全文获取类型
收费全文 | 3105篇 |
免费 | 578篇 |
国内免费 | 838篇 |
专业分类
测绘学 | 479篇 |
大气科学 | 478篇 |
地球物理 | 631篇 |
地质学 | 1719篇 |
海洋学 | 447篇 |
天文学 | 79篇 |
综合类 | 221篇 |
自然地理 | 467篇 |
出版年
2024年 | 29篇 |
2023年 | 96篇 |
2022年 | 177篇 |
2021年 | 233篇 |
2020年 | 178篇 |
2019年 | 225篇 |
2018年 | 198篇 |
2017年 | 204篇 |
2016年 | 215篇 |
2015年 | 229篇 |
2014年 | 204篇 |
2013年 | 241篇 |
2012年 | 260篇 |
2011年 | 256篇 |
2010年 | 258篇 |
2009年 | 193篇 |
2008年 | 220篇 |
2007年 | 193篇 |
2006年 | 170篇 |
2005年 | 136篇 |
2004年 | 76篇 |
2003年 | 75篇 |
2002年 | 78篇 |
2001年 | 78篇 |
2000年 | 61篇 |
1999年 | 32篇 |
1998年 | 12篇 |
1997年 | 23篇 |
1996年 | 28篇 |
1995年 | 12篇 |
1994年 | 13篇 |
1993年 | 13篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 5篇 |
1988年 | 9篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1983年 | 6篇 |
1981年 | 3篇 |
1980年 | 4篇 |
1978年 | 3篇 |
1977年 | 3篇 |
1976年 | 8篇 |
1975年 | 3篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1969年 | 3篇 |
排序方式: 共有4521条查询结果,搜索用时 15 毫秒
1.
叙述了与Astrod工程有关的相对论天体力学基础内容。包括相对论天体力学、广义相对论基本原理、PPN方法体系、PPN多体问题、PPN二体问题。高阶PN二体问题等 相似文献
2.
3.
4.
5.
Dan Gill 《Mathematical Geology》1993,25(4):471-482
The ability of association analysis to discriminate sedimentary facies was tested on Purdy's modal analyses of modern sediments of the Great Bahama Bank. Purdy's data set has served in the past as a standard reference for evaluating various multivariate classification algorithms. In order to adapt Purdy's data to association analysis, the percent abundance of the 12 constituents was converted to binary form by dichotomizing each variable on its mean value. The results obtained by association analysis are virtually identical to those obtained by Purdy and other authors. The same four main sedimentary facies were discriminated; 86% of the samples were identically classified (97% when misclassified borderline cases are counted as matches); the total partition variance of the classification is only negligibly greater (4%); and the grouping of the variables yielded the same four groups. The rank order of the three division-attributes responsible for the sample classification is fines, oolites, and corals. Association analysis has been employed by other authors to differentiate meaningful facies groups in studies of ancient reef carbonates, modern reef sediments, and heavy minerals in stream sediments. In all these studies, the results were found to be compatible with those obtained by using the continuous quantitative measurements, indicating that qualitative binary data may often be sufficient for the purpose of facies discrimination in many branches of geology and that association analysis is an effective method for this purpose. 相似文献
6.
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
7.
We describe a microprocessor-based data capture and display system suited to the needs of many Spacelab experimenters. Although developed specifically for the needs of the FAUST ultraviolet astronomy telescope, several features of the system may make it attractive to other groups who need to interact with their Spacelab data in real or near-real time. The display system captures data from the serial data stream originating in the Spacelab experiment computer input/output (ECIO) data channel, and can reformat and display several hundred variables per second in real time. The system offers a combination of Cathode Ray Tube (CRT) display and analog paper strip-chart output. A facility is also provided for simultaneously creating floppy-disk records of short segments of data according to prearranged criteria, to allow detailed examination of critical events in the operation of the experiment. The simplicity, economy, reliability, and flexibility of the display system suggest its use for monitoring a variety of low- and medium-data-rate Spacelab experiments. 相似文献
8.
9.
天津地面沉降区土水比论述 总被引:1,自引:0,他引:1
天津市地面沉降分布广,沉降速率大。本文针对当前地面沉降研究和防治过程中所遇到的勘查资料严重缺乏、禁采难以全面实现等难题,提出了土水比指标量。通过概念分析和对多年数据的分析,认为土水比可以检验地下水开采量数据的统计精度,指示地下水资源补给及土层释水条件,并表明沉降的严重程度,反映地下水资源的保障程度。建议在沉降防治工作中,以土水比作为指标,通过相关分析模型来制定压采量。 相似文献
10.
A procedure is suggested for direct determination of Sr in seawater using diluted seawater sample and background emission correction by FES. The standard deviation for 8 ppm Sr is better then 2 %, and the recovery of the added Sr is 97-105 %. 相似文献