全文获取类型
收费全文 | 22968篇 |
免费 | 1250篇 |
国内免费 | 12篇 |
专业分类
电工技术 | 365篇 |
综合类 | 59篇 |
化学工业 | 4634篇 |
金属工艺 | 638篇 |
机械仪表 | 521篇 |
建筑科学 | 929篇 |
矿业工程 | 127篇 |
能源动力 | 360篇 |
轻工业 | 2868篇 |
水利工程 | 151篇 |
石油天然气 | 27篇 |
无线电 | 1304篇 |
一般工业技术 | 5643篇 |
冶金工业 | 3146篇 |
原子能技术 | 173篇 |
自动化技术 | 3285篇 |
出版年
2023年 | 268篇 |
2022年 | 178篇 |
2021年 | 462篇 |
2020年 | 400篇 |
2019年 | 379篇 |
2018年 | 732篇 |
2017年 | 721篇 |
2016年 | 814篇 |
2015年 | 681篇 |
2014年 | 837篇 |
2013年 | 1642篇 |
2012年 | 1035篇 |
2011年 | 1230篇 |
2010年 | 1033篇 |
2009年 | 959篇 |
2008年 | 1064篇 |
2007年 | 1049篇 |
2006年 | 748篇 |
2005年 | 574篇 |
2004年 | 487篇 |
2003年 | 489篇 |
2002年 | 483篇 |
2001年 | 424篇 |
2000年 | 351篇 |
1999年 | 374篇 |
1998年 | 1068篇 |
1997年 | 659篇 |
1996年 | 517篇 |
1995年 | 374篇 |
1994年 | 311篇 |
1993年 | 286篇 |
1992年 | 148篇 |
1991年 | 149篇 |
1990年 | 139篇 |
1989年 | 108篇 |
1988年 | 124篇 |
1987年 | 114篇 |
1986年 | 87篇 |
1985年 | 185篇 |
1984年 | 190篇 |
1983年 | 126篇 |
1982年 | 135篇 |
1981年 | 154篇 |
1980年 | 134篇 |
1979年 | 90篇 |
1978年 | 104篇 |
1977年 | 131篇 |
1976年 | 206篇 |
1975年 | 93篇 |
1973年 | 74篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
941.
Sandrine Hönig Dietmar Koch Steffen Weber Simon Etzold Thorsten Tonnesen Rainer Telle Nicolas Traon 《International Journal of Applied Ceramic Technology》2019,16(5):1723-1733
The determination of elastic properties at application temperature is fundamental for the design of fibre reinforced ceramic composite components. An attractive method to characterize the flexural modulus at room and high temperature under specific atmosphere is the nondestructive Resonant Frequency Damping Analysis (RFDA). The objective of this paper was to evaluate and validate the modulus measurement via RFDA for orthotropic C/C-SiC composites at the application temperature. At room temperature flexural moduli of C/C-SiC with 0/90° reinforcement were measured under quasi-static 4-point bending loads and compared with dynamic moduli measured via RFDA longitudinally to fibre direction. The dynamic modulus of C/C-SiC was then measured via RFDA up to 1250°C under flowing inert gas and showed an increase with temperature which fitted with literature values. The measured fundamental frequencies were finally compared to those resulting from numerical modal analyses. Dynamic and quasi-static flexural moduli are comparable and the numerical analyses proved that bending modes are correctly modeled by means of dynamic modulus measured via RFDA. The nondestructive RFDA as well as the numerical modeling approach are suitable for evaluation of C/C-SiC and may be transferred to other fibre reinforced ceramic composite materials. 相似文献
942.
Silvia Bierlich Timmy Reimann Frauke Gellersen Arne F. Jacob Jörg Töpfer 《Journal of the European Ceramic Society》2019,39(10):3077-3081
Sc3+ substituted M-type ferrites are effective microwave magnetic materials with a ferromagnetic resonance frequency in the range of 20 GHz–50 GHz. We report on the fabrication of oriented ferrite thick films as microwave components for application in the Ka-band at 30 GHz. Films of BaFe11.5.Sc0.5O19 were prepared by screen-printing on alumina substrates, drying in an external magnetic field, and sintering at 900 °C. Low-temperature sintering is achieved through use of a mixed BBSZ/CuO sintering aid. A strong anisotropy of the sintered ferrite films is revealed by XRD analysis. Microwave properties of the films were determined in a coplanar waveguide setup. The ferromagnetic resonance frequency of the films is at 30 GHz and the textured films possess good nonreciprocal properties which scale with film thickness. The films were tested in a Y-junction circulator, and represent promising materials for self-biased microwave components fabricated in thick film technology. 相似文献
943.
