首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   9807篇
  免费   123篇
  国内免费   3篇
电工技术   68篇
综合类   3篇
化学工业   820篇
金属工艺   118篇
机械仪表   122篇
建筑科学   181篇
矿业工程   12篇
能源动力   101篇
轻工业   530篇
水利工程   41篇
石油天然气   20篇
无线电   653篇
一般工业技术   795篇
冶金工业   5900篇
原子能技术   64篇
自动化技术   505篇
  2022年   27篇
  2021年   41篇
  2020年   45篇
  2019年   51篇
  2018年   56篇
  2017年   61篇
  2016年   76篇
  2015年   49篇
  2014年   63篇
  2013年   250篇
  2012年   108篇
  2011年   173篇
  2010年   123篇
  2009年   134篇
  2008年   157篇
  2007年   151篇
  2006年   136篇
  2005年   121篇
  2004年   157篇
  2003年   157篇
  2002年   125篇
  2001年   125篇
  2000年   113篇
  1999年   271篇
  1998年   1735篇
  1997年   1069篇
  1996年   661篇
  1995年   404篇
  1994年   367篇
  1993年   413篇
  1992年   126篇
  1991年   128篇
  1990年   148篇
  1989年   124篇
  1988年   140篇
  1987年   126篇
  1986年   121篇
  1985年   126篇
  1984年   65篇
  1983年   78篇
  1982年   92篇
  1981年   95篇
  1980年   93篇
  1979年   55篇
  1978年   58篇
  1977年   194篇
  1976年   382篇
  1975年   51篇
  1974年   43篇
  1973年   37篇
排序方式: 共有9933条查询结果,搜索用时 15 毫秒
1.
Currently there are design barriers inhibiting the implementation of high-precision digital signal processing (DSP) objects with field programmable logic (FPL) devices. This paper explores overcoming these barriers by fusing together the popular distributed arithmetic (DA) method with the residue number system (RNS) for use in FPL-centric designs. The new design paradigm is studied in the context of a high-performance filter bank and a discrete wavelet transform (DWT). The proposed design paradigm is facilitated by a new RNS accumulator structure based on a carry save adder (CSA). The reported methodology also introduces a polyphase filter structure that results in a reduced look-up table (LUT) budget. The 2C-DA and RNS-DA are compared, in the context of a FPL implementation strategy, using a discrete wavelet transform (DWT) filter bank as a common design theme. The results show that the RNS-DA, compared to a traditional 2C-DA design, enjoys a performance advantage that increases with precision (wordlength).  相似文献   
2.
The results presented in the literature, which attempt to elucidate the mechanisms by which triglyceride oils are bleached by earths, are reviewed. The impact of this work and how the mechanistic proposals affect changes in oil properties are considered, with particular emphasis on the needs of the palm oil processor. Important properties include color, metals and phosphorus content and oxidative stability of the oil. Investigations made in our own laboratories have been aimed at elucidating the effect of varying physical and chemical properties of the bleaching earth on the quality of bleached and deodorized oils. Techniques used in this work are pore-size distribution, surface area, scanning and transmission electron microscopy and a variety of chemical and X-ray analysis methods. The ability to vary such parameters in montmorillonite clays by alteration of process conditions to give materials with specific performance characteristics is demonstrated. Comparisons are made between acid-activated montmorillonites and other clay types.  相似文献   
3.
Power distribution systems have been significantly affected by many outage-causing events. Good fault cause identification can help expedite the restoration procedure and improve the system reliability. However, the data imbalance issue in many real-world data sets often degrades the fault cause identification performance. In this paper, the E-algorithm, which is extended from the fuzzy classification algorithm by Ishibuchi to alleviate the effect of imbalanced data constitution, is applied to Duke Energy outage data for distribution fault cause identification. Three major outage causes (tree, animal, and lightning) are used as prototypes. The performance of E-algorithm on real-world imbalanced data is compared with artificial neural network. The results show that the E-algorithm can greatly improve the performance when the data are imbalanced  相似文献   
4.
A novel, heat-resistant and Pronase-sensitive, inhibitor of eukaryotic DNA topoisomerase I has been purified from Xenopus laevis ovaries. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the most purified fraction revealed three bands with apparent molecular masses of 25, 28.5, and 33.5 kDa. The 25- and 33.5-kDa peptides recovered from an SDS-PAGE gel inhibited X. laevis DNA topoisomerase I. The purified inhibitor was specific to DNA topoisomerase I and did not inhibit other DNA enzymes tested. The inhibitor blocked the catalytic activity of DNA topoisomerase I by interacting with the enzyme, rather than by competing for binding sites on substrate DNA. Binding of DNA topoisomerase I to substrate DNA was blocked by the inhibitor, as was the cleavage reaction catalyzed by DNA topoisomerase I. Inhibition of DNA topoisomerase I was relieved by divalent cations Ca2+, Mg2+, or Mn2+.  相似文献   
5.
α,β‐Unsaturated nitriles have been synthesized by Knoevenagel condensation of a carbonylic compound with malononitrile, assisted by sonochemical irradiation. Two alkaline‐promoted clays (Li+‐ and Cs+‐exchanged saponites) have been employed as catalysts. The influence of the carbonylic compound (benzaldehyde or cyclohexanone) and the use of a solvent on the catalytic activity have been studied. Remarkable increase in the conversion values has been found when the reaction is activated by ultrasound, as compared with the thermal activation. In this green, solvent‐free procedure, α,β‐unsaturated nitriles have been produced in very high yields (97%) when the Cs+‐saponite is used as catalyst. Copyright © 2004 Society of Chemical Industry  相似文献   
6.
7.
8.
9.
10.
The design and evaluation of an optically triggered, fully integrated sample and hold circuit (OS/H) is described. Measured results are presented that demonstrate operation of this circuit at 250 Ms/s and with effective resolution approaching 8 bits. The integrated circuit, which measures 2.1 mm×1.4 mm, is realized in -1.0-V threshold, 20-GHz ft GaAs MESFET technology, consumes approximately 200 mW of power, and requires one optical address. The OS/H will find applications in high precision, hybrid, and integrated signal processing systems where high speed, high levels of parallelism, and low timing jitter are important. Measured results of a series photoconducting (Auston switch) OS/H realized in the same technology are presented for comparison purposes  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号