全文获取类型
收费全文 | 9629篇 |
免费 | 1999篇 |
国内免费 | 2952篇 |
专业分类
测绘学 | 1301篇 |
大气科学 | 1624篇 |
地球物理 | 2265篇 |
地质学 | 5306篇 |
海洋学 | 1552篇 |
天文学 | 343篇 |
综合类 | 886篇 |
自然地理 | 1303篇 |
出版年
2024年 | 80篇 |
2023年 | 267篇 |
2022年 | 589篇 |
2021年 | 719篇 |
2020年 | 587篇 |
2019年 | 642篇 |
2018年 | 654篇 |
2017年 | 592篇 |
2016年 | 651篇 |
2015年 | 630篇 |
2014年 | 686篇 |
2013年 | 762篇 |
2012年 | 794篇 |
2011年 | 710篇 |
2010年 | 671篇 |
2009年 | 684篇 |
2008年 | 642篇 |
2007年 | 567篇 |
2006年 | 485篇 |
2005年 | 386篇 |
2004年 | 315篇 |
2003年 | 257篇 |
2002年 | 261篇 |
2001年 | 241篇 |
2000年 | 236篇 |
1999年 | 224篇 |
1998年 | 214篇 |
1997年 | 193篇 |
1996年 | 143篇 |
1995年 | 126篇 |
1994年 | 120篇 |
1993年 | 88篇 |
1992年 | 78篇 |
1991年 | 50篇 |
1990年 | 36篇 |
1989年 | 36篇 |
1988年 | 31篇 |
1987年 | 24篇 |
1986年 | 21篇 |
1985年 | 6篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 10篇 |
1981年 | 6篇 |
1980年 | 5篇 |
1979年 | 7篇 |
1977年 | 4篇 |
1964年 | 2篇 |
1958年 | 9篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Stefanie Cable Bo Elberling Aart Kroon 《Boreas: An International Journal of Quaternary Research》2018,47(2):423-442
This paper presents the history and cryostratigraphy of the upper permafrost in the High‐Arctic Adventdalen Valley, central Svalbard. Nineteen frozen sediment cores, up to 10.7 m long, obtained at five periglacial landforms, were analysed for cryostructures, ice, carbon and solute contents, and grain‐size distribution, and were 14C‐ and OSL‐dated. Spatial variability in ice and carbon contents is closely related to the sedimentary history and mode of permafrost aggradation. In the valley bottom, saline epigenetic permafrost with pore ice down to depths of 10.7 m depth formed in deltaic sediments since the mid‐Holocene; cryopegs were encountered below 6 m. In the top 1 to 5 m, syngenetic and quasi‐syngenetic permafrost with microlenticular, lenticular, suspended and organic‐matrix cryostructures developed due to loess and alluvial sedimentation since the colder late Holocene, which resulted in the burial of organic material. At the transition between deltaic sediments and loess, massive ice bodies occurred. A pingo developed where the deltaic sediments reached the surface. On hillslopes, suspended cryostructure on solifluction sheets indicates quasi‐syngenetic permafrost aggradation; lobes, in contrast, were ice‐poor. Suspended cryostructure in eluvial deposits reflects epigenetic or quasi‐syngenetic permafrost formation on a weathered bedrock plateau. Landform‐scale spatial variations in ground ice and carbon relate to variations in slope, sedimentation rate, moisture conditions and stratigraphy. Although the study reveals close links between Holocene landscape evolution and permafrost history, our results emphasize a large uncertainty in using terrain surface indicators to infer ground‐ice contents and upscale from core to landform scale in mountainous permafrost landscapes. 相似文献
2.
Barley(Hordeum vulgare L.) is one of the earliest domesticated crop species and ranked as the fourth largest cereal production worldwide. Forward genetic studies in barley have greatly advanced plant genetics during the last century; however, most genes are identified by the conventional mapping method. Array genotyping and exome-capture sequencing have also been successfully used to target the causal mutation in barley populations, but these techniques are not widely adopted because of associated costs and partly due to the huge genome size of barley. This review summarizes three mapping cases of barley cuticle mutants in our laboratory with the help of RNA-sequencing. The causal mutations have been successfully identified for two of them and the target genes are located in the pericentromeric regions. Detailed information on the mapping-by-sequencing, mapping-and-sequencing, and RNA-sequencing assisted linkage mapping are presented and some limitations and challenges on the mapping assisted by RNA sequencing are also discussed. The alternative and elegant methods presented in this review may greatly accelerate forward genetics of barley mapping, especially for laboratories without large funding. 相似文献
3.
