全文获取类型
收费全文 | 5375篇 |
免费 | 844篇 |
国内免费 | 1456篇 |
专业分类
测绘学 | 1018篇 |
大气科学 | 26篇 |
地球物理 | 1669篇 |
地质学 | 3618篇 |
海洋学 | 164篇 |
天文学 | 17篇 |
综合类 | 803篇 |
自然地理 | 360篇 |
出版年
2024年 | 10篇 |
2023年 | 65篇 |
2022年 | 147篇 |
2021年 | 186篇 |
2020年 | 213篇 |
2019年 | 235篇 |
2018年 | 212篇 |
2017年 | 260篇 |
2016年 | 272篇 |
2015年 | 291篇 |
2014年 | 323篇 |
2013年 | 320篇 |
2012年 | 339篇 |
2011年 | 383篇 |
2010年 | 282篇 |
2009年 | 388篇 |
2008年 | 359篇 |
2007年 | 370篇 |
2006年 | 354篇 |
2005年 | 287篇 |
2004年 | 316篇 |
2003年 | 286篇 |
2002年 | 232篇 |
2001年 | 187篇 |
2000年 | 188篇 |
1999年 | 172篇 |
1998年 | 146篇 |
1997年 | 164篇 |
1996年 | 137篇 |
1995年 | 110篇 |
1994年 | 103篇 |
1993年 | 89篇 |
1992年 | 69篇 |
1991年 | 41篇 |
1990年 | 38篇 |
1989年 | 27篇 |
1988年 | 26篇 |
1987年 | 18篇 |
1986年 | 12篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1979年 | 3篇 |
1975年 | 1篇 |
1954年 | 3篇 |
排序方式: 共有7675条查询结果,搜索用时 15 毫秒
41.
42.
43.
Two-Dimensional Mathematical Model of Tidal Current and Sediment for Oujiang Estnary and Wenzhou Bay 总被引:1,自引:0,他引:1
A 2-D mathematical model of tidal current and sediment has been developed for the Oujiang Estuary and the WenzhouBay. This model accomodates complicated features including multiple islands, existence of turbidity, and significant differ-ence in size distribution of bed material. The governing equations for non-uniform suspended load and bed load transport arepresented in a boundary-fitted orthogonal curvilinear coordinate system. The numerical solution procedures along with theirinitial conditions, boundary conditions, and movable boundary technique are presented. Strategies for computation of thecritical condition of deposition or erosion, sediment transport capacity, non-uniform bed load discharge, etc. are suggested.The model verification computation shows that, the tidal levels computed from the model are in good agreement with the fielddata at the 18 tidal gauge stations. The computed velocities and flow directions also agree well with the values measuredalong the totally 52 synchronously observed verticals distributed over 8 cross sections. The computed tidal water throughputsthrough the Huangda‘ao cross section are close to the measured data. And the computed values of bed deformation fromYangfushan to the estuary outfall and in the outer-sea area are in good agreement with the data observed from 1986 to 1992.The changes of tidal volumes through the estuary, velocities in different channels and the bed form due to the influence of thereclamation project on the Wenzhou shoal are predicted by means of this model. 相似文献
44.
45.
AbstractWith the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing. 相似文献
46.
Since the beginning of formation of Proto-Taiwan, the subducting Philippine (PH) Sea plate has moved continuously through
time in the N307° direction with respect to Eurasia (EU), tearing the EU plate. The subducting EU plate includes a continental
part in the north and an oceanic part in the south. The boundary B between these two domains corresponds to the eastern prolongation
of the northeastern South China Sea ocean-continent transition zone. In the Huatung Basin (east of Taiwan), the Taitung Canyon
is N065° oriented and is close and parallel to B. Seismic profiles show that the southern flank of the canyon corresponds
to a fault with a normal component of a few tens of meters in the sediments and possible dextral shearing. Several crustal
earthquakes of magnitude >%6 are located beneath the trend of the Taitung Canyon and focal mechanisms suggest that the motion
is right-lateral. Thus, faulting within the sedimentary sequence beneath the Taitung Canyon is a consequence of underlying
dextral strike-slip crustal motions. As the continental part of the EU slab located north of B has been recently detached,
some subsequent dextral strike-slip motion might be expected within the EU slab, along the ocean-continent transition zone,
which is a potential zone of weakness. We suggest that the dextral strike-slip motion along the ocean-continent boundary of
the EU slab might trigger the observed dextral strike-slip motion within the overlying PH Sea crust and the associated faulting
within the sediments of the Huatung Basin, beneath the Taitung Canyon.
An erratum to this article is available at . 相似文献
47.
土工布充砂袋的应用及其研究进展 总被引:10,自引:1,他引:10
对土工布充砂袋技术和国内外的应用进行了介绍。鉴于土工布充砂袋属于一种新兴起的土工新材料和新技术,在设计和工程实际中还存在着许多急待解决的问题,着重对各种典型状态和典型环境下的土工布充砂袋的变形、应力和土工布充砂袋堆的稳定性研究进展进行综述,最后提出进一步研究的思路。 相似文献
48.
49.
哀牢山-红河断裂带中段应变分析 总被引:1,自引:0,他引:1
对哀牢山—红河断裂带中段和平—水塘剖面、墨江—元江剖面和其它地段的岩石应变及磁组构进行了分析,表明应变强度的校正磁各向异性度PJ从断裂带向西至三叠系明显降低,变形强度向西迅速减弱。磁化率椭球体主轴展布反映出剪切带内、外变形方式的改变。剪切带内,以水平走滑运动为主;向西则以水平缩短为主。在应变分析中,对断裂带内的S—C组构两组面理夹角、杏仁体和石榴石应变标志体进行了测量,结果显示,剪切带内的磁组构和岩石组构间关系较差。此外,还对这两条剖面中的三叠系进行了应变和磁组构分析,找出了它们与磁化率椭球体对应轴率间的相关性。 相似文献
50.
在大型压力容器的部件焊接过程中,由于预热、焊接等工艺流程会导致各部件产生变形,从而引起部件之间的位置关系产生变化。为保证压力容器成品满足设计要求,必须在制造过程中实施变形监测,依据变形数据适当调整焊接工艺流程,控制变形量。提出采用智能全站仪配以自动变形监测软件对大型压力容器焊接变形进行实时监测,并应用于生产实践中,监测结果表明该方法自动化程度高、实时性好,能同时给出位置和姿态变形数据。 相似文献