全文获取类型
收费全文 | 1054篇 |
免费 | 49篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 194篇 |
金属工艺 | 20篇 |
机械仪表 | 19篇 |
建筑科学 | 32篇 |
矿业工程 | 5篇 |
能源动力 | 47篇 |
轻工业 | 96篇 |
水利工程 | 10篇 |
石油天然气 | 8篇 |
无线电 | 113篇 |
一般工业技术 | 212篇 |
冶金工业 | 159篇 |
原子能技术 | 19篇 |
自动化技术 | 158篇 |
出版年
2023年 | 7篇 |
2022年 | 30篇 |
2021年 | 46篇 |
2020年 | 9篇 |
2019年 | 36篇 |
2018年 | 35篇 |
2017年 | 35篇 |
2016年 | 36篇 |
2015年 | 19篇 |
2014年 | 43篇 |
2013年 | 77篇 |
2012年 | 48篇 |
2011年 | 69篇 |
2010年 | 49篇 |
2009年 | 52篇 |
2008年 | 50篇 |
2007年 | 37篇 |
2006年 | 33篇 |
2005年 | 14篇 |
2004年 | 25篇 |
2003年 | 20篇 |
2002年 | 17篇 |
2001年 | 18篇 |
2000年 | 9篇 |
1999年 | 18篇 |
1998年 | 43篇 |
1997年 | 28篇 |
1996年 | 18篇 |
1995年 | 17篇 |
1994年 | 23篇 |
1993年 | 14篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1987年 | 6篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 3篇 |
1977年 | 10篇 |
1976年 | 7篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1971年 | 3篇 |
排序方式: 共有1104条查询结果,搜索用时 15 毫秒
71.
The society of telecommunication and computer networks encompasses a wide variety of organizations, forums and industry companies
that specify, standardize, evaluate, implement and deploy network infrastructures. These infrastructures are well defined
and deployed in order to offer high quality end-user services and meet the need for interconnectivity, expandability and upgradeability.
What users see and experience is the tip of the iceberg. Great amount of time and money is spent in specification, standardization,
design, debugging, testing (both conformance and stress) and finally evaluating network components or subsystems before the
deployment takes place. The framework, proposed in the current paper and implemented in open source software library, provides
an object oriented methodology for the implementation of network protocols and the software realization of network components.
The method is formed in respect to: (a) operating system architecture (b) network architecture and (c) Object Oriented (OO)
methodology. 相似文献
72.
P. Elias C. Kontoes O. Sykioti A. Avallone S. Van Gorp P. Briole 《International journal of remote sensing》2013,34(14):3079-3086
On 7 September 1999 a magnitude MW = 5.9 earthquake occurred in the Athens area of Greece producing a subsidence of 6–7 cm detected by radar interferometry. This study introduces a processing technique, which produces a clear deformation pattern of the earthquake, mostly released from artefacts due to orbital effects, unwrapping cycle slipping errors and atmospherics disturbances. A set of 17 ERS‐1 and ERS‐2 SAR images acquired between December 1997 and January 2001 has been used. The contribution of each artefact to the interferograms was calculated, both in the frequency and spatial domains. 相似文献
73.
We consider the wavelet transform { W a ( t ), −∞ < t } < ∞}, at scale a > 0, of a fractional Brownian motion. A simple and mathematically rigorous proof is given to establish the existence of the spectral density f Wa (λ) of the wavelet transform and provide an expression for it. 相似文献
74.
The radioisotope X-ray fluorescence method was applied to studies of the provenance of the ceramics fragments originated from the Mar-Takla site in Syria.The samples were irradiated 1000s by a ^109Cd radioisotope source and 13 elements (Ca,Ti,Mn,Fe,Zn,Ga,As,Rb,Sr,Y,Zr,Nb,and Pb)were determined in 35 samples.The data were subjected to two multivariate statistical methods,cluster and principal components analysis(PCA).It was shown from the combination of the statistical techniques and the determination of elemental composition of the samples that 94% of the ceramic samples analyzed can be considered to be manufactured using two sources of raw materials. 相似文献
75.
