全文获取类型
收费全文 | 26806篇 |
免费 | 4909篇 |
国内免费 | 6410篇 |
专业分类
测绘学 | 1184篇 |
大气科学 | 5907篇 |
地球物理 | 7210篇 |
地质学 | 13354篇 |
海洋学 | 2927篇 |
天文学 | 1379篇 |
综合类 | 3047篇 |
自然地理 | 3117篇 |
出版年
2024年 | 128篇 |
2023年 | 503篇 |
2022年 | 1154篇 |
2021年 | 1343篇 |
2020年 | 1116篇 |
2019年 | 1204篇 |
2018年 | 1510篇 |
2017年 | 1334篇 |
2016年 | 1604篇 |
2015年 | 1254篇 |
2014年 | 1628篇 |
2013年 | 1488篇 |
2012年 | 1353篇 |
2011年 | 1394篇 |
2010年 | 1503篇 |
2009年 | 1466篇 |
2008年 | 1323篇 |
2007年 | 1275篇 |
2006年 | 1020篇 |
2005年 | 885篇 |
2004年 | 779篇 |
2003年 | 797篇 |
2002年 | 741篇 |
2001年 | 690篇 |
2000年 | 919篇 |
1999年 | 1390篇 |
1998年 | 1119篇 |
1997年 | 1115篇 |
1996年 | 1006篇 |
1995年 | 881篇 |
1994年 | 828篇 |
1993年 | 696篇 |
1992年 | 546篇 |
1991年 | 439篇 |
1990年 | 325篇 |
1989年 | 303篇 |
1988年 | 270篇 |
1987年 | 171篇 |
1986年 | 147篇 |
1985年 | 115篇 |
1984年 | 70篇 |
1983年 | 57篇 |
1982年 | 70篇 |
1981年 | 56篇 |
1980年 | 30篇 |
1979年 | 29篇 |
1978年 | 10篇 |
1977年 | 4篇 |
1976年 | 7篇 |
1958年 | 27篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
利用NOAA-AVHRR数据分析1982-2001年间中国植被的动态变化 总被引:1,自引:0,他引:1
The authors derived the normalized difference vegetation index (NDVI) from the NOAA/AVHRR Land dataset, at a spatial resolution of 8km and 15-day intervals, to investigate the vegetation variations in China during the period from 1982 to 2001. Then, GIS is used to examine the relationship between precipitation and the Normalized Difference Vegetation Index (NDVI) in China, and the value of NDVI is taken as a tool for drought monitoring. The results showed that in the study period, China’s vegetation cover h... 相似文献
72.
This paper systematically studies the statistical diagnosis and hypothesis testing for the semiparametric linear regression model according to the theories and methods of the statistical diagnosis and hypothesis testing for parametric regression model.Several diagnostic measures and the methods for gross error testing are derived.Especially,the global and local influence analysis of the gross error on the parameter X and the nonparameter s are discussed in detail;at the same time,the paper proves that the d... 相似文献
73.
A global, 2-hourly atmospheric precipitable water (PW) dataset is produced from ground-based GPS measurements of zenith tropospheric delay (ZTD) using the International Global Navigation Satellite Systems (GNSS) Service (IGS) tropospheric products (~80–370 stations, 1997–2006) and US SuomiNet product (169 stations, 2003–2006). The climate applications of the GPS PW dataset are highlighted in this study. Firstly, the GPS PW dataset is used as a reference to validate radiosonde and atmospheric reanalysis data. Three types of systematic errors in global radiosonde PW data are quantified based on comparisons with the GPS PW data, including measurement biases for each of the fourteen radiosonde types along with their characteristics, long-term temporal inhomogeneity and diurnal sampling errors of once and twice daily radiosonde data. The comparisons between the GPS PW data and three reanalysis products, namely the NCEP-NCAR (NNR), ECMWF 40-year (ERA-40) and Japanese reanalyses (JRA), show that the elevation difference between the reanalysis grid box and the GPS station is the primary cause of the PW difference. Secondly, the PW diurnal variations are documented using the 2-hourly GPS PW dataset. The PW diurnal cycle has an annual-mean, peak-to-peak amplitude of 0.66, 0.53 and 1.11 mm for the globe, Northern Hemisphere, and Southern Hemisphere, respectively, with the time of the peak ranging from noon to late evening depending on the season and region. Preliminary analyses suggest that the PW diurnal cycle in Europe is poorly represented in the NNR and JRA products. Several recommendations are made for future improvements of IGS products for climate applications. 相似文献
74.
张克非 《武汉大学学报(信息科学版)》1990,15(3):29-35
本文在顾及局部地形改正、椭球改正及大气改正的情况下,采用实测数据,应用Meissel方法和Wenzel频谱分析方法,对某盆地边缘的高程异常进行了实际计算。并将计算结果同多普勒高程异常进行了比较,证明结果是良好的。此外还对我国精确高程异常的确定提出了一些建议。 相似文献
75.
三维城市模型的研究与实践(英文) 总被引:3,自引:0,他引:3
The way we interact with spatial data has been changed from 2D map to 3D Virtual Geographic Environment (VGE). Three-dimensional
representations of geographic information on a computer are known as VGE, and in particular 3D city models provide an efficient
way to integrate massive, heterogenous geospatial information and georeferenced information in urban areas. 3D city modeling
(3DCM) is an active research and practice topic in distinct application areas. This paper introduces different modeling paradigms
employed in 3D GIS, virtual environment, and AEC/FM. Up-to-date 3DCM technologies are evolving into a data integration and
collaborative approach to represent the full spatial coverage of a city, to model both aboveground and underground, outdoor
and indoor environments including man-made objects and natural features with 3D geometry, appearance, topology and semantics.
Supported by the National Natural Science Foundation of China ( No. 40871212, No. 40671158), the Leading Academic Discipline
Project of Shanghai Educational Committee( No.J50104). 相似文献
76.
根据抗差估计中误差的最基本假设一对称分布,考虑到ρ函数的条件及把反对称估计作为抗差估计计算迭代的初始值,验证了定位参数的抗差估计值也一定是反对称估计,满足无偏性条件,得到定位参数的抗差估计是无偏估计. 相似文献
77.
78.
79.
80.
单窗算法的大气参数估计方法 总被引:95,自引:10,他引:95
根据地表热辐射传导方程,提出了一个简单可行且精度较高的专门用于从TM6数据中演算地表温度的方法——单窗算法.这一算法把大气和地表状态对地表热传导的影响直接包括在演算公式中.该方法需要两个大气参数进行地表温度的演算,即大气平均作用温度和大气透射率.本文论述这两个大气参数的估计方法:根据大气水分含量或地表附近空气湿度来估计大气透射率;通过分析标准大气剖面资料,尤其是大气水分和气温随高程的变化规律,根据地表温度推算大气平均作用温度. 相似文献