全文获取类型
收费全文 | 5116篇 |
免费 | 927篇 |
国内免费 | 1238篇 |
专业分类
测绘学 | 751篇 |
大气科学 | 798篇 |
地球物理 | 946篇 |
地质学 | 2835篇 |
海洋学 | 700篇 |
天文学 | 87篇 |
综合类 | 429篇 |
自然地理 | 735篇 |
出版年
2024年 | 34篇 |
2023年 | 122篇 |
2022年 | 203篇 |
2021年 | 279篇 |
2020年 | 226篇 |
2019年 | 263篇 |
2018年 | 241篇 |
2017年 | 255篇 |
2016年 | 285篇 |
2015年 | 292篇 |
2014年 | 288篇 |
2013年 | 351篇 |
2012年 | 394篇 |
2011年 | 404篇 |
2010年 | 373篇 |
2009年 | 377篇 |
2008年 | 367篇 |
2007年 | 410篇 |
2006年 | 358篇 |
2005年 | 289篇 |
2004年 | 235篇 |
2003年 | 185篇 |
2002年 | 208篇 |
2001年 | 198篇 |
2000年 | 171篇 |
1999年 | 92篇 |
1998年 | 47篇 |
1997年 | 52篇 |
1996年 | 48篇 |
1995年 | 33篇 |
1994年 | 30篇 |
1993年 | 25篇 |
1992年 | 25篇 |
1991年 | 19篇 |
1990年 | 16篇 |
1989年 | 11篇 |
1988年 | 19篇 |
1987年 | 3篇 |
1986年 | 4篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 3篇 |
1982年 | 7篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1975年 | 2篇 |
1963年 | 2篇 |
1958年 | 3篇 |
1957年 | 2篇 |
1934年 | 1篇 |
排序方式: 共有7281条查询结果,搜索用时 15 毫秒
1.
私营企业主是我们社会主义市场经济的建设者 ,是否“合法”是我们正确解读私营企业主的关键。我国目前的私营企业主分为两类三种。合法经营的私营企业主中的优秀分子是吸收入党的主要对象 相似文献
2.
3.
This paper presents a method that incorporates a non‐associated flow rule into the limit analysis to investigate the influence of the dilatancy angle on the factor of safety for the slope stability analysis. The proposed method retain's the advantage of the upper bound method, which is simple and has no stress involvement in the calculation of the energy dissipation and the factor of safety. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
4.
基于Windows消息机制的人机交互的研究与应用 总被引:1,自引:0,他引:1
结合实例着重介绍了如何通过串行通讯利用Windows的消息机制来解决目前工业设备控制中人机交互的模拟问题,并对这两种技术进行了详细的论述. 相似文献
5.
近年来激光物理与应用的进展促成了激光天文动力学空间任务概念的提出。在激光天文动力学任务概念研究方面 ,必须对由远程航天器上传回的激光进行讯号的测量与处理。激光经过长距离的传输后 ,功率大幅下降 ,因此在空间任务概念的考虑上 ,弱光锁相是计划中关键性的技术。由航天器射来的激光 ,经过望远镜聚光后与本地激光进行锁相 ,由本地激光承载及传达太空激光的相位信息。实验中 ,我们使用 2支半导体激光泵浦非平面环形共振腔钇镏石激光 (Diodelaserpumpednon -planarringcavityNd :YAGlaser) ,分别代表远程的弱光及代表本地的强光 ,建立弱光锁相环路系统 (weak -lightphase -lockedloopsystem)。以中性光强度滤光器 (ND -filter;neutraldensityfilter)减弱光讯号来仿真远程激光传来的弱光。在相位探测部分使用均衡探测法 ,消除激光强度噪声 ,以提高讯噪比。同时配合适当的环路滤波器 ,控制激光频率 ,提高锁相的能力。对 2nW的弱光与 2mW的强光可长时间锁相 ,其均方根相位误差为 57mrad。 2 0 0pW的弱光与 2 0 0 μW的强光锁相时间可达 2h以上 ,其相位误差为 2 0 0mrad。 2 0pW的弱光与 2 0 0 μW的强光锁相时间亦可达 2h以上 ,其相位误差为 1 60mrad。最后 ,我们对 2pW的弱光与 2 0 0 μW的强光锁相 , 相似文献
6.
Observation of fluid parcel pathways in the Kuroshio Stream revealed a striking crossstream pattern associated with the Kuroshio‘‘ s meanders. In order to understand the observed pattern, a two-dimensional kinematic model of a meandering jet was developed which could be used to examine the relationship between streamfunction patterns and fluid parcel trajectories. The experiments designed to investigate the dependence of the water exchanges between the Kuroshio water and its surroundings on the characteristics of the Kuroshio‘‘s meanders involved the downstream speed,phase speed and the amplitude of other propagating waves. The results suggested that fluid parcels could cross the meandering jet to and fro; and that the water exchanges between the Kuroshio and its surroundings increased with a) increasing meander amplitude, b) decreasing downstream speed, and c) increasing wave phase speed. The results also showed that when the meandering jet was disturbed by other propagating waves, more effective water exchanges could be induced. 相似文献
7.
8.
9.
Development of a 3D GIS and its application to karst areas 总被引:1,自引:0,他引:1
There is a growing interest in modeling and analyzing karst phenomena in three dimensions. This paper integrates geology,
groundwater hydrology, geographic information system (GIS), database management system (DBMS), visualization and data mining
to study karst features in Huaibei, China. The 3D geo-objects retrieved from the karst area are analyzed and mapped into different
abstract levels. The spatial relationships among the objects are constructed by a dual-linker. The shapes of the 3D objects
and the topological models with attributes are stored and maintained in the DBMS. Spatial analysis was then used to integrate
the data in the DBMS and the 3D model to form a virtual reality (VR) to provide analytical functions such as distribution
analysis, correlation query, and probability assessment. The research successfully implements 3D modeling and analyses in
the karst area, and meanwhile provides an efficient tool for government policy-makers to set out restrictions on water resource
development in the area. 相似文献
10.
Unconsolidated sand, gravel and clay deposits near Beihai and in the Leizhou Peninsula in southern China form an unconfined
aquifer, aquitard and a confined aquifer. Water and soil samples were collected from the two aquifers in the coastal Beihai
area for the determination of chemical compositions, minerals and soluble ions. Hydrogeochemical modeling of three flow paths
through the aquitard are carried out using PHREEQC to determine water–rock interactions along the flow paths. The results
indicate that the dissolution of anorthite, fluorite, halite, rhodochrosite and CO2, and precipitation of potash feldspar and kaolinite may be occurring when groundwater leaks through the aquitard from the
unconfined aquifer to the confined aquifer. Cation exchanges between Na and Ca can also happen along the flow paths. 相似文献