全文获取类型
收费全文 | 56755篇 |
免费 | 768篇 |
国内免费 | 595篇 |
专业分类
测绘学 | 1495篇 |
大气科学 | 4061篇 |
地球物理 | 10617篇 |
地质学 | 20301篇 |
海洋学 | 5201篇 |
天文学 | 13339篇 |
综合类 | 195篇 |
自然地理 | 2909篇 |
出版年
2022年 | 378篇 |
2021年 | 666篇 |
2020年 | 696篇 |
2019年 | 749篇 |
2018年 | 1630篇 |
2017年 | 1559篇 |
2016年 | 1935篇 |
2015年 | 1056篇 |
2014年 | 1812篇 |
2013年 | 3034篇 |
2012年 | 1937篇 |
2011年 | 2499篇 |
2010年 | 2199篇 |
2009年 | 2818篇 |
2008年 | 2410篇 |
2007年 | 2444篇 |
2006年 | 2309篇 |
2005年 | 1718篇 |
2004年 | 1720篇 |
2003年 | 1622篇 |
2002年 | 1544篇 |
2001年 | 1360篇 |
2000年 | 1259篇 |
1999年 | 1038篇 |
1998年 | 1089篇 |
1997年 | 984篇 |
1996年 | 873篇 |
1995年 | 823篇 |
1994年 | 729篇 |
1993年 | 644篇 |
1992年 | 642篇 |
1991年 | 642篇 |
1990年 | 669篇 |
1989年 | 534篇 |
1988年 | 548篇 |
1987年 | 575篇 |
1986年 | 522篇 |
1985年 | 671篇 |
1984年 | 752篇 |
1983年 | 668篇 |
1982年 | 625篇 |
1981年 | 543篇 |
1980年 | 516篇 |
1979年 | 527篇 |
1978年 | 506篇 |
1977年 | 407篇 |
1976年 | 381篇 |
1975年 | 387篇 |
1974年 | 336篇 |
1973年 | 375篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
S. N. Arteha 《Astrophysics and Space Science》1996,246(1):51-64
A self-consistent statistical approach to the problem of planetary and stellar magnetism is suggested. The mechanism of magnetic field generation in the astronomical objects, where the existence of fields is associated with the axial rotation of objects, is discussed. In the general case the light pressure, the centrifugal, gravitational and other forces produce partial -separation of the charges. As a result of the system rotation, the magnetic fields of the currents of these charges are not compensated. The influence of various factors on the magnetic field of some object is analysed. 相似文献
182.
Philipp Tesch Robert S. Reece James R. Markello Juan Carlos Laya Michael C. Pope 《Basin Research》2020,32(2):388-401
We developed a seismic geomorphology-based procedure to enhance traditional trajectory analysis with the ability to visualize and quantify lateral variability along carbonate prograding-margin types (ramps and rimmed shelves) in 3D and 4D. This quantitative approach analysed the shelf break geometric evolution of the Oligo-Miocene carbonate clinoform system in the Browse Basin and delineated the feedback between antecedent topography and carbonate system response as controlling factor on shelf break rugosity. Our geometrical analysis identified a systematic shift in the large-scale average shelf break strike direction over a transect of 10 km from 62° to 55° in the Oligo-Miocene interval of the Browse Basin, which is likely controlled by far-field allogenic forcing from the Timor Trough collision zone. Plotting of 3D shelf break trajectories represents a convenient way to visualize the lateral variability in shelf break evolution. Shelf break trajectories that indicate contemporaneous along-strike progradation and retrogradation correlate with phases of autogenic slope system re-organization and may be a proxy for morphological stability of the shelf break. Shelf break rugosity and shelf break trajectory rugosity are not inherited parameters and antecedent topography does not dictate long-term differential movement of the shelf margin through successive depositional sequences. The autogenic carbonate system response to antecedent topography smooths high-rugosity areas by filling accommodation and maintains a relatively constant shelf break rugosity of ~150 m. Color-coding of the vertical component in the shelf break trajectory captures the creation and filling of accommodation, and highlights areas of the transect that are likely to yield inconsistent 2D sequence stratigraphic interpretations. 相似文献
183.
