首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   23150篇
  免费   237篇
  国内免费   131篇
测绘学   357篇
大气科学   1224篇
地球物理   4401篇
地质学   9063篇
海洋学   2247篇
天文学   5334篇
综合类   47篇
自然地理   845篇
  2022年   267篇
  2021年   436篇
  2020年   401篇
  2019年   467篇
  2018年   955篇
  2017年   876篇
  2016年   891篇
  2015年   373篇
  2014年   781篇
  2013年   1300篇
  2012年   903篇
  2011年   1108篇
  2010年   1062篇
  2009年   1234篇
  2008年   1059篇
  2007年   1232篇
  2006年   1067篇
  2005年   568篇
  2004年   540篇
  2003年   550篇
  2002年   566篇
  2001年   512篇
  2000年   416篇
  1999年   338篇
  1998年   326篇
  1997年   331篇
  1996年   259篇
  1995年   271篇
  1994年   239篇
  1993年   187篇
  1992年   211篇
  1991年   183篇
  1990年   195篇
  1989年   187篇
  1988年   156篇
  1987年   182篇
  1986年   171篇
  1985年   205篇
  1984年   199篇
  1983年   197篇
  1982年   188篇
  1981年   170篇
  1980年   160篇
  1979年   178篇
  1978年   157篇
  1977年   141篇
  1976年   130篇
  1975年   135篇
  1974年   126篇
  1973年   165篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Doklady Earth Sciences - The seismotectonic position of the strong earthquake that occurred in the southern part of Sakhalin Island on September 13, 2020, is considered. The maximum shaking...  相似文献   
992.
993.
This paper describes a soil‐structure coupling method to simulate blast loading in soil and structure response. For the last decade, simulation of soil behavior under blast loading and its interaction with semi buried structure in soil becomes the focus of computational engineering in civil and mechanical engineering communities. In current design practice, soil‐structure interaction analysis often assumes linear elastic properties of the soil and uses small displacement theory. However, there are numerous problems, which require a more advanced approach that account for soil‐structure interaction and appropriate constitutive models for soil. In simplified approaches, the effect of soil on structure is considered using spring‐dashpot‐mass system, and the blast loading is modeled using linearly decaying pressure–time history based on equivalent trinitrotoluene and standoff distance, using ConWep, a computer program based on semi‐empirical equations. This strategy is very efficient from a CPU time computing point of view but may not provide accurate results for the dynamic response of the structure, because of its significant limitations, mainly when soil behavior is strongly nonlinear and when the buried charge is close to the structure. In this paper, both soil and explosive are modeled using solid elements with a constitutive material law for soil, and a Jones–Wilkins–Lee equation of state for explosive. One of the problems we have encountered when solving fluid structure interaction problems is the high mesh distortion at the contact interface because of high fluid nodal displacements and velocities. Similar problems have been encountered in soil structure interaction problems. To prevent high mesh distortion for soil, a new coupling algorithm is performed at the soil structure interface for structure loading. The coupling method is commonly used for fluid structure interaction problems in automotive and aerospace industry for fuel sloshing tank, and bird impact problems, but rarely used for soil structure interaction problems, where Lagrangian contact type algorithms are still dominant. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
994.
995.
996.
997.
The Matt Wilson structure is a circular 5.5 km-diameter structure in Early Mesoproterozoic or Neoproterozoic rocks of the Victoria Basin, Northern Territory. It lies in regionally horizontal to gently dipping Wondoan Hill and Stubb Formations (Tijunna Group) and Jasper Gorge Sandstone (Auvergne Group). An outer circumferential syncline with dips of 5?–?40° in the limbs surrounds an intermediate zone with faulted sandstone displaying horizontal to low dips, and a central steeply dipping zone about 1.5 km across. Several thrust faults in the outer syncline appear to indicate outward-directed forces. The central zone, marked by steeply dipping to overturned Tijunna Group and possibly Bullita Group sandstone and mudstone, indicates uplift of at least 300 m. The rocks are intensely fractured with some brecciation, and contain numerous planar to subtly undulating surfaces displaying striae which resemble shatter cleavage. Thin-sections of sandstone from the central area show zones of intense microbrecciation and irregular and planar fractures in quartz, but no melt-rocks have been identified. The planar fractures occur in multiple intersecting parallel sets typical of relatively low-level (5?–?10 GPa) shock-pressure effects. Alternative mechanisms, i.e. igneous intrusion, carbonate collapse, diapirism and regional deformation processes, have been discounted. The circular nature, central uplift, faulting, shatter features and planar fractures are all consistent with an impact origin. The Matt Wilson structure is most likely a deeply eroded impact structure in which the more highly shocked rocks of the original crater floor have been removed by erosion. Estimates of the age of the Auvergne and Tijunna Groups range from Early Mesoproterozoic (which we favour) to Late Neoproterozoic. Early Cambrian Antrim Plateau Volcanics near the impact structure show no signs of impact effects, allowing the age of impact to be constrained between Early Mesoproterozoic and Early Cambrian. The presence of widespread soft-sediment deformation features, apparently confined to a single horizon in the Saddle Creek Formation some 700?–?1000 m stratigraphically higher in the Auvergne Group than the rocks at the impact site, and apparently increasing in thickness towards the Matt Wilson structure, lead us to speculate that this probable event horizon is related to the impact event: if correct the impact occurred during deposition of the Saddle Creek Formation.  相似文献   
998.
999.
The neotectonic structures of the Lower Oka (Nizhneokskii) Region formed under different geodynamic conditions. This is attested by the morphology, orientation, internal structure, and jointing of the structures. The Oka-Tsna arc formed under the effect of tension from an inner source on the one hand and stress from the Alpian belt on the other hand. The latitudinally-oriented structures of the northwestern slope of the Tokmovo arc emerged as a result of uplift and widening. Both types of structure are combined within the limits of the Oka-Murom trough, which is a geodynamically active zone.  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号