全文获取类型
收费全文 | 65405篇 |
免费 | 8888篇 |
国内免费 | 5541篇 |
专业分类
电工技术 | 6333篇 |
技术理论 | 3篇 |
综合类 | 7248篇 |
化学工业 | 8764篇 |
金属工艺 | 2573篇 |
机械仪表 | 3891篇 |
建筑科学 | 4041篇 |
矿业工程 | 2213篇 |
能源动力 | 2036篇 |
轻工业 | 2825篇 |
水利工程 | 1560篇 |
石油天然气 | 3441篇 |
武器工业 | 978篇 |
无线电 | 8354篇 |
一般工业技术 | 7016篇 |
冶金工业 | 1999篇 |
原子能技术 | 927篇 |
自动化技术 | 15632篇 |
出版年
2024年 | 108篇 |
2023年 | 1080篇 |
2022年 | 1649篇 |
2021年 | 2013篇 |
2020年 | 2230篇 |
2019年 | 1818篇 |
2018年 | 1661篇 |
2017年 | 2156篇 |
2016年 | 2338篇 |
2015年 | 2614篇 |
2014年 | 3946篇 |
2013年 | 4061篇 |
2012年 | 5079篇 |
2011年 | 5531篇 |
2010年 | 4314篇 |
2009年 | 4403篇 |
2008年 | 4450篇 |
2007年 | 5211篇 |
2006年 | 4442篇 |
2005年 | 3831篇 |
2004年 | 3105篇 |
2003年 | 2637篇 |
2002年 | 2058篇 |
2001年 | 1773篇 |
2000年 | 1402篇 |
1999年 | 1098篇 |
1998年 | 845篇 |
1997年 | 716篇 |
1996年 | 614篇 |
1995年 | 506篇 |
1994年 | 425篇 |
1993年 | 305篇 |
1992年 | 276篇 |
1991年 | 219篇 |
1990年 | 190篇 |
1989年 | 167篇 |
1988年 | 97篇 |
1987年 | 79篇 |
1986年 | 64篇 |
1985年 | 50篇 |
1984年 | 59篇 |
1983年 | 45篇 |
1982年 | 33篇 |
1981年 | 15篇 |
1980年 | 22篇 |
1979年 | 15篇 |
1978年 | 9篇 |
1977年 | 10篇 |
1976年 | 10篇 |
1951年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
In the recent advancements in image and video analysis, the detection of salient regions in the image becomes the initial step. This plays a crucial role in deciding the performance of such algorithms. In this work, a Multi-Resolution Feature Extraction (MRFE) technique that makes use of Discrete Wavelet Convolutional Neural Network (DWCNN) for generating features is employed. An Enhanced Feature Extraction (EFE) module extracts additional features from the high level features of the DWCNN, which are used to frame both channel as well as spatial attention models for yielding contextual attention maps. A new hybrid loss function is also proposed, which is a combination of Balanced Cross Entropy (BCE) loss and Edge based Structural Similarity (ESSIM) loss that effectively identifies and segments the salient regions with clear boundaries. The method is tested exhaustively with five different benchmark datasets and is proved superior to the existing state-of-the-art methods with a minimum Mean Absolute error (MAE) of 0.03 and F-measure of 0.956. 相似文献
2.
Xiao-Lei Qiu Zi-Rui Fan Yang-Yang Liu Ding-Fu Wang Shi-Xin Wang Chun-Xia Li 《International journal of molecular sciences》2021,22(8)
A self-nanoemulsifying drug delivery system (SNEDDS) was developed to enhance the absorption of heparin after oral administration, in which heparin was compounded with phospholipids to achieve better fat solubility in the form of heparin-phospholipid (HEP-Pc) complex. HEP-Pc complex was prepared using the solvent evaporation method, which increased the solubility of heparin in n-octanol. The successful preparation of HEP-Pc complex was confirmed by differential scanning calorimetry (DSC), Fourier-transform infrared (FT-IR) spectroscopy, NMR, and SEM. A heparin lipid microemulsion (HEP-LM) was prepared by high-pressure homogenization and characterized. HEP-LM can enhance the absorption of heparin after oral administration, significantly prolong activated partial thromboplastin time (APTT) and thrombin time (TT) in mice, and reduce fibrinogen (FIB) content. All these outcomes indicate that HEP-LM has great potential as an oral heparin formulation. 相似文献
3.
