全文获取类型
收费全文 | 20813篇 |
免费 | 3835篇 |
国内免费 | 1806篇 |
专业分类
电工技术 | 697篇 |
技术理论 | 2篇 |
综合类 | 2078篇 |
化学工业 | 1290篇 |
金属工艺 | 885篇 |
机械仪表 | 1061篇 |
建筑科学 | 2502篇 |
矿业工程 | 626篇 |
能源动力 | 605篇 |
轻工业 | 512篇 |
水利工程 | 738篇 |
石油天然气 | 286篇 |
武器工业 | 203篇 |
无线电 | 4921篇 |
一般工业技术 | 2354篇 |
冶金工业 | 406篇 |
原子能技术 | 76篇 |
自动化技术 | 7212篇 |
出版年
2024年 | 71篇 |
2023年 | 477篇 |
2022年 | 707篇 |
2021年 | 904篇 |
2020年 | 920篇 |
2019年 | 809篇 |
2018年 | 847篇 |
2017年 | 936篇 |
2016年 | 1053篇 |
2015年 | 1152篇 |
2014年 | 1602篇 |
2013年 | 1465篇 |
2012年 | 1700篇 |
2011年 | 1793篇 |
2010年 | 1242篇 |
2009年 | 1184篇 |
2008年 | 1243篇 |
2007年 | 1397篇 |
2006年 | 1257篇 |
2005年 | 1079篇 |
2004年 | 881篇 |
2003年 | 694篇 |
2002年 | 536篇 |
2001年 | 437篇 |
2000年 | 367篇 |
1999年 | 297篇 |
1998年 | 293篇 |
1997年 | 233篇 |
1996年 | 179篇 |
1995年 | 128篇 |
1994年 | 121篇 |
1993年 | 88篇 |
1992年 | 76篇 |
1991年 | 44篇 |
1990年 | 38篇 |
1989年 | 28篇 |
1988年 | 30篇 |
1987年 | 12篇 |
1986年 | 48篇 |
1985年 | 12篇 |
1984年 | 11篇 |
1983年 | 19篇 |
1982年 | 9篇 |
1981年 | 8篇 |
1980年 | 12篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1973年 | 3篇 |
1959年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Vinod Singh Shivani Dhall Akshey Kaushal Bodh R. Mehta 《International Journal of Hydrogen Energy》2018,43(2):1025-1033
In the present work, the effect of carbon shell around size selected palladium (Pd) nanoparticles on hydrogen (H2) sensing has been studied by investigating the sensing response of Pd-C core-shell nanoparticles having a fixed core size and different shell thickness. The H2 sensing response of sensors based on Pd and Pd-C nanoparticles deposited on SiO2 and graphene substrate has been measured over a temperature range of 25 °C–150 °C. It is observed that Pd-C nanoparticle sensor shows higher sensitivity with increase in shell thickness and faster response/recovery in comparison to that of Pd nanoparticle samples. Pd-C nanoparticles show room temperature H2 sensitivity in contrast to Pd nanoparticles which respond only at higher temperatures. Role of carbon shell is also understood by investigating H2 sensing properties of Pd and Pd-C nanoparticles on graphene substrates. These results show that higher catalytic activity and electronic interaction at Pd-C interface, a complete coverage and protection of Pd surface by carbon and presence of structural defects in nanoparticle core are important for room temperature and higher sensing response. 相似文献
52.
Multi-focus image fusion aims to produce an all-in-focus image by merging multiple partially focused images of the same scene. The main work is identifying the focused region and then composing all the focused regions. In this paper, a novel efficient multi-focus image fusion method based on distributed compressed sensing (DCS) is proposed. Firstly, the low-frequency and high-frequency images are obtained by comparing the variance of the source images, which are further utilized to get the low-frequency and high-frequency dictionaries. Secondly, DCS using joint sparsity model-1 (JSM-1) is applied to reconstruct the precise high-frequency images. Thirdly, the decision map is obtained based on all the high-frequency images and then improved by the morphological processing. Finally, the focused pixels are chosen from the source images through the decision map. Experimental results indicate that the proposed DCS-based method can be competitive with or even outperform some state-of-the-art methods in terms of both visual and quantitative metric evaluations. 相似文献
53.
比较基于压缩感知关联成像(CGI)与伪逆关联成像(PGI)两者之间的成像效果差异,探讨形态学权重自适应对关联成像去除噪声的效果。选择不同的图像,通过MATLAB软件开展仿真实验,对目标图像分别采样64、256、512、1 024、2 048、3 000次,首先通过关联成像、基于压缩感知关联成像与伪逆关联成像三种方法重构图像,再对比压缩感知与伪逆两种方法重构图像的效果,以峰值信噪比(PSNR)、相关系数(CC)为量化指标,将基于压缩感知关联成像与伪逆关联成像在不同采样次数下进行对比分析。同时,通过实验分析形态学权重自适应去除关联成像中噪声的效果。伪逆关联成像在低次数采样的情况下比基于压缩感知关联成像的成像效果更好,在高采样次数下,基于压缩感知关联成像的成像效果更好。在实际重构中压缩感知关联成像重构的图像仍有噪声,形态学权重自适应可以有效去除关联成像实验中产生的噪声。 相似文献
54.
Along with the progress in nanoscience, a variety of advanced functional nanomaterials were constructed to develop effective and innovative analytical techniques for food safety surveillance. In this review, we summarized the advanced analytical methods that have been developed based upon advanced functional nanomaterials, including plasmonic nanomaterial-based colorimetric methods, fluorescent nanomaterial-based fluorescent methods, advanced functional material-based molecular imprinting technology, advanced functional material-based chromatographic methods, plasmonic nanomaterial-based surface enhanced Raman scattering technology, and advanced functional material-based electrochemical methods. This review provides a progressive roadmap for further development of portable, rapid, and in situ detection technology to promote food safety surveillance from bench to market and eventually reduce the gap between research in the laboratory and industrial applications. 相似文献
55.
