全文获取类型
收费全文 | 14325篇 |
免费 | 1641篇 |
国内免费 | 1762篇 |
专业分类
测绘学 | 5006篇 |
大气科学 | 2013篇 |
地球物理 | 2254篇 |
地质学 | 2991篇 |
海洋学 | 1184篇 |
天文学 | 1237篇 |
综合类 | 1416篇 |
自然地理 | 1627篇 |
出版年
2024年 | 66篇 |
2023年 | 145篇 |
2022年 | 447篇 |
2021年 | 601篇 |
2020年 | 594篇 |
2019年 | 668篇 |
2018年 | 472篇 |
2017年 | 760篇 |
2016年 | 669篇 |
2015年 | 690篇 |
2014年 | 812篇 |
2013年 | 1032篇 |
2012年 | 894篇 |
2011年 | 824篇 |
2010年 | 643篇 |
2009年 | 805篇 |
2008年 | 840篇 |
2007年 | 996篇 |
2006年 | 923篇 |
2005年 | 751篇 |
2004年 | 729篇 |
2003年 | 548篇 |
2002年 | 465篇 |
2001年 | 396篇 |
2000年 | 320篇 |
1999年 | 286篇 |
1998年 | 233篇 |
1997年 | 167篇 |
1996年 | 162篇 |
1995年 | 149篇 |
1994年 | 131篇 |
1993年 | 119篇 |
1992年 | 69篇 |
1991年 | 69篇 |
1990年 | 40篇 |
1989年 | 40篇 |
1988年 | 35篇 |
1987年 | 21篇 |
1986年 | 19篇 |
1985年 | 14篇 |
1984年 | 16篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 5篇 |
1977年 | 11篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 5篇 |
1954年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
951.
952.
953.
Jean S. Kane Philip J. Potts Thomas Meisel Michael Wiedenbeck 《Geostandards and Geoanalytical Research》2007,31(3):285-288
The International Association of Geoanalysts (IAG) published a protocol for the certification of reference materials in close accord with the International Organisation for Standardisation (ISO) guidelines (Kane et al. 2003). This article supplements that protocol, providing additional discussion of best approaches for pre-selecting laboratories for participation in certification projects. This discussion also makes a distinction between inter-laboratory certifications, where n = 15 is the general standard, and expert laboratory certifications, where a much smaller number of laboratories will be deemed qualified to provide data of the quality needed for certification. 相似文献
954.
Kriging Regionalized Positive Variables Revisited: Sample Space and Scale Considerations 总被引:1,自引:0,他引:1
Frequently, regionalized positive variables are treated by preliminarily applying a logarithm, and kriging estimates are back-transformed
using classical formulae for the expectation of a lognormal random variable. This practice has several problems (lack of robustness,
non-optimal confidence intervals, etc.), particularly when estimating block averages. Therefore, many practitioners take exponentials
of the kriging estimates, although the final estimations are deemed as non-optimal. Another approach arises when the nature
of the sample space and the scale of the data are considered. Since these concepts can be suitably captured by an Euclidean
space structure, we may define an optimal kriging estimator for positive variables, with all properties analogous to those
of linear geostatistical techniques, even for the estimation of block averages. In this particular case, no assumption on
preservation of lognormality is needed. From a practical point of view, the proposed method coincides with the median estimator
and offers theoretical ground to this extended practice. Thus, existing software and routines remain fully applicable. 相似文献
955.
A modified counter propagation network model and an extended self-organizing map model have the same three-layer network architecture
while employing slightly different learning rules. Their network architecture comprises an input layer, a Kohonen layer and
an output layer. The neurons between two neighboring layers are fully connected and the neighboring neurons within the Kohonen
layer also have neighborhood connections. The modified counter propagation network model employs the Kohonen algorithm to
train the Kohonen layer while using the Widrow–Hoff rule to train the output layer. However, the extended self-organizing
map model applies a modified Kohonen’s learning rule to train both the Kohonen layer and the output layer. This paper compares
the performances of these two models in supervised classification of remotely sensed data. The training results show that
compared to the extended self-organizing map model, the modified counter propagation model has faster learning speed but larger
output errors. The classification results indicate that the extended self-organizing map model has a faster classification
speed and a much higher classification precision than the modified counter propagation model. 相似文献
956.
介绍了内陆湖泊水质遥感监测的特点及遥感监测水质的机理;总结了国内外近年来用于内陆湖泊水质参数反演的3种常用方法:经验模型、半经验法和机理模型法,并分析了3种模型的优缺点;讨论了目前遥感在水质监测应用中存在的问题和未来该领域研究的重点。 相似文献
957.
958.
The abilities of typhoon (TC) track prediction by a medium-range forecast model T213L31 at National Meteorological Center are analyzed and its ability to improve its TC forecasts is discussed. The results show that about 57% of the TCs could be predicted by T213L31 but the initial position errors are large.The 43% area without the prediction of TC tracks is concentrated between 13°N and 20°N and east of 120°E and lack of conventional observation data is the main reason for the absence of TC prediction in this area.The adding of bogus TC could improve the ability of TC track prediction when there is no TC vortex in the analysis field, but could only have positive effects on the short-range TC track prediction when there is TC vortex in the T213L31 analysis field. 相似文献
959.
广西自动气象站平行观测资料质量评估 总被引:1,自引:0,他引:1
对广西2004年投入运行的39个自动气象站的自动观测资料与人工观测资料进行对比分析,形成了各个观测要素的质量评估,并对两种观测资料差异的原因进行了初步探讨。 相似文献
960.