全文获取类型
收费全文 | 1734篇 |
免费 | 75篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 24篇 |
综合类 | 2篇 |
化学工业 | 509篇 |
金属工艺 | 68篇 |
机械仪表 | 66篇 |
建筑科学 | 68篇 |
矿业工程 | 3篇 |
能源动力 | 95篇 |
轻工业 | 127篇 |
水利工程 | 24篇 |
石油天然气 | 29篇 |
无线电 | 205篇 |
一般工业技术 | 283篇 |
冶金工业 | 135篇 |
原子能技术 | 9篇 |
自动化技术 | 173篇 |
出版年
2023年 | 19篇 |
2022年 | 50篇 |
2021年 | 55篇 |
2020年 | 52篇 |
2019年 | 80篇 |
2018年 | 68篇 |
2017年 | 40篇 |
2016年 | 52篇 |
2015年 | 44篇 |
2014年 | 63篇 |
2013年 | 135篇 |
2012年 | 77篇 |
2011年 | 99篇 |
2010年 | 68篇 |
2009年 | 70篇 |
2008年 | 65篇 |
2007年 | 63篇 |
2006年 | 60篇 |
2005年 | 38篇 |
2004年 | 32篇 |
2003年 | 36篇 |
2002年 | 35篇 |
2001年 | 28篇 |
2000年 | 18篇 |
1999年 | 24篇 |
1998年 | 30篇 |
1997年 | 26篇 |
1996年 | 19篇 |
1995年 | 26篇 |
1994年 | 16篇 |
1993年 | 19篇 |
1992年 | 27篇 |
1991年 | 28篇 |
1990年 | 20篇 |
1989年 | 14篇 |
1988年 | 15篇 |
1987年 | 15篇 |
1986年 | 11篇 |
1985年 | 20篇 |
1984年 | 21篇 |
1983年 | 21篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 17篇 |
1979年 | 7篇 |
1976年 | 9篇 |
1973年 | 7篇 |
1971年 | 10篇 |
1970年 | 8篇 |
1966年 | 6篇 |
排序方式: 共有1820条查询结果,搜索用时 15 毫秒
31.
Magdy M. Senna Ateyat M. Yossef Fatma M. Hossam Abdel Wahab M. El‐Naggar 《应用聚合物科学杂志》2007,106(5):3273-3281
Foamy low‐density polyethylene/plasticized starch (LDPE/PLST) blends at different compositions were produced in the presence of azodicarbonamide (ACA) compound as foaming agent. The LDPE/PLST blends before and after electron beam irradiation were investigated in terms of mechanical properties, bulk density, and structure morphology. Moreover, the biodegradability of these materials was evaluated by the soil burial test for 2 months, in which the buried sheets were also examined by scanning electron microscopy (SEM). The results showed that the increase of PLST content from 24 to 30% was accompanied by a decrease in the yield and break stresses of 10 and 20% for the unirradiated blends without the foaming agent, respectively. Further decrease in these mechanical parameters was observed after the foaming process. The bulk density, void fraction, cell size measurements as well as the examination by SEM illustrate clearly the cell growth of the foam structure. The soil burial test and SEM micrographs indicate the growth of microorganisms overall the blend sheets and that the blend was completely damaged after two months of burying. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 相似文献
32.
Ayman M. Atta Manar E. Abdel‐Raouf Shimaa M. Elsaeed Abdel‐Azim A. Abdel‐Azim 《应用聚合物科学杂志》2007,103(5):3175-3182
Unsaturated polyester resin (UP) was prepared from glycolyzed oligomer of poly(ethylene terephthalate) (PET) waste based on diethylene glycol (DEG). New diacrylate and dimethacrylate vinyl ester resins prepared from glycolysis of PET with tetraethylene glycol were blended with UP to study the mechanical characteristics of the cured UP. The vinyl ester resins were used as crosslinking agents for unsaturated polyester resin diluted with styrene, using free‐radical initiator and accelerator. The mechanical properties of the cured UP resins were evaluated. The compressive properties of the cured UP/styrene resins in the presence of different vinyl ester concentrations were evaluated. Increasing the vinyl ester content led to a pronounced improvement in the compression strength. The chemical resistances of the cured resins were evaluated through hot water, solvents, acid, and alkali resistance measurements. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3175–3182, 2007 相似文献
33.
