全文获取类型
收费全文 | 57661篇 |
免费 | 747篇 |
国内免费 | 695篇 |
专业分类
测绘学 | 1250篇 |
大气科学 | 4097篇 |
地球物理 | 11348篇 |
地质学 | 20511篇 |
海洋学 | 5401篇 |
天文学 | 13209篇 |
综合类 | 158篇 |
自然地理 | 3129篇 |
出版年
2022年 | 343篇 |
2021年 | 614篇 |
2020年 | 643篇 |
2019年 | 706篇 |
2018年 | 1510篇 |
2017年 | 1388篇 |
2016年 | 1711篇 |
2015年 | 943篇 |
2014年 | 1550篇 |
2013年 | 3051篇 |
2012年 | 1868篇 |
2011年 | 2442篇 |
2010年 | 2154篇 |
2009年 | 2855篇 |
2008年 | 2503篇 |
2007年 | 2585篇 |
2006年 | 2347篇 |
2005年 | 1754篇 |
2004年 | 1654篇 |
2003年 | 1620篇 |
2002年 | 1578篇 |
2001年 | 1414篇 |
2000年 | 1328篇 |
1999年 | 1178篇 |
1998年 | 1089篇 |
1997年 | 1109篇 |
1996年 | 943篇 |
1995年 | 866篇 |
1994年 | 769篇 |
1993年 | 674篇 |
1992年 | 694篇 |
1991年 | 640篇 |
1990年 | 650篇 |
1989年 | 586篇 |
1988年 | 538篇 |
1987年 | 611篇 |
1986年 | 579篇 |
1985年 | 703篇 |
1984年 | 762篇 |
1983年 | 729篇 |
1982年 | 689篇 |
1981年 | 616篇 |
1980年 | 580篇 |
1979年 | 558篇 |
1978年 | 554篇 |
1977年 | 488篇 |
1976年 | 448篇 |
1975年 | 460篇 |
1974年 | 451篇 |
1973年 | 491篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
The joint evolution of organic matter and silica in petroliferous sequences is considered in the terms of the laws of transformation of dispersion systems. The dispersion systems are transformed under conditions of low-temperature solid-phase processes accompanied by the silica phase transition and dehydration that favors the evolution of organic matter. 相似文献
72.
73.
74.
The Lagrangian diffusion equation appropriate for the dispersion of current followers (e. g., floats, drogues, drifters) is proposed. The analytical solution to the equation is obtained for a uniform deformation field, characterized by Lagrangian deformations and anisotropic eddy diffusivities both varying with time. Expressions are derived for the patch area and its elongation and rotation. For small values of elapsed time after the initial release the patch area can be accounted for by the exponential of the cumulative value of the horizontal divergence; the relative rate of change of the patch area can be accounted for by the horizontal divergence. 相似文献
75.
The wadic project: A comprehensive field evaluation of directional wave instrumentation 总被引:1,自引:0,他引:1
J. Allender T. Audunson S. F. Barstow S. Bjerken H. E. Krogstad P. Steinbakke L. Vartdal L. E. Borgman C. Graham 《Ocean Engineering》1989,16(5-6)
The results of a comprehensive field trial of nearly all commercially available directional wave measurement systems at the Edda field in the North Sea during winter 1985-86 are presented. The results summarize the accuracy of the principal engineering wave parameters from each system and the dependence on sea state. Limiting factors on system performance and operational problems are also included in the assessment. Overall experience has been good with systems utilizing widely different measurement principles returning consistent results. 相似文献
76.
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
77.
Trends in emigration from Ireland over time are reviewed. "During the eighteenth and nineteenth centuries overseas migration to the United States and seasonal harvest migration to Britain were the main types of movement, but over the past 100 years the Irish have developed a special affinity for settling in British towns. Although the outflow was halted for a time during the 1970s, when return migration took over, the 1980s have seen a renewal of the exodus. This time, however, the character of the flow has changed from predominantly low-skill construction and factory workers to embrace better-educated emigrants, including many graduates. This shift reflects Ireland's changing position in the international market for labour." 相似文献
78.
79.
80.