全文获取类型
收费全文 | 1372篇 |
免费 | 282篇 |
国内免费 | 403篇 |
专业分类
测绘学 | 294篇 |
大气科学 | 56篇 |
地球物理 | 369篇 |
地质学 | 951篇 |
海洋学 | 164篇 |
天文学 | 47篇 |
综合类 | 94篇 |
自然地理 | 82篇 |
出版年
2024年 | 8篇 |
2023年 | 25篇 |
2022年 | 54篇 |
2021年 | 45篇 |
2020年 | 78篇 |
2019年 | 91篇 |
2018年 | 71篇 |
2017年 | 70篇 |
2016年 | 90篇 |
2015年 | 102篇 |
2014年 | 114篇 |
2013年 | 108篇 |
2012年 | 87篇 |
2011年 | 121篇 |
2010年 | 82篇 |
2009年 | 73篇 |
2008年 | 68篇 |
2007年 | 101篇 |
2006年 | 101篇 |
2005年 | 83篇 |
2004年 | 83篇 |
2003年 | 48篇 |
2002年 | 39篇 |
2001年 | 43篇 |
2000年 | 38篇 |
1999年 | 31篇 |
1998年 | 23篇 |
1997年 | 30篇 |
1996年 | 23篇 |
1995年 | 23篇 |
1994年 | 25篇 |
1993年 | 21篇 |
1992年 | 7篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 6篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 7篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1982年 | 2篇 |
1979年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有2057条查询结果,搜索用时 15 毫秒
991.
根据反对称矩阵和罗德里格矩阵的性质,针对线性转换模型线性化复杂、计算量大和误差大等缺点,通过采用反对称矩阵中的三个独立参数来代替旋转矩阵中的九个相关参数,推导出了基于罗德里格矩阵的坐标转换模型。相对于其他的一些线性转换模型,该模型简单且便于计算,其较高的计算精度也通过将基于罗德里格矩阵的坐标转换模型应用于盾构姿态测量中而得到了验证。 相似文献
992.
HaoTian Yang LiChao Liu XinRong Li YongPing Wei YanHong Gao XiaoJun Li RongLiang Ji Lei Huang 《寒旱区科学》2012,4(5):0408-0416
Soil water repellency (SWR) is one of the most important physical properties of soils found all over the world, and it may have significant effects on the eco-hydrological processes of land ecosystems. In this study, the Capillary Rise Method was used to measure the SWR in the artificial vegetation area in Shapotou, located in the southeast area of the Tengger Desert, Ningxia Province of western China. The variation of the soil water repellency among different minor topographies, different depths and different particle sizes was analyzed. The results of the study indicate that the SWR shows distinct changes with vegetation restoration, and it increases with an increase in the period of dune stabilization. In the same vegetation area, the SWR of soils in inter-dune depressions or windward slopes is slightly greater than that in crest or leeward slopes. The SWR of 0–3 cm topsoil is significantly greater than that in the 3–6 cm soil layer. The SWR decreases with an increase in grain size and the differences among the SWRs of different sieved soil fractions are found to be significant. There is also a significantly positive correlation between the SWR and the proportion of soils with grain sizes of 0–0.05, 0.05–0.01 and 0.01–0.15 mm, and a significantly negative correlation between the SWR and the propotion of soils with grain sizes exceeding 0.15 mm. The increase of SWR in revegetation areas may depend on the continuous depositing of atmospheric dust on the stabilized dune surface as well as the formation of biological soil crusts, especially on the formation of algal and lichen crusts. Enhanced SWR influences the effectiveness of water use of sand plants inhabiting the sand dunes. 相似文献
993.
推出了在线路坐标系下任意中桩点的切线方位角和中桩点的坐标计算公式,求出了该中桩处横断面上任意点的坐标,提出了将GPS-RTK技术应用于路线横断面测量的基本思路和数据处理方法. 相似文献
994.
