全文获取类型
收费全文 | 117609篇 |
免费 | 3280篇 |
国内免费 | 1391篇 |
专业分类
电工技术 | 2240篇 |
技术理论 | 4篇 |
综合类 | 3851篇 |
化学工业 | 17255篇 |
金属工艺 | 6268篇 |
机械仪表 | 4620篇 |
建筑科学 | 3831篇 |
矿业工程 | 1314篇 |
能源动力 | 2286篇 |
轻工业 | 5766篇 |
水利工程 | 1700篇 |
石油天然气 | 1349篇 |
武器工业 | 146篇 |
无线电 | 14498篇 |
一般工业技术 | 21166篇 |
冶金工业 | 5311篇 |
原子能技术 | 640篇 |
自动化技术 | 30035篇 |
出版年
2024年 | 105篇 |
2023年 | 449篇 |
2022年 | 864篇 |
2021年 | 1195篇 |
2020年 | 929篇 |
2019年 | 802篇 |
2018年 | 15197篇 |
2017年 | 14176篇 |
2016年 | 10727篇 |
2015年 | 1659篇 |
2014年 | 1631篇 |
2013年 | 2297篇 |
2012年 | 5071篇 |
2011年 | 11580篇 |
2010年 | 10004篇 |
2009年 | 7346篇 |
2008年 | 8592篇 |
2007年 | 9419篇 |
2006年 | 1671篇 |
2005年 | 2435篇 |
2004年 | 2215篇 |
2003年 | 2335篇 |
2002年 | 1925篇 |
2001年 | 1270篇 |
2000年 | 989篇 |
1999年 | 763篇 |
1998年 | 1026篇 |
1997年 | 716篇 |
1996年 | 618篇 |
1995年 | 482篇 |
1994年 | 399篇 |
1993年 | 340篇 |
1992年 | 258篇 |
1991年 | 243篇 |
1990年 | 225篇 |
1989年 | 199篇 |
1988年 | 179篇 |
1987年 | 153篇 |
1986年 | 129篇 |
1985年 | 127篇 |
1984年 | 110篇 |
1983年 | 75篇 |
1982年 | 70篇 |
1981年 | 59篇 |
1980年 | 81篇 |
1978年 | 60篇 |
1977年 | 58篇 |
1976年 | 76篇 |
1955年 | 71篇 |
1954年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
111.
112.
In this paper, we argue that successful integration of knowledge across work domains in the short-term can mask the generation of long-term consequences. We explore a setting, the introduction of environmental considerations into semiconductor manufacturing, where the eventual adoption of common measurement artifacts and associated practices enabled knowledge integration, but failed to address significant underlying consequences. Drawing from observational, interview, and archival data we develop an understanding of the work practices of the Tech and EnviroTech groups as structured by the material world and broader collective conventions. We introduce the concept of knowledge regime to outline the differences in knowledge across these work domains. More specifically, we find that differences in the causal specificity and developmental time horizon of knowledge and the measurement artifacts that result contribute to the relative power of one knowledge regime over another. Understanding these sources of incompatibility provides insight into the design requirements of information systems as boundary objects for knowledge integration, but also specifies the potential limits to any design effort. 相似文献
113.
Yi‐Hung Chen Ching‐Yuan Chang Wei‐Ling Su Chun‐Yu Chiu Yue‐Hwa Yu Pen‐Chi Chiang Chiung‐Fen Chang Je‐Lueng Shie Chyow‐San Chiou Sally IM Chiang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(1):68-75
This study investigates the ozonation of CI Reactive Black 5 (RB5) by using the rotating packed bed (RPB) and completely stirred tank reactor (CSTR) as ozone contactors. The RPB, which provides high gravitational force by adjusting the rotational speed, was employed as a novel ozone contactor. The same ozone dosage was separately introduced into either the RPB or the CSTR for the investigation, while the experimental solution was continuously circulated within the apparatus consisting of the RPB and CSTR. The decolorization and mineralization efficiencies of RB5 in the course of ozonation are compared for these two methods. Moreover, the dissolved and off‐gas ozone concentrations were simultaneously monitored for the further analysis. As a result, the ozone mass transfer rate per unit volume of the RPB was significantly higher because of its higher mass transfer coefficient and gas–liquid concentration driving force. Furthermore, ozonation kinetics was found to be independent of the gravitational magnitude of an ozone gas–liquid contactor. Therefore, the results suggest employing RPBs as ozone‐contacting devices with the advantage of volume reduction. The experimental results, which can be used for further modeling of the ozonation process in the RPB, also show the requirement of correct design for the RPB. Consequently, the present study is useful for the understanding of practical application of RPBs. Copyright © 2004 Society of Chemical Industry 相似文献
114.
