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   256篇
  免费   14篇
电工技术   4篇
化学工业   60篇
金属工艺   6篇
机械仪表   6篇
建筑科学   8篇
能源动力   8篇
轻工业   41篇
水利工程   2篇
无线电   17篇
一般工业技术   67篇
冶金工业   20篇
原子能技术   1篇
自动化技术   30篇
  2023年   3篇
  2022年   6篇
  2021年   12篇
  2020年   3篇
  2019年   8篇
  2018年   6篇
  2017年   12篇
  2016年   3篇
  2015年   8篇
  2014年   8篇
  2013年   18篇
  2012年   8篇
  2011年   12篇
  2010年   10篇
  2009年   11篇
  2008年   7篇
  2007年   14篇
  2006年   15篇
  2005年   11篇
  2004年   4篇
  2003年   3篇
  2002年   8篇
  2001年   5篇
  2000年   6篇
  1999年   11篇
  1998年   8篇
  1997年   6篇
  1996年   3篇
  1995年   4篇
  1994年   6篇
  1993年   2篇
  1992年   2篇
  1991年   3篇
  1990年   2篇
  1988年   2篇
  1987年   2篇
  1986年   1篇
  1985年   2篇
  1984年   1篇
  1983年   2篇
  1982年   3篇
  1981年   2篇
  1980年   2篇
  1979年   2篇
  1978年   1篇
  1977年   1篇
  1972年   1篇
排序方式: 共有270条查询结果,搜索用时 109 毫秒
41.
Due to dependency on Plug Setting (PS), Time Dial Setting (TDS), size of the network, more than one back-up relays for one primary relay and other technical constraints, coordination of Directional Overcurrent Relays (DOCRs) is an extremely constrained and nonlinear optimization problem. In this paper, a new Gravitational Search (GS) based algorithm is presented for achieving optimal coordination of directional overcurrent relays. The proposed algorithm utilizes user defined characteristic for inverse time overcurrent relays than the predefined standard curves. The user defined relay characteristic deals with constants that control the shape of the characteristics as variable adjustable values which are optimally chosen along with TDS and Plug Setting Multiplier (PSM). The performance of the proposed algorithm has been evaluated on 8-bus, 15-bus and IEEE 30-bus distribution network at different fault locations (near-end, far-end and middle point). In addition, the time of operation of some of the primary relays at different fault locations on IEEE 30-bus distribution network is also presented. At the end, comparative evaluation of the proposed algorithm with other optimization algorithms having different relay characteristics presented in the literature clearly indicates its effectiveness and superiority in terms of the sum of total primary relays operating time.  相似文献   
42.
Three‐dimensional polymer nanofibrous mats with tunable wettability have been fabricated using a single step non‐conductive template assisted electrospinning process. Cellulose acetate nanofibers are electrospun over a nylon mesh, which acts as the template. The as‐deposited fiber mat is removed from this template to produce a free standing three‐dimensional micropatterned nanofibrous mat. By simply varying the template mesh dimensions, the fraction of the air‐liquid interface can be changed which allows control of the wetting mechanics. It is shown that the water contact angle can be varied from about 30° for a planar network to about 140° for a patterned mat implying a complete transition from hydrophilic to hydrophobic behavior. Furthermore, upon stretching the fiber mat loses its pattern irreversibly and reducing the contact angle from 140° to 110° with increasing stretching. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44709.  相似文献   
43.
In this paper a new power efficient routing algorithm for MANETs with self-organizing and self-routing features is described and its performance analyzed in different simulation scenarios. The algorithm has the logic of a non-cooperative routing algorithm based on the evaluation of a weight parameter, the latter being a function of properties of the MANET nodes related to the nominal available power and the transmission range. A self-estimation of this weight parameter for each node is introduced in the routing process based on the status and functional history of the node. The routing is based on network layering, formation of service areas in each layer and choice of nodes from these areas to have the functionality of default gateways. The proposed algorithm, named service zone gateway prediction (SZGP), is a hybrid type of routing mechanism, incorporating pre-computed multipath hop-by-hop distributed routing, with a periodically updated hierarchical multilayered structure. The results from the simulation experiments show that the performance of the proposed SZGP algorithm in relation to the basic performance parameters such as packet delivery ratio, delay and throughput are similar to those of the well-known AODV algorithm, but in relation to power efficiency the proposed algorithm outperforms AODV significantly. This is due to the fact that such an approach reduces the overall number of broadcasts in the network and ensures a reliable and energy efficient connection by balancing the load among the nodes.  相似文献   
44.
 The influence of water on the rheological characteristics of biscuit dough and quality of biscuits was studied. A variation of even 1% in water content considerably changed the various rheological characteristics of biscuit dough. Increasing water content by 3% significantly increased the compliance from 32.6% to 45.6%, and decreased the extrusion time from 100 s to 34 s, the apparent biaxial extensional viscosity from 3.06×105 Pas to 1.5×105 Pas, and the consistency from 943 Ns to 620 Ns for dough based on weak wheat flour. The elastic recovery of biscuit dough increased significantly from 0.425 mm to 0.535 mm. Dough became more cohesive and adhesive with increasing water content, whilst biscuits became harder, as indicated by increases in density, breaking strength and compression strength. Received: 14 September 1998  相似文献   
45.
The chevron geometry in the SmC* phase of ferroelectric liquid crystals (FLC) has been a major obstacle in the use of FLC in displays as it results in poor electro‐optical performance. The present paper reports a novel method to overcome this problem, by doping a small amount of polymer in the FLC matrix. In addition to the improvement in smectic ordering, polymer doping is also found to be useful in improving the vital electro‐optical properties. The various electro‐optical parameters like switching time, tilt angle, contrast ratio etc. show improvement in polymer mixed guest host mixture of FLC samples. POLYM. COMPOS., 31:1776–1781, 2010. © 2010 Society of Plastics Engineers.  相似文献   
46.
