全文获取类型
收费全文 | 1468篇 |
免费 | 73篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 19篇 |
综合类 | 6篇 |
化学工业 | 271篇 |
金属工艺 | 26篇 |
机械仪表 | 20篇 |
建筑科学 | 97篇 |
矿业工程 | 1篇 |
能源动力 | 74篇 |
轻工业 | 223篇 |
水利工程 | 12篇 |
石油天然气 | 4篇 |
无线电 | 68篇 |
一般工业技术 | 207篇 |
冶金工业 | 246篇 |
原子能技术 | 12篇 |
自动化技术 | 262篇 |
出版年
2023年 | 8篇 |
2022年 | 11篇 |
2021年 | 24篇 |
2020年 | 22篇 |
2019年 | 28篇 |
2018年 | 40篇 |
2017年 | 39篇 |
2016年 | 36篇 |
2015年 | 28篇 |
2014年 | 47篇 |
2013年 | 92篇 |
2012年 | 77篇 |
2011年 | 91篇 |
2010年 | 68篇 |
2009年 | 71篇 |
2008年 | 91篇 |
2007年 | 99篇 |
2006年 | 77篇 |
2005年 | 56篇 |
2004年 | 55篇 |
2003年 | 48篇 |
2002年 | 41篇 |
2001年 | 27篇 |
2000年 | 21篇 |
1999年 | 21篇 |
1998年 | 14篇 |
1997年 | 13篇 |
1996年 | 18篇 |
1995年 | 16篇 |
1994年 | 26篇 |
1993年 | 20篇 |
1992年 | 23篇 |
1991年 | 10篇 |
1990年 | 11篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1987年 | 16篇 |
1986年 | 15篇 |
1985年 | 21篇 |
1984年 | 12篇 |
1983年 | 19篇 |
1982年 | 10篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 6篇 |
1976年 | 5篇 |
1975年 | 9篇 |
1974年 | 4篇 |
排序方式: 共有1548条查询结果,搜索用时 93 毫秒
31.
Ritesh Rawal Antonio Feteira Alberto Arenas Flores Neil C. Hyatt Anthony R. West Derek C. Sinclair Kumaravinothan Sarma Neil McN. Alford 《Journal of the American Ceramic Society》2006,89(1):336-339
The dielectric properties of dense ceramics of the "twinned" 8H-hexagonal perovskite Ba8 Nb4 Ti3 O24 are reported. Single-phase powders were obtained from the mixed-oxide route at 1325°C and ceramics (>92% of the theoretical X-ray density) by sintering in air or flowing O2 at 1400°–1450°C. The ceramics are dc insulators with a band gap >3.4 eV that resonate at microwave frequencies with relative permittivity, ɛr ∼44–48, quality factor, Q × f r ∼21 000–23 500 GHz (at f r ∼5.5 GHz) and temperature coefficient of resonant frequency, TC f ,∼+115 ppm/K. 相似文献
32.
We present a model of spatial navigation based on the non-convergent dynamics of brain activity. The system includes a hippocampal module that processes global spatial information and a cortical module that deals with local sensory information. We test the model using several spatial navigation paradigms: goal finding, shortcutting and detouring. Computer simulations show that the performance of the agent qualitatively matches that of animals and related models. This new approach provides a novel interpretation of how the brain accomplishes spatial navigation. 相似文献
33.
Holger Schnädelbach Tim Coughlan Genovefa Kefalidou Derek McAuley Rupert Meese 《International journal of human-computer interaction》2013,29(11):790-804
The Creativity Bento Box is a physical resource pack, designed to support casual social interaction and break taking in an intensive, computer-mediated social activity. It was developed within the Creativity Greenhouse project, which piloted a mechanism to create research proposals and distribute funding at a distance. This involved facilitated phases of collaboration and competition over multiple days of computer-mediated work, where participants communicate and interact through a virtual world. During the iterative development process, the lack of time for socializing, the intense focus on virtual resources, and a lack of time spent away from the screen were reported as negative issues in feedback from participants. This article reports on the development of the Creativity Bento Box and how it helped to address these issues. By providing physical resources that contrasted with the properties of the virtual world, it supported people to socialize and take breaks from their primary activity, allowed them to include physical space and artifacts in their interactions, and provoked moves away from the otherwise intense focus on the computer. The article reflects on the roles of the Bento Box as a gift, in bridging between physical and virtual contexts, its higher suitability during the earlier phases of ideation and group development, and its perception by participants as something “framed.” Through this, we highlight the underexplored potential of using physical, offline resources as a means to solve difficulties in distanced social interactions. 相似文献
34.
