-EoS), simultaneously refining V
0 and K
0 using the data weighted by the uncertainties in V. The bulk modulus is K
0 = 99(1) GPa, with K′ fixed to 4. Refinements of third order equations-of-state yielded values of K′ that did not differ significantly from 4. The compressibility of the unit-cell is strongly anisotropic with the c axis (K
0(c) = 49.7 ± 0.5 GPa) approximately four times more compressible than the a axis (K
0(a) = 195 ± 3 GPa). 相似文献
6.
应用车贝雪夫多项式分析过渡季节(6—7月)澳大利亚冷高压与赤道辐合带的关系,得出了对赤道辐合带北移的主要形势以及过程演变特征,最后用合成方法得到它的演变概念模式,为赤道辐合带的北移影响西太平洋及南海地区提供了中期预报的依据。 相似文献
7.
8.
9.
10.