全文获取类型
收费全文 | 426篇 |
免费 | 32篇 |
国内免费 | 23篇 |
专业分类
测绘学 | 217篇 |
大气科学 | 18篇 |
地球物理 | 73篇 |
地质学 | 62篇 |
海洋学 | 40篇 |
天文学 | 35篇 |
综合类 | 25篇 |
自然地理 | 11篇 |
出版年
2023年 | 2篇 |
2022年 | 2篇 |
2021年 | 4篇 |
2020年 | 6篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 15篇 |
2016年 | 6篇 |
2015年 | 14篇 |
2014年 | 21篇 |
2013年 | 18篇 |
2012年 | 25篇 |
2011年 | 22篇 |
2010年 | 14篇 |
2009年 | 28篇 |
2008年 | 37篇 |
2007年 | 39篇 |
2006年 | 29篇 |
2005年 | 14篇 |
2004年 | 18篇 |
2003年 | 22篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 8篇 |
1999年 | 20篇 |
1998年 | 8篇 |
1997年 | 11篇 |
1996年 | 9篇 |
1995年 | 11篇 |
1994年 | 7篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 4篇 |
1990年 | 3篇 |
1989年 | 3篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1981年 | 1篇 |
1977年 | 1篇 |
排序方式: 共有481条查询结果,搜索用时 312 毫秒
81.
利用GPS相关技术,通过对比,分析了新疆大地控制网点2000国家大地坐标系成果在新疆测绘领域应用情况,验证了相关的数学精度,并提出了相关的应用分析结论。 相似文献
82.
本文介绍了使用EXCEL处理高斯坐标的正算、反算问题,着重阐述了计算公式的编制,具有使用方便、实用性较强的特点。 相似文献
83.
84.
现时许多地方和工程坐标系在坐标数值和方位上与国家标准3°带里的偏差很大,使得其地形图无法与国家标准3°带的对接,并导致工程实践中许多的麻烦和不便;许多地方坐标系有效带宽太小。本文通过一个简单的公式,一次完成控制网的换带、旋转、放大、平移,获得控制网的"假3°带坐标系"坐标。假3°带坐标系具有诸多优点:坐标数值和方位与国家标准3°带的偏差极小,地形图可与国家的对接;有效带宽极大;便于CORS系统流动站使用;做法简单,适用广泛,可用于全国绝大部分地方坐标系。文章还对大城市坐标系的建立提出了有益建议。 相似文献
85.
Researches on breaking-induced currents by waves are summarized firstly in this paper. Then, a combined numerical model in orthogonal curvilinear coordinates is presented to simulate wave-induced current in areas with curved boundary or irregular coastline. The proposed wave-induced current model includes a nearshore current module established through orthogonal curvilinear transformation form of shallow water equations and a wave module based on the curvilinear parabolic approximation wave equation. The wave module actually serves as the driving force to provide the current module with required radiation stresses. The Crank-Nicolson finite difference scheme and the alternating directions implicit method are used to solve the wave and current module, respectively. The established surf zone currents model is validated by two numerical experiments about longshore currents and rip currents in basins with rip channel and breakwater. The numerical results are compared with the measured data and published numerical results. 相似文献
86.
A scale free representation of a general non-isochoric 2D deformation is presented which is amenable to mathematical analysis. By describing deformation in 2D in terms of polar coordinates the stretching and rotational histories of linear elements separate and are easily analysed both qualitatively and quantitatively. An analysis of finite strain combined with dynamical considerations allows the derivation of equations which may be used to estimate finite strain, area change and kinematic vorticity number. Numerical investigation of method developed here was carried out and it was found to perform well unless large area changes occur in combination with large components of simple shear. A re-analysis of natural data indicates the method is consistent. 相似文献
87.