Elias Kiassos Stefania Mylonaki Dimitris P. Makris Panagiotis Kefalas 《Innovative Food Science and Emerging Technologies》2009,10(2):246-252
An experimental setup based on a 23-full factorial, central composite design was implemented with the aim to optimising recovery of polyphenols from onion solid wastes (OSW). In order to allow for the establishment of a sustainable process, reusable and non-toxic solutions composed of water/ethanol/citric acid were employed as extracting media. The factors considered were (i) the pH of the medium, (ii) the extraction time and (iii) the ethanol concentration. The model obtained produced a satisfactory fitting of the experimental data with regard to total polyphenol extraction (R2 = 0.97, p = 0.0025) and the reducing power of the extracts (R2 = 0.97, p = 0.0033), but not with the antiradical activity (R2 = 0.89, p = 0.0592). The 2nd order polynomial equations obtained after elaboration of the experimental data indicated that all parameters considered were significant in respect with the efficiency of total polyphenol recovery. The highest total polyphenol yield was theoretically predicted to be 9342 ± 1435 mg gallic acid equivalents per 100 g dry weight, under optimal conditions (60% EtOH, pH 2 and 4.2 h). Liquid chromatography-electrospray ionisation mass spectrometry of the optimally obtained extract revealed that the principal phytochemicals recovered were quercetin 3,4′-diglucoside, quercetin 4′-glucoside and quercetin. Simple linear regression analysis between the total polyphenol and the antiradical activity of the OSW extracts showed that there was no correlation in a statistically significant manner, as opposed to reducing power.Industrial relevanceThe recovery of value-added substances from agri-food industrial wastes is an issue with importance pertaining to both the reduction of the waste load released to the environment, and the development of novel, natural food additives with functional properties. Up to date, the examinations pertaining to the clarification of factors that can affect extractability were based on rather unilateral assessment, while it is generally accepted that the retrieval depends on several parameters, which render the phenomenon a particular complexity. In this view, the implementation of factorial design with respect to investigating in parallel several factors pertaining to efficient polyphenol recovery becomes imminent. Thus the establishment of models on such a sound experimental basis is expected to provide a reliable background for more costand resource-effective processes, with a potential direct industrial applicability. 相似文献
76.
Nicolas Charalambakis Elias C. Aifantis 《International Journal of Engineering Science》1991,29(12):1639-1650
We examine the role of higher order strain gradients in the instability and localization of deformation during the shearing of a thermoviscoplastic material. We take the point of view that thermal softening is the leading mechanism of instability. A gradient dependent yield condition is assumed in order to stabilize the behavior within the softening regime. It turns out that the critical conditions for both instability and localization are different than those obtained in the absence of higher order strain gradients. Moreover, the thermomechanical constitutive parameters of strain hardening, strain rate sensitivity and thermal softening do not suffice to define the stability regime. In particular, a specific value of strain dependent on the aforementioned thermomechanical coefficients and the control parameter is required in order that loss of stability to occur. Such loss of stability may occur either “locally” through the growth of localized non-uniformities or “globally” throughout the material strip in a catastrophic manner. 相似文献
77.
Daniel Walgraef Elias C. Aifantis 《International Journal of Engineering Science》1985,23(12):1359-1364
We consider the motion and interaction of dislocation species on the slip plane via two-dimensional partial differential equations of the reaction-diffusion type. We distinguish between slow moving dislocations with mobilities along both the slip direction and the direction perpendicular to it (random motion), and fast moving dislocations with mobility along the slip direction only (stress-driven motion). The competition between gradients and nonlinearities leads to stable periodic dislocation structures with wavevector parallel to the slip direction and an intrinsic wavenumber given by the same formula as in the one dimensional analysis of Part I. In addition to the one-dimensional results, however, we find here that splitting of the periodic structures and development of superdefects is possible, according to experimental observations. 相似文献
78.
GH Posner MH Parker J Northrop JS Elias P Ploypradith S Xie TA Shapiro 《Canadian Metallurgical Quarterly》1999,42(2):300-304
In only three chemical operations, natural trioxane lactone artemisinin (1) was converted into a series of C-10 carbon-substituted 10-deoxoartemisinin compounds 4-9. The three steps involved lactone reduction, replacement of the anomeric lactol OH by F using diethylaminosulfur trifluoride, and finally boron trifluoride-promoted substitution of F by aryl, heteroaryl, and acetylide nucleophiles. All of these C-10 nonacetal, chemically robust, enantiomerically pure compounds 4-9 have high antimalarial potencies in vitro against Plasmodium falciparum malaria parasites, and furans 5a and 5b and pyrrole 7a are antimalarially potent also in vivo even when administered to rodents orally. 相似文献
79.
Elias Pentti Juho Rysti Anssi Salmela Alexander Sebedash Juha Tuoriniemi 《Journal of Low Temperature Physics》2011,165(3-4):132-165
We present results of low-temperature experiments on dilute mixtures of 3He in 4He and on pure 3He, obtained by means of two kinds of mechanical oscillators immersed in the liquid sample: vibrating wires and quartz tuning forks. The helium sample was cooled either by adiabatic demagnetization of an immersed copper nuclear stage or by adiabatic melting of 4He in superfluid 3He. The measured effect of the surrounding fluid on the mechanical resonance of the oscillators is compared with existing theories. We also discuss resonances of second sound and the state of supersaturation, both observed by a tuning fork in helium mixtures. 相似文献
80.
Elias Penelope K.; Elias Merrill F.; Robbins Michael A.; Gage Paulette 《Canadian Metallurgical Quarterly》1987,2(4):340
A total of 45 subjects in three age groups (younger, middle-age, older) were trained to word process on microcomputers using a commercial training program and an experimenter-designed test and evaluation protocol. Although all of the subjects mastered the essentials of word processing, the older group took significantly longer to complete the training and evaluation procedures and performed more poorly on a review examination that tested their knowledge of the word-processing commands and techniques. The results are discussed in relation to requirements for trainer assistance, motivational factors, and the need to design training protocols that meet the needs of older adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献