FEASIBLE STUDY ON THE INTEGRATION SYSTEM FOR THE SPACE MONITORING OF MAJOR EARTHQUAKES AND VOLCANOES IN TERRESTRIAL LAND 总被引:1,自引:1,他引:0
BOLi-qun 《中国地理科学(英文版)》2002,12(4):350-353
With the rapid development of space technology, earth observation technology and sky observatory technolo-gy, they have played a more and more important part in monitoring and predicting of earthquakes and volcanoes in the terres-trial land. In recent years, the related agencies have done the experiments and researches on monitoring and predicting ofearthquakes and volcanoes in the forewarning period by means of many approaches, such as satellite thermal infrared re-mote sensing (TIRS), Global Positioning System (GPS), differential interferometric synthesis aperture radar (D-INSAR),astronomical time-latitude residual anomaly, and Geographic Information Systems (GIS), etc. A quite large number of re-search foundation has been built in the fundamental theories and application methods. The experiments and researcheshave shown that these technology is efficient methods for high frequency crust movement. If the existed separate scientificforces and results are possibly assembled together to form a more complete integration monitoring system with the combina-tion of space, sky observation, ground, deep geology and macro anomaly, it will come into a new stage of monitoring andpredicting of earthquakes and volcanic eruptions. 相似文献
4.
5.
6.
Microwave Type III bursts with positive frequency drifting rate were found by Stahli and Benz (1987) for first time. Type III events are especially interesting because they are well-known to be signatures of electron beams in coronal plasma, and they are effective means for diagnosting of source plasma. A microwave burst consisting of some microwave type III burst groups was registered at Beijing Astronomical Observatory with the 2545–2645–2840 MHz synchronous observing system. The distributions of frequency drifting rate, half power duration, and intensity for each impulse in the groups have been statistically analysed. From this analysis, some important parameters for the dynamic process in the flare are deduced and discussed. 相似文献
7.
首先指出目前星风吸积模型中理论上的不自洽,考虑到δr≠0,重新推导轨道参量变化方程,消去了理论上的不自洽.提出一个新模型:首次将星风吸积同内禀AGB星核合成模型结合起来计算钡(Ba)星的重元素超丰,并将计算结果与观测值进行了比较.各参量按标准情况取值时,计算结果不太理想.取Bondihoyle吸积率的0.5倍或取较大的星风速率时,对于较长轨道周期(P>1000天)的Ba星,计算结果与观测值基本符合;而较短轨道周期(P<600天)的Ba星,其重元素超丰机制可能是盘吸积 相似文献
8.
Dynamic analysis of three-dimensional marine cables 总被引:1,自引:0,他引:1
Shan Huang 《Ocean Engineering》1994,21(6)
Marine cables are widely used in a variety of offshore activities. In this paper, a numerical approach is presented which is capable of predicting the dynamic behaviour of three-dimensional marine cables. The solution of this problem is of practical importance in the estimation of dybamic loading and motion, and thus has direct application to the enhancement of safety and the effectiveness of the offshore activities. The approach is based upon the lump-mass-and-spring model and the finite difference method. Mathematical analysis is provided on the basic characteristics of the model and the numerical stability. A numerical example is given to demonstrate the validity of the approach. 相似文献
9.
应用地壳波浪与镶嵌构造学说对富氏谱分析法提取地壳垂直形变信息的科学性做了地质学意义上的阐释 ,并提出了根据多期形变资料提取特定波段上构造策应力的数学模型 相似文献
10.
In this paper, we idealize the actual solar atmosphere as a multi-isothermal-layer system so as to obtain the energy transmittance of the linear Alfvén wave that propagates through such a system in presence of a uniform oblique magnetic filed. The results indicate that the two-layer model is essentially different to the three-layer one. In the two-layer model, the temperature jump acts as a high pass filter. In the three-layer model, resonant transfer will take place and the transmittance undergoes oscillation as the trigonometric function terms dominate its behavior. For actual solar atmosphere, the result reveals that the lower parts of solar atmosphere are more suitable for those Alfvén waves with period of seconds to transfer their energy. 相似文献