全文获取类型
收费全文 | 6030篇 |
免费 | 2775篇 |
国内免费 | 1320篇 |
专业分类
测绘学 | 898篇 |
大气科学 | 1322篇 |
地球物理 | 1313篇 |
地质学 | 4011篇 |
海洋学 | 1022篇 |
天文学 | 196篇 |
综合类 | 598篇 |
自然地理 | 765篇 |
出版年
2025年 | 12篇 |
2024年 | 254篇 |
2023年 | 310篇 |
2022年 | 552篇 |
2021年 | 556篇 |
2020年 | 488篇 |
2019年 | 573篇 |
2018年 | 495篇 |
2017年 | 479篇 |
2016年 | 533篇 |
2015年 | 505篇 |
2014年 | 527篇 |
2013年 | 482篇 |
2012年 | 577篇 |
2011年 | 522篇 |
2010年 | 498篇 |
2009年 | 420篇 |
2008年 | 357篇 |
2007年 | 337篇 |
2006年 | 263篇 |
2005年 | 211篇 |
2004年 | 142篇 |
2003年 | 97篇 |
2002年 | 85篇 |
2001年 | 95篇 |
2000年 | 91篇 |
1999年 | 120篇 |
1998年 | 88篇 |
1997年 | 69篇 |
1996年 | 66篇 |
1995年 | 67篇 |
1994年 | 47篇 |
1993年 | 43篇 |
1992年 | 43篇 |
1991年 | 28篇 |
1990年 | 24篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 9篇 |
1986年 | 2篇 |
1985年 | 6篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 2篇 |
1980年 | 3篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1958年 | 4篇 |
1957年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
Lei Li 《Acta Geophysica》2008,56(2):518-528
In the paper by Chattopadhyay and Rajneesh (2006, “Reflection and refraction of waves at the interface of an isotropic medium
over a highly anisotropic medium’, Acta Geophysica, vol. 54, no. 3, pp. 239–249), the authors proposed a process to calculate
R/T (reflection and transmission) coefficients at the interface between isotropic and triclinic half-spaces, with incident qP waves in triclinic media. Unfortunately, besides several misprints, the authors made a fatal assumption that there is no
transmitted SH wave generated in isotropic media, which led the successive analytical derivations and numerical calculations thoroughly
wrong. In this paper, the errors are analyzed at length and corrections are given. Then an alternative approach to solve the
problem is proposed and numerical results are shown and discussed. 相似文献
22.
Weqiang Zhang Qiang Sun Yuliang Zhang Lei Xue Fanfan Kong 《Environmental Earth Sciences》2018,77(9):350
The evolution of porosity and changes in wave velocity in granite after high-temperature treatment has been experimentally investigated in different studies. Statistical analysis of the test results shows that there is a temperature threshold value that leads to variations in porosity and wave velocity. At a temperature that is less than 200 °C, the porosity of granite slowly increases with increases in temperature, while the wave velocity decreases. When the temperature is greater than 200 °C (especially between 400 and 600 °C), the porosity quickly increases, while the wave velocity substantially decreases. The temperature ranges of room temperature to 200 and 200–400 °C correspond to the undamaged state and the micro-damage state, respectively. The results confirm that there is an important link between the variations of physical and mechanical properties in response to thermal treatment. By studying the relationships among rock porosity, wave velocity and temperature, this provides the basis for solving multi-variable coupling problems under high temperatures for the thermal exploitation of petroleum and safe disposal of nuclear waste. 相似文献
23.
24.
Science China Earth Sciences - In the context of global warming, glaciers in the Asian High Mountains (AHMs) are shrinking at an accelerating rate. Projecting their future change is helpful for... 相似文献
25.
