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   422篇
  免费   33篇
电工技术   1篇
化学工业   152篇
金属工艺   7篇
机械仪表   10篇
建筑科学   19篇
矿业工程   2篇
能源动力   23篇
轻工业   90篇
水利工程   2篇
石油天然气   3篇
无线电   16篇
一般工业技术   62篇
冶金工业   13篇
自动化技术   55篇
  2024年   8篇
  2023年   12篇
  2022年   18篇
  2021年   23篇
  2020年   17篇
  2019年   20篇
  2018年   25篇
  2017年   19篇
  2016年   17篇
  2015年   14篇
  2014年   26篇
  2013年   35篇
  2012年   33篇
  2011年   38篇
  2010年   24篇
  2009年   33篇
  2008年   24篇
  2007年   21篇
  2006年   9篇
  2005年   12篇
  2004年   4篇
  2003年   4篇
  2002年   2篇
  2001年   3篇
  2000年   3篇
  1999年   1篇
  1998年   1篇
  1992年   2篇
  1989年   1篇
  1988年   3篇
  1987年   1篇
  1985年   1篇
  1983年   1篇
排序方式: 共有455条查询结果,搜索用时 15 毫秒
101.
102.
Although Person?×?Situation (P?×?S) interactionism is central in current social-cognitive conceptions of personality organization, its implications for the encoding of the self remain unexplored. Two studies examined the causal role of P?×?S interactionism in self-encoding on affect regulation and discriminative social perception. Following failure (Studies 1 and 2) and success (Study 2) ideation, participants were prompted to encode the self either in P?×?S interactionist terms (I am…when…) or in traitlike unconditional terms (I am…). Interactionist (compared with unconditional) self-encoding led to less affective extremity, suggesting that such encoding may prevent individuals from generalizing specific success and failure experiences to the self as a whole. Study 2 also found that interactionist self-encoding attenuated the endorsement of global stereotypes, suggesting that such encoding may enhance fine-grained social perception as well. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
103.

Non-Orthogonal Multiple Access (NOMA) has been proposed as a new radio access technique for cellular networks as an alternative to OMA (Orthogonal Multiple Access) in which the users of a group (pairs or triples of users in a group are considered in this paper) are allowed to use the wireless channel simultaneously. In this paper, for downlink single-input single-output SISO-NOMA, a heuristic power allocation algorithm within a group is first proposed which attempts to ensure that the users of a group benefit from simultaneous transmission equally in terms of achievable throughput. Moreover, a user group scheduling algorithm is proposed for downlink NOMA systems by which a user group is to be dynamically selected for transmission while satisfying long term temporal fairness among the individual contending users. The effectiveness of the proposed power allocation method along with the temporal fair scheduling algorithm for downlink NOMA is validated with simulations and the performance impact of the transmit power and the coverage radius of the base station as well as the number of users are thoroughly studied.

  相似文献   
104.
Various physical, chemical and genetic approaches have been applied in order to enhance enzyme stability and activity. In this study, the aim was to investigate the capability of sub- and supercritical carbon dioxide to alter the stability and activity of α-amylase as an alternative technique. The effects of operational parameters such as pressure (50-300 bar), temperature (28-80 °C), CO? flow (2-10 g min?1) and time (60-180 min) were evaluated in regard to the activity and stability of fungal based α-amylase from Aspergillus oryzea. The activity of untreated enzyme was determined as 17,726 μmol/ml/min. While both sub- and supercritical conditions enhanced the activity, the increase in flow rate had an adverse effect and the activity was decreased by 28.9% at a flow rate of 10 g min?1 under supercritical conditions. Nuclear magnetic resonance (NMR) spectra of untreated enzyme and treated samples exhibiting the lowest and the highest activities were almost identical except for the chemical shifts observed at the lowest activity sample from 4.0 to 4.4 ppm which were assigned to protons of hydrogen-bonded groups. Optimum conditions were determined as 240 bar, 41 °C, 4 g min?1 CO? flow and 150 min of process duration yielding 67.7% (29,728 μmol/ml/min) higher activity than the untreated enzyme providing fundamental basis for enzymatic applications.  相似文献   
105.
