全文获取类型
收费全文 | 14389篇 |
免费 | 2198篇 |
国内免费 | 1147篇 |
专业分类
电工技术 | 3724篇 |
综合类 | 1406篇 |
化学工业 | 1839篇 |
金属工艺 | 331篇 |
机械仪表 | 896篇 |
建筑科学 | 568篇 |
矿业工程 | 296篇 |
能源动力 | 411篇 |
轻工业 | 1251篇 |
水利工程 | 138篇 |
石油天然气 | 438篇 |
武器工业 | 188篇 |
无线电 | 1930篇 |
一般工业技术 | 1322篇 |
冶金工业 | 249篇 |
原子能技术 | 88篇 |
自动化技术 | 2659篇 |
出版年
2024年 | 117篇 |
2023年 | 334篇 |
2022年 | 466篇 |
2021年 | 565篇 |
2020年 | 643篇 |
2019年 | 509篇 |
2018年 | 506篇 |
2017年 | 598篇 |
2016年 | 606篇 |
2015年 | 702篇 |
2014年 | 850篇 |
2013年 | 843篇 |
2012年 | 990篇 |
2011年 | 1100篇 |
2010年 | 829篇 |
2009年 | 847篇 |
2008年 | 864篇 |
2007年 | 1099篇 |
2006年 | 938篇 |
2005年 | 755篇 |
2004年 | 643篇 |
2003年 | 564篇 |
2002年 | 450篇 |
2001年 | 388篇 |
2000年 | 345篇 |
1999年 | 261篇 |
1998年 | 201篇 |
1997年 | 153篇 |
1996年 | 135篇 |
1995年 | 91篇 |
1994年 | 84篇 |
1993年 | 59篇 |
1992年 | 59篇 |
1991年 | 26篇 |
1990年 | 29篇 |
1989年 | 19篇 |
1988年 | 7篇 |
1987年 | 14篇 |
1986年 | 6篇 |
1985年 | 10篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 7篇 |
1980年 | 4篇 |
1979年 | 1篇 |
1974年 | 2篇 |
1964年 | 1篇 |
1959年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
基于区域GAC模型的二值化水平集图像分割算法 总被引:2,自引:1,他引:1
针对测地线主动轮廓(GAC)模型进行了改进,提出了一种基于区域的GAC模型.通过构造基于区域统计信息的符号压力函数取代边界停止函数,有效解决了弱边界目标或离散状边界目标的分割问题.该模型采用二值化水平集方法实现,避免了传统实现方法水平集函数需要重新初始化为符号距离函数,从而导致稳定性差、计算量大、实现复杂等缺点.对不同类型图像的试验结果表明:该算法迭代收敛速度比GAC模型传统实现方法明显加快,且可有效防止边界泄漏,分割效果优于传统GAC模型与C-V模型. 相似文献
83.
介绍了一种可应用于被动声纳的时频域联合捕捉主动声纳信号的方法及其工作流程。仿真相同噪声环境下使用该方法的发现距离与主动声纳探测距离,仿真结果表明使用该方法的发现距离远超过主动声纳探测距离,使用该方法可实现对目标的远程发现。 相似文献
84.
低频唤醒技术在微功耗主动式RFID中的应用研究 总被引:1,自引:1,他引:0
微功耗主动式RFID系统的标签一般采用纽扣电池供电,其功耗是一个很关键的问题,目前常采用定时唤醒的工作方式,本文介绍了低频唤醒技术的实现原理,并讨论了将其应用到微功耗主动式RFID系统中解决射频标签内发射模块的功耗问题,给出了低频唤醒的关键电路和程序流程,实践证明该方案可以很好地解决主动式RFID的功耗问题. 相似文献
85.
Computer simulations of signal transduction mechanism in {alpha}1B-adrenergic and m3-muscarinic receptors 总被引:2,自引:0,他引:2
Fanelli Franceses; Menziani M.Cristina; de Benedetti Pier G. 《Protein engineering, design & selection : PEDS》1995,8(6):557-564
Molecular dynamices simulations of the hamster 1Badrenergicand the rat m3-muscarinic seven-helix bundle receptor modelshave been carried out. The free, agonist-bound and antagonist-boundforms have been considered. Moreover, three mutant forms ofthe m3-muscarinic recep-tor (N507A, N507D and N507S) have alsobeen simulated; among these, the N507S mutant shows a constitutiveactivity. A comparative structural/dynamics analysis has beenperformed to elucidate (i) the perturbations induced by thefunctionally different ligands upon binding to their targetreceptor, (ii) the features of the three single-point mutantswith respect to the receptor wild type and (iii) the propertiesshared by the agonist-boundforms of the 1B-adrenergic receptorand the m3-muscarinic receptor and by the constitutively activemutant N507S. The consistency obtained between the structuralrearrangement of the transmembrane seven-helix bundle modelsconsidered, and the experimental pharmacological efficaciesof the ligands and of the mutants, constitute an important validationof the 3-D models obtained and allow the inference of the mechanismof ligand- or mutation-induced receptor activation at the molecularlevel. 相似文献
86.
