全文获取类型
收费全文 | 66764篇 |
免费 | 10967篇 |
国内免费 | 6627篇 |
学科分类
工业技术 | 84358篇 |
出版年
2024年 | 657篇 |
2023年 | 1805篇 |
2022年 | 3101篇 |
2021年 | 3364篇 |
2020年 | 3220篇 |
2019年 | 2589篇 |
2018年 | 2229篇 |
2017年 | 2771篇 |
2016年 | 3049篇 |
2015年 | 3434篇 |
2014年 | 5282篇 |
2013年 | 4466篇 |
2012年 | 5543篇 |
2011年 | 5813篇 |
2010年 | 4424篇 |
2009年 | 4432篇 |
2008年 | 4350篇 |
2007年 | 4830篇 |
2006年 | 3877篇 |
2005年 | 3214篇 |
2004年 | 2420篇 |
2003年 | 2063篇 |
2002年 | 1594篇 |
2001年 | 1195篇 |
2000年 | 941篇 |
1999年 | 719篇 |
1998年 | 591篇 |
1997年 | 421篇 |
1996年 | 423篇 |
1995年 | 281篇 |
1994年 | 218篇 |
1993年 | 186篇 |
1992年 | 156篇 |
1991年 | 133篇 |
1990年 | 112篇 |
1989年 | 64篇 |
1988年 | 65篇 |
1987年 | 38篇 |
1986年 | 42篇 |
1985年 | 35篇 |
1984年 | 32篇 |
1983年 | 29篇 |
1982年 | 23篇 |
1981年 | 23篇 |
1980年 | 21篇 |
1979年 | 7篇 |
1978年 | 7篇 |
1959年 | 15篇 |
1956年 | 7篇 |
1951年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
电梯门机控制系统的运行曲线设计 总被引:1,自引:0,他引:1
为了实现电梯轿厢门的开门和关门快速且平稳地运行,介绍了一种基于高性能微型机的门机控制系统结构和门位移的检测原理,以门位移量作为控制系统的反馈量,对门机运行速度进行了分区设计。在高速附近的变化区,门机速度匀速变化时,进行了门机开门和关门控制曲线的计算,推导出运行位移与门机速度具有二次曲线的关系,进而对微型机控制的软件流程进行了设计,达到了门机高低速运行的平稳过渡。最后,给出了实际运行系统的主电路电压波形。 相似文献
32.
The width of the transition layer between the crystalline and amorphous zones in nylon 1010 was determined by SAXS with point collimation and long-slit collimation, respectively. The width of the transition layer, E, was found to be 1.7 nm. The results show that the width of the transition layer is independent of crystallinity. 相似文献
33.
针对铜鼓县小水电站联网时存在的问题及其不利影响进行了分析,井提出了改进途径,指出小水电站的联网改造应立足安全,争取效益。 相似文献
34.
35.
Mulcahy Nicholas J.; Call Josep; Dunbar Robin I. M. 《Canadian Metallurgical Quarterly》2005,119(1):23
Two important elements in problem solving are the abilities to encode relevant task features and to combine multiple actions to achieve the goal. The authors investigated these 2 elements in a task in which gorillas (Gorilla gorilla) and orangutans (Pongo pygmaeus) had to use a tool to retrieve an out-of-reach reward. Subjects were able to select tools of an appropriate length to reach the reward even when the position of the reward and tools were not simultaneously visible. When presented with tools that were too short to retrieve the reward, subjects were more likely to refuse to use them than when tools were the appropriate length. Subjects were proficient at using tools in sequence to retrieve the reward. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
36.
37.
R. GRAY† M. HILARY STEVENSON‡ 《International Journal of Food Science & Technology》1991,26(6):669-672
One hundred and twenty-five pairs of chicken drumsticks were randomly allocated to one of five dose rates: 5, 10, 15, 20 or 600 kGyh-. The highest dose rate was obtained using a linear accelerator whilst the remaining dose rates were provided using a 60 Co gamma source. Each batch of 25 pairs was further divided into groups five of which were stored at 4°C for 0, 7, 14, 21 or 28 days. ESR spectroscopy was used to measure the intensity of the radiation-induced signal. There was a quadratic relationship between ESR signal strength and dose rate, which although statistically significant is unlikely to be of practical importance. The magnitude of the ESR signal declined by about 20% over the first 14 days of storage at 4°C and thereafter the decrease was minimal. 相似文献
38.
39.
J. Balakrishnan W. A. Sethares C. R. Johnson 《International Journal of Adaptive Control and Signal Processing》2002,16(4):309-323
A method of approximate channel identification is proposed that is based on a simplification of the correlation estimator. Despite the numerical simplification (no multiplications or additions are required, only comparisons and an accumulator), the performance of the proposed estimator is not significantly worse than that of the standard correlation estimator. A free (user selectable) parameter moves ‘smoothly’ from a situation with small sum‐squared channel estimation error but hard‐to‐identify channel peaks, to one with a larger sum‐squared estimation error but easy‐to‐identify channel peaks. The proposed estimator is shown to be biased and its behaviour is analysed in a number of situations. Applications of the proposed estimator to sparsity detection, symbol timing recovery and to the initialization of blind equalizers are suggested. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
40.
When humans plan to execute a tool-use action, they can only specify the bodily movement parameters by taking into account the external target or goal of the tool-use action and the target-movement mapping implemented by the tool. In this study, the authors used the movement precuing method to investigate how people prepare for actions made with tools. More specifically, they asked whether people would be able to specify the spatial target and the target-movement mapping of the tool-use action independently of each other, and to what degree they would be able to prepare these components in advance. In 3 experiments, they precued either the target or the target-movement mapping of tool-use actions involving either a compatible or an incompatible target-movement mapping. Results indicate that participants benefit from partial advance information about the target-movement mapping, whereas no significant effects were found for precuing the spatial target of the action. These results occurred regardless of whether the target-movement mapping was compatible or incompatible and provide evidence for the notion that the target-movement mapping of a tool-use action is part of its cognitive representation. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献