全文获取类型
收费全文 | 13204篇 |
免费 | 1123篇 |
国内免费 | 593篇 |
专业分类
电工技术 | 793篇 |
技术理论 | 1篇 |
综合类 | 803篇 |
化学工业 | 2087篇 |
金属工艺 | 847篇 |
机械仪表 | 739篇 |
建筑科学 | 913篇 |
矿业工程 | 352篇 |
能源动力 | 409篇 |
轻工业 | 836篇 |
水利工程 | 237篇 |
石油天然气 | 762篇 |
武器工业 | 91篇 |
无线电 | 1672篇 |
一般工业技术 | 1631篇 |
冶金工业 | 808篇 |
原子能技术 | 163篇 |
自动化技术 | 1776篇 |
出版年
2024年 | 75篇 |
2023年 | 199篇 |
2022年 | 337篇 |
2021年 | 507篇 |
2020年 | 374篇 |
2019年 | 334篇 |
2018年 | 407篇 |
2017年 | 432篇 |
2016年 | 382篇 |
2015年 | 487篇 |
2014年 | 630篇 |
2013年 | 692篇 |
2012年 | 789篇 |
2011年 | 816篇 |
2010年 | 713篇 |
2009年 | 708篇 |
2008年 | 708篇 |
2007年 | 720篇 |
2006年 | 697篇 |
2005年 | 603篇 |
2004年 | 398篇 |
2003年 | 457篇 |
2002年 | 445篇 |
2001年 | 388篇 |
2000年 | 360篇 |
1999年 | 361篇 |
1998年 | 341篇 |
1997年 | 316篇 |
1996年 | 304篇 |
1995年 | 212篇 |
1994年 | 172篇 |
1993年 | 128篇 |
1992年 | 94篇 |
1991年 | 84篇 |
1990年 | 66篇 |
1989年 | 46篇 |
1988年 | 33篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 5篇 |
1979年 | 3篇 |
1973年 | 2篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
It is shown that even pure quartz, other silicas or aluminas can enhance the aromatization activity of a ZSM-5 zeolite. Incorporation of gallium oxide onto these supports increases further the production of aromatics. The use of supported gallium oxide co-catalyst obtained by co-evaporation of a colloidal silica and a Ga salt has led to extremely high aromatization performance for the hybrid catalyst. 相似文献
62.
Magnetic‐field probes can be used for electromagnetic interference measurement of high‐speed circuits. The main magnetic probe performance includes sensitivity, spatial resolution, electric‐field suppression ratio (EFSR), and measurement accuracy. In this article, a pair of differential magnetic‐field probes is proposed to improve measurement accuracy without reducing sensitivity. The proposed differential probes consist of two asymmetric loop probes, which are designed in the same plane and separated by a row of periodic vias. The proposed differential probes are fabricated under PCB process. High accuracy can be achieved by measuring difference between outputs of the two probes. In addition, EFSR can be improved by size optimization of the differential magnetic‐field probes. Simulation and measurement results show the operating bandwidth is from 100 MHz to 12 GHz, the measurement error is 3.4% and the EFSR is about 40 dB. The proposed probes have higher measurement accuracy and higher EFSR than the conventional single probe, and larger operation bandwidth than the stacked differential probes. 相似文献
63.
电力大用户最大需量控制是降低电网峰值负荷、节约用户电费成本的重要技术手段.面向强波动性和冲击性工业电能需量控制,研究了超短期需量负荷的多步预测问题.基于集成经验模态分解(EE-MD)方法,通过二次分解有效分离时间序列中不同频率的信号,采用长短期记忆网络(LSTM)对各信号子序列进行独立预测,最后组合预测结果.实验结果表明,本方法能很好的预测工业需量负荷变化,M A PE/MAE/NRMSE精度指标基本控制在2% 以内,明显优于多种现行主流时序预测模型和最新文献方法,且消除了多步预测的传递误差,预测模型精度和稳定性满足需量控制要求. 相似文献
64.
Shuixian Yang Hetuo Chen Jianmin Li Hao Guo Xiaojian Mao Run Tian Jian Zhang Shiwei Wang 《Journal of the American Ceramic Society》2021,104(2):1040-1046
The oxidation behavior and mechanism of aluminum oxynitride (AlON) powder exposed to air at elevated temperatures between 800°C and 1300°C was investigated by X-ray diffractometry (XRD), scanning electron microscope (SEM), electron spin resonance (ESR), nuclear magnetic resonance (NMR), and simultaneous thermogravimetry, differential thermal analysis, and mass spectrometry techniques (TG-DTA-MS). The weight of AlON gradually increases to a maximum value at 1150°C and then decreases with further heating. Meanwhile, AlON powder undergoes chemical changes, as evidenced by lattice expansion, and turns eventually into alumina. ESR spectra reveal the occurrence of lone pair electrons in the oxidized products and the intensity of corresponding resonance signal increases before disappearing with the increase in temperature. Combined with the results of NMR and TG-DTA-MS, the measured data suggest that Al-N in [AlO3N] tetrahedron and [AlO5N] octahedron are gradually oxidized into Al-O-N group with lone pair electrons, which causes continuous weight gain and lattice expansion. Further oxidation at higher temperatures results in alumina and N2. 相似文献
65.
66.
67.
68.
Most automatic steering systems for large tractors are designed with hydraulic systems that run on either constant flow or constant pressure. Such designs are limited in adaptability and applicability. Moreover, their control valves can unload in the neutral position and eventually lead to serious hydraulic leakage over long operation periods. In response to the problems noted above, a multifunctional automatic hydraulic steering circuit is presented. The system design is composed of a 5-way-3- position proportional directional valve, two pilot-controlled check valves, a pressure-compensated directional valve, a pressurecompensated flow regulator valve, a load shuttle valve, and a check valve, among other components. It is adaptable to most open-center systems with constant flow supply and closed-center systems with load feedback. The design maintains the lowest pressure under load feedback and stays at the neutral position during unloading, thus meeting the requirements for steering. The steering controller is based on proportional-integral-derivative (PID) running on a 51-microcontroller-unit master control chip. An experimental platform is developed to establish the basic characteristics of the system subject to stepwise inputs and sinusoidal tracking. Test results show that the system design demonstrates excellent control accuracy, fast response, and negligible leak during long operation periods. 相似文献
69.
70.