Radiation‐induced graft copolymerization of maize starch/acrylic acid has been performed. Also, natural byproduct wood pulp was used after chemical treatment for the removal of metal ions from the investigated wastewater. The surface and structure morphology of the wood pulp and starch/acrylic acid were investigated by scanning electron microscopy and infrared spectroscopy. The physical parameters, such as swelling, gel percentage, and grafting efficiency (%) of starch/acrylic acid copolymer, were studied. The factors affecting the abilities of the prepared materials for removing heavy metal ions and dyes from aqueous solutions were studied. It was found that the maximum metal uptake is in the following sequence: Fe3+ > Cr3+ > Pb2+ > Cd2+. The adsorption capacity of such investigated metal ions increases with the increase of pH values. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006 相似文献
34.
Rehman Hafeez Ur Ghani Anwar Chaudhry Shehzad Ashraf Alsharif Mohammed H. Nabipour Narjes 《Multimedia Tools and Applications》2021,80(11):16907-16931
Multimedia Tools and Applications - The advancement in communication and computation technologies has paved a way for connecting large number of heterogeneous devices to offer specified services.... 相似文献
35.
J.Q. Xie A.E. Bayoumi H.M. Zbib 《International Journal of Machine Tools and Manufacture》1996,36(7):835-847
A simplified theory of instability of plastic flow is applied in this paper to analyze the formation of shear localized chips in orthogonal machining. A flow localization parameter is expressed in terms of associated cutting conditions and properties of the workpiece material. The analysis is used to investigate the effect of cutting conditions on the onset of shear localization and the formation of adiabatic shear banding in metal cutting. Comparisons are made between the analysis and experiments in which the flow localization parameter is obtained for several workpiece materials. The results of this investigation are thought to lend a strong justification for the analysis and its potential benefits in analyzing and/or remedying problems associated with chip formation and temperature generated in metal cutting. 相似文献
36.
Analytical and experimental study of shear localization in chip formation in orthogonal machining 总被引:3,自引:0,他引:3
J. Q. Xie A. E. Bayoumi H. M. Zbib 《Journal of Materials Engineering and Performance》1995,4(1):32-39
A simplified theory of instability of plastic flow is applied to analyze the formation of shear localized chips in orthogonal
machining. A flow localization parameter is expressed in terms of associated cutting conditions and properties of the workpiece
material. The analysis, which indicates the important parameters in the cutting process, is used to investigate the effect
of cutting conditions on the onset of shear localization and the formation of adiabatic shear banding in metal cutting. Comparisons
are made between the analysis and experiments in which the flow localization parameter is obtained for several workpiece materials.
The results of this investigation seem to support the analysis and its potential benefits in analyzing and/or remedying problems
associated with chip formation and temperature generated in metal cutting.
Presently at Advanced Technology Center, Valenite, Inc., Madison Heights,MI 48071, USA 相似文献
37.
Amorphous Al50Ta60 alloy powders have been synthesized by mechanical alloying (MA) from elemental powders of aluminium and tantalum, and mechanical disordering (MD) from crystalline intermetallic compound powders of AlTa respectively using the rod milling technique. The mechanically alloyed and the mechanically disordered alloy powders were characterized by X-ray diffraction, scanning electron microscopy, electron probe microanalysis, transmission electron microscopy, differential thermal analysis, differential scanning calorimetry and chemical analysis. The results have shown that the crystal-to amorphous transformation in the MD process occurs through one stage, while the crystallineto-amorphous formation in the MA process occurs through three stages. At the early and intermediate stages of the MA time, heating the alloy powders to 700 K leads to the formation of an amorphous phase by a solid-state amorphizing reaction. At the final stage of the MA time, the amorphous phase is crystallized through a single sharp exothermic peak. Contrary to this, amorphous alloy powders produced by MD are crystallized through two broad exothermic peaks. 相似文献
38.