Investigation of karst collapse based on 3-D seismic technique and DDA method at Xieqiao coal mine, China 总被引:1,自引:0,他引:1
Jian-Ping Zuo Su-Ping Peng Yong-Jun Li Zhong-Hui Chen He-Ping Xie 《International Journal of Coal Geology》2009,78(4):1800
Karst collapse is a serious geological problem in most of the coal mines in the north of China, but recently it has been found in the south as well. The present study is aimed at investigating subsidence mechanism and deformation field of a karst collapse column at Xieqiao, in the south of China. A method of three-dimensional (3-D) seismic technique has been successful in exploring the spatial morphology of the karst collapse at Xieqiao, and the discontinuous deformation analysis (DDA) method is used to calculate the deformation field and analyze the subsidence mechanism. The results indicated that DDA could approximately simulate and back analyze the subsidence process and strata deformation fields. The subsidence processes of the collapse column depend on the sizes of the karst caves. With the continuous expansion of the karst caves, a semi-elliptic stress field, local separation strata and fracture zone will be formed around the karst cave. Moreover, they will gradually expand upwards along the vertical direction. The paper also indicates that the subsidence failure stage may trigger a sudden collapse of the karst column because of the sudden energy release. Also, it will make a great impact on the vicinity working face so as to cause a rock burst. The effects of the friction angle of rock strata on the subsidence mechanism were reported firstly based on DDA. 相似文献
995.
An analytical method has been proposed to predict the ultimate uplift capacity of single vertical piles embedded in sand considering
arching effect. The present analysis takes into consideration of various pile and soil parameters such as length (L), diameter (d) of the pile, angle of internal friction of soil (ϕ), soil pile friction angle (δ) and unit weight of soil (γ). A modified value of coefficient of lateral earth pressure in uplift has been developed considering the arching effect of
soil. A comparative assessment of the uplift capacity of piles predicted by using proposed theory and the existing available
theories is made with the existing field and model test results. It has been observed that the present model considering the
arching effect predicts the results closer. 相似文献
996.
针对中东地区油藏普遍存在油水界面倾斜的特征,以伊朗雅达(Yada)油田为例对其成因进行探讨。通过对层序界面三维地震资料精细解释,以及系统的构造演化分析,认为研究区油气成藏关键期集中于新生代扎格罗斯前陆盆地演化阶段,而该阶段经历了多期较强烈的南北向差异性构造活动,在扎格罗斯东西向持续挤压背景下,后期南北向构造反转形成的长轴背斜圈闭对早期古油藏短轴背斜圈闭进行改造,从而形成了油水界面倾斜、继承性构造高点含油幅度最大、构造反转越强油水过渡带跨度越大等特征的非稳态油气藏。结果表明,研究区南北向差异性构造演化控制了油气成藏模式和油藏形态。 相似文献
997.
以北斗仿真星座为对象,探讨UHF波段与Ka波段的不同星间链路建链条件下GEO、IGSO及MEO卫星的可见链路数及PDOP值的变化。此外,还针对不同星间链路构型方案,分别采用其对应仿真观测数据进行60 d自主导航解算,通过对解算结果精度的分析,探讨星间链路测距模式及星间链路构型对自主导航的影响。结果显示,星间链路测距模式对自主导航精度无影响,而星间链路构型则对自主导航精度存在cm量级的影响。在星间链路设计过程中应综合考虑导航精度、链路负荷及建设成本等因素,以达到最优效果。 相似文献
998.
轨道误差是InSAR数据处理中的一个重要因素,对从最初的图像配准到最后的高程值或形变值图像的生成都有着重要影响。含有误差的轨道参数造成基线误差以残差条纹的形式存在于干涉图中。本文利用4个条带的61景PALSAR升轨数据,通过InSAR干涉测量得到覆盖2011日本Tohoku地震的雷达视线向的地表同震位移场。通过联合GPS同震位移数据,采用二次多项式曲面拟合的方法去除InSAR同震形变数据中的卫星轨道误差,并分析雷达入射角变化对轨道误差去除的影响。对干涉图中拟合残差进行分析,改正后的InSAR同震形变场精度得到较大提高。 相似文献
999.
1000.
通过定义距离势函数,提出一种适用于空间任意凸多面体单元的三维距离势函数离散单元法。该方法采用归一化的计算方式,将势函数表征为接触体间的距离函数,并基于此建立接触力计算方程,明确了势函数的物理意义,使接触力计算更加合理,无需对各种可能的接触形式进行差异化处理。新方法克服了原有势函数物理意义不明、接触力计算受单元形式影响等重要缺陷,并突破了四面体单元的限制,可采用空间任意凸多面体单元。通过若干算例说明新方法的正确性和有效性。数值模拟结果表明新方法能够很好处理空间任意多面体单元复杂接触变换过程,准确处理复杂非连续介质的运动过程。 相似文献