Chitosan microspheres containing bromocresol green, cresol red, and phenolphthalein for corrosion detection, through pH change, are synthesized in order to be used in protective coatings for aluminium alloys. Microspheres containing corrosion detection species are characterized morphologically (SEM) and physico‐chemically (FTIR, TGA). Release studies (UV–vis) are performed in corrosion‐promoting conditions (pH, NaCl), and detection studies by immersion in media associated with corrosion activity while microspheres' sensing activity is evaluated visually. Electrochemical characterization of AA2024 substrates in the presence of chitosan spheres is performed to understand material performance, and a color change is observed as a result of local pH increase in cathodic areas when corrosion takes place. These findings can be correlated with the results from release studies and seem a promising approach for corrosion sensing purposes, not only because pH increase is possible to detect due to corrosion, but also because chitosan is considered an environmentally friendly material. 相似文献
56.
Ming Hu Qinyu Han Prof. Dr. Bengang Xing 《Chembiochem : a European journal of chemical biology》2020,21(17):2512-2517
γ-Hydroxybutyric acid (GHB) functions as a depressant on the central nerve system and serves as a pharmaceutical agent in the treatment of narcolepsy and alcohol withdraw. In recent years, GHB has been misused as a recreational drug due to its ability to induce euphoric feelings. Moreover, it has gained increasing attention as a popular drug of abuse that is frequently related to drug-facilitated sexual assaults. At the moment, detection methods based on chromatography exhibit extraordinary sensitivity for GHB sensing. However, such techniques require complicated sample treatment prior to analysis. Optical sensors provide an alternative approach for rapid and simple analysis of GHB samples. Unfortunately, currently reported probes are mostly based on hydrogen bonding to recognize GHB, and this raises concerns about, for example, the lack of specificity. In this work, we report a bioinspired strategy for selective sensing of GHB. The method is based on specific enzyme recognition to allow highly selective detection of GHB with minimum interference, even in a complex sample matrix (e. g., simulated urine). In addition, the result can be obtained by either quantitative spectroscopy analysis or colorimetric change observed by the naked-eye, thus demonstrating its potential application in drug screening and forensic analysis. 相似文献
57.
Apoorva Karamchandani Hojae Yi Virendra M. Puri 《Particulate Science and Technology》2018,36(4):447-456
Mechanical and physical properties of ground corn stover, switchgrass, and willow were measured and compared in addition to the quality of pellets. Biomass was size-reduced with two different screen sizes (3.175 and 6.35?mm) and conditioned to obtain samples at two different moisture contents (17.5 and 20% on wet basis). Ground switchgrass had the smallest and willow had the highest D50 when size-reduced with the same screen size. Hydrostatic triaxial compression tests were performed using the cubical triaxial tester to determine the bulk modulus, compression index, and spring-back index at specific unloading pressures (20, 45, 70, and 95?kPa). The trends of pressure vs. volumetric strain and void ratio vs. natural log of pressure were similar for all three materials; however, the magnitudes were different. Willow, size-reduced with 3.175?mm screen size at 17.5% wet basis, had the highest bulk modulus among different conditions of all the three biomass. Pellet durability values for all the three materials were higher than 80%. Corn stover pellets formed with 3.175?mm screen size at 20% wet basis had the highest diametral tensile and axial compressive strengths among different conditions for all the three biomass, however the values were not significantly different (p?>?0.05). 相似文献
58.
59.
Double‐network hydrogels were conveniently synthesized by the one‐shot radical polymerization of an ionic monomer for the first network and a non‐ionic monomer for the second network in the presence of crosslinkers by simultaneous addition of the monomers, that is, one‐shot and spontaneous two‐step polymerization accompanying the delay of polymerization of a second network monomer. We analyzed the polymerization process based on the conversion of each monomer during the reaction in the absence of crosslinkers. Then we fabricated the double‐network hydrogels using several polymerization systems consisting of a conjugated monomer and a non‐conjugated monomer in the presence of the dual crosslinkers. We analyzed the swelling, mechanical and viscoelastic properties of hydrogels synthesized by one‐shot radical polymerization to confirm the production mechanism and the network structure of the hydrogels. © 2020 Society of Chemical Industry 相似文献
60.
Double nanocrystalline engineering for effective enhanced photoluminescence of Tb3+ in glass ceramic
Yongmin Duan Panpan Li Yang Lu Shiqing Xu Junjie Zhang 《Ceramics International》2021,47(11):15219-15227
Despite possessing good feature for optical thermometry, the rare (RE) ions-based temperature sensing (TS) has innate shortcoming of thermally coupled levels (TCLs) energy gap overlap, which reduces the sensitivity. In this work, a dual-luminous centers TS based on Tb3+ doped Cs4PbBr6 quantum dots (QDs) glass ceramic is fabricated. By locating in low phonon energy crystal field environment of Cs2ZnSi5O12 nanocrystalline (NS) and Cs4PbBr6 QDs, the emission intensity of Tb3+ can be enhanced by 14 times. The large exciton binding energy (420 meV) indicates that the prepared QDs glass ceramic has a good thermal stability and the PL intensity of Cs4PbBr6 QDs and Tb3+ can be well-maintained above 70% and 89% after 8 thermal cycles between 323K and 373K. Furthermore, the obtained maximum absolute sensitivity (Sa) and relative sensitivity (Sr) is as high as 0.2541 K-1 and 2.68% K?1, respectively. It is expected that the finding of this work can offer a help in exploring novel QDs/RE ions-based TS and further optimize their practical applications. 相似文献