A multiyear solution of the SIRGAS-CON network was used to estimate the strain rates of the earth surface from the changing directions of the velocity vectors of 140 geodetic points located in the South American plate. The strain rate was determined by the finite element method using Delaunay triangulation points that formed sub-networks; each sub-network was considered a solid and homogeneous body. The results showed that strain rates vary along the South American plate and are more significant on the western portion of the plate, as expected, since this region is close to the subduction zone of the Nazca plate beneath the South American plate. After using Euler vectors to infer Nazca plate movement and to orient the velocity vectors of the South American plate, it was possible to estimate the convergence and accommodation rates of the Nazca and South American plates, respectively. Strain rate estimates permitted determination of predominant contraction and/or extension regions and to establish that contraction regions coincide with locations with most of the high magnitude seismic events. Some areas with extension and contraction strains were found to the east within the stable South American plate, which may result from different stresses associated with different geological characteristics. These results suggest that major movements detected on the surface near the Nazca plate occur in regions with more heterogeneous geological structures and multiple rupture events. Most seismic events in the South American plate are concentrated in areas with predominant contraction strain rates oriented northeast-southwest; significant amounts of elastic strain can be accumulated on geological structures away from the plate boundary faults; and, behavior of contractions and extensions is similar to what has been found in seismological studies. 相似文献
88.
本文首次利用完全相同两颗卫星(CLUSTER C1和C3)的数据对地球激波前兆区太阳风的减速和偏转特性进行了统计研究.结果表明,在激波前兆坐标系中,太阳风减小的速度随观测点到激波的距离DBS增大而减小,随行星际磁场与激波法向夹角θBN增大也减小,在ULF波动区深度DWS小于6Re(Re为地球半径)的范围内最为显著;伴随着太阳风减速的另外一个现象——太阳风的偏转,也存在相似的规律.其最大减速和最大偏转角度分别为10 km/s和3°.太阳风减速和偏转,以及随之变化的太阳风动压,可能会引起地球磁层顶位置和形状发生改变,同时也为激波前兆区弥散(diffuse)离子的起源及加热提供了一种可能的机制. 相似文献
89.
Maria V. Pastor Josep L. Pelegrí Alonso Hernández-Guerra Jordi Font Jordi Salat Mikhail Emelianov 《Continental Shelf Research》2008
A historical data set is used to describe the coastal transition zone off Northwest Africa during spring 1973 and fall 1975, from 17° to 26°N, with special emphasis on the interaction between subtropical (North Atlantic Central Waters) and tropical (South Atlantic Central Waters) gyres. The near-surface geostrophic circulation, relative to 300 m, is quite complex. Major features are a large cyclonic pattern north of Cape Blanc (21°N) and offshore flow at the Cape Verde front. The large cyclone occurs in the region of most intense winds, and resembles a large meander of the baroclinic southward upwelling jet. The Cape Verde frontal system displays substantial interleaving that may partly originate as mesoscale features at the coastal upwelling front. Property–property diagrams show that the front is an effective barrier to all properties except temperature. The analysis of the Turner angle suggests that the frontal system is characterized by large heat horizontal diffusion as a result of intense double diffusion, which results in the smoothing of the temperature horizontal gradients. Nine cross-shore sections are used to calculate along-shore geostrophic water-mass and nutrient transports and to infer exchanges between the coastal transition zone and the deep ocean (import: deep ocean to transition zone; export: transition zone to deep ocean). These exchanges compare well with mean wind-induced transports and actual geostrophic cross-shore transport estimates. The region is divided into three areas: southern (18–21°N), central (21–23.5°N), and northern (23.5–26°N). In the northern area geostrophic import is roughly compensated with wind-induced export during both seasons. In the central area geostrophic import is greater than wind-induced export during spring, resulting in net import of both water (0.8 Sv) and nitrate (14 kmol s−1), but during fall both factors again roughly cancel. In the southern area geostrophy and wind join to export water and nutrients during both seasons, they increase from 0.6 Sv and 3 kmol s−1 during fall to 2.9 Sv and 53 kmol s−1 during spring. 相似文献
90.