全文获取类型
收费全文 | 1586篇 |
免费 | 138篇 |
国内免费 | 14篇 |
专业分类
电工技术 | 33篇 |
综合类 | 12篇 |
化学工业 | 376篇 |
金属工艺 | 34篇 |
机械仪表 | 84篇 |
建筑科学 | 75篇 |
矿业工程 | 3篇 |
能源动力 | 109篇 |
轻工业 | 104篇 |
水利工程 | 28篇 |
石油天然气 | 67篇 |
无线电 | 112篇 |
一般工业技术 | 297篇 |
冶金工业 | 46篇 |
原子能技术 | 11篇 |
自动化技术 | 347篇 |
出版年
2024年 | 7篇 |
2023年 | 27篇 |
2022年 | 44篇 |
2021年 | 84篇 |
2020年 | 91篇 |
2019年 | 115篇 |
2018年 | 165篇 |
2017年 | 138篇 |
2016年 | 137篇 |
2015年 | 80篇 |
2014年 | 128篇 |
2013年 | 183篇 |
2012年 | 117篇 |
2011年 | 121篇 |
2010年 | 85篇 |
2009年 | 73篇 |
2008年 | 46篇 |
2007年 | 35篇 |
2006年 | 16篇 |
2005年 | 6篇 |
2004年 | 13篇 |
2003年 | 4篇 |
2002年 | 6篇 |
2001年 | 1篇 |
2000年 | 1篇 |
1998年 | 5篇 |
1995年 | 1篇 |
1994年 | 2篇 |
1992年 | 1篇 |
1991年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1981年 | 1篇 |
排序方式: 共有1738条查询结果,搜索用时 15 毫秒
131.
The longest path problem is the problem of finding a simple path with the maximum number of vertices in a given graph, and so far it has been solved polynomially only for a few classes of graphs. This problem generalizes the well-known Hamiltonian path problem, hence it is NP-hard in general graphs. In this paper, first we give a sequential linear-time algorithm for the longest path problem in meshes. Then based on this algorithm, we present a constant-time parallel algorithm for the problem, which can be run on every parallel machine. 相似文献
132.
Alireza Hamedianfar Shattri Mansor Noordin Ahmad 《International journal of remote sensing》2013,34(5):1876-1899
Urbanization is commonly accepted as an important contributor to the growth of man-made structures and as a rapid convertor of natural environments to impervious surfaces. Roofs are one class of impervious surface whose materials can highly influence the quality of urban surface water. In this study, two data sources, WorldView-2 (WV-2) imagery and a combination of WV-2 and lidar data, were utilized to map intra-urban targets, with 13 classes. Images were classified using object-based image analysis. Pixel-based classifications using the support vector machine (SVM) and maximum likelihood (ML) methods were also tested for their abilities to use both lidar data and WV-2 imagery. ML and SVM classifications yielded overall accuracies of 72.46% and 75.69%, respectively. The results of these classifiers exhibited mixed pixels and salt-and-pepper effects. Spectral, spatial, and textural attributes as well as various spectral indices were employed in the object-based classification of WV-2 imagery. Feature classification of WV-2 imagery resulted in 85% overall accuracy. Lidar data were added to WV-2 imagery to assist in the spatial and spectral diversities of urban infrastructures. Classified image made from WV-2 imagery and lidar data achieved 92.84% overall accuracy. Rule-sets of these fused datasets effectively reduced the spectral variation and spatial heterogeneities of intra-urban classes, causing finer boundaries among land-cover classes. Therefore, object-based classification of WV-2 imagery and lidar data efficiently improved detailed characterization of roof types and other urban surface materials. 相似文献
133.
Principal component analysis with optimum order sample correlation coefficient for image enhancement
Qiuming Cheng Linhai Jing Alireza Panahi 《International journal of remote sensing》2013,34(16):3387-3401
Principal component analysis (PCA) has been commonly used and has played an important role in remote sensing for information extraction. However, the ordinary PCA based on second‐order covariance or correlation is capable of forming components on the basis of the statistical properties of a majority of pixel values – pixel values around mean values. For many applications, principal components should be constructed on the basis of optimum correlation coefficients so that the components can represent low or high values of minority pixels of interest. A new version of the PCA has been proposed on the basis of an optimum order sample correlation coefficient for enhancing the contribution of the image bands including the low or high minority pixel values that can assist in extracting weak information for image classification and pattern recognition. The ordinary PCA becomes the special case of the new version of the PCA introduced in this paper. The new method was validated with a case study of identification of Au/Cu‐associated alteration zones from a Landsat Thematic Mapper (TM) image in the Mitchell‐Sulphurets district, Canada. 相似文献
134.
Alireza Farhadi Jonathan Dumon Carlos Canudas-de-Wit 《International journal of control》2013,86(5):946-958
This paper presents a supervisory multi-agent control policy over an acoustic communication network subject to imperfections (packet dropout and transmission delay) for localisation of an underwater flow source (e.g., source of chemical pollution, fresh water, etc.) with an unknown location at the bottom of the ocean. A two-loop control policy combined with a coding strategy for reliable communication is presented to perform the above task. A simulator is developed and used to evaluate the trade-offs between quality of communication, transmission delay and control for a fleet of autonomous underwater vehicles supervised over a noisy acoustic communication network by an autonomous surface vessel. It is illustrated that without compensation of the effects of severe random packet dropout, localisation of an unknown underwater flow source is not possible for the condition simulated just by implementing a two-loop control policy. But a two-loop control policy combined with a strategy for reliable communication locates the unknown location of flow source. 相似文献
135.