Drainage basin object-based method for regional-scale landform classification: a case study of loess area in China 总被引:1,自引:0,他引:1
Landform classification is one of the most important procedures in recognizing and dividing earth surface landforms. However, topographical homogeneity and differences in regional-scale landforms are often ignored by traditional pixel- and object-based landform classification methods based on digital elevation models (DEMs). In this work, a drainage basin object-based method for classifying regional-scale landforms is proposed. Drainage basins with least critical areas are first delineated from DEMs. Then, terrain derivatives of mean elevation, mean slope, drainage density, drainage depth, and terrain texture are employed to characterize the morphology of the drainage basins. Finally, a decision tree based on the topographical characteristics of the drainage basins is constructed and employed to determine the landform classification law. The experiment is validated in the landform classification of regional-scale loess areas in China. Results show that clear boundaries exist in different landforms at the regional scale. Landform type in a specific region shows significant topographical homogeneity under its specific regional geomorphological process. Classification accuracies are 87.3 and 86.3% for the field investigation and model validation, respectively. Spatial patterns of classified landforms and their proximity to sediment sources and other factors can be regarded as indicators of the evolutionary process of loess landform formation. 相似文献
26.
Journal of Paleolimnology - The Songliao Basin, northeast China, possesses an excellent Cretaceous lake sediment record that provides an opportunity to investigate Cretaceous terrestrial climate... 相似文献
27.
江苏溧阳天目湖地区地貌单元的划分可以提升分区、分类型、分层次的地表基质调查效率。基于天目湖地区5 m分辨率的数字高程模型(DEM),应用GIS软件提取高程、坡度、地形起伏度信息;在提取地形起伏度的过程中运用邻域分析法与均值变点法,确定提取地形起伏度的最佳分析窗口大小为37×37像元。将地形起伏度、海拔高程及坡度3种地形要素进行空间叠加分析,并对地貌分布格局与差异变化进行初步探讨,提出将天目湖地区地貌指标划分为平原、河流阶地、山间谷地、台地、丘陵5种类型,其中以山间谷地与台地地貌为主,二者分别占32.97%、21.96%。划分结果符合天目湖地区地貌格局差异及空间分布,有效体现出天目湖地区平原向丘陵过渡的地貌特征,为后续开展地表基质的调查工作提供较为可靠的地理依据,对探究地貌分布格局与地表基质属性差异具有一定的意义。 相似文献
28.
非饱和含黏砂土的广义土-水特征曲线试验研究 总被引:4,自引:0,他引:4
利用非饱和土4联固结仪和非饱和三轴仪,解决了用压力板仪测试土-水特征曲线无法考虑体变、净竖向压力和净平均应力影响的问题,进行了考虑净竖向压力和净平均应力影响的土-水特征曲线研究,对未考虑净竖向压力或净平均应力的土-水特征曲线同考虑净竖向压力或净平均应力的广义土-水特征曲线的试验结果得出,净竖向压力或净平均应力是影响非饱和土土-水特征曲线的重要因素,试验结果与理论公式稳合较好,并结合非饱和理论和试验结果,拟合了可以反映净竖向压力或净平均应力影响的广义土-水特征曲线公式,与试验结果吻合较好。 相似文献
29.
地下介质受到多期构造运动的作用,裂缝以多组形式存在的现象比较普遍,多组裂隙之间的连通性会影响介质的弹性参数.计算含两组交错裂缝饱和岩石弹性模量时,对于裂隙连通的情况,先计算干燥岩石的弹性参数,再通过各向异性流体替换获得含流体裂隙介质的弹性参数.对于不相交裂隙的情况,先对两组裂隙分别计算其饱和裂纹韧度,再计算饱和裂隙岩石的总体弹性参数.研究结果表明:①油水饱和条件下,当裂隙连通时,剪切波分裂参数随着油饱和度的增加变化较小;当裂隙不连通时,剪切波分裂参数随着油饱和度的增加变化较大;②随着裂隙倾角θ的增大,剪切波分裂参数减小;③在油饱和条件下,当裂隙连通时,剪切波分裂参数随着孔隙度的增加稍稍增加;当裂隙不连通情况时,剪切波分裂参数随着孔隙度的增加而减小,减小程度相对较大. 相似文献
30.