全文获取类型
收费全文 | 81426篇 |
免费 | 9501篇 |
国内免费 | 5900篇 |
专业分类
电工技术 | 6374篇 |
综合类 | 7692篇 |
化学工业 | 12731篇 |
金属工艺 | 8249篇 |
机械仪表 | 7023篇 |
建筑科学 | 9031篇 |
矿业工程 | 2704篇 |
能源动力 | 4669篇 |
轻工业 | 2449篇 |
水利工程 | 2523篇 |
石油天然气 | 2526篇 |
武器工业 | 1479篇 |
无线电 | 7999篇 |
一般工业技术 | 11170篇 |
冶金工业 | 3110篇 |
原子能技术 | 954篇 |
自动化技术 | 6144篇 |
出版年
2024年 | 368篇 |
2023年 | 1378篇 |
2022年 | 2193篇 |
2021年 | 2787篇 |
2020年 | 3030篇 |
2019年 | 2578篇 |
2018年 | 2494篇 |
2017年 | 3174篇 |
2016年 | 3372篇 |
2015年 | 3486篇 |
2014年 | 4907篇 |
2013年 | 5198篇 |
2012年 | 5923篇 |
2011年 | 6162篇 |
2010年 | 4528篇 |
2009年 | 4734篇 |
2008年 | 4276篇 |
2007年 | 5398篇 |
2006年 | 5040篇 |
2005年 | 3955篇 |
2004年 | 3343篇 |
2003年 | 2897篇 |
2002年 | 2513篇 |
2001年 | 2186篇 |
2000年 | 1964篇 |
1999年 | 1548篇 |
1998年 | 1248篇 |
1997年 | 1144篇 |
1996年 | 905篇 |
1995年 | 748篇 |
1994年 | 615篇 |
1993年 | 472篇 |
1992年 | 431篇 |
1991年 | 357篇 |
1990年 | 318篇 |
1989年 | 282篇 |
1988年 | 209篇 |
1987年 | 109篇 |
1986年 | 88篇 |
1985年 | 89篇 |
1984年 | 83篇 |
1983年 | 61篇 |
1982年 | 66篇 |
1981年 | 41篇 |
1980年 | 32篇 |
1979年 | 20篇 |
1977年 | 12篇 |
1975年 | 6篇 |
1959年 | 13篇 |
1951年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
The evaluation of the volumetric accuracy of a machine tool is an open challenge in the industry, and a wide variety of technical solutions are available in the market and at research level. All solutions have advantages and disadvantages concerning which errors can be measured, the achievable uncertainty, the ease of implementation, possibility of machine integration and automation, the equipment cost and the machine occupation time, and it is not always straightforward which option to choose for each application. The need to ensure accuracy during the whole lifetime of the machine and the availability of monitoring systems developed following the Industry 4.0 trend are pushing the development of measurement systems that can be integrated in the machine to perform semi-automatic verification procedures that can be performed frequently by the machine user to monitor the condition of the machine. Calibrated artefact based calibration and verification solutions have an advantage in this field over laser based solutions in terms of cost and feasibility of machine integration, but they need to be optimized for each machine and customer requirements to achieve the required calibration uncertainty and minimize machine occupation time.This paper introduces a digital twin-based methodology to simulate all relevant effects in an artefact-based machine tool calibration procedure, from the machine itself with its expected error ranges, to the artefact geometry and uncertainty, artefact positions in the workspace, probe uncertainty, compensation model, etc. By parameterizing all relevant variables in the design of the calibration procedure, this simulation methodology can be used to analyse the effect of each design variable on the error mapping uncertainty, which is of great help in adapting the procedure to each specific machine and user requirements. The simulation methodology and the analysis possibilities are illustrated by applying it on a 3-axis milling machine tool. 相似文献
2.
Brian Lawn David Marshall Rishi Raj Greg Hirth Trevor Page Julie Yeomans 《Journal of the American Ceramic Society》2021,104(1):23-26
Crystalline quartz has long been identified as among the weakest of abundant crustal minerals. This weakness is particularly evident around the α–β phase inversion at 573°C, in which Si–O bonds undergo a displacive structural transformation from trigonal to hexagonal symmetry. Here we present data using indentation testing methodologies that highlight the precipitous extent of the transformational weakening. Although the indentations are localized over relatively small specimen contact areas, the data quantify the essential deformation and fracture properties of quartz in a predominantly (but not exclusively) compressive stress field, at temperatures and pressures pertinent to conditions in the earth's crust. 相似文献
3.
