全文获取类型
收费全文 | 3824篇 |
免费 | 209篇 |
国内免费 | 6篇 |
专业分类
电工技术 | 73篇 |
综合类 | 2篇 |
化学工业 | 872篇 |
金属工艺 | 130篇 |
机械仪表 | 229篇 |
建筑科学 | 94篇 |
矿业工程 | 1篇 |
能源动力 | 143篇 |
轻工业 | 336篇 |
水利工程 | 13篇 |
石油天然气 | 1篇 |
无线电 | 689篇 |
一般工业技术 | 776篇 |
冶金工业 | 240篇 |
原子能技术 | 43篇 |
自动化技术 | 397篇 |
出版年
2023年 | 42篇 |
2022年 | 57篇 |
2021年 | 83篇 |
2020年 | 73篇 |
2019年 | 78篇 |
2018年 | 110篇 |
2017年 | 116篇 |
2016年 | 128篇 |
2015年 | 107篇 |
2014年 | 160篇 |
2013年 | 261篇 |
2012年 | 233篇 |
2011年 | 306篇 |
2010年 | 210篇 |
2009年 | 228篇 |
2008年 | 211篇 |
2007年 | 171篇 |
2006年 | 184篇 |
2005年 | 143篇 |
2004年 | 146篇 |
2003年 | 120篇 |
2002年 | 103篇 |
2001年 | 96篇 |
2000年 | 81篇 |
1999年 | 56篇 |
1998年 | 124篇 |
1997年 | 76篇 |
1996年 | 63篇 |
1995年 | 41篇 |
1994年 | 36篇 |
1993年 | 22篇 |
1992年 | 20篇 |
1991年 | 23篇 |
1990年 | 16篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 7篇 |
1986年 | 8篇 |
1985年 | 14篇 |
1984年 | 9篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 6篇 |
1974年 | 3篇 |
1973年 | 5篇 |
1972年 | 2篇 |
1969年 | 2篇 |
排序方式: 共有4039条查询结果,搜索用时 15 毫秒
971.
Citrus canker detection using hyperspectral reflectance imaging and PCA-based image classification method 总被引:4,自引:0,他引:4
Jianwei Qin Thomas F. Burks Moon S. Kim Kuanglin Chao Mark A. Ritenour 《Sensing and Instrumentation for Food Quality and Safety》2008,2(3):168-177
Citrus canker is one of the most devastating diseases that threaten marketability of citrus crops. Technologies that can efficiently
identify citrus canker would assure fruit quality and safety and enhance the competitiveness and profitability of the citrus
industry. This research was aimed to investigate the potential of using hyperspectral imaging technique for detecting canker
lesions on citrus fruit. A portable hyperspectral imaging system consisting of an automatic sample handling unit, a light
source, and a hyperspectral imaging unit was developed for citrus canker detection. The imaging system was used to acquire
reflectance images from citrus samples in the wavelength range between 400 and 900 nm. Ruby Red grapefruits with normal and
various diseased skin conditions including canker, copper burn, greasy spot, wind scar, cake melanose, and specular melanose
were tested. Hyperspectral reflectance images were analyzed using principal component analysis (PCA) to compress the 3-D hyperspectral
image data and extract useful image features that could be used to discriminate cankerous samples from normal and other diseased
samples. Image processing and classification algorithms were developed based upon the transformed images of PCA. The overall
accuracy for canker detection was 92.7%. Four optimal wavelengths (553, 677, 718, and 858 nm) were identified in visible and
short-wavelength near-infrared region that could be adopted by a future multispectral imaging solution for detecting citrus
canker on a sorting machine. This research demonstrated that hyperspectral imaging technique could be used for discriminating
citrus canker from other confounding diseases. 相似文献
972.
A continuous model for heterostructure field-effect transistors (HFETs) suitable for circuit simulation and device characterization is proposed. The model is based on the analytical solution of a two-dimensional Poisson equation in the saturation region. The HFET saturation current and saturation voltage have been experimentally determined by differentiating the output characteristics in a unified and unambiguous way. The results are used for the systematic extraction of device and process parameters. The deduced values agree well with other independent measurements. The results of experimental studies of HFETs with nominal gate lengths of 1, 1.4, 2, and 5 μm are reported. The models and techniques presented here are successfully applied to all these devices. A large short-channel effect is observed for the 1-μm-gate HFET. The gate length dependences of the device parameters determined by the method reveal that the effective gate length in the self-aligned structures is approximately 0.25 μm shorter than the nominal gate length 相似文献
973.
