全文获取类型
收费全文 | 5032篇 |
免费 | 1110篇 |
国内免费 | 1248篇 |
专业分类
测绘学 | 442篇 |
大气科学 | 854篇 |
地球物理 | 1346篇 |
地质学 | 2792篇 |
海洋学 | 660篇 |
天文学 | 294篇 |
综合类 | 410篇 |
自然地理 | 592篇 |
出版年
2024年 | 26篇 |
2023年 | 97篇 |
2022年 | 229篇 |
2021年 | 278篇 |
2020年 | 218篇 |
2019年 | 271篇 |
2018年 | 303篇 |
2017年 | 283篇 |
2016年 | 282篇 |
2015年 | 263篇 |
2014年 | 303篇 |
2013年 | 324篇 |
2012年 | 328篇 |
2011年 | 349篇 |
2010年 | 333篇 |
2009年 | 305篇 |
2008年 | 280篇 |
2007年 | 243篇 |
2006年 | 220篇 |
2005年 | 220篇 |
2004年 | 187篇 |
2003年 | 188篇 |
2002年 | 224篇 |
2001年 | 211篇 |
2000年 | 185篇 |
1999年 | 191篇 |
1998年 | 168篇 |
1997年 | 149篇 |
1996年 | 124篇 |
1995年 | 88篇 |
1994年 | 95篇 |
1993年 | 91篇 |
1992年 | 68篇 |
1991年 | 54篇 |
1990年 | 45篇 |
1989年 | 30篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 20篇 |
1985年 | 17篇 |
1984年 | 14篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1974年 | 1篇 |
1958年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有7390条查询结果,搜索用时 15 毫秒
91.
92.
邛崃地震发生后,成都市地震局很快做出反应,及时开展了地震考察并做出了正确的震后趋势判断,取得了较好的社会效益。 相似文献
93.
利用格点尝试法首先分区对鄂尔多斯地块周边的 30 0 0多个小震震源机制解进行了处理。结果显示 ,在震源机制解覆盖的时段内 ,地块周边地区的平均构造应力场有以下特征 :地块周边主要以水平构造作用力为主 ,且其主压应力轴走向以地块西南侧为中心 ,从北至东呈扇形展布。在分区基础上 ,对各区的平均主应力轴分布进行了扫描 ,得到了其随时间的变化过程。其中渭河、六盘山和银川区的构造应力场相对稳定 ,临汾和同心区的构造应力场变化复杂 ,临河、包头、呼和、大同和太原区的构造应力场变化与该区的几次中强地震有密切关系。另外 ,地块周边除个别区外大多数区域在 1992年和 1996年前后 ,主压应力轴走向有趋近于N75°E的现象 相似文献
94.
琼北火山区是中国的主要火山群之一。笔者应用HDS - 1型快速数字闪烁测氡仪对琼北火山群马鞍岭和雷虎岭段的火山及断裂活动性进行了勘测和研究 ,对荣山 -岭南断裂进行了重点测量 ,查明了该断裂的具体位置 ,研究了火山及断裂的气体释放特征。发现Rn(氡 ) ,Th(钍 )的变化与断裂构造有密切关系 ,在Ⅰ ,Ⅱ测线上Th ,Rn异常对断裂的反映相当好。根据Th ,Rn的展布特征和浓度变化比较深入地分析了断裂的活动性。在雷虎岭西南 ,荣山 -岭南断裂活动性最强 ,而且 ,自西北向东南断裂规模及活动性均有增强的趋势。此外 ,还对火山的活动性进行了讨论和分析 相似文献
95.
Introduction With the development of global tectonics and overall detections for global tectonics with multi-geophysical methods, ones can roundly study on the geological tectonics of sampling and magnetic stripe image, so as to summarize and interpret the geometrical and kinematical charac-teristics for the distribution of the ocean and the land, and spreading state of the global tectonics in a global scale. From a comprehensive view, the South and North hemispheres are clearly unsym-metrical… 相似文献
96.
The Vincent Thomas Bridge in the Los Angeles metropolitan area, is a critical artery for commercial traffic flow in and out of the Los Angeles Harbor, and is at risk in the seismically active Southern California region, particularly because it straddles the Palos Verdes fault zone. A combination of linear and non‐linear system identification techniques is employed to obtain a complete reduced‐order, multi‐input–multi‐output (MIMO) dynamic model of the Vincent Thomas Bridge based on the dynamic response of the structure to the 1987 Whittier and 1994 Northridge earthquakes. Starting with the available acceleration measurements (which consists of 15 accelerometers on the bridge structure and 10 accelerometers at various locations on its base), an efficient least‐squares‐based time‐domain identification procedure is applied to the data set to develop a reduced‐order, equivalent linear, multi‐degree‐of‐freedom model. Although not the main focus of this study, the linear system identification method is also combined with a non‐parametric identification technique, to generate a reduced‐order non‐linear mathematical model suitable for use in subsequent studies to predict, with good fidelity, the total response of the bridge under arbitrary dynamic environments. Results of this study yield measurements of the equivalent linear modal properties (frequencies, mode shapes and non‐proportional damping) as well as quantitative measures of the extent and nature of non‐linear interaction forces arising from strong ground shaking. It is shown that, for the particular subset of observations used in the identification procedure, the apparent non‐linearities in the system restoring forces are quite significant, and they contribute substantially to the improved fidelity of the model. Also shown is the potential of the identification technique under discussion to detect slight changes in the structure's influence coefficients, which may be indicators of damage and degradation in the structure being monitored. Difficulties associated with accurately estimating damping for lightly damped long‐span structures from their earthquake response are discussed. The technical issues raised in this paper indicate the need for added spatial resolution in sensor instrumentation to obtain identified mathematical models of structural systems with the broadest range of validity. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
97.
98.
党政机关电子政务建设的若干问题 总被引:1,自引:4,他引:1
以从事政务信息化建设的实践经验为基础 ,对电子政务建设的基本问题进行了系统分析 ,内容包括 :信息关系和信息控制、信息分类、数据库结构、软件系统开发思路、电子政务的工作目标、服务对象、服务模式、电子政务建设的技术措施等。 相似文献
99.
100.
ZHANGJin MAZongjin RENWenjun LEIYongliang 《大地构造与成矿学(英文版)》2003,27(1):165-178
There are many thrust-related structures occurring in the Paleozoic strata of the Niushou Mountain in the central part of Ningxia Hui Autonomous Region. The fault-related folds are the typical structures in this area. Based on the analysis about these structures and their relationships, the processes by which these structures of the Miboshan Formation were formed are reconstructed, and the strata underwent about three stages of deformation: (1) horizontal shortening, (2) folding, and (3) thrusting. And the fact that the Niushou Mountain is the leading edge of an old thrust sheet was proved, the Niushou Mountain, the Daluo Mountain and the Xiaoluo Mountain together constitute the front part of this old thrust zone, so the Niushou Mountain and the Ordovician strata in the central and southern parts of Ningxia now are likely allochthons. In the period from middle Ordovician to Devonian, the areas of the central and southern Ningxia belonged to the back-arc foreland basin of North Qilianshan orogen, which was adjacent to the continent in the north. In the later part of the early Paleozoic period, the Niushou Mountain was formed after the closure of the back-arc foreland basin. 相似文献