全文获取类型
收费全文 | 3662篇 |
免费 | 544篇 |
国内免费 | 722篇 |
专业分类
测绘学 | 519篇 |
大气科学 | 606篇 |
地球物理 | 826篇 |
地质学 | 1639篇 |
海洋学 | 386篇 |
天文学 | 80篇 |
综合类 | 393篇 |
自然地理 | 479篇 |
出版年
2024年 | 12篇 |
2023年 | 44篇 |
2022年 | 192篇 |
2021年 | 238篇 |
2020年 | 179篇 |
2019年 | 226篇 |
2018年 | 244篇 |
2017年 | 196篇 |
2016年 | 236篇 |
2015年 | 199篇 |
2014年 | 224篇 |
2013年 | 263篇 |
2012年 | 249篇 |
2011年 | 249篇 |
2010年 | 230篇 |
2009年 | 194篇 |
2008年 | 187篇 |
2007年 | 173篇 |
2006年 | 150篇 |
2005年 | 115篇 |
2004年 | 92篇 |
2003年 | 78篇 |
2002年 | 136篇 |
2001年 | 125篇 |
2000年 | 97篇 |
1999年 | 107篇 |
1998年 | 81篇 |
1997年 | 67篇 |
1996年 | 72篇 |
1995年 | 61篇 |
1994年 | 49篇 |
1993年 | 33篇 |
1992年 | 37篇 |
1991年 | 19篇 |
1990年 | 22篇 |
1989年 | 10篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 3篇 |
1983年 | 3篇 |
1982年 | 2篇 |
1981年 | 4篇 |
1957年 | 2篇 |
排序方式: 共有4928条查询结果,搜索用时 15 毫秒
991.
Crop discrimination in Northern China with double cropping systems using Fourier analysis of time-series MODIS data 总被引:4,自引:0,他引:4
Zhang Mingwei Zhou Qingbo Chen Zhongxin Liu Jia Zhou Yong Cai Chongfa 《International Journal of Applied Earth Observation and Geoinformation》2008,10(4):476
Crop identification is the basis of crop monitoring using remote sensing. Remote sensing the extent and distribution of individual crop types has proven useful to a wide range of users, including policy-makers, farmers, and scientists. Northern China is not merely the political, economic, and cultural centre of China, but also an important base for grain production. Its main grains are wheat, maize, and cotton. By employing the Fourier analysis method, we studied crop planting patterns in the Northern China plain. Then, using time-series EOS-MODIS NDVI data, we extracted the key parameters to discriminate crop types. The results showed that the estimated area and the statistics were correlated well at the county-level. Furthermore, there was little difference between the crop area estimated by the MODIS data and the statistics at province-level. Our study shows that the method we designed is promising for use in regional spatial scale crop mapping in Northern China using the MODIS NDVI time-series. 相似文献
992.
993.
994.
995.
GPS Solutions - Frequency diversity is expected to benefit the ambiguity resolution (AR) with the modernization of global navigation satellite system. As one classic AR method, triple-carrier AR... 相似文献
996.
针对现有植被净初级生产力研究对城市圈、城市带尺度缺乏关注的问题,基于MODIS遥感数据、地面气象资料等,利用改进的CASA模型,结合回归分析、相关分析等方法探究了2000—2013年皖江城市带植被NPP的时空变化及其对气候因子的响应,为区域生态环境质量评价提供参考。结果表明:近14年来,皖江城市带植被NPP总体呈增加趋势;不同土地利用类型NPP差异显著,林地草地耕地建设用地未利用土地水体;年NPP均值呈现由南部向西北部减少的空间分布特征;植被NPP年际变化率较小,介于±10gC·m-2·a-1范围内;温度是影响研究区植被NPP时空变化的主要气候因子。 相似文献
997.
Xuejie GAO Ying SHI Zhenyu HAN Meili WANG Jia WU Dongfeng ZHANG Ying XU Filippo GIORGI 《大气科学进展》2017,34(4):441-455
A long-term simulation for the period 1990–2010 is conducted with the latest version of the International Centre for Theoretical Physics' Regional Climate Model(RegCM4), driven by ERA-Interim boundary conditions at a grid spacing of 25 km. The Community Land Model(CLM) is used to describe land surface processes, with updates in the surface parameters,including the land cover and surface emissivity. The simulation is compared against observations to evaluate the model performance in reproducing the present day climatology and interannual variability over the 10 main river basins in China,with focus on surface air temperature and precipitation. Temperature and precipitation from the ERA-Interim reanalysis are also considered in the model assessment. Results show that the model reproduces the present day climatology over China and its main river basins, with better performances in June–July–August compared to December–January–February(DJF).In DJF, we find a warm bias at high latitudes, underestimated precipitation in the south, and overestimated precipitation in the north. The model in general captures the observed interannual variability, with greater skill for temperature. We also find an underestimation of heavy precipitation events in eastern China, and an underestimation of consecutive dry days in northern China and the Tibetan Plateau. Similar biases for both mean climatology and extremes are found in the ERA-Interim reanalysis, indicating the difficulties for climate models in simulating extreme monsoon climate events over East Asia. 相似文献
998.
The in situ combustion (ISC) process is of interest as an enhanced oil recovery method because it is an alternative to traditional steam-based processes for heavy oil and bitumen recovery. ISC is a technique applicable outside the window of reservoir conditions deemed appropriate for steam injection (such as deeper and thinner reservoirs). The process involves complex chemical reactions and physical recovery mechanisms, and predicting the likelihood of successful ISC in field applications remains challenging. This paper describes a numerical investigation of the capability of different ISC kinetic models to predict the combustion behaviors of different types of oils (light oil, heavy oil, and bitumen). Three kinetic models (of Coats, Crookston, and Belgrave) were selected from literature and compared using data from four published combustion-tube experiments. The comparison procedure is as follows: (1) validate the numerical modeling of each kinetic model by matching the selected experimental results or duplicating the numerical results found in published literature; (2) adjust fluid viscosities and densities to match the fluid properties of each experiment;and (3) use each validated kinetic model to predict the performance of the other experiments without further tuning the kinetic parameters. The knowledge derived from the experiments provides guidance for choosing the appropriate kinetic model when no other data are available and for the preliminary design and screening study of a potential ISC project. 相似文献
999.
在对GPS/GLONASS组合定位的周跳探测和修复方法进行深入研究的基础上,论述了适合于两种数据联合解算的GPS/GLONASS模糊度迭代处理方法及相应的基于FARA方法的整周模糊度固定方法。在现有BERNESE Ver4.0GSP数据处理软件的基础上,增加及改进了其中的若干模块,从而研制出组合定位系统高精度数据处理软件,并进行了试验计算。结果表明,所开发的组合定位系统数据处理软件内、外符合精度均达到mm级,证明了这种高精度相对定位理论、方法、软件的正确性和可行性。 相似文献
1000.
中国陆区S波分型与上地幔地震各向异性 总被引:2,自引:2,他引:2
本文利用中国大陆区共8个台站所观测到地震事件的S波数据,采用相关分析的手段以 观测数据重建的技术,进行了S波分裂参数-快慢波延迟时间与快波偏振方向的计算,并分析了S波分裂参数与中国陆区上地幔物质运动的相互关系,研究了结果表明,兰州台下的S波分裂时差最小,北京台下的最大,中国东部地区上地幔运动方向以西北向为主,西部地区以北偏西为优势。 相似文献