Jieyun Tu Xinghui Shi Yuanrong Jing Huimin Zou Jakub Kadlcak Zhanfu Yong Susu Liu Guangyong Liu 《Polymer Engineering and Science》2021,61(8):2213-2221
Equilibrium swelling and rheological tests were adopted to systematically investigate the effects of softener type and dosage on the crosslink densities. The results turned out that the chemical crosslink density could be distinguished from the physical crosslink density by comparing the results of equilibrium swelling and rheological tests. The liquid butadiene (LB) as a softener leads to the greatest reduction in crosslink density, followed by polyethylene wax (PW) and paraffinic oil (PO). The tensile strength decreases with increasing PO content while shows peak values with increase of LB and PW contents. The dependencies of chemical crosslink density on the aging time under 150°C are quite different for the three softeners, which can be expected from the double crosslinking networks consisting of small softener and large main crosslinking networks. Further investigation has been performed to correlate the tensile strength with chemical crosslink density of ethylene propylene diene monomer elastomer vulcanizates. Three different linear relationships can be obtained for the softeners independent of the aging time. It can now be expected from this study that the role of some new softeners in rubber compounds is not only confined to plasticization but also forms crosslinking networks in the peroxide-cured rubbers. 相似文献
4.
Yujing Zhang Pin Liu Kumara Raja Kandula Wenru Li Yanfeng Qin Haibo Zhang Guangzu Zhang 《Journal of the European Ceramic Society》2021,41(1):360-367
The applications of antiferroelectric (AFE) materials in miniaturized and integrated electronic devices are limited by their low energy density. To address the above issue, the antiferroelectricity of the reinforced material was designed to improve its AFE-ferroelectric (FE) phase transition under electric fields. In this present study, the composition of Zr4+ (0.72 Å) and Ti4+ (0.605 Å) at B-site of Pb0.97La0.02(ZrxSn0.05Ti0.95-x)O3 ceramics with orthogonal reflections are synthesized via the tape-casting method. These ceramics are modified to enhance their antiferroelectricity by reducing their tolerance factor. A recoverable energy storage density Wrec 12.1 J/cm3 was obtained for x = 0.93 under 376 kV/cm, which is superior value than reported until now in lead-based energy storage systems. Moreover, the discharge energy density can reach 10.23 J/cm3, and 90 % of which can be released within 5.66 μs. This work provides a new window and potential materials for further industrialization of pulse power capacitors. 相似文献
5.
Yunyan Liu Ning Jiang Yao Liu Dawei Cui Chang-Feng Yu Huiqiang Liu Zhao Li 《Ceramics International》2021,47(16):22416-22423
Pulsed laser deposition (PLD) was used to prepare tungsten trioxide (WO3) films on ITO substrates with a varying laser power density of 4.0–5.5 W/cm2. XPS indicated that when the laser power density decreased, the peak positions of the W 4f and O 1s orbits shifted slightly to low energy due to the difference in oxygen vacancies. As the laser power density decreased, W6+ gradually replaced the lattice position of O2?, increasing oxygen vacancies in the lattice. The transmittance modulated values (ΔT) were over 44% at 830 nm, indicating strong absorption by the WO3 thin films in the near-infrared ray. The switching time of the WO3 thin films between bleached states and coloured states decreased as the laser power density increased due to the amorphous structure, morphology, and lower oxygen deficiency at a high power density. The high ΔT and very fast switching time of tb (1.09 s) and tc (6.01 s) demonstrated the excellent electrochromic (EC) properties of the WO3 films prepared by PLD. 相似文献
6.
生物质基喷气燃料是指全部或大部分来源于生物资源的喷气燃料,符合清洁低碳、安全高效的现代能源体系的要求。以生物质基喷气燃料替代传统石油基喷气燃料有助于我国早日实现“碳达峰、碳中和”的远大目标。在阐述生物质基喷气燃料生产工艺的发展历程及生物质基喷气燃料应用现状的基础上,提出高密度的生物质基喷气燃料是未来喷气燃料的发展方向,具有多环结构的生物质是合成高密度生物质基喷气燃料组分的优质原料;同时,总结了高密度生物质基喷气燃料组分生产工艺的研究进展,展望了生物质基喷气燃料未来的发展及挑战。 相似文献
7.
