全文获取类型
收费全文 | 966篇 |
免费 | 137篇 |
国内免费 | 177篇 |
专业分类
测绘学 | 364篇 |
大气科学 | 170篇 |
地球物理 | 174篇 |
地质学 | 229篇 |
海洋学 | 169篇 |
天文学 | 23篇 |
综合类 | 124篇 |
自然地理 | 27篇 |
出版年
2024年 | 2篇 |
2023年 | 17篇 |
2022年 | 48篇 |
2021年 | 62篇 |
2020年 | 68篇 |
2019年 | 65篇 |
2018年 | 31篇 |
2017年 | 53篇 |
2016年 | 49篇 |
2015年 | 65篇 |
2014年 | 68篇 |
2013年 | 80篇 |
2012年 | 75篇 |
2011年 | 69篇 |
2010年 | 41篇 |
2009年 | 49篇 |
2008年 | 46篇 |
2007年 | 63篇 |
2006年 | 50篇 |
2005年 | 38篇 |
2004年 | 42篇 |
2003年 | 33篇 |
2002年 | 32篇 |
2001年 | 30篇 |
2000年 | 23篇 |
1999年 | 22篇 |
1998年 | 20篇 |
1997年 | 6篇 |
1996年 | 7篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 4篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 2篇 |
排序方式: 共有1280条查询结果,搜索用时 31 毫秒
71.
海底电场传感器原理及研制技术 总被引:6,自引:1,他引:6
因海底电场信号微弱,海下自然环境复杂以及海水导电介质以氯离子为主等原因,用于海下电场测量的电场传感器在材料和结构上有其特殊性。研制海底电场传感器成为开展海洋大地电磁探测的重要技术内容之一。研制过程遇到的主要技术问题有;海底电极材料的选择;电极的制作工艺;承压与密封技术;海水运动对测量产生不利影响的克服办法;水下弱信号传输的抗干扰问题,等等,阐述了对上述问题的解决办法。提出了海底电场传感器的全套研制方案。并列举了相关的室内模拟实验和海洋试验的结果。 相似文献
72.
PWM驱动电机的电流环设计 总被引:4,自引:0,他引:4
郑舒 《华东地质学院学报》2002,25(2):174-177
总结了PWM驱动电机电流环的设计及提取反馈电流的方法,提出了一种无超调的电流环设计方法--积分反馈校正方法,并探讨了小电流时电流环的设计各种获取电流的方法。 相似文献
73.
This paper explores the application of Artificial Intelligent (AI) techniques for climate forecast. It pres ents a study on modelling the monsoon precipitation forecast by means of Artificial Neural Networks (ANNs). Using the historical data of the total amount of summer rainfall over the Delta Area of Yangtze River in China, three ANNs models have been developed to forecast the monsoon precipitation in the corre sponding area one year, five-year, and ten-year forward respectively. Performances of the models have been validated using a 'new' data set that has not been exposed to the models during the processes of model development and test. The experiment results are promising, indicating that the proposed ANNs models have good quality in terms of the accuracy, stability and generalisation ability. 相似文献
74.
从美国发射其第一颗遥感卫星一陆地卫星-1算起的30余年里,世界范围内商业遥感卫星技术已经有了巨大的进步,越来越多的国家和国际团体拥有自己的遥感卫星。除了更多各类的遥感器得以使用外,卫星的图像分辨率和覆盖能力也有了很大的改进。未来的发展更加令人振奋。国外遥感卫星(包括已经发射和计划要发射的卫星)简介是根据从国内外出版物中获得的信息整编而成,旨在给遥感应用提供一个现在和未来图像信息源的总的概念。 相似文献
75.
76.
Hans Güsten Günther Heinrich Ralf W. H. Schmidt Ulrich Schurath 《Journal of Atmospheric Chemistry》1992,14(1-4):73-84
A small, lightweight (1.5 kg) and fast-response ozone sensor for direct eddy flux measurements has been built. The basis for detection is the chemiluminescence of an organic dye adsorbed on dry silica gel in the reaction with ozone. The chemiluminescence is monitored with a cheap and small blue-sensitive photomultiplier. At a flow rate of 100 l min-1 the ozone sensor has a 90% response time of significantly better than 0.1 s with a detection limit lower than 50 ppt at S/N=3. There are no interferences from other atmospheric trace gases like NOx, H2O2 and PAN. Water vapour and SO2 enhance the chemiluminescence efficiency of the ozone sensor. Since their response times are 22 seconds and 30 minutes, respectively, no correlation between rapid ozone fluctuations and those of these two trace gases is noticed by the ozone sensor when operating at a frequency of 10 Hz.The ozone sensor was tested for several weeks in continuous measurements of ozone fluxes and deposition velocities over different croplands using the eddy correlation technique. Good agreement was found between ozone dry deposition velocities derived from profile measurements and by eddy correlation. 相似文献
77.
PANHeping ZHANGChunsen 《地球空间信息科学学报》2003,6(2):48-54
This paper describes the structure,geometric model and geo-metric calibration of Photogrammetron I-the first type of photogrammetron which is designed to be a coherent stereo photogrammetric system in which two cameras are mounted on a physical base but driven by an intelligent agent architecture.The system calibration is divided into two parts:the in-lab calibration determines the fixed parameters in advance of system operation,and the insitu calibration keeps tracking the free parameters in real-time during the system operation.In a video surveillance set-up, prepared control points are tracked in stereo image sequences,so that the free parameters of the system can be continuously updated through iterative bundle adjustment and kalman filtering. 相似文献
78.
测汞用光纤传感器的初步研制 总被引:1,自引:0,他引:1
利用原子吸收原理初步研制了一种测示用光纤传感器,解决了光纤探头部分的技术难题。与传统的测汞仪器相比,该仪器的最大优点是可动的。中介绍了仪器的工作原理及主要技术性能。实验表明,可以利用光纤传感技术来实现汞测量。 相似文献
79.
This paper presents a linear predictor (LP)‐based lossless sensor data compression algorithm for efficient transmission, storage and retrieval of seismic data. Auto‐Regressive with eXogenous input (ARX) model is selected as the model structure of LP. Since earthquake ground motion is typically measured at the base of monitored structures, the ARX model parameters are calculated in a system identification framework using sensor network data and measured input signals. In this way, sensor data compression takes advantage of structural system information to maximize the sensor data compression performance. Numerical simulation results show that several factors including LP order, measurement noise, input and limited sensor number affect the performance of the proposed lossless sensor data compression algorithm concerned. Generally, the lossless data compression algorithm is capable of reducing the size of raw sensor data while causing no information loss in the sensor data. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
80.
本自动监测冰厚装置原理,是通过测量冰层底面与冰下水中一固定端之间垂直距离来实现的。该距离是一只浮桶从固定端运动到冰层底面的行程。随浮桶一起运动的压差式水位传感器分别给出浮桶位于固定端和冰层底面的位置,而浮桶的运动则依靠数据采集仪控制浮桶内水泵排吸水改变浮桶的重力来实现,并且该仪器能够记录传感器的信号和设置水泵开关的开、闭时间。为了避免浮桶对冰层厚度变化的影响且浮桶不至于与冰层底面冻结,浮桶只是在测量行程时上浮到冰层底面,其他时间均在固定端位置。文中给出系统的工作原理和现场实测结果的初步分析。 相似文献