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   218篇
  免费   13篇
电工技术   2篇
化学工业   73篇
金属工艺   1篇
机械仪表   2篇
建筑科学   4篇
能源动力   7篇
轻工业   39篇
水利工程   2篇
石油天然气   1篇
无线电   23篇
一般工业技术   32篇
冶金工业   19篇
原子能技术   4篇
自动化技术   22篇
  2023年   1篇
  2022年   6篇
  2021年   13篇
  2020年   12篇
  2019年   4篇
  2018年   11篇
  2017年   8篇
  2016年   6篇
  2015年   5篇
  2014年   6篇
  2013年   11篇
  2012年   23篇
  2011年   20篇
  2010年   13篇
  2009年   9篇
  2008年   10篇
  2007年   9篇
  2006年   4篇
  2005年   7篇
  2004年   4篇
  2003年   5篇
  2002年   5篇
  2001年   6篇
  2000年   4篇
  1999年   4篇
  1998年   2篇
  1997年   1篇
  1996年   9篇
  1995年   1篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1990年   1篇
  1988年   2篇
  1986年   2篇
  1982年   3篇
排序方式: 共有231条查询结果,搜索用时 15 毫秒
11.
Experimental studies indicate that recognition of emotions, particularly negative emotions, decreases with age. However, there is no consensus at which age the decrease in emotion recognition begins, how selective this is to negative emotions, and whether this applies to both facial and vocal expression. In the current cross-sectional study, 607 participants ranging in age from 18 to 84 years (mean age = 32.6 ± 14.9 years) were asked to recognize emotions expressed either facially or vocally. In general, older participants were found to be less accurate at recognizing emotions, with the most distinctive age difference pertaining to a certain group of negative emotions. Both modalities revealed an age-related decline in the recognition of sadness and—to a lesser degree—anger, starting at about 30 years of age. Although age-related differences in the recognition of expression of emotion were not mediated by personality traits, 2 of the Big 5 traits, openness and conscientiousness, made an independent contribution to emotion-recognition performance. Implications of age-related differences in facial and vocal emotion expression and early onset of the selective decrease in emotion recognition are discussed in terms of previous findings and relevant theoretical models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
12.
A novel, highly efficient and economical route is developed for the synthesis of polyaniline micro-/nanostructure. Materials were characterized by a complementary combination of X-ray diffraction, Scanning electron microscopy, Fourier-transform infrared, and UV-visible spectrophotometer. Morphology of polyaniline can be tailored by varying the structure-directing agents and pH of the synthesis condition. Ethylene glycol and polyethylene glycol formed a three-dimensional flower-like structure whereas block-copolymer (ethylene oxide and propylene oxide based co-polymer EO20PO70EO20) formed leaf-like structure when the synthesis was performed at pH 7. Using these structure-directing agents, nanorod and granular morphologies were obtained when the samples were synthesized at pH 3 and 1, respectively.  相似文献   
13.
We have designed and manufactured a micromachined moving plate capacitor to be used as an AC voltage reference in electrical metrology. The reference is based on the characteristic AC current–voltage curve of the component having a maximum, the value of which ideally depends only on the geometry of the component and material properties of single crystalline silicon. The electrode surface stability is essential in this application and hence a new fabrication process has been developed to metallize both surfaces of an electrostatically actuated micromachined structure. The stability of the AC reference voltage at a frequency of 100 kHz and an RMS voltage value 6.4 V was measured to be ±60 ppm over 14 h.  相似文献   
14.
Photoconduction behaviour of 75 MeV oxygen ion irradiated (Fluences: 1.8 × 1011, 1.8 × 1012 and 1.8 × 1013 ions/cm2) kapton-H polyimide film in the visible region has been investigated at different temperatures ranging 400-2500 °C and at various electric fields ranging 40-600 kV/cm. A photoinduced exciton formation is the major source for providing charge carriers through thermolization and field-assisted dissociation processes. An attempt has been made to fit the field dependence of the steady state photocurrent to one of the several possible conduction mechanisms. In the high and low fluence (1.8 × 1013 and 1.8 × 1011 ions/cm2) irradiated samples there exists a possibility of Poole-Frankel type of photoconduction mechanism, whereas at intermediate fluence (1.8 × 1012 ions/cm2) a Schottky type photoconduction mechanism may be operative. The log Ips versus 1/T plots consist of two straight lines with a knee point around 800-1000 °C. The activation energy estimated from the slope of these lines is field dependent varying from 0.40 to 0.73 eV and 0.18 to 0.23 eV above and below the knee point, respectively. This indicates the presence of more than one type of trapping levels in irradiated kapton-H polyimide.  相似文献   
15.
A three-tiered, enterprise, geographic information system architecture offers a robust, efficient, and secure platform to potentially revolutionize disaster management by enabling support of all of the phases of governmental activity that must occur before, during, and after a disaster. Presently, both publicly and privately initiated, computer-based systems designed for disaster management cannot meet the real-time data access and analysis needs at crucial stages, especially those occurring during an actual disaster. Impediments are reflective of the proprietary, stand alone, and segregated nature of current systems. This paper proposes an integrated, infrastructure management information system as a reliable and effective alternative. Issues related to sharing data, customizing applications, supporting multiple data formats, querying visually, facilitating ubiquitous computing, and upgrading are all addressed. Achieving maximum flexibility and capacity in a disaster management system relies upon recent advances in the following areas: (1) standardized data specifications; (2) middleware services; and (3) Web-enabled, distributed computing. Key resources in designing and implementing such an arrangement are prototyped in a system that was initially designed for addressing disaster management of urban explosions. The critical details of that system are presented herein.  相似文献   
16.
