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   6568篇
  免费   211篇
  国内免费   8篇
电工技术   157篇
综合类   14篇
化学工业   1548篇
金属工艺   138篇
机械仪表   149篇
建筑科学   483篇
矿业工程   11篇
能源动力   147篇
轻工业   820篇
水利工程   38篇
石油天然气   13篇
无线电   436篇
一般工业技术   1076篇
冶金工业   905篇
原子能技术   65篇
自动化技术   787篇
  2022年   52篇
  2021年   82篇
  2020年   79篇
  2019年   67篇
  2018年   77篇
  2017年   98篇
  2016年   130篇
  2015年   148篇
  2014年   175篇
  2013年   285篇
  2012年   245篇
  2011年   278篇
  2010年   233篇
  2009年   262篇
  2008年   257篇
  2007年   282篇
  2006年   220篇
  2005年   228篇
  2004年   224篇
  2003年   153篇
  2002年   170篇
  2001年   145篇
  2000年   122篇
  1999年   105篇
  1998年   175篇
  1997年   146篇
  1996年   130篇
  1995年   105篇
  1994年   92篇
  1993年   99篇
  1992年   92篇
  1991年   63篇
  1990年   70篇
  1989年   68篇
  1988年   50篇
  1987年   74篇
  1986年   60篇
  1985年   78篇
  1984年   68篇
  1983年   68篇
  1982年   70篇
  1981年   78篇
  1980年   72篇
  1979年   74篇
  1978年   56篇
  1977年   63篇
  1976年   69篇
  1975年   56篇
  1974年   69篇
  1973年   52篇
排序方式: 共有6787条查询结果,搜索用时 15 毫秒
51.
This paper deals with the design of an algorithmic switched-capacitor analog-to-digital converter (ADC), operating with a single reference voltage, a single-ended amplifier, a single-ended comparator, and presenting a small input capacitance. The ADC requires two clock phases per conversion bit and N clock cycles to resolve the N-bits. The ADC achieves a measured peak signal-to-noise-ratio (SNR) of 49.9 dB and a peak signal-to-noise-and-distortion-ratio (SNDR) of 46.7 dB at Pin = ?6dBFS with a sampling rate of 0.25 MS/s. The measured differential-non-linearity and integral-non-linearity are within +0.6/?0.5 and +0.2/?0.5 LSB, respectively. The ADC power consumption is 300 μW and it is implemented in 90 nm CMOS technology with a single power supply of 1.2 V. The ADC saves power at system-level by requiring only a single reference voltage. At system level, this solution is therefore not only robust but competitive as well.  相似文献   
52.
车载网络让汽车驶上安全、舒适、环保的快车道   总被引:1,自引:0,他引:1  
车载网络(IVN)正悄然掀起一场汽车技术革命.过去二十年来,车载网络的应用淘汰了曾用来控制电路的笨拙线束,提高了汽车的安全性和可靠性,并实现了刹车防抱系统、安全气囊、引擎控制、传输控制和电动转向等多种舒适而方便的功能.  相似文献   
53.
The nucleotide sequence of a 26·7 kb DNA segment from the left arm of Saccharomyces cerevisiae chromosome IV is presented. An analysis of this segment revealed 11 open reading frames (ORFs) longer than 300 bp and one split gene. These ORFs include the genes encoding the large subunit of RNA polymerase II, the biotin apo-protein ligase, an ADP-ribosylation factor (ARF 2), the ‘L35’-ribosomal protein, a rho GDP dissociation factor, and the sequence encoding the protein phosphatase 2A. Further sequence analysis revealed a short ORF encoding the ribosomal protein YL41B, an intron in a 5′ untranslated region and an extended homology with another cosmid (X83276) located on the same chromosome. The potential biological relevance of these findings is discussed. The sequence was submitted to the EMBL database under Accession Number X96876.  相似文献   
54.
In this paper, we analyze the performance of cognitive amplify‐and‐forward (AF) relay networks with beamforming under the peak interference power constraint of the primary user (PU). We focus on the scenario that beamforming is applied at the multi‐antenna secondary transmitter and receiver. Also, the secondary relay network operates in channel state information‐assisted AF mode, and the signals undergo independent Nakagami‐m fading. In particular, closed‐form expressions for the outage probability and symbol error rate (SER) of the considered network over Nakagami‐m fading are presented. More importantly, asymptotic closed‐form expressions for the outage probability and SER are derived. These tractable closed‐form expressions for the network performance readily enable us to evaluate and examine the impact of network parameters on the system performance. Specifically, the impact of the number of antennas, the fading severity parameters, the channel mean powers, and the peak interference power is addressed. The asymptotic analysis manifests that the peak interference power constraint imposed on the secondary relay network has no effect on the diversity gain. However, the coding gain is affected by the fading parameters of the links from the primary receiver to the secondary relay network. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
55.
