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   1318篇
  免费   25篇
  国内免费   2篇
电工技术   113篇
综合类   3篇
化学工业   195篇
金属工艺   35篇
机械仪表   26篇
建筑科学   22篇
能源动力   31篇
轻工业   109篇
水利工程   1篇
石油天然气   6篇
无线电   151篇
一般工业技术   188篇
冶金工业   310篇
原子能技术   25篇
自动化技术   130篇
  2023年   6篇
  2022年   10篇
  2021年   20篇
  2020年   5篇
  2019年   8篇
  2018年   18篇
  2017年   11篇
  2016年   22篇
  2015年   10篇
  2014年   30篇
  2013年   57篇
  2012年   47篇
  2011年   43篇
  2010年   51篇
  2009年   36篇
  2008年   51篇
  2007年   41篇
  2006年   40篇
  2005年   46篇
  2004年   38篇
  2003年   39篇
  2002年   23篇
  2001年   30篇
  2000年   31篇
  1999年   45篇
  1998年   125篇
  1997年   79篇
  1996年   38篇
  1995年   49篇
  1994年   33篇
  1993年   24篇
  1992年   13篇
  1991年   16篇
  1990年   8篇
  1989年   22篇
  1988年   15篇
  1987年   9篇
  1986年   14篇
  1985年   12篇
  1984年   14篇
  1983年   16篇
  1982年   14篇
  1981年   9篇
  1980年   16篇
  1979年   8篇
  1978年   8篇
  1977年   9篇
  1976年   13篇
  1974年   5篇
  1970年   4篇
排序方式: 共有1345条查询结果,搜索用时 15 毫秒
61.
Distribution centers, which are essential to our society, are becoming increasingly important. Although the efficiency of an AVS/RS (Autonomous vehicle storage and retrieval system) makes it a promising system, there is still much to be studied regarding its effective use and design. This paper proposes a method of designing AVS/RSs through a quantitative consideration of group constraint by utilizing probability theory. The proposed algorithm also deals with the problem of designing the sizes of several buffers, and considers the effect of load fluctuations, which are important for real-world operation, by use of queuing network theory. Effectiveness of the proposed algorithm is shown with simulations of various number of groups, those of various safety factors for fluctuations, and those of various evasion rates for buffer overflow. The design results are shown to be much different from those which do not consider those factors. The results prove that the proposed method provides an accurate quantitative assessment of the AVS/RS’s constraints.  相似文献   
62.
The authors examined the association of anxiety, depressive symptoms, and their co-occurrence on cognitive processes in 102 community-dwelling older adults. Participants completed anxiety and depression questionnaires as well as measures of episodic and semantic memory, word fluency, processing speed/shifting attention, and inhibition. Participants with only increased anxiety had poorer processing speed/shifting attention and inhibition, but depressive symptoms alone were not associated with any cognitive deficits. Although coexisting anxiety and depressive symptoms were associated with deficits in 3 cognitive domains, reductions in inhibition were solely attributed to anxiety. Findings suggest an excess cognitive load on inhibitory ability in normal older adults reporting mild anxiety. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
63.
Using 3D-CFD code, Nusselt number correlations for a microchannel heat exchanger (MCHE) with S-shaped fins used for hot water suppliers are obtained through numerical experiments and then validated. The supercritical carbon dioxide working fluid is assumed to operate around the pseudo-critical point, where fluid properties change radically. Calculations with 20 different temperatures are executed to produce Nusselt number correlations for each side. The fluid inlet temperature in each calculation is defined as 2 °C lower or higher than the constant wall temperature, respectively, for cold and hot side simulations. The small temperature difference of 2 °C is sufficiently small to regard thermal–hydraulic properties as constant. A new integrating method using the correlations to calculate the heat-transfer-performance is proposed. The resultant heat-transfer-performance is compared with that of another numerical result, which is reduced from large geometry and integration. The results agree within 3% error; the calculation accuracy of the method is confirmed. Experimental results with MCHE verify the correlations. The difference is approximately 5%. Using few computer resources, these Nusselt number correlations and the heat-transfer-performance calculation methods using correlation information are sufficiently accurate to evaluate heat exchangers.  相似文献   
64.
