全文获取类型
收费全文 | 85677篇 |
免费 | 1024篇 |
国内免费 | 412篇 |
专业分类
电工技术 | 788篇 |
综合类 | 2317篇 |
化学工业 | 12022篇 |
金属工艺 | 4846篇 |
机械仪表 | 3060篇 |
建筑科学 | 2236篇 |
矿业工程 | 567篇 |
能源动力 | 1160篇 |
轻工业 | 3758篇 |
水利工程 | 1275篇 |
石油天然气 | 342篇 |
无线电 | 9420篇 |
一般工业技术 | 16690篇 |
冶金工业 | 2740篇 |
原子能技术 | 290篇 |
自动化技术 | 25602篇 |
出版年
2022年 | 32篇 |
2021年 | 50篇 |
2020年 | 31篇 |
2019年 | 32篇 |
2018年 | 14477篇 |
2017年 | 13414篇 |
2016年 | 9996篇 |
2015年 | 632篇 |
2014年 | 290篇 |
2013年 | 311篇 |
2012年 | 3250篇 |
2011年 | 9533篇 |
2010年 | 8370篇 |
2009年 | 5640篇 |
2008年 | 6887篇 |
2007年 | 7862篇 |
2006年 | 221篇 |
2005年 | 1280篇 |
2004年 | 1187篇 |
2003年 | 1228篇 |
2002年 | 612篇 |
2001年 | 137篇 |
2000年 | 216篇 |
1999年 | 87篇 |
1998年 | 98篇 |
1997年 | 71篇 |
1996年 | 81篇 |
1995年 | 41篇 |
1994年 | 38篇 |
1993年 | 40篇 |
1992年 | 27篇 |
1991年 | 41篇 |
1990年 | 21篇 |
1988年 | 26篇 |
1981年 | 19篇 |
1976年 | 19篇 |
1969年 | 29篇 |
1968年 | 44篇 |
1967年 | 33篇 |
1966年 | 42篇 |
1965年 | 44篇 |
1963年 | 28篇 |
1962年 | 22篇 |
1960年 | 30篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1956年 | 34篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Aminollah Mahabadi Hamid Sarbazi-Azad Ebrahim Khodaie Keivan Navi 《The Journal of supercomputing》2008,45(1):1-14
This paper proposes an efficient parallel algorithm for computing Lagrange interpolation on k-ary n-cube networks. This is done using the fact that a k-ary n-cube can be decomposed into n link-disjoint Hamiltonian cycles. Using these n link-disjoint cycles, we interpolate Lagrange polynomial using full bandwidth of the employed network. Communication in the
main phase of the algorithm is based on an all-to-all broadcast algorithm on the n link-disjoint Hamiltonian cycles exploiting all network channels, and thus, resulting in high-efficiency in using network
resources. A performance evaluation of the proposed algorithm reveals an optimum speedup for a typical range of system parameters
used in current state-of-the-art implementations.
相似文献
Hamid Sarbazi-AzadEmail: Email: |
92.
This paper is concerned with the derivation of infinite schedules for timed automata that are in some sense optimal. To cover
a wide class of optimality criteria we start out by introducing an extension of the (priced) timed automata model that includes
both costs and rewards as separate modelling features. A precise definition is then given of what constitutes optimal infinite
behaviours for this class of models. We subsequently show that the derivation of optimal non-terminating schedules for such
double-priced timed automata is computable. This is done by a reduction of the problem to the determination of optimal mean-cycles
in finite graphs with weighted edges. This reduction is obtained by introducing the so-called corner-point abstraction, a
powerful abstraction technique of which we show that it preserves optimal schedules.
This work has been mostly done while visiting CISS at Aalborg University in Denmark and has been supported by CISS and by
ACI Cortos, a program of the French Ministry of Research. 相似文献
93.
Gemma Robles 《Journal of Logic, Language and Information》2008,17(2):161-181
In this paper, consistency is understood in the standard way, i.e. as the absence of a contradiction. The basic constructive
logic BKc4, which is adequate to this sense of consistency in the ternary relational semantics without a set of designated points, is
defined. Then, it is shown how to define a series of logics by extending BKc4 up to minimal intuitionistic logic. All logics defined in this paper are paraconsistent logics. 相似文献
94.
John Stachurski 《Computational Economics》2008,31(2):141-160
This paper studies fitted value iteration for continuous state numerical dynamic programming using nonexpansive function approximators.
A number of approximation schemes are discussed. The main contribution is to provide error bounds for approximate optimal
policies generated by the value iteration algorithm.
相似文献
95.
This work presents a driving system for a peristaltic micropump that is based on piezoelectric actuation. The effects of the
actuation sequence on pump performance are also considered. A valveless peristaltic micropump based on piezoelectric actuation
is designed and fabricated using microelectromechanical system technology. The pump has three parts––silicon, Pyrex glass
and commercially available bulk PZT (lead zirconate titanate) chips. The peristaltic micropump actuated by PZT chips comprises
three chambers that are in series. The driving system consists of an ATmega 8535 microprocessor, a high voltage power supply,
three differential amplifiers, a phase controller, an A/D converter, a 555 oscillator and an LCD module. It is supplied via
a 110 Vrms 60-Hz AC line and is programmable. The system can produce step-function signals with voltages of up to 100 Vpp and frequencies ranging from 10 Hz to 1 kHz, as the inputs for the pump. Fluid pumping with air is successfully demonstrated.
