全文获取类型
收费全文 | 2778篇 |
免费 | 416篇 |
国内免费 | 375篇 |
专业分类
测绘学 | 1273篇 |
大气科学 | 374篇 |
地球物理 | 444篇 |
地质学 | 669篇 |
海洋学 | 310篇 |
天文学 | 49篇 |
综合类 | 371篇 |
自然地理 | 79篇 |
出版年
2024年 | 5篇 |
2023年 | 33篇 |
2022年 | 88篇 |
2021年 | 112篇 |
2020年 | 143篇 |
2019年 | 175篇 |
2018年 | 99篇 |
2017年 | 167篇 |
2016年 | 162篇 |
2015年 | 183篇 |
2014年 | 197篇 |
2013年 | 203篇 |
2012年 | 216篇 |
2011年 | 193篇 |
2010年 | 142篇 |
2009年 | 159篇 |
2008年 | 150篇 |
2007年 | 179篇 |
2006年 | 160篇 |
2005年 | 124篇 |
2004年 | 102篇 |
2003年 | 77篇 |
2002年 | 66篇 |
2001年 | 60篇 |
2000年 | 51篇 |
1999年 | 32篇 |
1998年 | 57篇 |
1997年 | 38篇 |
1996年 | 31篇 |
1995年 | 24篇 |
1994年 | 32篇 |
1993年 | 37篇 |
1992年 | 14篇 |
1991年 | 16篇 |
1990年 | 17篇 |
1989年 | 7篇 |
1988年 | 8篇 |
1987年 | 5篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1977年 | 1篇 |
1954年 | 1篇 |
排序方式: 共有3569条查询结果,搜索用时 31 毫秒
151.
遥感影像镶嵌时拼接缝的消除方法 总被引:29,自引:0,他引:29
对现有的影像并接缝消除方法的优缺点进行了分析,提出了拼接缝消除的强制改正方法,并用大量的实际图像进行了试验。结果表明:所提出的方法具有较好的拼接缝消除效果,且算法简单,易于实现,可以处理彩色和黑白等多种图像。 相似文献
152.
Wavelet filter analysis of atmospheric pressure effects in the long-period seismic mode band 总被引:2,自引:0,他引:2
The importance of the reduction of atmospheric pressure effects becomes very clear when investigating seismic normal-mode spectra below 1.5 mHz. The usual simple correction method consists in subtracting a term converted from local atmospheric pressure (pressure multiplied by a frequency-independent admittance) from the gravity record in time domain. Thus, estimating an efficient admittance is the key for an improved correction. Band-pass filters derived from dyadic orthogonal wavelet transform, having narrow pass-bands with good frequency response but without Gibbs phenomenon and causing no phase lag, are very helpful to estimate an efficient admittance, which is both time and frequency-dependent. Processing of high quality superconducting gravimeter (SG) records for the great Sumatra earthquake (Mw = 9.3, Dec 26, 2004) with wavelet filters reveal the three very well resolved splitting singlets of overtone 2S1 with a single gravity record after correction with time-dependent and frequency-dependent admittances. We also observe all coupled toroidal modes below 1.5 mHz, except 0T5, 0T7 and 1T1, with good signal-to-noise ratio (SNR); moreover, toroidal modes 1T2 and 1T3 are for the first time unambiguously revealed in vertical components. 相似文献
153.
Chang Li Robert D. van der Hilst M. Nafi Toksöz 《Physics of the Earth and Planetary Interiors》2006,154(2):180-195
We have produced a P-wave model of the upper mantle beneath Southeast (SE) Asia from reprocessed short period International Seismological Centre (ISC) P and pP data, short period P data of the Annual Bulletin of Chinese Earthquakes (ABCE), and long period PP-P data. We used 3D sensitivity kernels to combine the datasets, and mantle structure was parameterized with an irregular grid. In the best-sampled region our data resolve structure on scale lengths less than 150 km. The smearing of crustal anomalies to larger depths is reduced by a crustal correction using an a priori 3D model. Our tomographic inversions reveal high-velocity roots beneath the Archean Ordos Plateau, the Sichuan Basin, and other continental blocks in SE Asia. Beneath the Himalayan Block we detect high seismic velocities, which we associate with subduction of Indian lithospheric mantle. This structure is visible above the 410 km discontinuity and may not connect to the remnant of the Neo-Tethys oceanic slab in the lower mantle. Our images suggest that only the southwestern part of the Tibetan plateau is underlain by Indian lithosphere and, thus, that the upper mantle beneath northeastern Tibet is primarily of Asian origin. Our imaging also reveals a large-scale high-velocity structure in the transition zone beneath the Yangtze Craton, which could have been produced in multiple subduction episodes. The low P-wave velocities beneath the Hainan Island are most prominent in the upper mantle and transition zone; they may represent counter flow from the surrounding subduction zones, and may not be unrelated to processes beneath eastern Tibet. 相似文献
154.