Abdul Rehman Akbar Huihui Hu Muhammad Bilal Qadir Muhammad Tahir Zubair Khaliq Zhikang Liu Chuanxi Xiong Quanling Yang 《Ceramics International》2021,47(4):4648-4658
Technical development in electronic devices is frequently stifled by their insufficient capacity and cyclic stability of energy-storage devices. The nano-structured materials have sensational importance for providing novel and optimized combination to overcome exiting boundaries and provide efficient energy storage systems. Metal hydroxide materials with high capacity for pseudo-capacitance properties have grabbed special attention. Lately, the blend of nickel and cobalt hydroxides has been considered as a favorable class of metallic hydroxide materials owing to their comparatively high capacitance and exceptional redox reversibility. The sulfonated carbon nanotube fluid (SCNTF) was prepared by the ion exchange method to be utilized as the exceptional templates due to astonishing specific surface area, ensuring the maximum utilization of the active material. The CoNi-layered double hydroxides (LDHs)/SCNTF core-shell nanocomposite was prepared by the simple solvothermal method. Structural analysis showed that the composite material had the high conductance of carbon materials, the pseudo-capacitance characteristics of metal hydroxides, and porous structure, which facilitates the ion shuttle when the electrolyte reacts with the active material. Electrochemical analysis results showed that CoNi-LDHs/SCNTF had excellent rate performance, reversible charge-discharge properties and cycle stability. It exhibited an extreme specific capacity of 1190.5 F g?1 at a current density of 1 A g?1; whereas specific capacity remained 953.7 F g?1 at the current density was 10 A g?1. In addition, the capacity retention rate after 5000 charge-discharge cycles at a current density of 20 A g?1 was 81.0%. The results indicated that the CoNi-LDHs/SCNTF core-shell nanocomposite material is cost efficient and an effective substitute in energy storage applications. 相似文献
8.
Gang Liu Ya Wang Jianpeng Li Ying Liu Maryam Salehabadi 《Journal of Sulfur Chemistry》2021,42(1):40-50
Based on the experimental reports, Au-decoration on the ZnO nanostructures dramatically increases the electronic sensitivity to H2S gas. In the current study, we computationally scrutinized the mechanism of Au-decoration on a ZnO nanotube (ZON) and the influence on its sensing behavior toward H2S gas. The intrinsic ZON weakly interacted with the H2S gas with an adsorption energy of ?11.2 kcal/mol. The interaction showed no effect on the HOMO–LUMO gap and conductivity of ZON. The predicted response of intrinsic ZON toward H2S gas is 6.3, which increases to 78.1 by the Au-decoration at 298 K. The corresponding experimental values are about 5.0 and 80.0, indicating excellent agreement with our findings. We showed that the Au atom catalyzes the reaction 3O2?+?2H2S?→?2SO2?+?2H2O. Our calculated energy barrier (at 298 K) is about 12.3 kcal/mol for this reaction. The gap and electrical conductance Au-ZON largely changed by this reaction are attributed to the electron donation and back-donation processes. The obtained recovery time is about 1.35 ms for desorption of generated gases from the surface of the Au-ZON sensor. 相似文献
9.
10.
According to the circle-packing theorem, the packing efficiency of a hexagonal lattice is higher than an equivalent square tessellation. Consequently, in several contexts, hexagonally sampled images compared to their Cartesian counterparts are better at preserving information content. In this paper, novel mapping techniques alongside the wavelet compression scheme are presented for hexagonal images. Specifically, we introduce two tree-based coding schemes, referred to as SBHex (spirally-mapped branch-coding for hexagonal images) and BBHex (breadth-first block-coding for hexagonal images). Both of these coding schemes respect the geometry of the hexagonal lattice and yield better compression results. Our empirical results show that the proposed algorithms for hexagonal images produce better reconstruction quality at low bits per pixel representations compared to the tree-based coding counterparts for the Cartesian grid. 相似文献