全文获取类型
收费全文 | 6456篇 |
免费 | 418篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 58篇 |
综合类 | 10篇 |
化学工业 | 2825篇 |
金属工艺 | 78篇 |
机械仪表 | 86篇 |
建筑科学 | 263篇 |
矿业工程 | 35篇 |
能源动力 | 160篇 |
轻工业 | 1130篇 |
水利工程 | 41篇 |
石油天然气 | 35篇 |
无线电 | 261篇 |
一般工业技术 | 937篇 |
冶金工业 | 321篇 |
原子能技术 | 15篇 |
自动化技术 | 630篇 |
出版年
2024年 | 16篇 |
2023年 | 112篇 |
2022年 | 668篇 |
2021年 | 774篇 |
2020年 | 231篇 |
2019年 | 211篇 |
2018年 | 254篇 |
2017年 | 207篇 |
2016年 | 263篇 |
2015年 | 224篇 |
2014年 | 271篇 |
2013年 | 449篇 |
2012年 | 374篇 |
2011年 | 412篇 |
2010年 | 276篇 |
2009年 | 274篇 |
2008年 | 276篇 |
2007年 | 243篇 |
2006年 | 214篇 |
2005年 | 152篇 |
2004年 | 139篇 |
2003年 | 113篇 |
2002年 | 99篇 |
2001年 | 55篇 |
2000年 | 47篇 |
1999年 | 55篇 |
1998年 | 35篇 |
1997年 | 42篇 |
1996年 | 43篇 |
1995年 | 35篇 |
1994年 | 36篇 |
1993年 | 31篇 |
1992年 | 27篇 |
1991年 | 16篇 |
1990年 | 23篇 |
1989年 | 11篇 |
1988年 | 18篇 |
1987年 | 14篇 |
1986年 | 7篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 17篇 |
1982年 | 6篇 |
1981年 | 11篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1974年 | 4篇 |
1966年 | 5篇 |
排序方式: 共有6885条查询结果,搜索用时 15 毫秒
31.
Andreas Förner Jan Vollhüter Anna Krapf Abdullah Jamjoom Daniel Hausmann Benjamin Wahlmann Zongwen Fu Carolin Körner Steffen Neumeier Mathias Göken 《Advanced Engineering Materials》2023,25(15):2300407
By increasing the density of interfaces in NiAl–CrMo in situ composites, the mechanical properties can be significantly improved compared to conventionally cast material. The refined microstructure is achieved by manufacturing through electron beam powder bed fusion (PBF-EB). By varying the process parameters, an equiaxed or columnar cell morphology can be obtained, exhibiting a plate-like or an interconnected network of the (Cr,Mo) reinforcement phase which is embedded in a NiAl matrix. The microstructure of the different cell morphologies is investigated in detail using scanning electron microscope, transmission electron microscopy, and atom probe tomography. For both morphologies, the mechanical properties at elevated temperatures are analyzed by compression and creep experiments parallel and perpendicular to the building direction. In comparison to cast NiAl and NiAl–(Cr, Mo), the yield strength of the PBF-EB fabricated specimens is significantly improved at temperatures up to 1,027 °C. While the columnar morphology exhibits the best improved mechanical properties at high temperatures, the equiaxial morphology shows nearly ideal isotropic mechanical behavior, which is a substantial advantage over directionally solidified material. 相似文献
32.
