全文获取类型
收费全文 | 11419篇 |
免费 | 2120篇 |
国内免费 | 2774篇 |
专业分类
测绘学 | 624篇 |
大气科学 | 2345篇 |
地球物理 | 3060篇 |
地质学 | 5641篇 |
海洋学 | 1307篇 |
天文学 | 583篇 |
综合类 | 1203篇 |
自然地理 | 1550篇 |
出版年
2024年 | 51篇 |
2023年 | 172篇 |
2022年 | 521篇 |
2021年 | 604篇 |
2020年 | 522篇 |
2019年 | 636篇 |
2018年 | 691篇 |
2017年 | 610篇 |
2016年 | 714篇 |
2015年 | 567篇 |
2014年 | 724篇 |
2013年 | 644篇 |
2012年 | 581篇 |
2011年 | 704篇 |
2010年 | 656篇 |
2009年 | 655篇 |
2008年 | 598篇 |
2007年 | 580篇 |
2006年 | 444篇 |
2005年 | 365篇 |
2004年 | 348篇 |
2003年 | 357篇 |
2002年 | 354篇 |
2001年 | 337篇 |
2000年 | 383篇 |
1999年 | 469篇 |
1998年 | 401篇 |
1997年 | 401篇 |
1996年 | 328篇 |
1995年 | 292篇 |
1994年 | 329篇 |
1993年 | 256篇 |
1992年 | 203篇 |
1991年 | 157篇 |
1990年 | 119篇 |
1989年 | 92篇 |
1988年 | 113篇 |
1987年 | 56篇 |
1986年 | 50篇 |
1985年 | 44篇 |
1984年 | 36篇 |
1983年 | 35篇 |
1982年 | 40篇 |
1981年 | 28篇 |
1980年 | 9篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1975年 | 2篇 |
1958年 | 12篇 |
1954年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
421.
422.
423.
424.
425.
426.
427.
428.
We study the fragmentation properties in the protoplanetary disk and properties of the resultant self-gravitating clumps using our newly constructed disk model. Our disk model includes the mass inflall term from a molecular cloud core and the photoevaporation winds effect. We adopt the conventional fragmentation criterion to judge whether a protoplanetary disk can fragment. In this work, we follow our previous work to investigate the properties of the resultant self-gravitating clumps. In our calculation, the initial masses of the resultant self-gravitating clumps lie in the range of tens of MJ to more than one hundred of MJ, where MJ is the Jupiter mass. These initial masses can seemingly account for the masses of extrasolar planets in magnitude. We also calculate the subsequent gas accretion of clumps in 1.27 × 104 yr after the formation of self-gravitating clumps. We find that the subsequent gas accretion of self-gravitating clumps is very efficient, and the clump masses grow to hundreds of MJ and the physical radii Rc of clumps increase to about 10 AU. Additionally, we also calculate the orbital migration of clumps. We find that most clumps have short migration timescale to be accreted onto the protostar, and only a small fraction of clumps have long migration timescale (>106 yr) to successfully become gas giant planets. These results are consistent with previous studies. 相似文献
429.
Due to the continuous and intense rainfall from June 26 to 28, 2016, Xinlu Village in Ganshui Town, Qijiang District, Chongqing, experienced a unitary-slip landslide at approximately UTC+8 19:30 on June 28. This landslide disrupted the Chuan-Qian railway and damaged four residential buildings. To analyze and rehabilitate the landslide, the engineering geology, hydrological conditions, and deformation instability mechanism of this landslide were investigated and comprehensively analyzed based on an in situ survey, geophysical drilling, and a laboratory quick-shearing test. The results show that the landslide is a typical gradual progressive landslide. 相似文献
430.
In geotechnical practice, it is of considerable importance to assess the behavior of vertical–lateral coupled loading piles in multilayered soil deposits. This study deals with a semi-analytical formulation for the performance of a pile suffering from combined vertical and lateral loads. The emphasis is on quantifying the mobilization of the subgrade reaction provided by the layered soil stratums. In the proposed method, subgrade reactions, correlated with both the accumulative axial load transfer and side resistances depending upon the pile–soil interaction, are abstracted as a series of nonlinear springs in both vertical and lateral directions. On account of this, an alternative transfer matrix method is applied to characterize the pile reaction along the depth under the identified boundary conditions atop the pile; meanwhile, the condition of static equilibrium, between two specific pile segments located at the border of soil layers, is also essential. On this basis, validation of the solution is conducted by comparing with observations from experiments and predictions obtained from other existing methods. In addition, the influence of properties in shallow soil layer and the vertical load on the lateral response of the pile is also discussed. The results indicate a reduction in the lateral displacement and the maximum bending moment within the pile with the increase in the shallow soil stiffness, but a growth with the increase in vertical load due to the “P-Δ effect.” 相似文献