全文获取类型
收费全文 | 31505篇 |
免费 | 4171篇 |
国内免费 | 2162篇 |
专业分类
电工技术 | 521篇 |
综合类 | 2101篇 |
化学工业 | 1632篇 |
金属工艺 | 5048篇 |
机械仪表 | 2891篇 |
建筑科学 | 2203篇 |
矿业工程 | 427篇 |
能源动力 | 295篇 |
轻工业 | 543篇 |
水利工程 | 297篇 |
石油天然气 | 191篇 |
武器工业 | 494篇 |
无线电 | 14640篇 |
一般工业技术 | 4243篇 |
冶金工业 | 913篇 |
原子能技术 | 386篇 |
自动化技术 | 1013篇 |
出版年
2024年 | 87篇 |
2023年 | 595篇 |
2022年 | 786篇 |
2021年 | 1021篇 |
2020年 | 992篇 |
2019年 | 816篇 |
2018年 | 780篇 |
2017年 | 1068篇 |
2016年 | 1055篇 |
2015年 | 1164篇 |
2014年 | 1577篇 |
2013年 | 1629篇 |
2012年 | 2083篇 |
2011年 | 1998篇 |
2010年 | 1579篇 |
2009年 | 1569篇 |
2008年 | 1843篇 |
2007年 | 2285篇 |
2006年 | 2088篇 |
2005年 | 1805篇 |
2004年 | 1658篇 |
2003年 | 1380篇 |
2002年 | 1167篇 |
2001年 | 1127篇 |
2000年 | 920篇 |
1999年 | 772篇 |
1998年 | 614篇 |
1997年 | 596篇 |
1996年 | 537篇 |
1995年 | 460篇 |
1994年 | 441篇 |
1993年 | 391篇 |
1992年 | 303篇 |
1991年 | 257篇 |
1990年 | 177篇 |
1989年 | 77篇 |
1988年 | 58篇 |
1987年 | 17篇 |
1986年 | 10篇 |
1985年 | 8篇 |
1984年 | 14篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1980年 | 8篇 |
1979年 | 3篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 4篇 |
1959年 | 3篇 |
1951年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
In recent years, porous silicon (PSi) has attracted a great deal of attention for sensing applications. However, the high reactivity of PSi surfaces causes serious problems of stability. In this work, we developed new thin films that can serve as stabilizer of PSi for CO2 gas sensors development. PSi surface was coated with carbon nitride (CNx) film which is one of the most important interfering to stabilize the PSi layer. CNx film was deposited by pulsed laser ablation. The effect of CO2 gas on the sensor response was investigated for different polarization voltages. The electrical properties of (Al/CNx/PSi/Si) structure were modified in the presence of the gas. The device shows a high sensitivity against CO2 gas. Furthermore, the current variation of the sensor as a function of time has been investigated. The results show that the Al/CNx/PSi/Si structure becomes stable after the first two weeks. 相似文献
72.
In this paper, we study the effects of thermal noise on the time evolution of a weak light pulse (probe) in the presence of a strong light pulse (pump) within a gain medium which includes random scatterer particles. Suitable thermal noise term is added to a set of four coupled equations including three diffusion equations for energy densities and a rate equation for the upper level population in a four-level gain medium. These equations have been solved simultaneously by Crank–Nicholson numerical method. The main result is that the back-scattered output probe light is increased as the thermal noise strength is increased and simultaneously, with the same rate, the amplified spontaneous emission is decreased. Therefore, the amplified response of the random laser in diffusion regime for the input probe pulse is enhanced due to effect of the thermal noise. 相似文献
73.
Evaldas Bal
inas Sara J Baldock Nadeda Drei Monika Grubliauskait Sarah Coultas David L Rochester Mindaugas Valius John G Hardy Daiva Baltriukien 《Polymer International》2019,68(11):1928-1940
Materials with microscale structures are gaining increasing interest due to their range of technical and medical applications. Additive manufacturing approaches to such objects via laser two‐photon polymerization, also known as multiphoton fabrication, enable the creation of new materials with diverse and tunable properties. Here, we investigate the properties of 3D structures composed of organometallic polymers incorporating aluminium, titanium, vanadium and zirconium. The organometallic polymer‐based materials were analysed using a variety of techniques including SEM, energy‐dispersive X‐ray spectroscopy, X‐ray photoelectron spectroscopy analysis and contact angle measurements and their biocompatibility was tested in vitro. Cell viability and mode of death were determined by 3‐(4,5‐dimethyl‐2‐thiazolyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide (MTT) assay and acridine orange/ethidium bromide staining. Polymers incorporating Al, Ti and Zr supported cell adhesion and proliferation, and showed low toxicity in vitro, whereas the organometallic polymer incorporating V was shown to be cytotoxic. Inductively coupled plasma optical emission spectrometry suggested that leaching of the V from the organometallic polymer is the likely cause of this. The preparation of the organometallic polymers is straightforward and both simple 2D and complex 3D structures can be fabricated with ease. Resolution tests of the newly developed organometallic polymer incorporating Al show that suspended lines with widths down to 200 nm can be fabricated. We believe that the materials described in this work show promising properties for the development of objects with sub‐micron features for biomedical applications (e.g. biosensors, drug delivery devices, tissue scaffolds etc.). © 2019 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry. 相似文献
74.