CERN's Large Hadron Collider (LHC) requires 48 twin aperture resistive quadrupoles in the beam cleaning insertions. Canada is contributing these magnets to CERN in the framework of the TRIUMF-LHC collaboration contracts. A pre-series magnet was produced by Canadian industry and delivered in March 2001. This magnet incorporates important design changes that resulted from experience with a prototype magnet. The construction of this pre-series magnet and the measurements made at ALSTOM and at CERN are reported. A comparison is made between high precision pole distance measurements and the magnetic measurements performed with a rotating coil mole. Conclusions for series production and possibilities for multipole corrections are outlined.  相似文献   
56.
The eutectic coarsening kinetics for 60Sn40Pb solder joints annealed at 50°C to 150° C was determined to be of the form
[`(D)]n - [`(D)]on = Ko exp( - Q/RT)t\bar D^n - \bar D_o^n = K_o \exp ( - Q/RT)t  相似文献   
57.
We propose an algorithm for 3-D multiview deblurring using spatially variant point spread functions (PSFs). The algorithm is applied to multiview reconstruction of volumetric microscopy images. It includes registration and estimation of the PSFs using irregularly placed point markers (beads). We formulate multiview deblurring as an energy minimization problem subject to L1-regularization. Optimization is based on the regularized Lucy-Richardson algorithm, which we extend to deal with our more general model. The model parameters are chosen in a profound way by optimizing them on a realistic training set. We quantitatively and qualitatively compare with existing methods and show that our method provides better signal-to-noise ratio and increases the resolution of the reconstructed images.  相似文献   
58.
r  × t × l) of the same origin were acetylated separately, but under the same conditions in the microwave reactor. The variation in acetyl content both within and between the samples was less than 2% units. In general, a somewhat higher acetyl content was obtained in the middle of the acetylated wood than in the outer part of it. Microwave energy was also shown to be efficient in the removal of excess acetic anhydride and by-product acetic acid by evaporation under vacuum. During the vacuum step, about 70% of the chemicals could be removed within the first 30 minutes. Pine and spruce wood samples acetylated for 2 hours at 130 °C followed by a vacuum step for two hours at 120 °C, obtained an acetyl content of about 17% and the content of residual chemicals was about 3% calculated on a basis of dry acetylated wood. The temperature in the wood samples could be maintained at about 130 °C even at very low contents of residual excess chemicals without any formation of hot spots.
r  × t × l) vom gleichen Ursprung nacheinander und unter gleichen Bedingungen acetyliert wurden. Die Variation des Acetylgehaltes lag sowohl innerhalb der einzelnen Proben, als auch zwischen den Proben unterhalb 2%. Allgemein war der acetylgehalt im Probeninneren etwas h?her, als in den ?u?eren Bereichen. Die Mikrowellenbestrahlung erlaubte zudem eine effektive Entfernung des überschüssigen Acetanhydrids und anderer Nebenprodukte durch Vakuumverdampfung. Unter Vakuum konnten ca. 70% der Chemikalien innerhalb von 30 min. entfernt werden. Keifern- und Fichtenholz enthielt nach 2-stündiger Acetylierung bei 130 °C und 2-stündiger Vakuumbehandlung bei 120 °C einen Acetylgehalt von 17%. Der Gehalt an restlichen Chemikalien betrug 3%, bezogen auf trockenes, acetyliertes Holz. Die Temperatur in den Holzproben konnte bei 130 °C gehalten werden, ohne Ausbildung von hei?en Zonen, auch wenn nur geringe überschüsse von Reaktionsmitteln verwendet wurden.
  相似文献   
59.
Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.  相似文献   
60.
Game theory is a branch of mathematics aimed at the modeling and understanding of resource conflict problems. Essentially, the theory splits into two branches: noncooperative and cooperative game theory. The distinction between the two is whether or not the players in the game can make joint decisions regarding the choice of strategy. Noncooperative game theory is closely connected to minimax optimization and typically results in the study of various equilibria, most notably the Nash equilibrium. Cooperative game theory examines how strictly rational (selfish) actors can benefit from voluntary cooperation by reaching bargaining agreements. Another distinction is between static and dynamic game theory, where the latter can be viewed as a combination of game theory and optimal control. In general, the theory provides a structured approach to many important problems arising in signal processing and communications, notably resource allocation and robust transceiver optimization. Recent applications also occur in other emerging fields, such as cognitive radio, spectrum sharing, and in multihop-sensor and adhoc networks.  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