全文获取类型
收费全文 | 97506篇 |
免费 | 30652篇 |
国内免费 | 56824篇 |
专业分类
测绘学 | 15754篇 |
大气科学 | 27089篇 |
地球物理 | 22990篇 |
地质学 | 69761篇 |
海洋学 | 25481篇 |
天文学 | 1612篇 |
综合类 | 9412篇 |
自然地理 | 12883篇 |
出版年
2024年 | 711篇 |
2023年 | 1807篇 |
2022年 | 4628篇 |
2021年 | 5840篇 |
2020年 | 5415篇 |
2019年 | 8501篇 |
2018年 | 7989篇 |
2017年 | 7463篇 |
2016年 | 7553篇 |
2015年 | 8172篇 |
2014年 | 7597篇 |
2013年 | 9319篇 |
2012年 | 9822篇 |
2011年 | 9958篇 |
2010年 | 9950篇 |
2009年 | 8991篇 |
2008年 | 8596篇 |
2007年 | 8299篇 |
2006年 | 7763篇 |
2005年 | 6703篇 |
2004年 | 5681篇 |
2003年 | 4588篇 |
2002年 | 4428篇 |
2001年 | 3993篇 |
2000年 | 3341篇 |
1999年 | 2334篇 |
1998年 | 1878篇 |
1997年 | 1935篇 |
1996年 | 1490篇 |
1995年 | 1372篇 |
1994年 | 1221篇 |
1993年 | 1202篇 |
1992年 | 1052篇 |
1991年 | 759篇 |
1990年 | 748篇 |
1989年 | 597篇 |
1988年 | 505篇 |
1987年 | 405篇 |
1986年 | 333篇 |
1985年 | 263篇 |
1984年 | 292篇 |
1983年 | 171篇 |
1982年 | 218篇 |
1981年 | 154篇 |
1980年 | 112篇 |
1979年 | 145篇 |
1978年 | 53篇 |
1977年 | 48篇 |
1971年 | 53篇 |
1954年 | 53篇 |
排序方式: 共有10000条查询结果,搜索用时 375 毫秒
181.
We have revised the regional crustal structure, oceanic age distribution, and conjugate margin segmentation in and around the Lena Trough, the oceanic part of the Fram Strait between the Norwegian–Greenland Sea and the Eurasia Basin (Arctic Ocean). The Lena Trough started to open after Eurasia–Greenland relative plate motions changed from right-lateral shear to oblique divergence at Chron 13 times (33.3 Ma; earliest Oligocene). A new Bouguer gravity map, supported by existing seismic data and aeromagnetic profiles, has been applied to interpret the continent–ocean transition and the influence of Eocene shear structures on the timing of breakup and initial seafloor spreading. Assuming that the onset of deep-water exchange depended on the formation of a narrow, oceanic corridor, the gateway formed during early Miocene times (20–15 Ma). However, if the initial Lena Trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep-water circulation, the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around Chron 5 times (9.8 Ma; Late Miocene). Paleoceanographic changes at ODP Site 909 (northern Hovgård Ridge) are consistent with both hypotheses of gateway formation. We cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the Lena Trough. The gravity, seismic and magnetic observations question the prevailing hypotheses on the Yermak Plateau and the Morris Jesup Rise as Eocene oceanic plateaus and the Hovgård Ridge as a microcontinent. 相似文献
182.
Alan Yong Susan E. Hough Michael J. Abrams Christopher J. Wills 《Journal of Earth System Science》2008,117(2):797
Estimation of the degree of local seismic wave amplification (site effects) requires precise information about the local site conditions. In many regions of the world, local geologic information is either sparse or is not readily available. Because of this, seismic hazard maps for countries such as Mozambique, Pakistan and Turkey are developed without consideration of site factors and, therefore, do not provide a complete assessment of future hazards. Where local geologic information is available, details on the traditional maps often lack the precision (better than 1:10,000 scale) or the level of information required for modern seismic microzonation requirements. We use high-resolution (1:50,000) satellite imagery and newly developed image analysis methods to begin addressing this problem. Our imagery, consisting of optical data and digital elevation models (DEMs), is recorded from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) sensor system. We apply a semi-automated, object-oriented, multi-resolution feature segmentation method to identify and extract local terrain features. Then we classify the terrain types into mountain, piedmont and basin units using geomorphometry (topographic slope) as our parameter. Next, on the basis of the site classification schemes from the Wills and Silva (1998) study and the Wills et al (2000) and Wills and Clahan (2006) maps of California, we assign the local terrain units with V s 30 (the average seismic shear-wave velocity through the upper 30m of the subsurface) ranges for selected regions in Mozambique, Pakistan and Turkey. We find that the applicability of our site class assignments in each region is a good first-approximation for quantifying local site conditions and that additional work, such as the verification of the terrain’s compositional rigidity, is needed. 相似文献
183.
184.
鱼卡煤田大煤沟组高分辨率层序地层特征及聚煤规律 总被引:1,自引:0,他引:1
利用高分辨率层序地层学理论和技术方法,综合地震、测井、岩芯和煤质资料对柴达木盆地北缘鱼卡煤田中下侏罗统大煤沟组地层河湖三角洲沉积体系进行高分辨率层序地层学分析,从中识别出短期、中期、长期3个级别的基准面旋回层序,划分出向上"变深"非对称型、向上"变浅"非对称型及对称型3种短期基准面旋回基本结构类型。依据等时地层对比法则进行不同级次基准面旋回层序的联井对比,建立了大煤沟组的等时地层格架,在等时地层格架内进行了煤层对比,并在等时地层格架内分析了聚煤规律。 相似文献
185.
186.
187.
188.
189.
190.