Two-beam laser welding (TBLW) is an advanced process for precise, low distortion joining of cylindrical miniature parts. The process is composed of a laser source, optics and various actuators, which form a sophisticated system for control and maintenance in high volume manufacturing. A well-established method for identifying welding defects and ensuring welding quality is the monitoring of plasma light emission in TBLW. Although such monitoring systems can detect a change in process status, they are not able to diagnose the nature of the fault. The main challenge in this research was to extend the use of quality-based monitoring systems to measure additional deterioration-related parameters and to estimate system deterioration from them by using expert knowledge.This paper shows a novel condition-based maintenance (CBM) for the TBLW system, which performs condition identification using online monitoring of plasma light emission in combination with offline inspection of the seam macrographs. A combination of quality parameters derived from seam macrographs of defective parts is used to identify process deterioration, such as contamination of the optics, misalignment of the optomechanical system, or reduced laser power. The information obtained is used to make predefined process adjustments based on expert domain knowledge. The implementation of the developed CBM in high volume manufacturing of piezoelectric pressure sensors resulted in more predictable TBLW by reducing system failures as well as shorter diagnosis times. 相似文献
75.
Inam Ridha Ali Basiri Sudhakar Godeshala Md Zubair Ebne Rafique Deepanjan Ghosh Jason Williams Nikhilesh Chawla Jung Keun Lee Jacquelyn Kilbourne Yu Yao Kaushal Rege 《Advanced functional materials》2021,31(6):2007811
Poor strength, infection, leakage, long procedure times, and inflammation limit the efficacy of common tissue sealing devices in surgeries and trauma. Light-activated sealing is attractive for tissue sealing and repair, and can be facilitated by the generation of local heat following absorption of nonionizing laser energy by chromophores. Here, the inherent ability of biomaterials is exploited to absorb nonionizing, mid-infrared (midIR) light in order to engender rapid photothermal sealing and repair of soft tissue wounds. In this approach, the biomaterial simultaneously acts as a photothermal convertor as well as a biosealant, which dispenses the need for exogeneous light-absorbing nanoparticles or dyes. Biomechanical recovery, mathematical modeling, histopathology analyses, tissue strain mapping using digital imaging correlation, and visualization of the biosealant-tissue interface using hyperspectral imaging indicate superior performance of midIR sealing in live mice compared to conventional sutures and glue. The midIR-biosealant approach demonstrates rapid sealing of soft tissues, improves cosmesis, lowers potential for scarring, obviates safety concerns because of the nonionizing light used, and allows adoption of a wide diversity of biomaterials. Taken together, the studies demonstrate a novel advance both in biomaterials for surgical sealing along with the use of nonionizing midIR light, with high potential for clinical translation. 相似文献
76.
77.
N. MAKUCH P. DZIARSKI M. KULKA A. PIASECKI M. TULIŃSKI R. MAJCHROWSKI 《中国有色金属学会会刊》2019,29(2):322-337
Laser alloying was used for production of thick layers on surface of Nimonic 80A-alloy. For laser surface modification, three types of pre-coated pastes were applied: with amorphous boron, with amorphous boron and molybdenum as well as with amorphous boron and niobium. The microstructure, hardness and wear resistance of produced layers were studied in details. The presence of different types of borides in re-melted zone depended on the paste composition and caused an increase in hardness up to about HV 1000. The wear resistance was evaluated by calculation of mass wear intensity factor Imw and relative mass loss of specimen and counter-specimen. The wear behavior of the tested frictional pairs was determined by 3D interference microscopy, scanning electron microscopy equipped with EDS microanalyzer. The significant increase in abrasive wear resistance was observed in comparison to untreated Nimonic 80A-alloy. The lowest mass loss intensity factor was characteristic of laser-alloyed Nimonic 80A-alloy with boron and niobium (Imw=1.234 mg/(cm2·h)). Laser alloyed-layers indicated abrasive wear mechanism with clearly visible grooves. Laser alloying with boron and niobium resulted in the additional oxidative wear mechanism. In this case, EDS patterns revealed presence of oxygen on the worn surface of specimen. 相似文献
78.
基于自主搭建的高频微振平台,进行316L不锈钢振动辅助激光焊接试验,探究高频微振激光焊接工艺对接头组织性能的影响. 结果表明,施加振动后,焊缝表面无飞溅,成形良好. 截面未出现塌陷、堆高,背部熔宽均匀. 振动的施加,能够明显细化焊缝区的晶粒,在共振频率1 467.5 Hz的高频微振激光焊条件下,晶粒尺寸最小. 点状颗粒物分布在奥氏体晶粒间,趋于弥散,新相及大颗粒物减少. 随着振动频率增加,焊缝区显微硬度值跟着增加,在较高共振频率显微硬度值增加显著,在共振频率1 467.5 Hz、加速度160 m/s2条件下,焊缝区平均硬度206 HV,与无振动相比,硬度值增加5.6%. 相似文献
79.
80.
研制了用于远程激光脉冲测距机的板条激光器。使用半导体泵浦的MOPA激光结构实现了大于250 mJ的脉冲激光输出,输出脉冲宽度为12.83 ns,最终输出激光光束束散角为0.18 mrad。该激光测照器可应用于远程激光测距。对激光测距机的测距与照射能力进行了理论计算与分析。理论分析表明,应用于机载平台时,该激光测照器能够实现50 km距离的激光测距。该型激光测距机具有测距距离远,重量轻,结构紧凑等特点,具有广泛的应用前景。 相似文献