全文获取类型
收费全文 | 25144篇 |
免费 | 3623篇 |
国内免费 | 4324篇 |
专业分类
测绘学 | 7155篇 |
大气科学 | 5506篇 |
地球物理 | 4144篇 |
地质学 | 7537篇 |
海洋学 | 2359篇 |
天文学 | 1381篇 |
综合类 | 2183篇 |
自然地理 | 2826篇 |
出版年
2024年 | 103篇 |
2023年 | 277篇 |
2022年 | 763篇 |
2021年 | 1018篇 |
2020年 | 998篇 |
2019年 | 1010篇 |
2018年 | 830篇 |
2017年 | 1271篇 |
2016年 | 1144篇 |
2015年 | 1232篇 |
2014年 | 1580篇 |
2013年 | 1743篇 |
2012年 | 1725篇 |
2011年 | 1603篇 |
2010年 | 1319篇 |
2009年 | 1516篇 |
2008年 | 1516篇 |
2007年 | 1920篇 |
2006年 | 1686篇 |
2005年 | 1437篇 |
2004年 | 1337篇 |
2003年 | 1105篇 |
2002年 | 877篇 |
2001年 | 823篇 |
2000年 | 702篇 |
1999年 | 619篇 |
1998年 | 523篇 |
1997年 | 406篇 |
1996年 | 367篇 |
1995年 | 304篇 |
1994年 | 296篇 |
1993年 | 238篇 |
1992年 | 179篇 |
1991年 | 140篇 |
1990年 | 95篇 |
1989年 | 81篇 |
1988年 | 73篇 |
1987年 | 46篇 |
1986年 | 35篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 9篇 |
1980年 | 11篇 |
1978年 | 8篇 |
1977年 | 16篇 |
1973年 | 6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 234 毫秒
61.
案例推理的地学应用背景和方法 总被引:3,自引:1,他引:2
案例推理 (CBR)研究 ,是人类认知的一种合理性模型 ,接近于人类认识、解决问题最原始的思维方式 ,具有在无法获取机理模型、确定规则或统计模型时 ,采用简单的历史相似性推理实现问题的定量求解和预测 ,成为人工智能领域近年来的研究热点。 相似文献
62.
Technique for Controlling Spread of Limnotic Oncomelania 总被引:1,自引:0,他引:1
Schistosomiasis is a parasitic disease mostly found in areas along the Changjiang River of China. The disease is spread solely through an intermediary named oncomelania, so its spread of schistosomiasis can be controlled by properly designing water intakes which prevent oncomelania from entering farming land or residential areas. This paper reports a successful design process and a new oncomelania-free intake device. The design of the new intake is based on a sound research program in which extensive experimental studies were carried out to gain knowledge of oncomelania eco-hydraulic behavior and detailed flow field information through CFD simulation. 相似文献
63.
Douglas P. Looze Markus Kasper Stefan Hippler Orhan Beker Robert Weiss 《Experimental Astronomy》2003,15(2):67-88
This paper develops a compensation algorithm based on Linear–Quadratic–Gaussian (LQG) control system design whose parameters
are determined (in part) by a model of the atmosphere. The model for the atmosphere is based on the open-loop statistics of
the atmosphere as observed by the wavefront sensor, and is identified from these using an auto-regressive, moving average
(ARMA) model. The (LQG) control design is compared with an existing compensation algorithm for a simulation developed at ESO
that represents the operation of MACAO adaptive optics system on the 8.2 m telescopes at Paranal, Chile.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
64.
65.
基于CTI技术的守时系统故障报警实现 总被引:2,自引:0,他引:2
介绍了计算机电话集成(CTI-Computer Telephony Integration)技术在守时系统故障自动报警中的应用。简要介绍了构成报警系统的两个关键产品,电话语音卡和TTS(Text-To-Speech),详细讨论了ActiveX控件(Phonic.OCX)编程接口的一系列事件和方法以及由此而开发的故障报警模块。该模块不仅用于守时主系统的故障报警,也将用于电源系统、钟房环境监控系统的故障报警。 相似文献
66.
67.
智能照明系统在现代建筑照明中的应用研究 总被引:1,自引:0,他引:1
陈丹 《成都信息工程学院学报》2007,22(6):735-738
在对传统照明系统和智能照明系统进行对比分析的基础上,剖析了智能照明系统的控制策略,并结合实际的工程应用,着重讨论了基于ABB I-Bus产品的智能照明控制系统的实现,结果表明该系统具有高效、便捷、节约能源等优点.同时,还对系统与建筑物楼宇自控系统问的系统集成方式进行了研究. 相似文献
68.
69.
Hari Om Vats 《Journal of Astrophysics and Astronomy》2006,27(2-3):227-235
Examples of extreme events of solar wind and their effect on geomagnetic conditions are discussed here. It is found that there
are two regimes of high speed solar wind streams with a threshold of ∼ 850 km s-1. Geomagnetic activity enhancement rate (GAER) is defined as an average increase in Ap value per unit average increase in
the peak solar wind velocity (Vp) during the stream. GAER was found to be different in the two regimes of high speed streams
with +ve and-ve IMF. GAER is 0.73 and 0.53 for solar wind streams with +ve and -ve IMF respectively for the extremely high
speed streams (< 850 km s-1). This indicates that streams above the threshold speed with +ve IMF are 1.4 times more effective in enhancing geomagnetic
activity than those with -ve IMF. However, the high speed streams below the threshold with -ve IMF are 1.1 times more effective
in enhancing geomagnetic activity than those with +ve IMF. The violent solar activity period (October–November 2003) of cycle
23 presents a very special case during which many severe and strong effects were seen in the environment of the Earth and
other planets; however, the z-component of IMF (Bz) is mostly positive during this period. The most severe geomagnetic storm
of this cycle occurred when Bz was positive. 相似文献
70.
G. Palladino A. Basili G. Di Cocco T. Franceschini G. Landini S. Silvestri A. Barbini M. Galimberti L. A. Gizzi 《Experimental Astronomy》2006,21(3):169-187
This paper describes the design of a star sensor based upon a high dynamic range CCD in order to reach an arcsec-level attitude
determination in balloon-borne missions. A custom star identification software was developed and laboratory-tested on a prototype
assembled using commercial components. A set of numerical simulations have been carried out to study the dependence on the
pointing precision of the centroid position accuracy, the number of detected stars and the effect of the image focusing. Moreover,
the role of the electronic noise and the discrete pixel structure on the light signals is identified by the analysis of numerical
simulations. Laboratory tests confirm that the arcsec pointing accuracy with a 1 Hz update rate can be achieved with our combination
of custom-developed software and selected hardware components. 相似文献