全文获取类型
收费全文 | 83916篇 |
免费 | 959篇 |
国内免费 | 409篇 |
专业分类
电工技术 | 771篇 |
综合类 | 2316篇 |
化学工业 | 11476篇 |
金属工艺 | 4809篇 |
机械仪表 | 3033篇 |
建筑科学 | 2155篇 |
矿业工程 | 562篇 |
能源动力 | 1112篇 |
轻工业 | 3602篇 |
水利工程 | 1267篇 |
石油天然气 | 341篇 |
无线电 | 9240篇 |
一般工业技术 | 16386篇 |
冶金工业 | 2640篇 |
原子能技术 | 256篇 |
自动化技术 | 25318篇 |
出版年
2023年 | 10篇 |
2022年 | 22篇 |
2021年 | 19篇 |
2020年 | 10篇 |
2019年 | 14篇 |
2018年 | 14461篇 |
2017年 | 13396篇 |
2016年 | 9970篇 |
2015年 | 613篇 |
2014年 | 236篇 |
2013年 | 223篇 |
2012年 | 3143篇 |
2011年 | 9421篇 |
2010年 | 8284篇 |
2009年 | 5542篇 |
2008年 | 6773篇 |
2007年 | 7785篇 |
2006年 | 122篇 |
2005年 | 1209篇 |
2004年 | 1127篇 |
2003年 | 1184篇 |
2002年 | 538篇 |
2001年 | 96篇 |
2000年 | 180篇 |
1999年 | 62篇 |
1998年 | 60篇 |
1997年 | 36篇 |
1996年 | 49篇 |
1995年 | 11篇 |
1994年 | 19篇 |
1993年 | 10篇 |
1992年 | 13篇 |
1991年 | 25篇 |
1988年 | 11篇 |
1969年 | 24篇 |
1968年 | 43篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1964年 | 11篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1961年 | 18篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Hsien-Chie Cheng You-Wei Chen Wen-Hwa Chen Su-Tsai Lu Shih-Ming Lin 《Journal of Electronic Materials》2018,47(3):1832-1846
In this study, the printing mechanism and performance of gravure-offset fine-line circuitry printing technology are investigated in terms of key printing parameters through experimental and theoretical analyses. First, the contact angles of the ink deposited on different substrates, blankets, and gravure metal plates are experimentally determined; moreover, their temperature and solvent content dependences are analyzed. Next, the ink solvent absorption and evaporation behaviors of the blankets at different temperatures, times, and numbers of printing repetitions are characterized by conducting experiments. In addition, while printing repeatedly, the surface characteristics of the blankets, such as the contact angle, vary with the amount of absorbed ink solvent, further affecting the ink transfer performance (ratio) and printing quality. Accordingly, the surface effect of the blanket due to ink solvent absorption on the ink contact angle is analyzed. Furthermore, the amount of ink transferred from the gravure plate to the blanket in the “off process” and from the blanket to the substrate in the “set process” is evaluated by conducting a simplified plate-to-plate experiment. The influences of loading rate (printing velocity), temperature, and solvent content on the ink transfer performance are addressed. Finally, the ink transfer mechanism is theoretically analyzed for different solvent contents using Surface Evolver. The calculation results are compared with those of the experiment. 相似文献
992.
Jun Li Wenjing Wu Yanqing Shen Pan Zhang You Wu Qingxin Meng Zhongxiang Zhou Dechang Jia 《Journal of Electronic Materials》2018,47(10):5773-5779
First-principles calculations were performed to investigate the coexistence of ferroelectricity and magnetism in Fe-doped tetragonal K0.5Na0.5NbO3 (KNN) with different Fe concentrations. It was found that all three systems can possess both magnetism and ferroelectricity, and the magnetism becomes stronger with an increase in the concentration of Fe. The magnetic properties are due to ferromagnetism of Fe, and the Fe-Nb and Fe-O bonds induce magnetic moments on Nb and O atoms. Ferroelectricity comes from the hybridization of Nb and O, as in the case of pure KNN. The predicted results provide insight into the origin of the induced magnetic moments and an approach for obtaining multiferroic materials. 相似文献
993.
Adan Garnica-Carrillo Felix Calderon Juan Flores 《Signal, Image and Video Processing》2018,12(5):869-876
This article presents a technique to solve the problem of multi-focus image fusion. This technique is based on the maximization of a linear function with spatial coherence constraints. The final fused image is computed as the sum of the source images using a segmentation map. We can compute the segmentation map using the Simplex method, where the objective function includes one variable associated with each pixel. The Simplex method requires a huge amount of memory resources to produce it. We present an algorithm called CPW-S, which uses some strategies to solve the problem in a context with fewer variables; images are split into regions, thus reducing the computational effort. We present results for two pairs of synthetic images in order to quantify the results, obtaining more than \(98\%\) of pixel accuracy for the segmentation map. We also present results for several pairs of real images (widely used in the literature) and a triad of multi-focus images. The resulting fused images are qualitatively good for all the real images included in the experiments. 相似文献
994.
