全文获取类型
收费全文 | 3773篇 |
免费 | 735篇 |
国内免费 | 1005篇 |
专业分类
测绘学 | 160篇 |
大气科学 | 770篇 |
地球物理 | 674篇 |
地质学 | 2493篇 |
海洋学 | 433篇 |
天文学 | 55篇 |
综合类 | 233篇 |
自然地理 | 695篇 |
出版年
2024年 | 16篇 |
2023年 | 70篇 |
2022年 | 165篇 |
2021年 | 162篇 |
2020年 | 185篇 |
2019年 | 202篇 |
2018年 | 171篇 |
2017年 | 179篇 |
2016年 | 224篇 |
2015年 | 172篇 |
2014年 | 267篇 |
2013年 | 306篇 |
2012年 | 269篇 |
2011年 | 285篇 |
2010年 | 239篇 |
2009年 | 246篇 |
2008年 | 253篇 |
2007年 | 260篇 |
2006年 | 281篇 |
2005年 | 173篇 |
2004年 | 194篇 |
2003年 | 151篇 |
2002年 | 124篇 |
2001年 | 102篇 |
2000年 | 97篇 |
1999年 | 96篇 |
1998年 | 98篇 |
1997年 | 80篇 |
1996年 | 89篇 |
1995年 | 54篇 |
1994年 | 68篇 |
1993年 | 51篇 |
1992年 | 52篇 |
1991年 | 27篇 |
1990年 | 20篇 |
1989年 | 18篇 |
1988年 | 22篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 1篇 |
1982年 | 3篇 |
1981年 | 4篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 5篇 |
1954年 | 2篇 |
排序方式: 共有5513条查询结果,搜索用时 20 毫秒
1.
2.
The Tamtsag Basin is located in the extreme eastern portion of the Mongolia. The Basin and its counterpart in China (the Hailar Basin) are united a whole basin on the structural setting. In recent years, the Tamtsag Basin attracts more and more attention with the important exploration discovered in the 19th block by SOCO and in Hailar Basin of China. This paper discusses the exploration potential of Tamtsag Basin from the viewpoint of petroleum geology. 相似文献
3.
In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l?1 and from 0.28 to 5.24 mg l?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l?1 and from 0.78 to 20.34 μg l?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m?3 and 938.1 mg C m?2 day?1 in the coastal waters and 4.3 mg m?3 and 636.5 mg C m?1 day?1 in the estuarine waters, respectively. ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September). 相似文献
4.
5.
A. S. Baranov 《Celestial Mechanics and Dynamical Astronomy》2003,87(3):241-256
For the complete system of biharmonic functions a suitable representation in spheroidal coordinates is found. It is used for expanding the distance between two arbitrary gravitating points and its inverse quantity in appropriate series. Such expansions can be of interest and useful in a number of problems of celestial mechanics and stellar dynamics. 相似文献
6.
CORROSION AND ADHERENCE AT SEA OIL-PLATFORM 总被引:1,自引:0,他引:1
Measurements of the adhesive corrosion and protective potentials of 3 Bohai Sea oilplatforms under different cathodic protection showed corrosion still occurred on these platforms undertheir designed protective potentials. Preliminary conclusions from indoor experiments on the relation betweenadhesive corrosion and cathodic protection showed adhering organisms caused the corrosion onthese platforms. 相似文献
7.
8.
Age estimates of coastal terraces in the Andaman and Nicobar Islands and their tectonic implications
Kusala Rajendran C.P. Rajendran Anil Earnest G.V. Ravi Prasad K. Dutta D.K. Ray R. Anu 《Tectonophysics》2008,455(1-4):53-60
The great Indian Ocean earthquake of December 26, 2004 caused significant vertical changes in its rupture zone. About 800 km of the rupture is along the Andaman and Nicobar Islands, which forms the outer arc ridge of the subduction zone. Coseismic deformation along the exposed land could be observed as uplift/subsidence. Here we analyze the morphological features along the coast of the Andaman and Nicobar Islands, in an effort to reconstruct the past tectonics, taking cues from the coseismic effects. We obtained radiocarbon dates from coastal terraces of the island belt and used them to compute uplift rates, which vary from 1.33 mm yr− 1 in the Little Andaman to 2.80 mm yr− 1 in South Andaman and 2.45 mm yr− 1 in the North Andaman. Our radiocarbon dates converge on 600 yr and 1000 yr old coastal uplifts, which we attribute to the level changes due to two major previous subduction earthquakes in the region. 相似文献
9.
Borehole data reveals that during Late Quaternary, the Ganga river was non-existent in its present location near Varanasi.
Instead, it was flowing further south towards peripheral craton. Himalayan derived grey micaceous sands were being carried
by southward flowing rivers beyond the present day water divide of Ganga and mixed with pink arkosic sand brought by northward
flowing peninsular rivers. Subsequently, the Ganga shifted to its present position and got incised. Near Varanasi, the Ganga
river is flowing along a NW-SE tectonic lineament. The migration of Ganga river is believed to have been in response to basin
expansion caused due to Himalayan tectonics during Middle Pleistocene times.
Multi-storied sand bodies generated as a result of channel migration provide excellent aquifers confined by a thick zone of
muddy sediments near the surface. Good quality potable water is available at various levels below about 70 m depth in sandy
aquifers. Craton derived gravelly coarse-to-medium grained sand forms the main aquifer zones of tens of meter thickness with
enormous yield. In contrast, the shallow aquifers made up of recycled interfluve silt and sandy silt occur under unconfined
conditions and show water-level fluctuation of a few meters during pre-and post-monsoon periods. 相似文献
10.
R. K. Prasad N. C. Mondal Pallavi Banerjee M. V. Nandakumar V. S. Singh 《Environmental Geology》2008,55(3):467-475
Remote Sensing and Geographic Information System has become one of the leading tools in the field of hydrogeological science,
which helps in assessing, monitoring and conserving groundwater resources. It allows manipulation and analysis of individual
layer of spatial data. It is used for analysing and modelling the interrelationship between the layers. This paper mainly
deals with the integrated approach of Remote Sensing and geographical information system (GIS) to delineate groundwater potential
zones in hard rock terrain. The remotely sensed data at the scale of 1:50,000 and topographical information from available
maps, have been used for the preparation of ground water prospective map by integrating geology, geomorphology, slope, drainage-density
and lineaments map of the study area. Further, the data on yield of aquifer, as observed from existing bore wells in the area,
has been used to validate the groundwater potential map. The final result depicts the favourable prospective zones in the
study area and can be helpful in better planning and management of groundwater resources especially in hard rock terrains. 相似文献