115.
116.
117.
Understanding consumer behaviour is of vital importance to consumer-oriented e-business models today. In this paper, we study the relationships between consumer perceptions of risk and trust and the attitude towards purchasing at a consumer-to-consumer electronic marketplace (EM). Typical for EM settings is that consumer behaviour is subject to perceptions of the selling party as well as of the institutional structures of the intermediary that is operating the EM. Building upon the well-established literature of trust, we consider the concepts of intermediary trust and seller trust. We extend this categorisation by introducing the concepts of intermediary risk and seller risk. We developed measurement instruments for intermediary risk and seller risk. All measurement scales have acceptable alphas and are unidimensional. An empirical study is conducted to explore the relationships between the risk and trust types and consumer purchase attitude. The results reveal significant, direct effects of seller trust and seller risk. Second-order effects of intermediary trust and intermediary risk are investigated and reported. The paper concludes with general observations and recommendations for research and practice. 相似文献
118.
Let Ψ be any adaptive sampling algorithm that can run in real time on a tapeless multichannel electrocardiogram (ECG) Holter system. Simple methods which can significantly improve Ψ's fidelity are described and their results are compared in this paper. It is shown that by adding some simple tests to Ψ, the signals reconstructed by Ψ can be improved as much as 5.45 dB. It is also shown that under the same data rate, a good data compressor with slowly sampled input ECG is preferable to a bad data compressor with highly sampled input ECG 相似文献
119.
Jenghwa Chang Graber H.L. Ping Chen Koo Aronson R. Barbour S.-L.S. Barbour R.L. 《IEEE transactions on medical imaging》1997,16(1):68-77
Presents a model suitable for computing images of absorption cross sections of thick tissue structures illuminated at near infrared (NIR) wavelengths from tomographic projection data. Image reconstruction is accomplished by solving a system of linear equations derived from transport theory. Reconstruction results using different algebraic solvers are shown for anatomical maps of the breast, derived from magnetic resonance imaging data, containing two simulated pathologies, in which case qualitatively good reconstructions were obtained. Evaluation of magnetic resonance (MR) data to optimize NIR optical tomographic imaging methods and to assess the feasibility of a combined MR-optical measurement scheme is discussed 相似文献
120.
Wen-Chau Liu Lih-Wen Laih Shiou-Ying Cheng Wen-Lung Chang Wei-Chou Wang Jing-Yuh Chen Po-Hung Lin 《Electron Devices, IEEE Transactions on》1998,45(2):373-379
In this paper, a new multiple negative-differential-resistance (MNDR) device based on a metal-insulator-semiconductor-insulator-metal (MISIM)-like structure with step-compositional InxGa1-x As quantum wells has been fabricated and demonstrated. The interesting MNDR phenomena are found in the current-voltage (I-V) characteristics of this device. At room temperature, the triple switching behaviours and quadruple stable operation states are obtained. In addition, the sixfold switching behaviors and a staircase-shaped I-V characteristic are observed at -105°C. A sequential carrier accumulation at InGaAs subwells and the potential lowering process are used to qualitatively explain the interesting MNDR phenomena. From the experimental results, it is shown that the studied device has good potential in multiple-valued logic applications 相似文献