Gold nanorods (AuNR) can be tailored to possess an intense and narrow longitudinal plasmon (LP) absorption peak in the far-red to near-infrared wavelength region, where tissue is relatively transparent to light. This makes AuNRs excellent candidates as contrast agents for photoacoustic imaging, and as photothermal therapeutic agents. The favorable optical properties of AuNR which depend on the physical parameters of shape, size and plasmonic coupling effects, are required to be stable during use. We investigate the changes that are likely to occur in these physical parameters in the setting of photothermal therapeutics, and the influence that these changes have on the optical properties and the capacity to achieve target cell death. To this end we study 3 sets of interactions: pulsed light with AuNR, AuNR with cells, and pulsed light with cells incubated with AuNR. In the first situation we ascertain the threshold value of fluence required for photothermal melting or reshaping of AuNR to shorter AuNR or nanospheres, which results in drastic changes in optical properties. In the second situation when cells are exposed to antibody-conjugated AuNR, we observe using transmission electron microscopy (TEM) that the particles are closely packed and clustered inside vesicles in the cells. Using dark-field microscopy we show that plasmonic interactions between AuNRs in this situation causes blue-shifting of the LP absorption peak. As a consequence, no direct lethal damage to cells can be inflicted by laser irradiation at the LP peak. On the other hand, using irradiation at the transverse peak (TP) wavelength in the green, at comparative fluences, extensive cell death can be achieved. We attribute this behavior on the one hand to the photoreshaping of AuNR into spheres and on the other hand to clustering of AuNR inside cells. Both effects create sufficiently high optical absorption at 532 nm, which otherwise would have been present at the LP peak. We discuss implications of these finding on the application of these particles in biomedicine.  相似文献   
47.
The tris(acetylacetonato)rhodium(III) catalyst is shown to be a versatile catalyst in the presence of DABCO (1,4‐diazabicyclo[2.2.2]octane) as ligand for the α‐alkylation of ketones followed by transfer hydrogenation, for the one‐pot β‐alkylation of secondary alcohols with primary alcohols and for the alkylation of aromatic amines in the presence of an inorganic base in toluene.  相似文献   
48.
 The response of Indian commercially milled flour to different additives was studied. The incorporation of reducing agents, such as l-cysteine hydrochloride (l-cysteine HCl), reduced the water absorption capacity (WAC) and stability of medium-strong wheat flour as well as weak wheat flour. This effect was also shown by other reducing agents or enzymes; however, the extent of change was found to be greater in medium-strong wheat flour. Surfactants/emulsifiers, such as glycerol monostearate, sodium stearoyl lactylate, and diacetyl tartaric esters of monoglycerides (DATEM), did not alter the WAC significantly, but marginally improved the stability of the dough. The change observed in the extensograph was greater with reducing agents and enzymes. In general, use of l-cysteine HCl or α-amylase or protease reduced the resistance to extension and increased the extensibility, depending on the level of addition. l-cysteine HCl, however, gave a greater reduction in the resistance to extension in medium-strong than in weak flour. On the other hand, use of surfactants/emulsifiers increased the resistance to extension and decreased the extensibility, and the effect was greater with DATEM. The bread volume improved considerably on incorporation of l-cysteine HCl, while DATEM also increased the loaf volume considerably at a 1% level in weak flour. Maximum improvement in loaf volume was found for DATEM in the case of weak flour, indicating that the responses of flour to different additives were different. Received: 10 February 1999 / Revised version: 27 April 1999  相似文献   
49.
Reducing the risk of Salmonella contamination in pet food is critical for both companion animals and humans, and its importance is reflected by the substantial increase in the demand for pathogen testing. Accurate and rapid detection of foodborne pathogens improves food safety, protects the public health, and benefits food producers by assuring product quality while facilitating product release in a timely manner. Traditional culture-based methods for Salmonella screening are laborious and can take 5 to 7 days to obtain definitive results. In this study, we developed two methods for the detection of low levels of Salmonella in pet food using real-time PCR: (i) detection of Salmonella in 25 g of dried pet food in less than 14 h with an automated magnetic bead-based nucleic acid extraction method and (ii) detection of Salmonella in 375 g of composite dry pet food matrix in less than 24 h with a manual centrifugation-based nucleic acid preparation method. Both methods included a preclarification step using a novel protocol that removes food matrix-associated debris and PCR inhibitors and improves the sensitivity of detection. Validation studies revealed no significant differences between the two real-time PCR methods and the standard U.S. Food and Drug Administration Bacteriological Analytical Manual (chapter 5) culture confirmation method.  相似文献   
50.
Finger millet seed coat is an edible material and contains good proportion of dietary fibre, minerals and phytochemicals. The seed coat matter (SCM) forms a by-product of millet milling, malting and decortication industries and can be utilised as composite flour in biscuit preparation. The SCM from native, malted and hydrothermally treated millet contained 9.5–12% protein, 2.6–3.7% fat and 40–48% dietary fibre, besides 3–5% polyphenols and 700–860 mg/100 g of calcium. The biscuits prepared using the composite flour were of crisp texture and exhibited breaking strength of 1480–1690 g compared to control biscuits (1560 g). The biscuits were of mild grey colour (ΔE = 40–50) and exhibited higher protein, dietary fibre and calcium contents. The sensory evaluation of the biscuits indicated that 10% of SCM from native and hydrothermally processed millet and 20% from malted millet could be used in composite biscuit flour.  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