A. S. Rogowski 《International journal of geographical information science》2013,27(4):455-475
Abstract Application of Geographical Information Systems (GIS) to environmental problems requires a spatial delineation of soil properties and some a priori knowledge of their variability. In the U.S.A. estimated soil properties are available from soil surveys published by the National Cooperative Soil Survey. However, information on the extent and nature of their variability is generally lacking. To remedy the situation, variability of selected soil properties measured at farm and watershed scales was compared with published values using geostatistical methods. Results showed that the variability of bulk density and hydraulic conductivity can be estimated by comparing regularized variograms of measured and published values. An overlay method was proposed that combines measured and published delineations of soil properties into an overlay with the properties of both. The technique makes it possible to incorporate variability into a GIS analysis using data available from published soil surveys. 相似文献
184.
河北平原水系密度与隐伏活动构造的关系 总被引:4,自引:1,他引:4
以1926年出版的比例尺为1:5万的顺直地形图作为基础图件,用地理信息系统技术对河北平原作水系密度计量分析,揭示隐伏在第四纪巨厚的沉积物之下活动构造的信息,研究结果证实水系线密度统计图与使用其它地球科学方法获得的成果,例如基底活动断块图,地貌类型图和第四纪厚度图都有很好的对应,特别与布格重力图对应更好,研究结果发现水系密度图与布格重力异常图在总体一致性较好的前提下,多处反向异常区均为近代强震发生的区域,提出这种地表水系密度统计研究的成果不仅可以揭示深部隐伏的活动构造,而且具有较明确的时间含义。 相似文献
185.
186.
187.
H. S. de Römer 《International Journal of Earth Sciences》1962,51(1):268-280
An attempt is made to correlate and separate in terms of style and time two contrasting sets of structural elements in the northwestern part of the Appalachian Uplands in the Province of Quebec, Canada. There is sufficient evidence to indicate that a fold system with north-south trending axes is superimposed on a fold system with east-west axes. It is suggested that the two sets of structures represent pulses of one long-continued deformation accompanied by corresponding early and late phases of metamorphism.
Zusammenfassung Es wurde versucht, in den Appalachen des südöstlichen Teiles der Provinz Quebec, Kanada, zwei ungleichzeitige tektonische Systeme verschiedenen Baustils zu trennen. Die komplexen Kleinstrukturen zeigen, da\ Ost-West streichende Faltenachsen von einer jüngeren Nord-Süd-Faltung überprägt worden sind. Der Autor ist der Meinung, da\ die zwei tektonischen Systeme, die von einer frühen und späten Phase der Metamorphose begleitet werden, den zeitlich getrennten Verformungsstadien einer Orogenese entsprechen.相似文献
188.
The 3D MHD algorithm developed by us has been adapted to modeling the interaction between two plasma bunches in the ionosphere, mainly in order to sufficiently correctly describe the physics of the interaction between two plasma regions with regard to the ionospheric inhomogeneity and the geomagnetic field action. Modeling has been performed for several versions of location of the plasma region centers. 相似文献
189.
The silica-scaled chrysophytes are being used increasingly in paleolimnological studies of lake acidification. This study compares the distribution of scaled chrysophytes in the surface sediment of a calibration set of lakes from the Adirondack Park and from northern New England. With the exception of two taxa, species distributions with respect to pH are similar in the two regions. The stratigraphic distribution of chrysophytes is then compared in five Adirondack and three New England lakes. All the presently acid lakes indicate recent lake acidification, with more acid tolerant chrysophytes increasing in relative frequency in the recent sediments. Because the timing of these species changes is unrelated to any watershed disturbances that may have occurred in the lakes' catchments, atmospheric deposition of acids is believed responsible for these recent pH changes.This is the seventh of a series of papers to be published by this journal which is a contribution of the Paleoecological Investigation of Recent Lake Acidification (PIRLA) project. Drs. D. F. Charles and D. R. Whitehead are guest editors for this series. 相似文献
190.
Karaevskaya E. S. Demidov N. E. Kazantsev V. S. Elizarov I. M. Kaloshin A. G. Petrov A. L. Karlov D. S. Schirrmeister L. Belov A. A. Wetterich S. 《Izvestiya Atmospheric and Oceanic Physics》2021,57(10):1254-1270
Izvestiya, Atmospheric and Oceanic Physics - The archaeal composition of permafrost samples taken during the drilling of frozen marine sediments in the area of the Barentsburg coal mine on the east... 相似文献