全文获取类型
收费全文 | 553篇 |
免费 | 31篇 |
专业分类
电工技术 | 24篇 |
化学工业 | 95篇 |
金属工艺 | 13篇 |
机械仪表 | 12篇 |
建筑科学 | 32篇 |
能源动力 | 10篇 |
轻工业 | 85篇 |
水利工程 | 2篇 |
石油天然气 | 1篇 |
无线电 | 118篇 |
一般工业技术 | 83篇 |
冶金工业 | 68篇 |
原子能技术 | 4篇 |
自动化技术 | 37篇 |
出版年
2024年 | 1篇 |
2023年 | 12篇 |
2022年 | 9篇 |
2021年 | 6篇 |
2020年 | 13篇 |
2019年 | 9篇 |
2018年 | 11篇 |
2017年 | 14篇 |
2016年 | 15篇 |
2015年 | 20篇 |
2014年 | 25篇 |
2013年 | 30篇 |
2012年 | 25篇 |
2011年 | 25篇 |
2010年 | 20篇 |
2009年 | 28篇 |
2008年 | 36篇 |
2007年 | 23篇 |
2006年 | 22篇 |
2005年 | 21篇 |
2004年 | 26篇 |
2003年 | 24篇 |
2002年 | 16篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 20篇 |
1998年 | 28篇 |
1997年 | 20篇 |
1996年 | 5篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1993年 | 5篇 |
1992年 | 6篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 4篇 |
1988年 | 4篇 |
1987年 | 3篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1981年 | 1篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 3篇 |
1969年 | 1篇 |
1968年 | 1篇 |
排序方式: 共有584条查询结果,搜索用时 46 毫秒
61.
S R Chae S H Lee J O Kim B C Paik Y C Song H S Park H S Shin 《Water science and technology》2004,49(5-6):257-264
As the sewerage system is incomplete, sewage in Korea lacks easily biodegradable organics for nutrient removal. In this country, about 11,400 tons of food waste of high organic materials is produced daily. Therefore, the potential of food waste as an external carbon source was examined in a pilot-scale BNR (biological nutrient removal) process for a half year. It was found that as the supply of the external carbon increased, the average removal efficiencies of T-N (total nitrogen) and T-P (total phosphorus) increased from 53% and 55% to 97% and 93%, respectively. VFAs (volatile fatty acids) concentration of the external carbon source strongly affected denitrification efficiency and EBPR (enhanced biological phosphorus removal) activity. Biological phosphorus removal was increased to 93% when T-N removal efficiency increased from 78% to 97%. In this study, several kinds of PHAs (poly-hydroxyalkanoates) in cells were observed. The observed PHAs was composed of 37% 3HB (poly-3-hydroxybutyrate), 47% 3HV (poly-3-hydroxyvalerate), 9% 3HH (poly-3-hydroxyhexanoate), 5% 3HO (poly-3-hydroxyoctanoate), and 2% 3HD (poly-3-hydroxydecanoate). 相似文献
62.
Ho-Young Son Jae-Woong Nah Kyung-Wook Paik 《Electronics Packaging Manufacturing, IEEE Transactions on》2005,28(3):274-281
Formation processes of Pb/63Sn solder droplets using a solder droplet jetting have not been sufficiently reported. Solving problems such as satellite droplets and position errors are very important for a uniform bump size and reliable flip-chip solder bump formation process. First, this paper presents the optimization of jet conditions of Pb/63Sn solder droplets and the formation process of Pb/63Sn solder bumps using a solder droplet jetting method. Second, interfacial reactions and mechanical strength of jetted Pb/63Sn solder bumps and electroless Ni-P/Au UBM joints have been investigated. Interfacial reactions have been investigated after the second solder reflow and aging, and results were compared with those of solder bumps formed by a solder screen-printing method. Third, jetted solder bumps with variable bump sizes have been demonstrated by a multiple jetting method and the control of waveform induced to a jet nozzle. Multiple droplets jetting method can control various height and size of solder bumps. Finally, real applications of jetted Pb/63Sn solder bumps have been successfully demonstrated on conventional DRAM chips and integrated passive devices (IPDs). 相似文献
63.
64.
DigiCipher, an all-digital HDTV (high-definition television) system, with transmission over a single 6 MHz VHF or UHF channel, is described. It provides full HDTV performance with virtually no visible transmission impairments due to noise, multipath, and interference. It offers high picture quality, while the complexity of the decoder is low. Furthermore, low transmitting power can be used, making it ideal for simulcast HDTV transmission using unused or prohibited channels. DigiCipher can also be used for cable and satellite transmission of HDTV. There is no satellite receive dish size penalty (compared to FM-NTSC) in the satellite delivery of DigiCipher HDTV. To achieve the full HDTV performance in a single 6 MHz bandwidth, a highly efficient unique compression algorithm based on DCT (discrete cosine transform) transform coding is used. Through the extensive use of computer simulation, the compression algorithm has been refined and optimized. Computer simulation results show excellent video quality for a variety of HDTV material. For error-free transmission of the digital data, power error correction coding combined with adaptive equalization is used. At a carrier-to-noise ratio of above 19 dB, essentially error-free reception can be achieved 相似文献
65.
On the basis of observed customer interaction patterns, the WebCatalog/sup Pers/ system creates integrated product catalogs that continuously adapt and can be restructured in a dynamic environment. 相似文献
66.
