全文获取类型
收费全文 | 28228篇 |
免费 | 5024篇 |
国内免费 | 6599篇 |
专业分类
测绘学 | 1469篇 |
大气科学 | 5919篇 |
地球物理 | 7186篇 |
地质学 | 14318篇 |
海洋学 | 3173篇 |
天文学 | 1294篇 |
综合类 | 3138篇 |
自然地理 | 3354篇 |
出版年
2024年 | 125篇 |
2023年 | 536篇 |
2022年 | 1218篇 |
2021年 | 1441篇 |
2020年 | 1183篇 |
2019年 | 1268篇 |
2018年 | 1564篇 |
2017年 | 1418篇 |
2016年 | 1655篇 |
2015年 | 1243篇 |
2014年 | 1673篇 |
2013年 | 1622篇 |
2012年 | 1424篇 |
2011年 | 1536篇 |
2010年 | 1508篇 |
2009年 | 1498篇 |
2008年 | 1367篇 |
2007年 | 1297篇 |
2006年 | 1075篇 |
2005年 | 1102篇 |
2004年 | 779篇 |
2003年 | 844篇 |
2002年 | 836篇 |
2001年 | 765篇 |
2000年 | 929篇 |
1999年 | 1363篇 |
1998年 | 1139篇 |
1997年 | 1226篇 |
1996年 | 1129篇 |
1995年 | 937篇 |
1994年 | 797篇 |
1993年 | 684篇 |
1992年 | 557篇 |
1991年 | 411篇 |
1990年 | 309篇 |
1989年 | 271篇 |
1988年 | 258篇 |
1987年 | 181篇 |
1986年 | 143篇 |
1985年 | 109篇 |
1984年 | 73篇 |
1983年 | 68篇 |
1982年 | 47篇 |
1981年 | 41篇 |
1980年 | 59篇 |
1979年 | 38篇 |
1978年 | 20篇 |
1977年 | 14篇 |
1975年 | 14篇 |
1958年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
It is well known that the Babuska–Brezzi stability criterion or the Zienkiewicz–Taylor patch test precludes the use of the finite elements with the same low order of interpolation for displacement and pore pressure in the nearly incompressible and undrained cases, unless some stabilization techniques are introduced for dynamic analysis of saturated porous medium where coupling occurs between the displacement of solid skeleton and pore pressure. The numerical manifold method (NMM), where the interpolation of displacement and pressure can be determined independently in an element for the solution of u–p formulation, is derived based on triangular mesh for the requirement of high accurate calculations from practical applications in the dynamic analysis of saturated porous materials. The matrices of equilibrium equations for the second‐order displacement and the first‐order pressure manifold method are given in detail for program coding. By close comparison with widely used finite element method, the NMM presents good stability for the coupling problems, particularly in the nearly incompressible and undrained cases. Numerical examples are given to illustrate the validity and stability of the manifold element developed. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
2.
A THREE-DIMENSIONAL ELASTIC NESTED-GRID MESO-(β-γ)SCALE ATMOSPHERIC MODEL——PARTI:MODEL DESCRIPTION 下载免费PDF全文
A three-dimensional elastic nonhydrostatic mesoscale(β-γ)model with nested-grid is presented.It uses a set of fullequations in terrain-following coordinates as its basic dynamic frame,which is solved with a time-splitting algorithmfor acoustic and gravity waves.The model physical parameterization includes a K-theory subgrid eddy mixing for cloudand free atmosphere,a bulk planetary boundary layer parameterization,and three types of sofisticated cloudmicrophysics schemes with double-parameters for hail-bearing clouds,warm clouds and snowing clouds respectively.The model is designed to be used flexibly for simulations of a variety of meso-and small-scale atmospheric processes,and can be improved as a regional and local operational NWP system in future. 相似文献
3.
4.
周全浩 《云南地理环境研究》1990,2(1):1-9
本文分析了中国石油生产近20年变化的原因,对一些学者认为80年代中国会成为超级产油大国,后又悲观断定80年代中国可能变成石油净进口国作了评述。同时对90年代中国石油生产前景作了初步展望。 相似文献
5.
The impact of wave loads and pore-water pressure generation on initiation of sediment transport 总被引:3,自引:0,他引:3
Edward C. Clukey Fred H. Kulhawy Philip L. -F. Liu George B. Tate 《Geo-Marine Letters》1985,5(3):177-183
The build-up of pore-water pressure by waves can lead to sediment liquefaction and subsequent transport by traction currents. This process was investigated by measuring pore-water pressures both in a field experiment and laboratory wave tank tests. Liquefaction was observed in the wave tank tests. The results suggest that sand is less susceptible than silts to wave-induced liquefaction because of the tendency to partially dissipate pore-water pressures. However, previous studies have determined that pore-water pressures must approach liquefaction before current velocities necessary to initiate transport are reduced. Once liquefaction has occurred more sediment can be transported. 相似文献
6.
Liu X-f 《International journal of population geography : IJPG》1997,3(1):15-29
"The humanitarian policy that the Canadian government implemented in response to the 1989 Tiananmen Square crackdown changed a migration system primarily based on personal networks into a brain drain. Post-Tiananmen mainland Chinese immigrants (MCIs) were better educated than those arriving in Canada previously. Among the post-Tiananmen MCIs, those who landed under the policy were better educated than those landing in other categories. The analysis suggests that post-Tiananmen MCIs represented a brain-drain rather than a refugee flow, that the humanitarian policy implicitly contained ideological and human capital concerns in addition to humanitarian concerns, and that Canada benefited from the policy by obtaining human capital as well as satisfying its humanitarian obligations and ideological aspirations." 相似文献
7.
8.
9.
本文通过对辽西及邻区中生代盆地火山岩稀土元素配分特征的研究及模拟运算,探讨了其岩浆成因及过程。结果显示南北岩区岩浆成因不同,南岩区岩源为MORB地幔和长期富集型幔熔融混合而成,北岩区为MORB和近期亏损型地幔熔融混合而成。 相似文献
10.