全文获取类型
收费全文 | 2329篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 26篇 |
化学工业 | 117篇 |
金属工艺 | 10篇 |
机械仪表 | 19篇 |
建筑科学 | 63篇 |
能源动力 | 32篇 |
轻工业 | 120篇 |
水利工程 | 5篇 |
石油天然气 | 13篇 |
无线电 | 115篇 |
一般工业技术 | 128篇 |
冶金工业 | 1565篇 |
原子能技术 | 9篇 |
自动化技术 | 139篇 |
出版年
2022年 | 10篇 |
2021年 | 9篇 |
2019年 | 13篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 22篇 |
2015年 | 13篇 |
2014年 | 22篇 |
2013年 | 19篇 |
2012年 | 31篇 |
2011年 | 39篇 |
2010年 | 41篇 |
2009年 | 38篇 |
2008年 | 50篇 |
2007年 | 37篇 |
2006年 | 40篇 |
2005年 | 33篇 |
2004年 | 36篇 |
2003年 | 34篇 |
2002年 | 24篇 |
2001年 | 26篇 |
2000年 | 34篇 |
1999年 | 68篇 |
1998年 | 485篇 |
1997年 | 276篇 |
1996年 | 190篇 |
1995年 | 118篇 |
1994年 | 83篇 |
1993年 | 111篇 |
1992年 | 25篇 |
1991年 | 36篇 |
1990年 | 31篇 |
1989年 | 34篇 |
1988年 | 30篇 |
1987年 | 20篇 |
1986年 | 25篇 |
1985年 | 28篇 |
1984年 | 12篇 |
1983年 | 5篇 |
1982年 | 6篇 |
1981年 | 10篇 |
1980年 | 20篇 |
1977年 | 33篇 |
1976年 | 55篇 |
1975年 | 5篇 |
1973年 | 5篇 |
1968年 | 6篇 |
1967年 | 5篇 |
1966年 | 4篇 |
1965年 | 4篇 |
排序方式: 共有2361条查询结果,搜索用时 0 毫秒
41.
Orofino DP Pedersen PC 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1993,40(3):238-249
The angular spectrum decomposition is evaluated in terms of plane wave angular range, angular resolution, and spatial aliasing error using two-dimensional FFT (2-D FFT). The algorithm makes possible the source plane decomposition of normal velocity and pressure fields radiated by transducers of arbitrary shape, with significantly faster results achievable for planar sources. Although the angular spectrum is equally applicable to fields far from the transducer, the efficient calculation is derived specifically for fields in or very close to the source plane. An antialiasing algorithm is proposed that allows the source to be discretized with fewer sample points for a given accuracy than required with simple discretization techniques. Guidelines for the selection of sampling interval, discretization size, etc. are developed on an application-specific basis and indicate the best ratio of numerical accuracy to computational cost. 相似文献
42.
Henrik Aanæs Anders Lindbjerg Dahl Kim Steenstrup Pedersen 《International Journal of Computer Vision》2012,97(1):18-35
Not all interest points are equally interesting. The most valuable interest points lead to optimal performance of the computer
vision method in which they are employed. But a measure of this kind will be dependent on the chosen vision application. We
propose a more general performance measure based on spatial invariance of interest points under changing acquisition parameters
by measuring the spatial recall rate. The scope of this paper is to investigate the performance of a number of existing well-established
interest point detection methods. Automatic performance evaluation of interest points is hard because the true correspondence
is generally unknown. We overcome this by providing an extensive data set with known spatial correspondence. The data is acquired
with a camera mounted on a 6-axis industrial robot providing very accurate camera positioning. Furthermore the scene is scanned
with a structured light scanner resulting in precise 3D surface information. In total 60 scenes are depicted ranging from
model houses, building material, fruit and vegetables, fabric, printed media and more. Each scene is depicted from 119 camera
positions and 19 individual LED illuminations are used for each position. The LED illumination provides the option for artificially
relighting the scene from a range of light directions. This data set has given us the ability to systematically evaluate the
performance of a number of interest point detectors. The highlights of the conclusions are that the fixed scale Harris corner
detector performs overall best followed by the Hessian based detectors and the difference of Gaussian (DoG). The methods based
on scale space features have an overall better performance than other methods especially when varying the distance to the
scene, where especially FAST corner detector, Edge Based Regions (EBR) and Intensity Based Regions (IBR) have a poor performance.
The performance of Maximally Stable Extremal Regions (MSER) is moderate. We observe a relatively large decline in performance
with both changes in viewpoint and light direction. Some of our observations support previous findings while others contradict
these findings. 相似文献
43.