Yeongin Kim Chenxin Zhu Wen-Ya Lee Anna Smith Haowen Ma Xiang Li Donghee Son Naoji Matsuhisa Jaemin Kim Won-Gyu Bae Sung Ho Cho Myung-Gil Kim Tadanori Kurosawa Toru Katsumata John W. F. To Jin Young Oh Seonghyun Paik Soo Jin Kim Lihua Jin Feng Yan Jeffrey B.-H. Tok Zhenan Bao 《Advanced materials (Deerfield Beach, Fla.)》2023,35(1):2203541
Hemispherical image sensors simplify lens designs, reduce optical aberrations, and improve image resolution for compact wide-field-of-view cameras. To achieve hemispherical image sensors, organic materials are promising candidates due to the following advantages: tunability of optoelectronic/spectral response and low-temperature low-cost processes. Here, a photolithographic process is developed to prepare a hemispherical image sensor array using organic thin film photomemory transistors with a density of 308 pixels per square centimeter. This design includes only one photomemory transistor as a single active pixel, in contrast to the conventional pixel architecture, consisting of select/readout/reset transistors and a photodiode. The organic photomemory transistor, comprising light-sensitive organic semiconductor and charge-trapping dielectric, is able to achieve a linear photoresponse (light intensity range, from 1 to 50 W m−2), along with a responsivity as high as 1.6 A W−1 (wavelength = 465 nm) for a dark current of 0.24 A m−2 (drain voltage = −1.5 V). These observed values represent the best responsivity for similar dark currents among all the reported hemispherical image sensor arrays to date. A transfer method was further developed that does not damage organic materials for hemispherical organic photomemory transistor arrays. These developed techniques are scalable and are amenable for other high-resolution 3D organic semiconductor devices. 相似文献
33.
The ageing of populations has been a topic of discussion during the last few decades, but how is this subject represented in the media, and what images of old age are produced? In this article we present the results of a quantitative content analysis that investigates how the concept of population ageing has been represented in Swedish local and national daily news press between 1988 and 2009, and the old age positions that are offered in these representations. We also use discourse analysis in order to qualitatively examine the ways in which the concept of population ageing is articulated in these news press articles and the old age positions that are thereby constituted. The results show that the concept is constituted as a naturalised expert concept, and is primarily used in order to contextualise articles about future political and economical difficulties or even crises. By articulating population ageing with both political policies, political economy and older people??s (as a group) reported need for care and services, population ageing was constituted as a political economic concern rather than a problem for the aged individual. 相似文献
34.
35.
In the area of product design, sensory dominance can be defined as the relative importance of different sensory modalities for product experience. It is often assumed that vision dominates the other senses. In the present study, we asked 243 participants to describe their experiences with consumer products in various situations: while buying a product, after the first week, the first month, and the first year of usage. The data suggest that the dominant sensory modality depends on the period of product usage. At the moment of buying, vision is the most important modality, but during the usage the other sensory modalities gain importance. The roles of the different modalities during usage are product-dependent. Averaged over 93 products analyzed in this study, after one month of usage touch becomes more important than vision, and after one year vision, touch and audition appear to be equally important. We conclude that to create a long-lasting positive product experience, designers need to consider user-product interaction at different stages of product usage and to determine which sensory modality dominates product experience at each stage. 相似文献
36.
Privacy policies for shared content in social network sites 总被引:1,自引:0,他引:1
Anna C. Squicciarini Mohamed Shehab Joshua Wede 《The VLDB Journal The International Journal on Very Large Data Bases》2010,19(6):777-796
Social networking is one of the major technological phenomena of the Web 2.0, with hundreds of millions of subscribed users.
Social networks enable a form of self-expression for users and help them to socialize and share content with other users.
In spite of the fact that content sharing represents one of the prominent features of existing Social network sites, they
do not provide any mechanisms for collective management of privacy settings for shared content. In this paper, using game
theory, we model the problem of collective enforcement of privacy policies on shared data. In particular, we propose a solution
that offers automated ways to share images based on an extended notion of content ownership. Building upon the Clarke-Tax
mechanism, we describe a simple mechanism that promotes truthfulness and that rewards users who promote co-ownership. Our
approach enables social network users to compose friendship based policies based on distances from an agreed upon central
user selected using several social networks metrics. We integrate our design with inference techniques that free the users
from the burden of manually selecting privacy preferences for each picture. To the best of our knowledge, this is the first
time such a privacy protection mechanism for social networking has been proposed. We also extend our mechanism so as to support
collective enforcement across multiple social network sites. In the paper, we also show a proof-of-concept application, which
we implemented in the context of Facebook, one of today’s most popular social networks. Through our implementation, we show
the feasibility of such approach and show that it can be implemented with a minimal increase in overhead to end-users. We
complete our analysis by conducting a user study to investigate users’ understanding of co-ownership, usefulness and understanding
of our approach. Users responded favorably to the approach, indicating a general understanding of co-ownership and the auction,
and found the approach to be both useful and fair. 相似文献
37.