Moon-Hee Lee Yeon-Kye Kim Ho Sung Moon Kyoung-Duck Kim Gwan-Gyu Kim Hyeon-Ah Cho Na Young Yoon Kil Bo Sim Hee-Yeon Park Doo-Seog Lee Chi-Won Lim Ho-Dong Yoon Sang-Kuk Han 《Food science and biotechnology》2012,21(5):1285-1291
The proximate composition, fatty acid, and amino acid profile of the body wall and viscera of each red and black sea cucumber (Apostichopus japonicus) from Ulleungdo(Island) and Dokdo(Island) in Korea were compared. Moisture, ash, crude protein, and crude lipid contents ranged between 80.26–91.49, 2.57–6.85, 1.13–3.99, and 0.14–2.12%, respectively. The fatty acid values varied depending on the species and the regions of collection. The anteiso C17:0, C16:1Δ9, C17:1Δ7, C18:1Δ11, and C16:2Δ7 were only observed in the body wall. Among the tested fatty acids, the C18:1Δ11 was specific in red sea cucumber, and C20:4Δ6 (17.7%) and C20:5Δ3 (17.6%) were the predominant polyunsaturated fatty acids (PUFA) in all samples. The contents of the C18:0 dimethyl acetal (C18:0 DMA), C16:1Δ7, C16:1Δ5, and C18:1Δ5 were compared in details. Total amino acids (TAA) of body wall were 1.3–1.9 times higher than those of viscera. Glutamic acid and aspartic acid constituted the major TAA of sea cucumbers. The ratio of essential amino acids (EAA): nonessential amino acids (NEAA) on TAA ranged from 1.15 to 0.67 of sea cucumbers. Viscera of red sea cucumber from Dokdo(Island) were rich in free amino acids (FAA) and showed a high content in leucine. 相似文献
974.
Ko Hoon Kim Hye Ran Moon Junseong Lee Jimin Kim Jae Nyoung Kim 《Advanced Synthesis \u0026amp; Catalysis》2015,357(7):1532-1544
The Wittig reaction of isatin derivatives with Morita–Baylis–Hillman bromides of cinnamaldehydes afforded 3‐dienylidene‐2‐oxindoles. These trienes were converted into the corresponding spirooxindoles in a stereoselective manner in refluxing toluene in good yields. The diastereomeric spirooxindoles could be obtained stereoselectively by adding a catalytic amount of palladium(II) acetate via the palladium‐catalyzed isomerization of EEE‐trienes to ZEE‐trienes followed by a more facile 6π‐electrocyclization process. The obtained spirooxindoles could be further functionalized by palladium‐catalyzed oxidative arylation, thionation with Lawesson’s reagent, catalytic hydrogenation and Friedel–Crafts‐type reaction.
975.
Air‐Stable Cesium Lead Iodide Perovskite for Ultra‐Low Operating Voltage Resistive Switching 下载免费PDF全文
Ji Su Han Quyet Van Le Jaeho Choi Kootak Hong Cheon Woo Moon Taemin Ludvic Kim Hyojung Kim Soo Young Kim Ho Won Jang 《Advanced functional materials》2018,28(5)
CsPbX3 (X = halide, Cl, Br, or I) all‐inorganic halide perovskites (IHPs) are regarded as promising functional materials because of their tunable optoelectronic characteristics and superior stability to organic–inorganic hybrid halide perovskites. Herein, nonvolatile resistive switching (RS) memory devices based on all‐inorganic CsPbI3 perovskite are reported. An air‐stable CsPbI3 perovskite film with a thickness of only 200 nm is successfully synthesized on a platinum‐coated silicon substrate using low temperature all‐solution process. The RS memory devices of Ag/polymethylmethacrylate (PMMA)/CsPbI3/Pt/Ti/SiO2/Si structure exhibit reproducible and reliable bipolar switching characteristics with an ultralow operating voltage (<+0.2 V), high on/off ratio (>106), reversible RS by pulse voltage operation (pulse duration < 1 ms), and multilevel data storage. The mechanical flexibility of the CsPbI3 perovskite RS memory device on a flexible substrate is also successfully confirmed. With analyzing the influence of phase transition in CsPbI3 on RS characteristics, a mechanism involving conducting filaments formed by metal cation migration is proposed to explain the RS behavior of the memory device. This study will contribute to the understanding of the intrinsic characteristics of IHPs for low‐voltage resistive switching and demonstrate the huge potential of them for use in low‐power consumption nonvolatile memory devices on next‐generation computing systems. 相似文献
976.