Qufei Xie Abdel E. Bayoumi L. Alden Kendall 《Journal of Materials Shaping Technology》1990,8(4):255-265
This paper presents the results of an investigation of induced residual stress, induced strain, and induced subsurface energy
in machined surfaces due to the machining process. The influence of tool wear on residual stress, strain, and energy is also
reported. The exact elasticity solution for a split ring was extended and used to calculate the residual stress in the machined
surface by using ring dimension changes caused by the electrochemical removal of a thin layer of residually stressed surface.
The strain distribution beneath the machined surface was determined by using the grid technique. The subsurface energy stored
in the machined surface was then obtained from the data of residual stress and strain. For the materials studied, this investigation
showed that such energy could not be neglected when establishing the total energy needed for machining a unit volume of material.
Tool coatings having different surface roughness and tools having various magnitudes of flank wear were investigated. The
experimental results show that tool wear is a dominant factor affecting the values of induced residual stress, strain, subsurface
energy, and the quality of the machined surface. The increase of tool wear caused an increase of residual stress and strain
beneath the machined surface. It was also found that the overall energy stored in the machined subsurface increases as the
tool wear increases and as the tool surface gets rougher. When the cutting tool is severely worn, the machined surface not
only becomes very rough, but also contains many partially fractured laps or cracks. This makes tool wear a key factor in controlling
the quality of the machined surface. 相似文献
39.
Ibrahim Abdelaziz Sherif Abdou Hassanin Al-Barhamtoshy 《Pattern Analysis & Applications》2016,19(4):1129-1141
The success of using Hidden Markov Models (HMMs) for speech recognition application has motivated the adoption of these models for handwriting recognition especially the online handwriting that has large similarity with the speech signal as a sequential process. Some languages such as Arabic, Farsi and Urdo include large number of delayed strokes that are written above or below most letters and usually written delayed in time. These delayed strokes represent a modeling challenge for the conventional left-right HMM that is commonly used for Automatic Speech Recognition (ASR) systems. In this paper, we introduce a new approach for handling delayed strokes in Arabic online handwriting recognition using HMMs. We also show that several modeling approaches such as context based tri-grapheme models, speaker adaptive training and discriminative training that are currently used in most state-of-the-art ASR systems can provide similar performance improvement for Hand Writing Recognition (HWR) systems. Finally, we show that using a multi-pass decoder that use the computationally less expensive models in the early passes can provide an Arabic large vocabulary HWR system with practical decoding time. We evaluated the performance of our proposed Arabic HWR system using two databases of small and large lexicons. For the small lexicon data set, our system achieved competing results compared to the best reported state-of-the-art Arabic HWR systems. For the large lexicon, our system achieved promising results (accuracy and time) for a vocabulary size of 64k words with the possibility of adapting the models for specific writers to get even better results. 相似文献
40.
Ahmed Hamed Attia Ahmed Sobhy Sherif Ghada Samy El-Tawel 《Soft Computing - A Fusion of Foundations, Methodologies and Applications》2016,20(8):3153-3161
Non-symmetric similarity relation-based rough set model (NS-RSM) is viewed as mathematical tool to deal with the analysis of imprecise and uncertain information in incomplete information systems with “?” values. NS-RSM relies on the concept of non-symmetric similarity relation to group equivalent objects and generate knowledge granules that are then used to approximate the target set. However, NS-RSM results in unpromising approximation space when addressing inconsistent data sets that have lots of boundary objects. This is because objects in the same similarity classes are not necessarily similar to each other and may belong to different target classes. To enhance NS-RSM capability, we introduce the maximal limited similarity-based rough set model (MLS-RSM) which describes the maximal collection of indistinguishable objects that are limited tolerance to each other in similarity classes. This allows accurate computation to be done for the approximation space. Furthermore, approximation accuracy comparisons have been conducted among NS-RSM and MLS-RSM. The results demonstrate that MLS-RSM model outperforms NS-RSM and can approximate the target set more efficiently. 相似文献