Typical methods for overlapping sound event detection (SED) do not fully consider the joint spectral and temporal transition characteristics of the audio signal. They are generally based on training models using either separate data from each event class or mixed signals containing simultaneous sound events. This paper introduced a new approach for SED in real-life audio using Nonnegative Matrix Factor 2-D Deconvolution and RUSBoost techniques. The idea is to capture the two-dimensional joint spectral and temporal information from the time-frequency representation while possibly separating the sound mixture into several sources. In addition, the RUSBoost technique is utilized to address the class imbalance problem of the training data. The proposed approach is evaluated using the TUT Sound Event 2016 and 2017 datasets. The results showed that the proposed method outperformed the baseline methods. For the TUT Sound Event 2016 dataset, the proposed method reduced the total error rate by 5% while increasing the F1 score by 13.8%. For the TUT Sound Event 2017 dataset, the proposed method reduced the total error rate by 3% while increasing the F1 score by 8.1%. 相似文献
995.
Magnifying micro-movements of natural videos that are undetectable by human eye has recently received considerable interests, due to its impact in numerous applications. In this paper, we use dual tree complex wavelet transform (DT-CWT), to analyze video frames in order to detect and magnify micro-movements to make them visible. We use DT-CWT, due to its excellent edge-preserving and nearly-shift invariant features. In order to detect any minor change in object’s spatial position, the paper proposes to modify the phases of the CWT coefficients decomposition of successive video frames. Furthermore, the paper applies Radon transform to track frame micro-movements without any temporal band-pass filtering. The paper starts by presenting a simple technique to design orthogonal filters that construct this CWT system. Next, it is shown that modifying the phase differences between the CWT coefficients of arbitrary frame and a reference one results in image spatial magnification. This in turn, makes these micro-movements seen and observable. Several simulation results are given, to show that the proposed technique competes very well to the existing micro-magnification approaches. In fact, as it manages to yield superior video quality in far less computation time. 相似文献
996.
997.
In this paper, we focus first on the time needed by a node to join a Time Slotted Channel Hopping (TSCH) network, this time is called joining time. Second, we are also interested in the network building time. Since the data generated by a sensor node remain unavailable as long as this node has not yet joined the wireless sensor network, these times are of prime importance for applications having strong latency requirements on data gathering. The joining time depends on the beacon advertising policy that has been left unspecified by the standard. The contribution of this paper is triple. First, we propose an Enhanced Deterministic Beacon Advertising algorithm, called EDBA, that ensures a collision-free advertising of beacons and minimizes the average joining time. Second, we model the behavior of a joining node by a Markov chain, validated by NS3 simulations, and compute the average joining time. Third, we compare the performance of EDBA with this of MBS, considered as the best beacon advertising algorithm in the literature. 相似文献
998.
Hui Li Erqing Xie Min Qiao Xiaojun Pan Yongzhe Zhang 《Journal of Electronic Materials》2007,36(9):1219-1223
Indium-doped zinc oxide (ZnO:In) films were prepared in an Ar:O2 plasma by reactive magnetron sputtering. The x-ray diffraction (XRD) patterns presented the crystal structures of ZnO:In
films, while transmission spectra and photoluminescence (PL) spectra showed the changed band gap and the visible emission
from defects, as compared to the PL spectra of undoped ZnO films. It was concluded that the increase of substrate temperature
enhanced the crystal quality of ZnO:In films; the incorporation of In made the c-axis constant of the samples larger than that of undoped ZnO films; the blue emission was due to the transition from an unknown
donor level by indium doping to the valance band; and the orange-green emission originated from acceptor defects (OZn) formed in the O-rich plasma. Meanwhile, the current- voltage characteristics and persistent photoconductivity phenomenon
also could be explained by the increased acceptor defects (OZn) that formed when the substrate temperature was increased. 相似文献
999.
Vladimir I. Shashkin Yuri A. Drjagin Vjacheslav R. Zakamov Sergei V. Krivov Lev M. Kukin Arcady V. Murel Yuri I. Chechenin 《Journal of Infrared, Millimeter and Terahertz Waves》2007,28(11):945-952
The principles of construction of millimeter wave detectors based on low-barrier Schottky diodes and planar antennas are discussed. The modified planar slot antenna with low beam spillover at the resonant frequency of 94 GHz has been developed. Experiments have been carried out to investigate detecting characteristics of the diodes with differential contact resistances \( R_{j} = 1 \div 1000\;{\text{k}}\Omega \) at zero bias. Experimental data are well correspond to calculations in a simple model of detector. At \( R_{j} = 20 \div 100\;{\text{k}}\,\OmegaΩ \) the maximum of rf-to-dc voltage sensitivity - more than 10000 V/W - is obtained. At lower values of \( R_{j} = 2 \div 6\;{\text{k}}\,\Omega Ω \) a better noise equivalent power (NEP), around 10?12 W Hz?1/2, is predicted. 相似文献
1000.
We report a sol–gel method to deposit a high-k dielectric, zirconium oxide (ZrO2). This solution-based approach has advantages of easy processing and low fabrication cost. Effects of annealing temperatures
on dielectric properties, such as tunneling current density and capacitance density, are reported. Morphological and chemical
characterizations suggest that the process temperature can be kept at or below 300°C. We have employed the solution-processed
ZrO2 dielectric in a zinc tin oxide thin-film transistor. Saturation mobility of 4.0 cm2/V s at operating voltage of 2 V has been observed. The measured subthreshold swing is 74 mV/decade, which is the result of
the combination of an electronically clean dielectric/semiconductor interface and high insulator capacitance. 相似文献