Airborne viable, non-viable, and allergenic fungi in a rural agricultural area of India: a 2-year study at five outdoor sampling stations 总被引:1,自引:0,他引:1
Adhikari A Sen MM Gupta-Bhattacharya S Chanda S 《The Science of the total environment》2004,326(1-3):123-141
The information on airborne allergenic fungal flora in rural agricultural areas is largely lacking. Adequate information is not available to the bioaerosol researchers regarding the choice of single versus multiple sampling stations for the monitoring of both viable and non-viable airborne fungi. There is no long-term study estimating the ratios of viable and non-viable fungi in the air and earlier studies did not focus on the fractions of airborne allergenic fungi with respect to the total airborne fungal load. To fill these knowledge gaps, volumetric paired assessments of airborne viable and non-viable fungi were performed in five outdoor sampling stations during two consecutive years in a rural agricultural area of India. Samples were collected at 10-day intervals by the Burkard Personal Slide Sampler and the Andersen Two-Stage Viable Sampler. The data on the concentrations of total and individual fungal types from five stations and 2 different years were analyzed and compared by statistical methods. The allergenicity of the prevalent airborne viable fungi was estimated by the skin-prick tests of >100 rural allergy patients using the antigenic fungal extracts from isolates collected with the Andersen sampler. The ranges of total fungal spore concentration were 82-2365 spores per cubic meter of air (spores/m3) in the first sampling year and 156-2022 spores/m3 in the second sampling year. The concentration ranges of viable fungi were 72-1796 colony-forming units per cubic meter of air (CFU/m3) in the first sampling year and 155-1256 CFU/m3 in the second sampling year. No statistically significant difference was observed between the total spore data of the 2 years, however, the data between five stations showed a significant difference (P<0.0001). No statistically significant difference existed between stations and years with respect to the concentration of viable fungi. When the data of individual allergenic fungal concentrations were compared between stations and years, no statistically significant difference was observed in all cases except for Aspergillus japonicus and Rhizopus nigricans, which showed significant difference in case of stations and years, respectively. The ratios between the total fungal spores collected by the Burkard sampler and the viable fungi collected by the Andersen sampler from all sampling stations ranged between 0.29 and 7.61. The antigenic extracts of eight prevalent viable airborne fungi (A. flavus, A. japonicus, A. fumigatus, Alternaria alternata, Cladosporium cladosporioides, Curvularia pallescens, Fusarium roseum, and R. nigricans) demonstrated >60% positive reactions in the skin prick test. These selected allergenic fungi collectively represented 31.7-63.2% of the total airborne viable fungi in different stations. The study concluded that: (i) a rich fungal airspora existed in the rural study area, (ii) to achieve representative information on the total airborne fungal spores of an area, the monitoring in multiple sampling stations is preferable over a single sampling station; for viable fungi, however, one station can be considered, (iii) the percentage of airborne fungal viability is higher in rural agricultural areas, and (iv) approximately 52% of the viable airborne fungi in the rural study area were allergenic. 相似文献
977.