Iryna Smokovych Manja Krüger Michael Scheffler 《Journal of the European Ceramic Society》2019,39(13):3634-3642
Silica-based coating systems were developed using polymer derived ceramics (PDCs) technology. Ceramic composites on the base of a SiO2 and SiNO matrix and homogeneously distributed Mo5SiB2, SiB6, Si and B fillers were manufactured. The coating systems have low porosity and provide a high oxidation resistance up to 100 h at 800 °C and 1100 °C in air. The influence of temperature and atmosphere of pyrolysis on the polymer precursor, the volume fraction of filler materials on the chemical composition of compacts as well as their high-temperature oxidation protection was investigated. 相似文献
944.
S. Vorberg B. Fischer M. Wenderoth U. Glatzel R. Völkl 《JOM Journal of the Minerals, Metals and Materials Society》2005,57(3):49-51
Precipitation-strengthened alloys in the system Pt-Al-Cr-Ni have been investigated by transmission-electron microscopy. Dense
dislocation networks were found in an alloy with the nominal composition, in atomic percent, Pt-14Al-3Cr-4Ni after homogenization
heat treatment and aging. Alloys with higher nickel content showed low overall dislocation densities and the γ/γ′ phase boundaries were almost free of dislocations. The loss of coherency in the alloy with a low nickel content is explained
by high lattice misfit.
For more information, contact Stefan Vorberg, University of Applied Sciences Jena, Department of Materials Technology, Carl-Zeiss-Promenade
2, Jena D-07745, Germany; +49-3641-205-466; fax +49-3641-205-451; e-mail stefan.vorberg@fh-jena.de. 相似文献
945.
B. Pricop U. Söyler N. M. Lohan B. Özkal L. G. Bujoreanu D. Chicet C. Munteanu 《Journal of Materials Engineering and Performance》2012,21(11):2407-2416
In order to produce shape memory rings for constrained-recovery pipe couplings, from Fe-14 Mn-6 Si-9 Cr-5 Ni (mass%) powders, the main technological steps were (i) mechanical alloying, (ii) sintering, (iii) hot rolling, (iv) hot-shape setting, and (v) thermomechanical training. The article generally describes, within its experimental-procedure section, the last four technological steps of this process the primary purpose of which has been to accurately control both chemical composition and the grain size of shape memory rings. Details of the results obtained in the first technological step, on raw powders employed both in an initial commercial state and in a mixture state of commercial and mechanically alloyed (MA) powders, which were subjected to several heating-cooling cycles have been reported and discussed. By means of differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and X-ray diffraction (XRD), the thermal behaviors of the two sample powders have been analyzed. The effects of the heating-cooling cycles, on raw commercial powders and on 50% MA powders, respectively, were argued from the point of view of specific temperatures and heat variations, of elemental diffusion after thermal cycling and of crystallographic parameters, determined by DSC, SEM, and XRD, respectively. 相似文献
946.
Franz Dietrich Christian Löchte Sabina Jeschke Annika Raatz 《Production Engineering》2012,6(4-5):531-539
This article is concerned with the control of the production of aircraft primary structures made of carbon fibre reinforced plastics. To increase the parallelization of the production, a scenario that implies new design paradigms is discussed. In order to realize this parallelization, mobile production entities work concurrently at the same primary structure of the fuselage. The present article proposes a software architecture for the control of such a production system. It is proposed that components are organized hierarchically. In enhancement to previous proposals, two perspectives of hierarchy are used here: grouping by functionality and grouping by timing context. The core of the architecture is a market-based multi-agent system, where the agents may operate in multiple timing contexts. Such a design yields advantages in terms of fast integration of new functionalities and scale-up of the production system. In brief, this article introduces a top-level control architecture for parallelized production of large reliable CFRP structures in a scalable production system. 相似文献
947.
