全文获取类型
| 收费全文 | 1131篇 |
| 免费 | 195篇 |
| 国内免费 | 254篇 |
专业分类
| 测绘学 | 33篇 |
| 大气科学 | 228篇 |
| 地球物理 | 259篇 |
| 地质学 | 532篇 |
| 海洋学 | 107篇 |
| 天文学 | 150篇 |
| 综合类 | 116篇 |
| 自然地理 | 155篇 |
出版年
| 2024年 | 4篇 |
| 2023年 | 11篇 |
| 2022年 | 40篇 |
| 2021年 | 44篇 |
| 2020年 | 40篇 |
| 2019年 | 47篇 |
| 2018年 | 52篇 |
| 2017年 | 49篇 |
| 2016年 | 51篇 |
| 2015年 | 71篇 |
| 2014年 | 74篇 |
| 2013年 | 103篇 |
| 2012年 | 85篇 |
| 2011年 | 76篇 |
| 2010年 | 74篇 |
| 2009年 | 60篇 |
| 2008年 | 68篇 |
| 2007年 | 52篇 |
| 2006年 | 41篇 |
| 2005年 | 35篇 |
| 2004年 | 29篇 |
| 2003年 | 21篇 |
| 2002年 | 32篇 |
| 2001年 | 29篇 |
| 2000年 | 24篇 |
| 1999年 | 32篇 |
| 1998年 | 32篇 |
| 1997年 | 51篇 |
| 1996年 | 25篇 |
| 1995年 | 32篇 |
| 1994年 | 32篇 |
| 1993年 | 29篇 |
| 1992年 | 23篇 |
| 1991年 | 19篇 |
| 1990年 | 11篇 |
| 1989年 | 10篇 |
| 1988年 | 14篇 |
| 1987年 | 6篇 |
| 1986年 | 8篇 |
| 1985年 | 5篇 |
| 1984年 | 3篇 |
| 1982年 | 5篇 |
| 1981年 | 4篇 |
| 1979年 | 3篇 |
| 1978年 | 2篇 |
| 1977年 | 3篇 |
| 1975年 | 3篇 |
| 1973年 | 4篇 |
| 1971年 | 6篇 |
| 1951年 | 1篇 |
排序方式： 共有1580条查询结果，搜索用时 62 毫秒
41.
42.
Potential seasonal calibration for palaeoenvironmental reconstruction using skeletal microstructures and strontium measurements from the cold‐water coral Lophelia pertusa 
下载免费PDF全文
下载免费PDF全文 43.
44.
45.
46.
47.
48.
It is generally recognized that the low strength and high compressibility are the characteristics of soft soil. In addition to other techniques, reinforcement can also be used in increasing the strength and decreasing the deformation of this kind of soil. The results of an investigation into the effects of a natural fiber on the consolidation and shear strength behavior of Shanghai clayey soil reinforced with wheat straw fibers are presented in this paper. A series of one dimensional consolidation and triaxial tests were conducted on samples of unreinforced and reinforced Shanghai clayey soil with different percentages of randomly distributed wheat straw fibers. The results show that the preconsolidation pressure decreases and the coefficient of swelling and compression generally increase with increasing the fiber content until a optimum content value. Furthermore, the addition of wheat straw fiber leads to a significant increase in shear strength and friction angle of the natural soil and there is an optimum wheat fiber content that makes this increase maximal. 相似文献
49.
Tidal current energy is renewable and sustainable, which is a promising alternative energy resource for the future electricity supply. The straight-bladed vertical-axis turbine is regarded as a useful tool to capture the tidal current energy especially under low-speed conditions. A 2D unsteady numerical model based on Ansys-Fluent 12.0 is established to conduct the numerical simulation, which is validated by the corresponding experimental data. For the unsteady calculations, the SST model, 2×10~5 and 0.01 s are selected as the proper turbulence model, mesh number, and time step, respectively. Detailed contours of the velocity distributions around the rotor blade foils have been provided for a flow field analysis. The tip speed ratio(TSR) determines the azimuth angle of the appearance of the torque peak, which occurs once for a blade in a single revolution. It is also found that simply increasing the incident flow velocity could not improve the turbine performance accordingly. The peaks of the averaged power and torque coefficients appear at TSRs of 2.1 and 1.8, respectively. Furthermore, several shapes of the duct augmentation are proposed to improve the turbine performance by contracting the flow path gradually from the open mouth of the duct to the rotor. The duct augmentation can significantly enhance the power and torque output. Furthermore, the elliptic shape enables the best performance of the turbine. The numerical results prove the capability of the present 2D model for the unsteady hydrodynamics and an operating performance analysis of the vertical tidal stream turbine. 相似文献
50.