James M. Chappell Azhar Iqbal M. A. Lohe Lorenz von Smekal Derek Abbott 《Quantum Information Processing》2013,12(4):1719-1735
The Grover search algorithm is one of the two key algorithms in the field of quantum computing, and hence it is desirable to represent it in the simplest and most intuitive formalism possible. We show firstly, that Clifford’s geometric algebra, provides a significantly simpler representation than the conventional bra-ket notation, and secondly, that the basis defined by the states of maximum and minimum weight in the Grover search space, allows a simple visualization of the Grover search analogous to the precession of a spin- ${\frac{1}{2}}$ particle. Using this formalism we efficiently solve the exact search problem, as well as easily representing more general search situations. We do not claim the development of an improved algorithm, but show in a tutorial paper that geometric algebra provides extremely compact and elegant expressions with improved clarity for the Grover search algorithm. Being a key algorithm in quantum computing and one of the most studied, it forms an ideal basis for a tutorial on how to elucidate quantum operations in terms of geometric algebra—this is then of interest in extending the applicability of geometric algebra to more complicated problems in fields of quantum computing, quantum decision theory, and quantum information. 相似文献
35.
We present a new, real‐time method for rendering soft shadows from large light sources or lighting environments on dynamic height fields. The method first computes a horizon map for a set of azimuthal directions. To reduce sampling, we compute a multi‐resolution pyramid on the height field. Coarser pyramid levels are indexed as the distance from caster to receiver increases. For every receiver point and every azimuthal direction, a smooth function of blocking angle in terms of log distance is reconstructed from a height difference sample at each pyramid level. This function's maximum approximates the horizon angle. We then sum visibility at each receiver point over wedges determined by successive pairs of horizon angles. Each wedge represents a linear transition in blocking angle over its azimuthal extent. It is precomputed in the order‐4 spherical harmonic (SH) basis, for a canonical azimuthal origin and fixed extent, resulting in a 2D table. The SH triple product of 16D vectors representing lighting, total visibility, and diffuse reflectance then yields the soft‐shadowed result. Two types of light sources are considered; both are distant and low‐frequency. Environmental lights require visibility sampling around the complete 360 ° azimuth, while key lights sample visibility within a partial swath. Restricting the swath concentrates samples where the light comes from (e.g. 3 azimuthal directions vs. 16‐32 for a full swath) and obtains sharper shadows. Our GPU implementation handles height fields up to 1024 × 1024 in real‐time. The computation is simple, local, and parallel, with performance independent of geometric content. 相似文献
36.
Derek A. Paley Naomi Ehrich Leonard Rodolphe Sepulchre 《Systems & Control Letters》2008,57(3):209-215
We provide a cooperative control algorithm to stabilize symmetric formations to motion around closed curves suitable for mobile sensor networks. This work extends previous results for stabilization of symmetric circular formations. We study a planar particle model with decentralized steering control subject to limited communication. Because of their unique spectral properties, the Laplacian matrices of circulant graphs play a key role. We illustrate the result for a skewed superellipse, which is a type of curve that includes circles, ellipses, and rounded parallelograms. 相似文献
37.
Derek Lea 《计算机光盘软件与应用》2008,(2):94-97
智能对象的出现使得在Photoshop和Illustrator中使用像素和矢量之间的差别迅速消失。Derek Lea将会在制作一个结构完美且矢量明显的作品的同时为你解释原因。 相似文献
38.
Derek Hull 《International Journal of Fracture》1994,70(1):59-79
A modification of Sommer's classical experiment [4] has been used to fracture rods of a brittle epoxy resin in mixed mode I/III stress conditions. The nucleation and growth of cracks in an increasing K
III/K
I stress field have been investigated, particularly in relation to the formation of river lines and the evolution of multiple cracks between river lines to form smooth helicoid surfaces. The fractographic features associated with the progressive development of river line patterns involving crack bowing at river line steps, interaction between arrays of cracks and the coalescence of river lines are described. As K
III/K
I increases the scale of the river line patterns increases but the patterns remain self similar. Using principles from differential geometry it is shown that helicoid surfaces can be generated entirely by crack evolution involving tilting without twiting.Emeritus Goldsmiths' Professor of Metallurgy, University of Cambridge, U.K. 相似文献
39.
Journal of Intelligent Information Systems - Offline evaluation of recommender systems (RSs) mostly relies on historical data, which is often biased. The bias is a result of many confounders that... 相似文献
40.
Kim Tak H. Sirdaarta Joseph P. Zhang Qian Eftekhari Ehsan St. John James Kennedy Derek Cock Ian E. Li Qin 《Nano Research》2018,11(4):2204-2216
Nano Research - The toxicity of nanoparticles in a biological system is an integration of effects arising from surface functionality, particle size, ionic dissolution, etc. This complexity suggests... 相似文献