全文获取类型
收费全文 | 43065篇 |
免费 | 5333篇 |
国内免费 | 2588篇 |
专业分类
电工技术 | 2387篇 |
综合类 | 3399篇 |
化学工业 | 6814篇 |
金属工艺 | 1596篇 |
机械仪表 | 3842篇 |
建筑科学 | 2325篇 |
矿业工程 | 757篇 |
能源动力 | 1559篇 |
轻工业 | 4745篇 |
水利工程 | 580篇 |
石油天然气 | 1764篇 |
武器工业 | 388篇 |
无线电 | 3682篇 |
一般工业技术 | 4094篇 |
冶金工业 | 1233篇 |
原子能技术 | 177篇 |
自动化技术 | 11644篇 |
出版年
2024年 | 83篇 |
2023年 | 616篇 |
2022年 | 928篇 |
2021年 | 1441篇 |
2020年 | 1481篇 |
2019年 | 1314篇 |
2018年 | 1275篇 |
2017年 | 1597篇 |
2016年 | 1722篇 |
2015年 | 1951篇 |
2014年 | 2777篇 |
2013年 | 2835篇 |
2012年 | 2969篇 |
2011年 | 3620篇 |
2010年 | 2747篇 |
2009年 | 2889篇 |
2008年 | 2751篇 |
2007年 | 3222篇 |
2006年 | 2659篇 |
2005年 | 2322篇 |
2004年 | 1910篇 |
2003年 | 1664篇 |
2002年 | 1291篇 |
2001年 | 1009篇 |
2000年 | 811篇 |
1999年 | 580篇 |
1998年 | 448篇 |
1997年 | 347篇 |
1996年 | 302篇 |
1995年 | 262篇 |
1994年 | 233篇 |
1993年 | 195篇 |
1992年 | 157篇 |
1991年 | 114篇 |
1990年 | 87篇 |
1989年 | 72篇 |
1988年 | 40篇 |
1987年 | 28篇 |
1986年 | 29篇 |
1985年 | 39篇 |
1984年 | 27篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1979年 | 18篇 |
1977年 | 7篇 |
1964年 | 7篇 |
1962年 | 6篇 |
1955年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
2.
Aiming at the performance degradation of the existing presentation attack detection methods due to the illumination variation, a two-stream vision transformers framework (TSViT) based on transfer learning in two complementary spaces is proposed in this paper. The face images of RGB color space and multi-scale retinex with color restoration (MSRCR) space are fed to TSViT to learn the distinguishing features of presentation attack detection. To effectively fuse features from two sources (RGB color space images and MSRCR images), a feature fusion method based on self-attention is built, which can effectively capture the complementarity of two features. Experiments and analysis on Oulu-NPU, CASIA-MFSD, and Replay-Attack databases show that it outperforms most existing methods in intra-database testing and achieves good generalization performance in cross-database testing. 相似文献
3.
《International Journal of Hydrogen Energy》2022,47(77):33014-33026
The present study investigates the combined influence of Channel to Rib Width (CRW) ratio and clamping pressure on the structure and performance of High Temperature-Polymer Electrolyte Membrane Fuel Cell (HT-PEMFC) using a three-dimensional numerical model developed previously. It also considers the impact of interfacial contact resistance between the Gas Diffusion Layer (GDL) and Bipolar Plate (BPP). The structural analysis of the single straight channel HT-PEMFC geometry shows that the von-Mises stress greatly increases in the GDL under the ribs as the CRW ratio increases resulting in considerably high deformation. The cell performance analysis depicts the significance of ohmic resistance and concentration polarization for different CRW ratios, particularly at higher operating current densities. However, in low to medium current density regions, the CRW ratio has little influence on cell performance. A substantial impact on the species, overpotential, and current distributions is observed. The findings also reveal that the CRW ratio significantly affects the temperature distribution in the cell. 相似文献
4.
Yarn-dyed fabric is often woven from warp and weft yarns in the same color depth to ensure a uniform color appearance. The difference in color depth between warp and weft tends to result in the uneven color of the yarn-dyed fabric. This article aims to establish a color tolerance for yarn-dyed fabric that can be woven with a qualified color appearance but from the warp and weft yarns in different color depths. A total of 27 yarn-dyed fabric samples in three color series (red, yellow, and blue) were evaluated by using the yarn-dyed fabric from warp and weft yarns in the same color depth of 2% (on weight of fabric, owf) as the standard. Visual assessment and instrumental measurement of color were carried out to establish the color tolerance ellipse that was defined as CMC (Color Measurement Committee) color differences (2:1) of no more than 1.00. It was found that the color strengths (K/S) and color differences (ΔECMC(2:1)) of these fabric samples for each color series had linear relationships with the color depths of warp and weft yarns. The color tolerance ellipses indicated that, even though the warp and weft yarns had an apparent color difference, they could be woven in fabrics with relatively uniform color appearance and meet the requirements for yarn-dyed fabric. This work provided valuable insight into the production of qualified yarn-dyed fabrics from unqualified dyed yarns. 相似文献
5.