Additionally, 3-, 4- and 6-phase actuation sequences for the pump are designed and used to study the effects on pump performance,
as revealed by the flow rate and the displacement of a pump diaphragm. The experimental results show that the flow rate and
the displacement of the diaphragm actuated by the 4-phase sequence exceed those actuated by the 3- and 6-phase sequences.
A flow rate of 17.6 μl min−1 and a displacement of 2.91 μm (peak-to-peak) in 4-phase peristaltic motion are achieved at 100 Hz and 100 Vpp. The results demonstrate that the pump actuated in the 4-phase sequence is the most efficient. Consequently, the actuation
sequences can affect the pump performance. 相似文献
96.
J. Jiang Fanghua Mei W. J. Meng G. B. Sinclair Sunggook Park 《Microsystem Technologies》2008,14(6):815-819
For direct imprinting of metals, hard materials such as diamond and SiC have been used to construct mold inserts in preference
to Si, despite the ease in fabricating Si-based micro-/nano- scale structures. In this communication, we demonstrate that
micron scale Al structures can be replicated with good fidelity at room temperature by compression molding with Si inserts
without incurring insert damage. We further report on results of a finite element analysis of the mechanics of the molding
process. The finite element results provide some understanding of the observed lack of damage to the Si inserts. 相似文献
97.
Collapse-free thermal bonding technique for large area microchambers in plastic lab-on-a-chip applications 总被引:1,自引:0,他引:1
Dong Sung Kim Hyun Sup Lee Jungyoup Han Se Hwan Lee Chong H. Ahn Tai Hun Kwon 《Microsystem Technologies》2008,14(2):179-184
Bonding is an essential step to form microchannels or microchambers in lab-on-a-chip applications. In this paper, we present
a novel plastic thermal bonding technique to seal and form large area microchambers (planar characteristic width and length
on the order of 1 mm and characteristic thickness on the order of 10–100 μm) without collapse by introducing a holed pressure
equalizing plate (HPEP) that includes holes of the same size and shape as the microchambers. To demonstrate the proposed technique,
two types of large area microchambers [(1) 20 × 10 mm and 40 μm thick and (2) 12 × 2.5 mm and 120 μm thick] with microchannels
were designed and replicated on plastic substrates by means of hot embossing and injection molding processes with prepared
two nickel mold inserts. The replicated large area microchambers as well as the microchannels in the plastic lab-on-a-chip
were successfully sealed (i.e., no leakage) and formed without any collapse by the proposed thermal bonding technique with
the help of the HPEP. 相似文献
98.
Image preview is a convenient way to browse large or multiple images on small displays. However, current signal-level image
resampling algorithms may remove many features of interest in the preview image. In this paper, we propose perceptual image
preview which retains more perceptual features such that users can inspect features of interest by viewing the preview image
only and without zooming in. This technology has two components, structure enhancement and perceptual feature visualization.
Structure enhancement enhances the image structure while suppressing subtle details using a gradient modulation method, thus
making the succedent perceptual features more apparent. For perceptual feature visualization, features of interest detected
in the picture is visualized on the structure enhanced preview image. We demonstrate with two examples of most commonly used image quality features, image blur and noise. The effectiveness of the proposed method is validated
by experimental results. 相似文献
99.
Vassilis Agouridas Alison McKay Henri Winand Alan de Pennington 《Requirements Engineering》2008,13(1):19-48
This paper reports results of research into the definition of requirements for new consumer products––specifically, electro-mechanical
products. The research dealt with the derivation of design requirements that are demonstrably aligned with stakeholder needs.
The paper describes a comprehensive process that can enable product development teams to deal with statements of product requirements,
as originally collected through market research activities, in a systematic and traceable manner from the early, fuzzy front
end, stages of the design process. The process described has been based on principles of systems engineering. A case study
from its application and evaluation drawn from the power sector is described in this paper. The case study demonstrates how
the process can significantly improve product quality planning practices through revision of captured product requirements,
analysis of stakeholder requirements and derivation of design requirements. The paper discusses benefits and issues from the
use of the process by product development teams, and identifies areas for further research. Finally, the conclusions drawn
from the reported research are presented.
相似文献
Vassilis AgouridasEmail: |
100.
About 20 years ago, Markus and Robey noted that most research on IT impacts had been guided by deterministic perspectives and had neglected to use an emergent perspective, which could account for contradictory findings. They further observed that most research in this area had been carried out using variance theories at the expense of process theories. Finally, they suggested that more emphasis on multilevel theory building would likely improve empirical reliability. In this paper, we reiterate the observations and suggestions made by Markus and Robey on the causal structure of IT impact theories and carry out an analysis of empirical research published in four major IS journals, Management Information Systems Quarterly (MISQ), Information Systems Research (ISR), the European Journal of Information Systems (EJIS), and Information and Organization (I&O), to assess compliance with those recommendations. Our final sample consisted of 161 theory-driven articles, accounting for approximately 21% of all the empirical articles published in these journals. Our results first reveal that 91% of the studies in MISQ, ISR, and EJIS focused on deterministic theories, while 63% of those in I&O adopted an emergent perspective. Furthermore, 91% of the articles in MISQ, ISR, and EJIS adopted a variance model; this compares with 71% from I&O that applied a process model. Lastly, mixed levels of analysis were found in 14% of all the surveyed articles. Implications of these findings for future research are discussed. 相似文献