The aims of this paper are to investigate the ultimate shear strength reduction characteristics of steel plates due to local impacts, and also to develop the ultimate shear strength design formulae of dented steel plates. The ANSYS nonlinear finite element code is used to investigate the effects of shape, size (depth, diameter), and location of the denting on the ultimate strength behavior of simply supported steel plates under edge shear loads. A closed-form expression for predicting the ultimate shear strength of dented steel plates is derived by the regression analysis based on the computed results. The results and insights developed from the present study will be very useful for damage tolerant design of steel plated structures with local denting. 相似文献
67.
Joongcheol Paik Fotis Sotiropoulos Michael J. Sale 《Canadian Metallurgical Quarterly》2005,131(6):441-456
A numerical method is developed for carrying out unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and detached-eddy simulations (DESs) in complex 3D geometries. The method is applied to simulate incompressible swirling flow in a typical hydroturbine draft tube, which consists of a strongly curved 90° elbow and two piers. The governing equations are solved with a second-order-accurate, finite-volume, dual-time-stepping artificial compressibility approach for a Reynolds number of 1.1 million on a mesh with 1.8 million nodes. The geometrical complexities of the draft tube are handled using domain decomposition with overset (chimera) grids. Numerical simulations show that unsteady statistical turbulence models can capture very complex 3D flow phenomena dominated by geometry-induced, large-scale instabilities and unsteady coherent structures such as the onset of vortex breakdown and the formation of the unsteady rope vortex downstream of the turbine runner. Both URANS and DES appear to yield the general shape and magnitude of mean velocity profiles in reasonable agreement with measurements. Significant discrepancies among the DES and URANS predictions of the turbulence statistics are also observed in the straight downstream diffuser. 相似文献
68.
Structural reliability theory is a useful tool for estimating the risks associated with deteriorating structures. The aim of this study is to develop and demonstrate a procedure for the assessment of box girder bridge ultimate strength reliability with the degradation of plate members due to general corrosion taken into account. A probabilistic model for ultimate steel-box girder strength is established on the basis of an analytic formula that considers corrosion-related, time-dependent strength degradation. The study involves the selection of representative structures, formulation of limit state functions, development of resistance models for corroded steel-box girders, development of load models, development of a reliability analysis method, reliability analysis of the selected bridges and development of the time-dependant reliability profiles, including deterioration due to corrosion. The results of this study can be used for the better prediction of the service life of deteriorating steel-box girder bridges and the development of optimal reliability-based maintenance strategies. 相似文献
69.
Mutations in the Delta7-sterol reductase gene in patients with the Smith-Lemli-Opitz syndrome 总被引:1,自引:0,他引:1
BU Fitzky M Witsch-Baumgartner M Erdel JN Lee YK Paik H Glossmann G Utermann FF Moebius 《Canadian Metallurgical Quarterly》1998,95(14):8181-8186
The Smith-Lemli-Opitz syndrome (SLOS) is an inborn disorder of sterol metabolism with characteristic congenital malformations and dysmorphias. All patients suffer from mental retardation. Here we identify the SLOS gene as a Delta7-sterol reductase (DHCR7, EC 1.3.1. 21) required for the de novo biosynthesis of cholesterol. The human and murine genes were characterized and assigned to syntenic regions on chromosomes 11q13 and 7F5 by fluorescense in situ hybridization. Among the mutations found in patients with the SLOS, are missense (P51S, T93M, L99P, L157P, A247V, V326L, R352W, C380S, R404C, and G410S), nonsense (W151X), and splice site (IVS8-1G>C) mutations as well as an out of frame deletion (720-735 del). The missense mutations L99P, V326L, R352W, R404C, and G410S reduced heterologous protein expression by >90%. Our results strongly suggest that defects in the DHCR7 gene cause the SLOS. 相似文献
70.
BACKGROUND: Der p 1, a major mite allergen, elicits IgE antibody responses in 80% of patients suffering from dust mite allergy. Given the potent IgE eliciting properties of Der p 1, there is considerable interest in studying the molecular architecture of the variable (Fv) region of IgE antibodies specific for this allergen. OBJECTIVES: IgE is present in human serum at extremely low concentrations, and as such it is practically impossible to purify sufficient quantities for structural studies. We have therefore sought to sequence and model a representative murine monoclonal (MoAb) anti-Der p 1 antibody, as a surrogate human IgE. METHODS: The cDNA coding for the Fv region of an anti-Der p 1 MoAb (2C7), that mimics the binding of human IgE to Der p 1, was amplified by PCR, cloned and sequenced. The predicted amino acid sequences were then compared with a directory of human germline V-gene segments. Modelling of the Fv region of MoAb 2C7 was carried out using the extensive database of existing immunoglobulin structures in the Brookhaven PDB. RESULTS: The MoAb 2C7 heavy chain showed greater than 70% homology with three members of the VH3 family, DP-35, DP-53 and DP-54. Similarly, the light chain showed greater than 70% homology with 11 VK sequences, including the VKII sequences DPK18, DPK19 and DPK28. A molecular model of the Fv region of MoAb 2C7 was generated and can be accessed from the EMBL databank. CONCLUSIONS: Antibodies similar to MoAb 2C7 could be generated as part of the human repertoire. The availability of 3-dimensional model of MoAb 2C7, as a surrogate human IgE antibody, combined with further data on its epitope specificity, will facilitate studies into IgE antibody responses to Der p 1. 相似文献