针对5G毫米波通信,研制了一种双极化有源相控阵天线模组。厚度为2 mm的多层PCB正面印制阵列天线,在其背面集成多通道波束成形芯片,通过中间层实现天线与芯片的互连以及供电、控制等。测试结果表明,研制的板状4×4双极化相控阵模组在E面和H面均实现了不小于±40度的波束扫描范围(不大于3 dB的电平下降)和低于-18 dB的归一化交叉极化电平,在24~27.5 GHz的频率范围内实现了V极化和H极化分别为42.6~45.7 dBm和43.5~46.1 dBm的等效全向辐射功率(EIRP)。 相似文献
87.
Shiyu Huang Yuan Chang Zhuwei Li Jiaqi Cao Yurou Song Junfeng Gao Licheng Sun Jungang Hou 《Advanced functional materials》2023,33(21):2211631
Photoredox catalysis is a green solution for organics transformation and CO2 conversion into valuable fuels, meeting the challenges of sustainable energy and environmental concerns. However, the regulation of single-atomic active sites in organic framework not only influences the photoredox performance, but also limits the understanding of the relationship for photocatalytic selective organic conversion with CO2 valorization into one reaction system. As a prototype, different single-atomic metal (M) sites (M2+ = Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) in hydrogen-bonded organic frameworks (M-HOF) backbone with bridging structure of metal-nitrogen are constructed by a typical “two-in-one” strategy for superior photocatalytic C N coupling reactions integrated with CO2 valorization. Remarkably, Zn-HOF achieves 100% conversion of benzylamine oxidative coupling reactions, 91% selectivity of N-benzylidenebenzylamine and CO2 conversion in one photoredox cycle. From X-ray absorption fine structure analysis and density functional theory calculations, the superior photocatalytic performance is attributed to synergic effect of atomically dispersed metal sites and HOF host, decreasing the reaction energy barriers, enhancing CO2 adsorption and forming benzylcarbamic acid intermediate to promote the redox recycle. This work not only affords the rational design strategy of single-atom active sites in functional HOF, but also facilitates the fundamental insights upon the mechanism of versatile photoredox coupling reaction systems. 相似文献
88.
Hui Zhang Yinkun Sun Junjie Yang Zhiyu Sun Yanxin Zhao Xin Li Wei Wang Dongwei Lu Jun Ma 《Advanced functional materials》2023,33(40):2302816
Precise adjustment of the pore size, damage repair, and efficient cleaning is all challenges for the wider application of inorganic membranes. This study reports a simple strategy of combining dry-wet spinning and electrosynthesis to fabricate stainless-steel metal–organic framework composite membranes characterized by customizable pore sizes, targeted reparability, and high catalytic activity for membrane cleaning. The membrane pore size can be precisely customized in the range of 14–212 nm at nanoscale, and damaged membranes can be repaired by targeted treatment in 120 s. In addition, advanced oxidation processes can be used to quickly clean the membrane and achieve 98% flux recovery. The synergistic actions of the membrane matrix and the selective layer increase the adsorption energy of active sites to oxidant, shorten the electron transfer cycle, and enhance the overall catalytic performance. This study can provide a new direction for the development of advanced membranes for water purification and high-efficiency membrane cleaning methods. 相似文献
89.
Nicola Pellicciotta Ojus Satish Bagal Viridiana Carmona Sosa Giacomo Frangipane Gaszton Vizsnyiczai Roberto Di Leonardo 《Advanced functional materials》2023,33(39):2214801
Biohybrid microbots integrate biological actuators and sensors into synthetic chassis with the aim of providing the building blocks of next-generation micro-robotics. One of the main challenges is the development of self-assembled systems with consistent behavior and such that they can be controlled independently to perform complex tasks. Herein, it is shown that, using light-driven bacteria as propellers, 3D printed microbots can be steered by unbalancing light intensity over different microbot parts. An optimal feedback loop is designed in which a central computer projects onto each microbot a tailor-made light pattern, calculated from its position and orientation. In this way, multiple microbots can be independently guided through a series of spatially distributed checkpoints. By exploiting a natural light-driven proton pump, these bio-hybrid microbots are able to extract mechanical energy from light with such high efficiency that, in principle, hundreds of these systems can be controlled simultaneously with a total optical power of just a few milliwatts. 相似文献
90.
Wenyue Xue Zezhou Liang Yabing Tang Chao Zhao Lihe Yan Wei Ma Han Yan 《Advanced functional materials》2023,33(42):2304960
Organic solar cells (OSCs) process fascinating solution-printing capability to achieve low-cost and large-scale manufacture. However, the rapid power conversion efficiency (PCE) decay with active layer thickness enlargement inhibits the implement of OSCs’ potential advantages. To overcome the bottlenecks of PCE decay in thick active layer OSCs, the electrical doping with componential selectivity in bulk heterojunction (BHJ) film is achieved by introducing a solid solvation additive. Benefiting from the higher exciton splitting efficiency together with the longer drift (Ldr) and diffusion (Ldiff) lengths, an OSC with 100 nm BHJ film demonstrates a PCE increment from 16.44% to 18.24% with prolonged dark and illuminated storage stabilities. Applying the solid solvation assisted (SSA) doping method in the OSCs with 500 nm active layer, the PCE significantly increases by 31.9%, from the original value of 11.79% to 15.55%. It further improves to 15.84% in a ternary blend thick-film device, which is the record value to the best of our knowledge. Besides, the SSA doping narrows the PCE gap between the 0.04 and 1 cm2 devices. All improvements demonstrate the great potential of SSA doping for OSC commercial manufacture, since it optimizes the photovoltaic performance under all practical conditions of long-term, thick-film, and large-area. 相似文献