In traditional wireless sensor network (WSN) applications, energy efficiency may be considered to be the most important concern whereas utilizing bandwidth and maximizing throughput are of secondary importance. However, recent applications, such as structural health monitoring, require high amounts of data to be collected at a faster rate. We present a multi-channel MAC protocol, MC-LMAC, designed with the objective of maximizing the throughput of WSNs by coordinating transmissions over multiple frequency channels. MC-LMAC takes advantage of interference and contention-free parallel transmissions on different channels. It is based on scheduled access which eases the coordination of nodes, dynamically switching their interfaces between channels and makes the protocol operate effectively with no collisions during peak traffic. Time is slotted and each node is assigned the control over a time slot to transmit on a particular channel. We analyze the performance of MC-LMAC with extensive simulations in Glomosim. MC-LMAC exhibits significant bandwidth utilization and high throughput while ensuring an energy-efficient operation. Moreover, MC-LMAC outperforms the contention-based multi-channel MMSN protocol, a cluster-based channel assignment method, and the single-channel CSMA in terms of data delivery ratio and throughput for high data rate, moderate-size networks of 100 nodes at different densities.  相似文献   
106.
107.
Utilization of renewable resources and development of new processes aimed at converting these materials into value added bio-products are gaining more emphasis. The scope of this study was to optimize supercritical CO2 extraction (SFE) parameters such as pressure, temperature and flow rate for the yields of unsaturated fatty acids from Pistacia terebinthus berries by a Box-Behnken statistical design. All samples were analyzed for fatty acids by GC-FID. The most effective variables were pressure (P < 0.005) and flow rate (P ≤ 0.005). Maximizing the evaluative criteria for dependent variables (oleic acid, linoleic acid and linolenic acid), optimal conditions were determined to be 240 bar, 60 °C and a flow rate of 16 g/min yielding 51.2% oleic acid, 26.5% linoleic acid and 1.0% linolenic acid. The amounts of unsaturated fatty acids in SFE samples (81.3%) were higher than the hexane (74.3%) and were similar to that of cold press samples (80.1%). High concentrations of unsaturated fatty acids can indicate the utilization of the berries as a major dietary source and demonstrate challenges for industrial application of SFE as a green technology.  相似文献   
108.
Because zinc borate is an effective smoke suppressant and cheaper than antimony trioxide, the main aim of this study was to investigate usability of zinc borate as the third component of a traditional binary Br/Sb2O3 system in acrylonitrile butadiene styrene. Limiting oxygen index, UL‐94, and mass loss cone calorimeter studies indicated that almost all flame retardancy parameters were kept when certain percentages of antimony trioxide were replaced with zinc borate. Residue analysis revealed that the predominant flame retardancy mechanism of the traditional system was gas phase action, whereas zinc borate contributes especially in the condensed phase action by forming thicker and stronger char layer. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   
109.
In this study, cylindrical porous glass tablets were plated by palladium using electroless plating technique. Hypophosphite and Co(II) complexes were used as reducing agents in the prepared plating baths. Experiments were carried out in an especially designed glass vessel in which helium gas was continuously bubbled through the solution to create uniform concentration and to remove hydrogen gas from the surface for the case of hypophosphite-based procedure. XRF analysis of the upper layer of the composite membrane prepared by the hypophosphite-based bath showed a Pd/Si ratio of 4.6. SEM photographs indicated impregnation of Pd into the substrate upto 200 μm. However, the thickness of the dense Pd layer was only about 15 μm. SEM photographs and XRF results showed that hypophosphite-based bath was much more successful than the Co(II) complex-bath in Pd plating. Permeation experiments carried out at different temperatures showed that the contribution of surface diffusion to the permeation was significant at low temperatures and solution–diffusion mechanism was not important in the 40–200 °C temperature range for these membranes. The selectivity ratio for H2/N2 was found to be about 7 at 200 °C.  相似文献   
110.
The retention diagrams of n‐octane, n‐nonane, n‐decane, n‐butyl acetate, isobutyl acetate, and isoamyl acetate on the polyarylate Ardel D‐100, a copolyester of bisphenol A with terephthalic acid and isophthalic acid, were plotted at temperatures between 120 and 260°C by an inverse gas chromatography technique. The glass‐transition temperature of the copolymer was determined to be 190°C from the discontinuity of these diagrams. The retention diagrams of benzene, ethyl benzene, n‐propyl benzene, isopropyl benzene, and chlorobenzene were also plotted between 200 and 260°C. The specific retention volume, weight fraction activity coefficient, Flory–Huggins polymer–solvent interaction parameter, hard‐core polymer–solvent interaction parameter, and effective exchange energy parameter were determined for the studied solvents. The parameters suggest that the studied aromatic hydrocarbons and aliphatic esters are moderately good solvents and chlorobenzene is a very good solvent for this copolyester, but the n‐alkanes are very poor solvents. The solubility parameter of this copolymer was determined to be 11.6 (cal/cm3)1/2 at room temperature by extrapolation of the values of the solubility parameters from the studied temperatures to 25°C. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2365–2368, 2005  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