《Ceramics International》2022,48(20):29959-29966
High-purity SiC ceramic devices are applied in semiconductor industry owing to their outstanding properties. Nevertheless, it is difficult to densify SiC ceramics without any sintering additive even by HP sintering. In this work, high-purity and dense SiC ceramics were fabricated by HP sintering with very low amounts of sintering aids. Residual B content was only 556 ppm and relative density was more than 99.5%. Furthermore, thermal conductivity of as-prepared SiC ceramics was improved from 155 W m?1 K?1 to 167 W m?1 K?1 by increasing holding time and their plasma corrosion resistance was promoted in the meantime. The as-prepared high-purity SiC ceramics have broad application prospects in the field of semiconductor industry. 相似文献
4.
5.
A new method for the polygonal approximation is presented. The method is based on the search for break points through a context-free grammar, that accepts digital straight segments with loss of information, as well as the decrease in the error committed employing the comparison of a tolerable error. We present an application of our method to different sets of objects widely used, as well as a comparison of our results with the best results reported in the literature, proving that our method achieves better values of error criteria. Besides, a new way to find polygonal approximations, with context-free grammars to recognize digital straight segments without loss of pixels, it is also addressed. 相似文献
6.
Yujie Chen Yiping Song Zhen Zhang Yali Chen Qiliang Deng Shuo Wang 《Advanced functional materials》2021,31(41):2104885
Various products, including foods and pharmaceuticals, are sensitive to temperature fluctuations. Thus, temperature monitoring during production, transportation, and storage is critical. Facile indicators are required to monitor temperature conditions via color changes in real time. This study aimed to prepare and apply thiol-functionalized covalent organic frameworks (COFs) as a novel indicator for monitoring thermal history and temperature abuse. The COFs underwent obvious color changes from bright yellow to purple after exposure to different temperatures for varying durations. The reaction kinetics are analyzed under isothermal conditions, which reveal that the order of reaction rates is k−20°C < k4°C < k20°C < k35°C < k55°C. The activation energy (Ea) of the COFs is calculated using the Arrhenius equation as 50.71 kJ moL−1. The COFs are capable of sensitive color changes and offer a broad temperature tracking range, thereby demonstrating their application potential for the monitoring of temperature and time exposure history during production, transportation, and storage. This excellent performance thermal history indicator also shows promise for expanding the application field of COFs. 相似文献
7.
Face aging (FA) for young faces refers to rendering the aging faces at target age for an individual, generally under 20s, which is an important topic of facial age analysis. Unlike traditional FA for adults, it is challenging to age children with one deep learning-based FA network, since there are deformations of facial shapes and variations of textural details. To alleviate the deficiency, a unified FA framework for young faces is proposed, which consists of two decoupled networks to apply aging image translation. It explicitly models transformations of geometry and appearance using two components: GD-GAN, which simulates the Geometric Deformation using Generative Adversarial Network; TV-GAN, which simulates the Textural Variations guided by the age-related saliency map. Extensive experiments demonstrate that our method has advantages over the state-of-the-art methods in terms of synthesizing visually plausible images for young faces, as well as preserving the personalized features. 相似文献
8.
Xiao-Mei Sha Li-Jun Zhang Wen-Mei Chen Guang-Yao Wang Jin-Lin Li Zi-Zi Hu Zong-Cai Tu 《International Journal of Food Science & Technology》2022,57(3):1573-1586
Thermal action in extraction process had effects on characteristic tryptic peptides identification and gelling properties of porcine gelatin. SDS-PAGE, HPLC-LTQ/Orbitrap high-resolution mass spectrometry, texture analyser and rheometer were used to evaluate collagen depolymerisation degree, characteristic tryptic peptides and gelling properties of gelatins prepared in various thermal actions. Results showed that with increasing temperature and time, depolymerisation degree enlarged, while gel strength, gelling and melting temperature decreased. Mass spectra showed that 47 and 49 common characteristic tryptic peptides were identified in gelatins extracted at 50 °C and 100 °C with various times, respectively. Moreover, 34 common characteristic tryptic peptides were identified in all gelatin samples. Further comparison between this work and our previous investigations yielded 20 common characteristic tryptic peptides, which stably exist in various thermal actions. These common characteristic tryptic peptides may be very helpful for the accurate authentication of porcine gelatin. 相似文献
9.
10.