65.
In this paper, we investigated the activation energies of the aggregation–disaggregation self-oscillation induced by the Belousov-Zhabotinsky (BZ) reaction by utilizing the nonthermoresponsive polymer chain in a wide temperature range. This is because the conventional type self-oscillating polymer chain, with thermoresponsive poly(Nisopropylacrylamide) (poly(NIPAAm) main-chain covalently bonded to the ruthenium catalyst (Ru(bpy)3) of the BZ reaction, cannot evaluate the activation energy over the lower critical solution temperature (LCST). The nonthermoresponsive self-oscillating polymer chain is composed of a poly-vinylpyrrolidone (PVP) main-chain with the ruthenium catalyst (Ru(bpy)3). As a result, we clarified that the activation energy of the aggregation–disaggregation self-oscillation of the polymer chain is hardly affected by the concentrations of the BZ substrates. In addition, the activation energy of the nonthermoresponsive self-oscillating polymer chain was found to be almost the same value as normal BZ reaction, i.e., not including the self-oscillating polymer system with Ru moiety.  相似文献   
66.
Information about breakdown time-lags under pulsed voltage stress is prerequisite to the insulation design of superconducting devices. Experiments have been carried out using a pulse generator which provides a step voltage with 200 ns rise time and a long decay time constant of more than 1 ms. The present experiments may bridge the information gap between time lag measurements in the ns range using extremely high field strengths, and existing data found with usual lightning impulse voltage. The test device is described in the paper, and some typical results are discussed in detail  相似文献   
67.
To determine the effects of the multifunctional iron-binding glycoprotein, lactoferrin (LF) and related compounds on the growth of leukemic cells, human myeloid leukemic cells (HL-60) were exposed to bovine lactoferrin (bLF) and proteolytic hydrolysates of bLF. Pepsin hydrolysates of bLF showed a greater growth suppressive effect than tryptic hydrolysates or mature bLF. Four peptides with proliferation inhibition activity were purified from pepsin hydrolysates by ion-exchange chromatography, reverse-phase HPLC, and gel-filtration. All peptides were from the N-terminal end, in a region where lactoferricin B (Lfcin B), an antibacterial peptide, is located. Among the four peptides, peptide 1 (pep1) was found to exhibit highest activity and corresponded to residues 17 to 38 of bLF, with a molecular weight of 2753.88. The IC50 value of this peptide was 6.3 micrograms/ml. Three other peptides were less active and corresponded to sequences 1 to 16 and 45 to 48, linked by disulfide-bridge (pep2, molecular mass of 2430.13), 1 to 15 and 45 to 46 linked by disulfide bridge (pep3, molecular mass of 2017,92) and from residues 1 to 13 (pep4, molecular mass of 1558.73). Cell proliferation inhibition activity of the peptides was thought to be due to induction of apoptosis, which was evaluated by DNA ladder formation, DNA fragmentation, enhanced expression of phosphatidyl serine, and morphological changes. The IC50 values of the three peptides were confirmed using synthetic peptides and were consistent with those of purified peptides.  相似文献   
68.
Abstract— Thin‐film transistors (TFTs) are field‐effect transistors that can be used to create large‐scale‐integrated (LSI) circuits. The combination of high‐performance TFTs and transfer technology of the TFTs has the potential to foster the rise of a new flexible microelectronics industry. This paper discusses the current status of flexible microelectronics, using a TFT fingerprint sensor (FPS) as an example. Technology used in active‐matrix displays can easily be applied to the TFT FPS. TFT technology should not be confined to the display industry; its use should be expanded into the semiconductor industry. With the result presented in this paper, we declare a new era of flexible microelectronics open.  相似文献   
69.