《中国稀土学报(英文版)》2022,40(11):1691-1698
White light-emitting diodes (WLEDs) fabricated by single-phase full color emitting phosphor are an emerging solution for health lighting. The crystallographic site occupation of activators in a proper host lattice is crucial for sophisticated design of such phosphor. Here, we report a high quality white light-emitting phosphor Ba2Ca(BO3)2:Ce3+(K+),Eu2+,Mn2+ with spectral distribution covering whole visible region. Blue light emission originates from Ce3+ ions occupying preferentially Ba2+ site by controlling synthesis conditions. Green and red lights are obtained from Eu2+ occupying Ba2+ (and Ca2+) site and Mn2+ occupying Ca2+ site, respectively. In this triple-doped phosphor, strong red emission with a low concentration of Mn2+ is realized by the efficient energy transfer from Ce3+ and Eu2+ to Mn2+. Furthermore, high quality white light is accomplished by properly tuning the relative doping amount of Ce3+(K+)/Eu2+/Mn2+ based on efficient simultaneous energy transfer. The results indicate that Ba2Ca(BO3)2:Ce3+(K+),Eu2+,Mn2+ is a promising white light-emitting phosphor in WLEDs application. 相似文献
6.
Rodrigo Montoya Allan G. Ruiz-García Alma Ortiz-Ozuna Blanca Ramírez-Barat Juan Genesca 《工业材料与腐蚀》2021,72(7):1259-1269
The electrochemical interactions between aluminum alloy 7075 and low-carbon steels under gelled electrolytes were studied. Such electrolytes provided the opportunity to investigate both thick and thin electrolyte systems. The electrolyte was chemically modified to visually track the acidic fronts during the anodic reaction and the subsequent hydrolysis process. Two mathematical models were validated for both thick and ultrathin electrolytes. The acidification of thick electrolytes was extended some millimeters beyond the aluminum alloy surface, whereas the acidic front was localized next to the metallic joint using ultrathin electrolytes. The combination of both numerical and experimental results allows proving (and explaining why) that the acidification process is more aggressive under dilute than under concentrated electrolytes. 相似文献
7.
Form selection of concomitant polymorphs: A case study informed by crystallization kinetics modeling
Weiwei Tang Yufeng Quan Junbo Gong Jingkang Wang Qiuxiang Yin Tonglei Li 《American Institute of Chemical Engineers》2021,67(4):e17129
Molecular mechanisms and process kinetics of crystallizing concomitant polymorphs remain poorly understood. Solvent-mediated phase transformation and concomitant crystallization are difficult to be distinguished in practice, as multiple forms can be detected at the same time. Herein, we developed a population balance model to simulate a concomitant crystallization process of two polymorphs of tolfenamic acid. Our kinetic modeling aims to understand concomitant crystallization and help guide form selection of such a molecular system. Crystallization kinetics of ethanolic solutions were uncovered from induction time measurements, as well as seeded and unseeded crystallization experiments. Experimental and simulation results demonstrate that the stable form I crystallizes concomitantly with the metastable form II. The faster growing form II results in an intermediate decline in the composition of form I in crystallized samples, a characteristic feature of the concomitantly crystallized system. A four-quadrant scheme of attainable polymorph outcome was simulated under various crystallization conditions. 相似文献
8.
9.
Kyuri Kim Young Seung Lee Nam Kim Hyung-Do Choi Dong-Jun Kang Hak Rim Kim Kyung-Min Lim 《International journal of molecular sciences》2021,22(1)
With the rapid growth of wireless communication devices, the influences of electromagnetic fields (EMF) on human health are gathering increasing attention. Since the skin is the largest organ of the body and is located at the outermost layer, it is considered a major target for the health effects of EMF. Skin pigmentation represents one of the most frequent symptoms caused by various non-ionizing radiations, including ultraviolet radiation, blue light, infrared, and extremely low frequency (ELF). Here, we investigated the effects of EMFs with long-term evolution (LTE, 1.762 GHz) and 5G (28 GHz) bandwidth on skin pigmentation in vitro. Murine and Human melanoma cells (B16F10 and MNT-1) were exposed to either LTE or 5G for 4 h per day, which is considered the upper bound of average smartphone use time. It was shown that neither LTE nor 5G exposure induced significant effects on cell viability or pigmentation. The dendrites of MNT-1 were neither lengthened nor regressed after EMF exposure. Skin pigmentation effects of EMFs were further examined in the human keratinocyte cell line (MNT-1-HaCaT) co-culture system, which confirmed the absence of significant hyper-pigmentation effects of LTE and 5G EMFs. Lastly, MelanoDerm™, a 3D pigmented human epidermis model, was irradiated with LTE (1.762 GHz) or 5G (28 GHz), and image analysis and special staining were performed. No changes in the brightness of MelanoDerm™ tissues were observed in LTE- or 5G-exposed tissues, except for only minimal changes in the size of melanocytes. Collectively, these results imply that exposure to LTE and 5G EMFs may not affect melanin synthesis or skin pigmentation under normal smartphone use condition. 相似文献
10.