Study on the processing method of nighttime CO_2 eddy covariance flux data in ChinaFLUX 总被引:1,自引:0,他引:1
《中国科学D辑(英文版)》2006,(Z2)
At present, using Eddy Covariance (EC) method to estimate the "true value" of carbon sequestration in terrestrial ecosystem arrests more attention. However, one issue is how to solve the uncertainty of observations (especially the nighttime CO2 flux data) appearing in post-processing CO2 flux data. The ratio of effective and reliable nighttime EC CO2 flux data to all nighttime data is relatively low (commonly, less than 50%) for all the long-term and continuous observation stations in the world. Thus, the processing method of nighttime CO2 flux data and its effect analysis on estimating CO2 flux annual sums are very important. In this paper, the authors analyze and discuss the reasons for underestimating nighttime CO2 flux using EC method, and introduce the general theory and method for processing nighttime CO2 flux data. By analyzing the relationship between nighttime CO2 flux and air fraction velocity u., we present an alternate method, Average Values Test (AVT), to determine the thresholds of fraction velocity (u.c) for screening the effective nighttime CO2 flux data. Meanwhile, taking the data observed in Yucheng and Changbai Mountains stations for an example, we analyze and discuss the effects of different methods or parameters on nighttime CO2 flux estimations. Finally, based on the data of part ChinaFLUX stations and related literatures, empirical models of nighttime respiration at different sites in ChinaFLUX are summarized. 相似文献
155.
通过对地形体及其密度信息数字图像化,利用计算机仿真能较精确地计算出地形体在任意一点的重力场强度。在重力异常地形校正时,用各测点的实测数据减去相应测点的地形体重力场强度,即得到地形改正和中间层改正后的重力场强度。这样,重力异常校正中的地形改正和中间层改正可一并完成,既简化了校正的工作步骤,又提高了准确性。通过地形体实例,分别用数字图像仿真计算和积分精确计算其重力场强度,结果表明,二者计算结果十分相近。用数字图像仿真计算地形体重力场强度,误差较小,准确性较高,该方法完全适合重力异常地形校正。 相似文献
156.
几种静校正方法的比较研究 总被引:3,自引:4,他引:3
为解决近地表速度异常和地形起伏引起的静校正问题,已出现了多种静校正方法,这常常使资料处理人员无所适从。这里从众多的静校正方法中选择了三个具有代表性的,在生产中用得较多的方法(折射静校正、无射线追踪层析静校正、非线性层析静校正),从方法原理、方法特点、实际应用效果等方面进行了比较研究,最后给出了针对不同目标选择适当静校正方法的建议,以帮助资料处理人员在实际资料处理中,有针对性地选择静校正方法,快速有效地完成资料处理任务,提高处理质量。 相似文献
157.
158.
该文对北京地区单双频地基GPS大气水汽监测网布网依据、单频与双频地基GPS测量数据解算技术应用、GAMIT和Bernese地基GPS数据分析处理软件应用、远程遥控GPS数据采集与通讯系统、资料分析与数值同化应用等方面的工作进展进行简要介绍,重点讨论了单双频地基GPS大气水汽资料的解算技术及其应用效果。结果表明:在北京天气敏感区通过单双频地基GPS接收机合理组网布局,可构建并利用高分辨率电离层延迟订正技术将单频接收机的大气水汽监测精度提高到实用水平,为强降水天气预报提供有价值的产品。 相似文献
159.
Peter J. Huber 《Journal of Geodesy》2006,80(6):283-303
The stochastic behavior of the length of day (LOD) process is analyzed and is modeled within statistical accuracy on a time-scale ranging from weeks to millennia by a three-component model comprising a global Brownian motion process, decadal fluctuations, and a 50-day Madden–Julian oscillation. While the model is intended to be phenomenological, some possible physical models underlying the three components are speculated upon. The model is applied to estimate long-range extrapolation errors. For example, it predicts a standard error of 1 h in the clock-time correction ΔT for extrapolation by 1,500 years from 500 to 2000 BC. 相似文献
160.
本文介绍了以IRS-P6卫星数据作为信息源完成大兴安岭林区的遥感影像地图制作的方法, 通过试验初步认识到:利用IRS-P6卫星数据制作遥感影像地图,可以满足1:50000、 1:25000比例尺的平面制图精度要求,在一些专业和专题应用中可以放大到1:15000比例尺使用。 相似文献