This paper discusses what a new paradigm can be in wireless communication systems of the twenty-first century. First, it suggests two directions for the new paradigm; one is “micro- and nano-device communication system” which is the projected scenario considering that the entities in source and destination have been shrinking throughout the history of wireless communication systems. The second direction is “networked robot system”, which emerges as a natural extension of mobile ad hoc networking where the networking is closely related to motion control of robots. Secondly, it shows two interesting research topics, “the new communication protocol design” and “signal processing”, respectively, that arise in the wake of the fusion between the two directions in the novel communication paradigm. Finally, it considers a new science of wireless communications in the twenty-first century. Shinsuke Hara received the B.Eng., M.Eng. and Ph.D. degrees in communications engineering from Osaka University, Osaka, Japan, in 1985, 1987 and 1990, respectively. From April 1990 to March 1997, he was an assistant professor in the Department of Communication Engineering, School of Engineering, Osaka University, and from October 1997 to September 2005, he was an associate professor in the Department of Electronic, Information and Energy Engineering, Graduate School of Engineering, Osaka University. Since October 2005, he has been a professor in the Department of Physical Electronics and Informatics, Graduate School of Engineering, Osaka City University. In addition, from April 1995 to March 1996, he was a visiting scientist at Telecommunications and Traffic Control Systems Group, Delft University of Technology, Delft, The Netherlands. His research interests include wireless communications systems and digital signal processing. Hiroyuki Yomo received B.S. degree in communication engineering from Department of Communication Engineering, Osaka University, Osaka, Japan, in 1997, and M.S. and Ph.D. degrees in communication engineering from Department of Electronic, Information, and Energy Engineering, Graduate School of Engineering, Osaka University, Osaka Japan, in 1999 and 2002, respectively. From April 2002 to March 2004, he was a Post-doctoral Fellow in Department of Communication Technology, Aalborg University, Denmark. From April 2004 to September 2004, he was at Internet System Laboratory, NEC Corporation, Japan. Since October 2004, he has been an Assistant Research Professor in Center for TeleInfrastructure (CTIF), Aalborg University, Denmark. His main research interests are access technologies, radio resource management, and link-layer techniques in the area of short-range communication, cellular network, cognitive radio, and sensor network. Petar Popovski received the Dipl.-Ing. in electrical engineering and M.Sc. in communication engineering from the Faculty of Electrical Engineering, Sts. Cyril and Methodius University, Skopje, Republic of Macedonia, in 1997 and 2000, respectively. He received a Ph.D. degree from Aalborg University, Denmark, in 2004. From 1998 to 2001 he was a teaching and research assistant at the Institute of Telecommunications, Faculty of Electrical Engineering in Skopje. He is currently Assistant Professor at the Department of Communication Technology at the Aalborg University. His research interests are related to the PHY-MAC aspects of wireless protocols, wireless sensor networks, random access protocols, and network coding. Kazunori Hayashi received the B.E., M.E. and Ph.D. degrees in communication engineering from Osaka University, Osaka, Japan, in 1997, 1999 and 2002, respectively. He spent 3 months in 2000 at Aalborg University, Denmark, as a Visiting Scholar. Since 2002, he has been with the Department of Systems Science, Graduate School of Informatics, Kyoto University. He is currently an Assistant Professor there. His research interests include digital signal processing for communications systems.  相似文献   
70.
Sinusoidal wavelength-scanning interferometric reflectometry   总被引:1,自引:0,他引:1  
Sasaki O  Kuwahara T  Hara R  Suzuki T 《Applied optics》2000,39(22):3847-3853
We propose interferometric reflectometry in which a sinusoidal wavelength-scanning tunable laser diode is used to detect positions and profiles of multiple reflecting surfaces. An objective signal extracted from an interference signal contains modulation amplitude Z and phase alpha, which are related to the positions and profiles, respectively, of multiple reflecting surfaces. By using values of the objective signal at special times, we can produce an image intensity that shows where the reflecting surfaces exist. To obtain exact values of Z or values of alpha, we estimated the objective signal by using a conjugate gradient method. Experimental results show that a resolution of two-optical-path difference (OPD) in the image intensity is ~60 mum, and the final OPD precisions are 2 and 8 mum for two and three reflecting surfaces, respectively, for a wavelength-scanning width of 7 nm. Profiles of the front and rear surfaces of a silica glass plate with a thickness of 20 mum have been measured with a precision of ~10 nm.  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