Bilal Ahmad Maria Batool Qurat ul Ain Moon Suk Kim Sangdun Choi 《International journal of molecular sciences》2021,22(17)
The novel coronavirus disease, caused by severe acute respiratory coronavirus 2 (SARS-CoV-2), rapidly spreading around the world, poses a major threat to the global public health. Herein, we demonstrated the binding mechanism of PF-07321332, α-ketoamide, lopinavir, and ritonavir to the coronavirus 3-chymotrypsin-like-protease (3CLpro) by means of docking and molecular dynamic (MD) simulations. The analysis of MD trajectories of 3CLpro with PF-07321332, α-ketoamide, lopinavir, and ritonavir revealed that 3CLpro–PF-07321332 and 3CLpro–α-ketoamide complexes remained stable compared with 3CLpro–ritonavir and 3CLpro–lopinavir. Investigating the dynamic behavior of ligand–protein interaction, ligands PF-07321332 and α-ketoamide showed stronger bonding via making interactions with catalytic dyad residues His41–Cys145 of 3CLpro. Lopinavir and ritonavir were unable to disrupt the catalytic dyad, as illustrated by increased bond length during the MD simulation. To decipher the ligand binding mode and affinity, ligand interactions with SARS-CoV-2 proteases and binding energy were calculated. The binding energy of the bespoke antiviral PF-07321332 clinical candidate was two times higher than that of α-ketoamide and three times than that of lopinavir and ritonavir. Our study elucidated in detail the binding mechanism of the potent PF-07321332 to 3CLpro along with the low potency of lopinavir and ritonavir due to weak binding affinity demonstrated by the binding energy data. This study will be helpful for the development and optimization of more specific compounds to combat coronavirus disease. 相似文献
978.
Benedikt Bitterli Fabrice Rousselle Bochang Moon José A. Iglesias‐Guitián David Adler Kenny Mitchell Wojciech Jarosz Jan Novák 《Computer Graphics Forum》2016,35(4):107-117
We address the problem of denoising Monte Carlo renderings by studying existing approaches and proposing a new algorithm that yields state‐of‐the‐art performance on a wide range of scenes. We analyze existing approaches from a theoretical and empirical point of view, relating the strengths and limitations of their corresponding components with an emphasis on production requirements. The observations of our analysis instruct the design of our new filter that offers high‐quality results and stable performance. A key observation of our analysis is that using auxiliary buffers (normal, albedo, etc.) to compute the regression weights greatly improves the robustness of zero‐order models, but can be detrimental to first‐order models. Consequently, our filter performs a first‐order regression leveraging a rich set of auxiliary buffers only when fitting the data, and, unlike recent works, considers the pixel color alone when computing the regression weights. We further improve the quality of our output by using a collaborative denoising scheme. Lastly, we introduce a general mean squared error estimator, which can handle the collaborative nature of our filter and its nonlinear weights, to automatically set the bandwidth of our regression kernel. 相似文献
979.
Jong Goo Han Tae Hee Park Yong Ho Moon Il Kyu Eom 《Machine Vision and Applications》2018,29(3):543-552
In this paper, we propose an efficient Markov feature extraction method for image splicing detection using discrete cosine transform coefficient quantization. The quantization operation reduces the information loss caused by the coefficient thresholding used to restrict the number of Markov features. The splicing detection performance is improved because the quantization method enlarges the discrimination of the probability distributions between the authentic and the spliced images. In this paper, we present two Markov feature selection algorithms. After quantization operation, we choose the sum of three directional Markov transition probability values at the corresponding position in the probability matrix as a first feature vector. For the second feature vector, the maximum value among the three directional difference values of the three color channels is used. A fixed number of features, regardless of the color channels and test datasets, are used in the proposed algorithm. Through experimental simulations, we demonstrate that the proposed method achieves high performance in splicing detection. The average detection accuracy is over than 97% on three well-known splicing detection image datasets without the use of additional feature reduction algorithms. Furthermore, we achieve reasonable forgery detection performance for more modern and realistic dataset. 相似文献
980.
Improved dielectric properties of CaCu3Ti4O12 thin films on oxide bottom electrode of La0.5Sr0.5CoO3
We report on the effect of La0.5Sr0.5CoO3 (LSCO) bottom electrode to the dielectric properties of CaCu3Ti4O12 (CCTO) thin films grown on Ir/Ti/SiO2/Si substrates. Compared with the films grown directly on Ir/Ti/SiO2/Si substrates, the dielectric constant has been increased greatly about 100%, and the dielectric loss decreased to lower than 0.2 in the frequency range of 1-100 kHz. The origin has been discussed in details based on the analysis of the X-ray diffraction and impedance spectra measurements. Results of the impedance spectra suggest that the absence of undesired interfacial layer between Ir/CCTO thin films might be one of the major reasons of the improvement of the dielectric properties when the LSCO was introduced as the bottom electrode. 相似文献