O'Brien TM Ritz AM Raphael BJ Laidlaw DH 《IEEE transactions on visualization and computer graphics》2010,16(6):918-926
In this work we present, apply, and evaluate a novel, interactive visualization model for comparative analysis of structural variants and rearrangements in human and cancer genomes, with emphasis on data integration and uncertainty visualization. To support both global trend analysis and local feature detection, this model enables explorations continuously scaled from the high-level, complete genome perspective, down to the low-level, structural rearrangement view, while preserving global context at all times. We have implemented these techniques in Gremlin, a genomic rearrangement explorer with multi-scale, linked interactions, which we apply to four human cancer genome data sets for evaluation. Using an insight-based evaluation methodology, we compare Gremlin to Circos, the state-of-the-art in genomic rearrangement visualization, through a small user study with computational biologists working in rearrangement analysis. Results from user study evaluations demonstrate that this visualization model enables more total insights, more insights per minute, and more complex insights than the current state-of-the-art for visual analysis and exploration of genome rearrangements. 相似文献
38.
Within the framework of research that describes the processes of collaborative knowledge construction in computer-supported collaborative learning (CSCL) environments, the present work has three objectives: (i) the identification of the strategies of six small groups of university students for the elaboration of written products in a CSCL environment; (ii) seek relations between the identified writing strategies and the processes and phases of collaborative knowledge construction in the groups; and (iii) relate these strategies and phases with the learning results obtained by the groups. We carried out a multiple-case study, with the analysis of four different didactic sequences, in two different virtual learning and teaching settings. In each setting, three student groups were studied, where each had to collaboratively develop between four and eight written products. For all the studied groups, the analysis enabled the identification of five types of strategies in the preparation of the elaboration of written products, and four types of phases of collaborative knowledge construction, which are interrelated and also connected with the grades that the groups obtained in each case. 相似文献
39.
On the convective nature of the instability of a front undergoing a supercritical Turing bifurcation
Fronts are traveling waves in spatially extended systems that connect two different spatially homogeneous rest states. If the rest state behind the front undergoes a supercritical Turing instability, then the front will also destabilize. On the linear level, however, the front will be only convectively unstable since perturbations will be pushed away from the front as it propagates. In other words, perturbations may grow but they can do so only behind the front. It is of interest to show that this behavior carries over to the full nonlinear system. It has been successfully done in a case study by Ghazaryan and Sandstede [A. Ghazaryan, B. Sandstede, Nonlinear convective instability of Turing-unstable fronts near onset: a case study, SIAM J. Appl. Dyn. Syst. 6 (2007) 319–347]. In the present paper, analogous results are obtained for the same system as in Ghazaryan and Sandstede (2007), but for a different parameter regime. 相似文献
40.
The present study investigates the interaction of NO2 gas and μ-carbido-bridged iron phthalocyanine (PcFeCFePc) films obtained by Langmuir–Blodgett (LB) and spin-coating (SC) techniques. The phthalocyanine bridged dimer under study belongs to the polynuclear unsubstituted phthalocyanines class and presents poor solubility: in contrast the corresponding N-base bis-adducts are soluble enough in organic solvents to be deposited by Langmuir–Blodgett and spin-coating techniques. The reaction with NO2 is monitored by visible spectra variation that shows identical behaviour for both kinds of films, indicating that the chemical reaction between the gas and the films is independent of the deposition method. The electrical conductivity change as a function of time with NO2 is instead dissimilar: for spin-coated films it shows a behaviour already observed for sandwich-type phthalocyanine whereas for LB films it resembles that of monomeric phthalocyanine. Such a response implies that the charges (holes) generated in the oxidation/reduction process are carried differently through the material, and we attempt to explain this behaviour taking into account the two different structural and morphological features induced by the two techniques. 相似文献