In this article, turbulent TiO2/water nanofluid flow and convective heat transfer in a horizontal tube is numerically investigated. Four computer codes were developed for each model (single phase, volume of fluid, mixture, and Eulerian) to simulate this problem. The Finite volume method is applied to solve the two-dimensional steady state governing equations. The results are compared with each other and an experimental work. A model with the most similar results to those of the experimental data and less amount of time for the CPU usage is chosen to develop two correlations for Nusselt number and friction factor based on dimensionless numbers. 相似文献
136.
T. Meissner S. K. Goh J. Haase B. Meier D. Rybicki P. L. Alireza 《Journal of Low Temperature Physics》2010,159(1-2):284-287
A novel approach that uses radio-frequency microcoils in the high-pressure region of anvil cells with Nuclear Magnetic Resonance (NMR) experiments is described. High-sensitivity Al NMR data at 70 kbar for Al metal are presented for the first time. An expected decrease in the Al Knight shift at 70 kbar is observed, as well as an unexpected change in the local charge symmetry at the Al nucleus. The latter is not predicted by chemical structure analysis under high pressure. 相似文献
137.
Majid Aryafar Ramin Raiszadeh Alireza Shalbafzadeh 《Journal of Materials Science》2010,45(11):3041-3051
The possibility of the bonding of the two layers of a double oxide film defect when held in liquid A356 Al alloy was investigated.
The defect was modelled experimentally by maintaining two aluminium oxide layers in contact with each other and the atmosphere
trapped between them in the A356 liquid alloy for varying lengths of time of between 30 s and 48 h. Any changes in the composition
and morphology of these layers were studied by SEM, EDX and XRD. The results showed that the two layers of a double oxide
film defect might bond to each other by two different mechanisms, one during the transformation of Al2O3 to MgAl2O4 spinel in relatively short holding times, which would cause the layers to bond at several points and the other during the
gradual transformation of spinel to MgO in longer times, which would cause strong bonding between the layers. It was shown
that any bonding can take place essentially only after the oxygen and nitrogen of the atmosphere within the defect are consumed. 相似文献
138.
Effects of the intensity and frequency of electromagnetic vibrations on the microstructural refinement of hypoeutectic Al-Si alloys 总被引:4,自引:0,他引:4
An experimental apparatus that uses a superconducting magnet and enables the simultaneous application of an alternating electric
field with a frequency of up to 50 kHz and a magnetic field of up to 10 T was designed and assembled. Electromagnetic vibrations
were induced in Al-7 wt pct Si alloy during solidification by simultaneous application of the two fields. The thorough investigation,
which was carried out over wide ranges of intensity (an electromagnetic pressure range of 0 to 2.25×105 Pa) and frequency (0 to 50 kHz), clarified the effects of the two main parameters on the microstructural refinement brought
about by electromagnetic vibrations. Low-intensity vibrations changed the highly columnar dendritic structure into one composed
of large, equiaxed dendrites. As the intensity, and consequently, the magnetic pressure were increased, at about 0.93×105 Pa, fine isolated grains started to appear and dominated the structure as the pressure was increased further. At low frequencies,
the structure was one with large, equiaxed dendrites, which disintegrated to form a fine and homogeneous structure as the
frequency was increased. At about 1.5 kHz, the trend reversed and the structure gradually became a completely columnar dendritic
one at frequencies higher than 10 kHz. Metallographic observations showed that the cavitation phenomenon has been a main factor
behind the observed microstructural refinement. The effects of mechanical vibrations of the experimental apparatus were also
investigated and found to have no contribution to the observed effects. 相似文献
139.
Alireza Karimi Reza Razaghi Mahdi Navidbakhsh Toshihiro Sera Susumu Kudo 《Journal of materials science. Materials in medicine》2016,27(4):74
Although there are some traditional models of the gunshot wounds, there is still a need for more modeling analyses due to the difficulties related to the gunshot wounds to the forehead region of the human skull. In this study, the degree of damage as a consequence of penetrating head injuries due to gunshot wounds was determined using a preliminary finite element (FE) model of the human skull. In addition, the role of polyvinyl alcohol (PVA) sponge, which can be used as an alternative to reinforce the kinetic energy absorption capacity of bulletproof vest and helmet materials, to minimize the amount of skull injury due to penetrating processes was investigated through the FE model. Digital computed tomography along with magnetic resonance imaging data of the human head were employed to launch a three-dimensional (3D) FE model of the skull. Two geometrical shapes of projectiles (steel ball and bullet) were simulated for penetrating with an initial impact velocity of 734 m/s using nonlinear dynamic modeling code, namely LS-DYNA. The role of the damaged/distorted elements were removed during computation when the stress or strain reached their thresholds. The stress distributions in various parts of the forehead and sponge after injury were also computed. The results revealed the same amount of stress for both the steel ball and bullet after hitting the skull. The modeling results also indicated the time that steel ball takes to penetrate into the skull is lower than that of the bullet. In addition, more than 21 % of the steel ball’s kinetic energy was absorbed by the PVA sponge and, subsequently, injury sternness of the forehead was considerably minimized. The findings advise the application of the PVA sponge as a substitute strengthening material to be able to diminish the energy of impact as well as the load transmitted to the object. 相似文献
140.