全文获取类型
收费全文 | 265670篇 |
免费 | 28450篇 |
国内免费 | 17921篇 |
专业分类
电工技术 | 22242篇 |
技术理论 | 7篇 |
综合类 | 23767篇 |
化学工业 | 38453篇 |
金属工艺 | 16965篇 |
机械仪表 | 17896篇 |
建筑科学 | 20901篇 |
矿业工程 | 9153篇 |
能源动力 | 7626篇 |
轻工业 | 24619篇 |
水利工程 | 7781篇 |
石油天然气 | 11664篇 |
武器工业 | 3279篇 |
无线电 | 28831篇 |
一般工业技术 | 26623篇 |
冶金工业 | 10366篇 |
原子能技术 | 3714篇 |
自动化技术 | 38154篇 |
出版年
2024年 | 1220篇 |
2023年 | 4181篇 |
2022年 | 9209篇 |
2021年 | 12166篇 |
2020年 | 8865篇 |
2019年 | 6781篇 |
2018年 | 7229篇 |
2017年 | 8218篇 |
2016年 | 7327篇 |
2015年 | 11095篇 |
2014年 | 13977篇 |
2013年 | 16313篇 |
2012年 | 20057篇 |
2011年 | 20981篇 |
2010年 | 19249篇 |
2009年 | 18739篇 |
2008年 | 18992篇 |
2007年 | 18507篇 |
2006年 | 17123篇 |
2005年 | 14168篇 |
2004年 | 10161篇 |
2003年 | 7532篇 |
2002年 | 7082篇 |
2001年 | 6407篇 |
2000年 | 5806篇 |
1999年 | 4186篇 |
1998年 | 2958篇 |
1997年 | 2450篇 |
1996年 | 2226篇 |
1995年 | 1946篇 |
1994年 | 1548篇 |
1993年 | 1147篇 |
1992年 | 944篇 |
1991年 | 722篇 |
1990年 | 575篇 |
1989年 | 521篇 |
1988年 | 404篇 |
1987年 | 275篇 |
1986年 | 196篇 |
1985年 | 105篇 |
1984年 | 77篇 |
1983年 | 57篇 |
1982年 | 72篇 |
1981年 | 49篇 |
1980年 | 68篇 |
1979年 | 43篇 |
1978年 | 3篇 |
1965年 | 3篇 |
1959年 | 32篇 |
1951年 | 49篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
ABSTRACT This study investigates the effects of strain, strain rates, and forming directions (RD-rolling direction, TD-transverse direction, and ND-normal direction) on adiabatic shear, via dynamic impact compression tests using the Split Hopkinson Pressure Bar (SHPB) apparatus. A modified Johnson-Cook (J-C) constitutive model is proposed, which used to analyse the influence of the constitutive parameters on the sensitivity of adiabatic shear, employing a finite element software. The different sensitivities of adiabatic shear under different directions are explained by combining microscopic analysis and results from mechanical responses. The results show that the sensitivity of adiabatic shear can be related to the time of stress collapse in the following trend: ND?>?TD?>?RD; the sensitivities of these constitutive parameters on adiabatic shear are calculated and compared. 相似文献
62.
63.
在国标法GB 7494—1987的基础上,将在线萃取、在线分离技术与分光光度法相结合,研究了自动测定水中阴离子表面活性剂的新方法,使国标法中的各个操作步骤完全实现自动化。结果表明,新的自动测定法在0.034~2.00 mg/L浓度范围内,线性相关系数为0.999 9,检出限为0.008 6 mg/L,相对标准偏差3.8%(n=6),实际样品加标回收率为88.3%~100.0%。测定全过程相对密闭,人体不接触三氯甲烷,保护了分析人员的自身安全,方法操作简便,测定时间也较短,单个样品测定时间7 min。 相似文献
64.
