全文获取类型
收费全文 | 7111篇 |
免费 | 1028篇 |
国内免费 | 433篇 |
学科分类
工业技术 | 8572篇 |
出版年
2024年 | 53篇 |
2023年 | 228篇 |
2022年 | 418篇 |
2021年 | 561篇 |
2020年 | 440篇 |
2019年 | 300篇 |
2018年 | 282篇 |
2017年 | 298篇 |
2016年 | 302篇 |
2015年 | 401篇 |
2014年 | 503篇 |
2013年 | 496篇 |
2012年 | 523篇 |
2011年 | 526篇 |
2010年 | 446篇 |
2009年 | 409篇 |
2008年 | 437篇 |
2007年 | 366篇 |
2006年 | 279篇 |
2005年 | 238篇 |
2004年 | 163篇 |
2003年 | 131篇 |
2002年 | 115篇 |
2001年 | 96篇 |
2000年 | 91篇 |
1999年 | 78篇 |
1998年 | 61篇 |
1997年 | 77篇 |
1996年 | 55篇 |
1995年 | 45篇 |
1994年 | 41篇 |
1993年 | 17篇 |
1992年 | 18篇 |
1991年 | 17篇 |
1990年 | 15篇 |
1989年 | 4篇 |
1988年 | 5篇 |
1987年 | 2篇 |
1985年 | 2篇 |
1984年 | 4篇 |
1983年 | 3篇 |
1981年 | 1篇 |
1980年 | 12篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1976年 | 2篇 |
1973年 | 1篇 |
1965年 | 1篇 |
1959年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有8572条查询结果,搜索用时 62 毫秒
21.
Chai-Chin Lin Chih-Ming Chen Jenn-Hwan Tarng Hsueh-Ming Hang Hsiao-Cheng Yu 《Broadcasting, IEEE Transactions on》2002,48(1):38-43
Field tests of the transmission performance of the ATSC DTV system have been conducted in Taiwan. The test results as well as comparisons against the NTSC system performance are reported and analyzed. From the measured results the reception characteristics of the DTV can be deduced and can provide guidelines for television stations to design the transmission system, schedule equipment deployment, plan service coverage areas, and improve the reception quality of the digital signal 相似文献
22.
23.
Microwave plasma synthesis of TiN and ZrN nanopowders 总被引:2,自引:0,他引:2
This work demonstrates that TiN and ZrN nanopowders can be prepared by microwave plasma synthesis method. The effects of flow rate of plasma forming gas, flow rate of carrier gas and feeding rate of precursor raw material to the average particle size were studied. The TiN and ZrN nanopowders were characterized by means of transmission electron microscopy (TEM) and X-ray diffraction (XRD). 相似文献
24.
In recent years, the Asia-Pacific region has experienced several financial setbacks, including speculative attacks in 1998 and the SARS outbreak in 2003. Financial stresses of this nature are unanticipated, and not all of the dangers can be predicted by the examination of market information and macroeconomic indicators. The Early Warning System (EWS) that has been adopted by the International Monetary Fund may not be able to predict future financial crises for all possible scenarios, because shocks come in many different forms. To supplement the EWS, this paper proposes a data mining framework to measure the resilience of an economy. The resilience framework does not predict a crisis, but rather assesses the current state of health of an economy and its ability to withstand a financial shock should one occur. The framework is based on a feedback system consisting of two stages. The first stage assigns a resilience score to each economy based on a fuzzy logic scoring scheme that is built on the ambiguous reasoning of experts. The second stage uses the classification tree approach to estimate thresholds for each economic indicator, and examines the quality of the fuzzy score. The result from the second stage is then passed back to the first stage as feedback. The final result is obtained when the feedback system reaches its equilibrium state. The proposed resilience framework is applied to the external-sector and the public-sector economies of several countries to illustrate its applicability. 相似文献
25.
26.
环氧油一步合成的反应机理和动力学研究 总被引:11,自引:0,他引:11
杭晓敏 《化学反应工程与工艺》1996,12(1):1-8
研究了环氧油一步合成的反应机理和动力学;结合实验结果和理论分析动力学模型,首次提出:在适当的反应条件下,油脂的一步环氧化反应动力学模型可以表示为过氧酸生成反应动力学模型;其实验动力学模型方程为:r0=k[H2O2](0.99)[HOAc](0.97),其中k与催化剂用量有关。 相似文献
27.
28.
29.
C.C. Hang 《Asian journal of control》2004,6(4):539-544
This paper revisits the effort over the last decade in making undergraduate control education more useful and attractive to both the control engineers and the engineers at large. With the help of further coverage in new textbooks, more practical and synthesis contents in the control courses have been incorporated. Gaps still exist, particularly in the areas of PID control and auto‐tuning, fuzzy control, overall control strategy, control structure and systems thinking, and these will be elaborated. A major challenge is in the coverage of more practical and synthesis contents in the introductory common control course for all engineers. How this may be resolved is discussed. Finally, the need for new teaching approaches such as the use of interesting case studies and the use of problem‐based learning will be outlined. 相似文献
30.
The notion of pseudorandomness is the theoretical foundation on which to consider the soundness of a basic structure used in some block ciphers. We examine the pseudorandomness of the block cipher KASUMI, which will be used in the next‐generation cellular phones. First, we prove that the four‐round unbalanced MISTY‐type transformation is pseudorandom in order to illustrate the pseudorandomness of the inside round function FI of KASUMI under an adaptive distinguisher model. Second, we show that the three‐round KASUMI‐like structure is not pseudorandom but the four‐round KASUMI‐like structure is pseudorandom under a non‐adaptive distinguisher model. 相似文献