Pavel Strunz Debashis Mukherji Přemysl Beran Ralph Gilles Lukas Karge Michael Hofmann Markus Hoelzel Joachim Rösler Gergely Farkas 《Metals and Materials International》2018,24(5):934-944
An addition of boron largely increases the ductility in polycrystalline high-temperature Co–Re alloys. Therefore, the effect of boron on the alloy structural characteristics is of high importance for the stability of the matrix at operational temperatures. Volume fractions of ε (hexagonal close-packed—hcp), γ (face-centered cubic—fcc) and σ (Cr2Re3 type) phases were measured at ambient and high temperatures (up to 1500 °C) for a boron-containing Co–17Re–23Cr alloy using neutron diffraction. The matrix phase undergoes an allotropic transformation from ε to γ structure at high temperatures, similar to pure cobalt and to the previously investigated, more complex Co–17Re–23Cr–1.2Ta–2.6C alloy. It was determined in this study that the transformation temperature depends on the boron content (0–1000 wt. ppm). Nevertheless, the transformation temperature did not change monotonically with the increase in the boron content but reached a minimum at approximately 200 ppm of boron. A probable reason is the interplay between the amount of boron in the matrix and the amount of σ phase, which binds hcp-stabilizing elements (Cr and Re). Moreover, borides were identified in alloys with high boron content. 相似文献
948.
Alcohol biosensors based on conducting polypyrrole (PPy), poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-ethylenedioxypyrrole) (PEDOP) were constructed. Alcohol oxidase (AlcOx, from Pichia pastoris) was immobilized during electropolymerization of the monomers in sodium dodecylsulfate (SDS) and phosphate buffer electrolysis medium. Optimization of several parameters was carried out. The highest affinity was observed for the PEDOT/AlcOx sensor. Lowry protein determination method was also used to calculate the amount of immobilized enzyme in sensors. Before testing the biosensors on alcoholic beverages effects of interferents (glucose, acetic acid, citric acid, and l-ascorbic acid) were determined. The alcohol contents of the distilled beverages (vodka, dry cin, whisky, and rak?) were determined with the sensors constructed. A good match with the chromatography results was observed. 相似文献
949.
Gerold M. Rangger Oliver T. Hofmann Benjamin Bröker Egbert Zojer 《Synthetic Metals》2010,160(13-14):1456-1462
A better understanding of metal-organic interfaces combined with means to control their properties is crucial for the further improvement of organic (opto)electronic devices. In this context, the use of organic acceptors is an efficient tool to modify metal work functions and hole-injection barriers, which has the potential to considerably improve the performance of organic devices. Here, we use density functional theory based calculations to discuss a particularly potent acceptor suitable for that purpose, 3,5-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane (F2HCNQ), which clearly outperforms the frequently applied and in the meantime prototypical system 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). Comparative calculations for a single monolayer of the two molecules adsorbed on an Ag(1 1 1) surface reveal that (i) the work-function increase induced by F2HCNQ is more than 20% higher than for F4TCNQ and that (ii) at the same time the adsorption energy basically is unaffected, while (iii) the electronic structure is slightly modified. In the end of the day, F2HCNQ is a highly promising candidate for applications in organic devices. 相似文献
950.
Zeynep Münteha Şahin Erdinç Doğancı S. Zeki Yıldız Murat Tuna Faruk Yılmaz Yusuf Yerli Mesut Görür 《Synthetic Metals》2010,160(17-18):1973-1980
Two-armed poly(?-caprolactone) (TAPCL) polymers were successfully synthesized via the ring opening polymerization (ROP) of ?-caprolactone (?-CL) using the Schiff's base complexes [Cu(SAEE)2] (1) and [Ni(SAEE)2] (2), which have two hydroxyl functional groups, as the two-site initiators and tin(II) 2-ethylhexanoate (Sn(Oct)2) as the catalyst in bulk at 115 °C. The Schiff's base complexes (1 and 2) were synthesized by utilizing the concentrated template synthesis method starting from salicyl aldehyde, 2-(2-aminoethoxy) ethanol and related metal acetate salts. The synthesized TAPCL polymers were characterized by GPC, FTIR, UV–vis, and electron paramagnetic resonance (EPR). The molecular weights of TAPCL polymers linearly increased with increasing molar ratio of the monomer to the initiator. The results obtained from FTIR, UV–vis, and EPR studies indicated that TAPCL polymers had the Schiff's base complexes at the junction point of PCL arms. The crystallization behavior of TAPCL was studied by using differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). Thermal behavior of TAPCL was also investigated by thermogravimetrical analysis (TGA). 相似文献