睡眠期间连续且准确的呼吸量监测有助于推断用户的睡眠阶段以及提供一些慢性疾病的线索。现有工作主要针对呼吸频率进行感知和监测,缺乏对呼吸量进行连续监测的手段。针对上述问题提出了一种基于商用无线射频识别(RFID)标签的无线感知用户睡眠期间呼吸量的系统——RF-SLEEP。RF-SLEEP通过阅读器连续收集附着在胸部表面的标签阵列返回的相位值及时间戳数据,计算出呼吸引起的胸部不同点的位移量,基于广义回归神经网络(GRNN)构建胸部不同点的位移量与呼吸量之间的关系模型,从而实现对用户睡眠期间呼吸量的评估。RF-SLEEP通过在用户肩膀处附着双参考标签,消除用户睡眠期间翻转身体对胸部位移计算造成的误差。实验结果表明,RFSLEEP对不同用户睡眠期间的呼吸量连续监测的平均精确度为92.49%。 相似文献
65.
66.
Yong Xu Yun Li Songlin Li Francis Balestra Gerard Ghibaudo Wenwu Li Yen‐Fu Lin Huabin Sun Jing Wan Xinran Wang Yufeng Guo Yi Shi Yong‐Young Noh 《Advanced functional materials》2020,30(20)
Unreliable mobility values, and particularly greatly overestimated values and severely distorted temperature dependences, have recently hampered the development of the organic transistor field. Given that organic field‐effect transistors (OFETs) have been routinely used to evaluate mobility, precise parameter extraction using the electrical properties of OFETs is thus of primary importance. This review examines the origins of the various mobilities that must be determined for OFET applications, the relevant extraction methods, and the data selection limitations, which help in avoiding conceptual errors during mobility extraction. For increased precision, the review also discusses device fabrication considerations, calibration of both the specific gate‐dielectric capacitance and the threshold voltage, the contact effects, and the bias and temperature dependences, which must actually be handled with great care but have mostly been overlooked to date. This review serves as a systematic overview of the OFET mobility extraction process to ensure high precision and will also aid in improving future research. 相似文献
67.
Adaptive backstepping repetitive learning control design for nonlinear discrete‐time systems with periodic uncertainties
下载免费PDF全文
![点击此处可从《International Journal of Adaptive Control and Signal Processing》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Qiao Zhu Jian‐Xin Xu Shiping Yang Guang‐Da Hu 《International Journal of Adaptive Control and Signal Processing》2015,29(4):524-535
This paper addresses a tracking problem for uncertain nonlinear discrete‐time systems in which the uncertainties, including parametric uncertainty and external disturbance, are periodic with known periodicity. Repetitive learning control (RLC) is an effective tool to deal with periodic unknown components. By using the backstepping procedures, an adaptive RLC law with periodic parameter estimation is designed. The overparameterization problem is overcome by postponing the parameter estimation to the last backstepping step, which could not be easily solved in robust adaptive control. It is shown that the proposed adaptive RLC law without overparameterization can guarantee the perfect tracking and boundedness of the states of the whole closed‐loop systems in presence of periodic uncertainties. In addition, the effectiveness of the developed controller is demonstrated by an implementation example on a single‐link flexible‐joint robot. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
68.
研究基于用户需求的设计方法在电热炉产品设计中的运用。以满足单身用户需求的电热炉产品设计为例,运用定性人物角色构建法构建出目标用户角色模型,使用户的需求具体化、形象化,在此基础上设计了具有多种加热模式且方便用户携带与收纳的电热炉结构与造型,通过计算机辅助设计与样品制作,验证了设计方案的可行性,为电热炉的开发设计提供参考。 相似文献
69.
Ionomics is a novel multidisciplinary field that uses advanced techniques to investigate the composition and distribution of all minerals and trace elements in a living organism and their variations under diverse physiological and pathological conditions. It involves both high-throughput elemental profiling technologies and bioinformatic methods, providing opportunities to study the molecular mechanism underlying the metabolism, homeostasis, and cross-talk of these elements. While much effort has been made in exploring the ionomic traits relating to plant physiology and nutrition, the use of ionomics in the research of serious diseases is still in progress. In recent years, a number of ionomic studies have been carried out for a variety of complex diseases, which offer theoretical and practical insights into the etiology, early diagnosis, prognosis, and therapy of them. This review aims to give an overview of recent applications of ionomics in the study of complex diseases and discuss the latest advances and future trends in this area. Overall, disease ionomics may provide substantial information for systematic understanding of the properties of the elements and the dynamic network of elements involved in the onset and development of diseases. 相似文献
70.