Optimization of practical trusses with constraints on eigenfrequencies, displacements, stresses, and buckling 总被引:1,自引:2,他引:1
In this paper we consider the optimization of general 3D truss structures. The design variables are the cross-sections of the truss bars together with the joint coordinates, and are considered to be continuous variables. Using these design variables we simultaneously carry out size optimization (areas) and shape optimization (joint positions). Topology optimization (removal and introduction of bars) is only considered in the sense that bars of minimum cross-sectional area will have a negligible influence on the performance of the structure. The structures are subjected to multiple load cases and the objective of the optimizations is minimum mass with constraints on (possibly multiple) eigenfrequencies, displacements, and stresses. For the case of stress constraints, we deal differently with tensile and compressive stresses, for which we control buckling on the element level. The stress constraints are imposed in correlation with industrial standards, to make the optimized designs valuable from a practical point of view. The optimization problem is solved using SLP (Sequential Linear Programming). 相似文献
44.
C. Thirstrup W. Zong M. Borre H. Neff H.C. Pedersen G. Holzhueter 《Sensors and actuators. B, Chemical》2004,100(3):298-308
Design, technological features, and performance of polymeric diffractive optical coupling elements (DOCEs), developed for surface plasmon resonance (SPR) sensors are reported. The concept is based on input and output coupling of collimated and perpendicularly incident light beams to exchangeable SPR sensor chips. In the SPR sensor chips, one DOCE couples the input light beam to a (bio-)chemical sensor surface and another DOCE images the output light beam onto a detector array. The manufacturing technique is based on an injection moulding process similarly to the manufacturing process of compact discs allowing precision manufacturing and reproduction of the grating topography of the DOCEs. The DOCE-based SPR sensor chip is specifically suitable for miniaturisation and large scale production, while maintaining high optical quality and performance. 相似文献
45.
Wetherell Julie Loebach; Gatz Margaret; Pedersen Nancy L. 《Canadian Metallurgical Quarterly》2001,16(2):187
The authors modeled depressive and anxiety symptom data from 1,391 participants in a longitudinal study of middle-aged and older Swedish twins (M age?=?60.9 years, SD?=?13.3). Although anxiety and depression were highly correlated, a model with distinct Anxiety and Depression factors fit the data better than models with Positive and Negative Affect factors or a single Mental Health factor. Lack of well-being was associated with anxiety rather than depression. Over two 3-year intervals, anxiety symptoms led to depressive symptoms, but the relationship was not reciprocal. Anxiety symptoms were more stable than depression. These findings provide additional support for the idea that anxiety symptoms may reflect a personality trait such as neuroticism more than do depressive symptoms and suggest that low positive affect may not be as specific to depression among older adults as in younger people. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
46.
Clinical and immunocytochemical analysis of twenty eight cases of giant cell tumour of bone was performed in this study. The results revealed that nine of the cases were benign, while the other nineteen were malignant. The female to male ratio was 2.5:1. The average age incidence was 28.18 years. The most common site of occurrence was the femur. anti endothelial antibody revealed negative immunocytochemical reaction of the stromal cells and giant cells for both benign and malignant cases; While using anti-HLA-DR antibody demonstrated positive immune reaction of some of the strumal and giant cells of all the cases examined. 相似文献
47.
A Angius M Pisano A Sanca G Casu I Persico S Pitzalis E De Gioia FM Grignolo A Loi G Sole A Cao P Spinelli G Ghillotti L Bonomi M Fossarello A Serra S Gandolfi G Alberti G Maraini A Serru N Orzalesi M Pirastu 《Canadian Metallurgical Quarterly》1998,(227):16-17
Glaucoma is a group of ocular diseases characterized by an optic neuropathy in which degeneration of retinal ganglion cells leads to a characteristic excavation of the optic nerve head. Primary open-angle glaucoma (POAG) can be subdivided into two groups according to age of onset:- 1. the more common middle- to late-age onset, chronic open-angle glaucoma (COAG) diagnosed after the age of 40 years; 2. the rarer juvenile open-angle glaucoma (JOAG), which is diagnosed between the age of 3 years and early adulthood. Recently, the gene coding for the trabecular meshwork-induced glucocorticoid response protein (TIGR), located in chromosome 1 (1q23-25), was found mutated in patients affected by POAG. In this work we describe the clinical and molecular genetic features of several Italian families affected by autosomal dominant POAG, collected in various regions of Italy. 相似文献
48.
49.
Mikael B. Skov Jesper Kjeldskov Jeni Paay Niels Husted Jacob Nørskov Kenneth Pedersen 《Pervasive and Mobile Computing》2013,9(2):216-227
Some movements within modern architecture particularly emphasise the importance of matching buildings to their surroundings. However, practicing such “contextual architecture” is highly challenging and typically not something the future inhabitants of a building are well equipped for participating in. This paper explores the potentials of using mobile phone technology for facilitating such client participation in the parts of an architecture process that take place on the building site. For this we introduce ArchiLens, a mobile system for interactive on-site 3D visualisation of houses, and findings from a field study with 40 participants in the process of building or modifying their home. The study showed that using the system helped evoke people’s imagination of the look and feel of their future house, and envision it in context. This enabled them to participate more closely in the design process on-site by iteratively reviewing design alternatives and exploring, for example, other placements and materials. 相似文献
50.
Developing solar power generating resources on dormant, suspect property is an evolving activity, growing in popularity. 相似文献