Meta-nitroaniline (m-NA) doped gold/polyvinyl alcohol (Au/PVA) nano-composites are prepared via in-situ reduction of gold salt by employing hydrazine hydrate (HH). Effect of the NLO (non-linear optical) active m-nitroaniline (m-NA) on the photo-physical properties of nano-particles of gold is studied in the colloidal as well as self-supported film form. The UV-Visible absorption bands between 530 and 555 nm due to surface plasmon resonance in Au nano-particles are observed. The absorption values show a shift in the position due to variation in m-NA with respect to the gold concentration. Additional absorption bands are observed after m-NA doping that influences the original position of gold absorption bands. The solutions and the films are further characterized by photoluminescence (PL), FTIR spectroscopy, XRD, TEM and thermal analysis. The particle size as shown by TEM is found to be less than 10 nm. Spin cast nano-composite films show single mode waveguide properties.  相似文献   
17.
A detailed chemisorption mechanism is proposed for the atomic layer deposition (ALD) of aluminium oxide nano layers using trimethyl aluminum (TMA) and water as precursors. Six possible chemisorption mechanisms, complete ligand exchange, partial ligand exchange, simple dissociation, complete dissociation via ligand exchange, complete dissociation and association, are proposed and related parameters like ligand to metal ratio (L/M), concentrations of metal atoms and methyl groups adsorbed are calculated and compared against reported values. The maximum number of methyl groups that can get attached on the surface is calculated in a different way which yields a more realistic value of 6·25 per nm2 substrate area. The dependence of the number of metal atoms adsorbed on OH concentration is explained clearly. It is proposed that a combination of complete ligand exchange and complete dissociation is the most probable chemisorption mechanism taking place at various OH concentrations.  相似文献   
18.
Currant oils have special health properties due to their moderate contents of α‐linolenic, γ‐linolenic and stearidonic acids. The distribution of fatty acids (FA) in the triacylglycerols (TAG) may affect the beneficial effects. Seed oils of wild northern red currant (NRC) (Ribes spicatum L.) from Northern Finland and of wild alpine currant (AC) (R. alpinum L.) from the South‐West coast of Finland were investigated. The purified TAG were analysed by tandem mass spectrometry by applying the ammonia negative ion chemical ionisation – collision‐induced dissociation method. Molecular weight fractions rich in C18:3 FA and C18:4 FA were investigated. Of the total oil, the molecular weight species 54:7 (ACN:DB), 54:8 and 54:9 were more abundant in NRC than in AC, being 21.0%, 15.8%, 7.4% and 16.2%, 11.2%, 4.8%, respectively (p <0.05). The species 52:6 was more abundant in AC (3.1%) than in NRC (2.6%) (p <0.05). The preferential order of FA to be in the sn‐2 position in both berries was typically C18:1 > C18:2 > C18:4 > C18:3. No difference was observed between relative locations of C16:0 FA and C18:3 FA in either of the oils. Within the TAG consisting of FA combinations C18:3/C18:3/C18:1 (54:7), C18:1 was more preferentially in the sn‐2 position (p <0.05) in AC (93.2%) than in NRC (74.6%), and in the case of C18:3, the preference was vice versa. Within the molecular weight species 54:9, FA combination C18:4/C18:3/C18:2, linoleic acid preferentially occupied the secondary position (p <0.005) in both berries, and the proportion of the TAG regioisomer pair sn‐C18:3‐C18:4‐C18:2 + sn‐C18:2‐C18:4‐C18:3 was more abundant (30.2%) in NRC than in AC (15.3%). Within the TAG species 52:6, proportions of all the existing combinations, C16:0/C18:3/C18:3, C16:0/C18:4/C18:2 and C16:1/C18:3/C18:2, varied between the two berry species (p <0.005).  相似文献   
19.
Let Y be a continuous, ordinal measure of a latent variable Θ. In general, for factorial designs, an analysis of variance of the observed variable Y cannot be used to draw inferences about main effects and interactions on the latent variable Θ even when the standard normality and equality of variance assumptions hold. If Y is a continuous, ordinal measure of a latent variable Θ; X?,…, Xn are continuous, ordinal measures of latent variables Φ?,…, Φn; and the observed measures have a multivariate normal distribution, then a multiple regression analysis of the observed criterion measure Y and predictors X?,…, Xn can be used to test hypotheses about multivariate associations among the latent variables. Furthermore, the predicted values Y′ are unbiased estimates of quantities that are monotonically related to predicted values on the latent criterion variable Θ. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
20.
Fruit preservation and packaging have been practiced since ages to maintain the constant supply of seasonal fruits over lengthened periods round the year. However, health and safety issues have attracted attention in recent decades. The safety and quality assurance of packaged fruits/fruit products are vital concerns in present day world-wide–integrated food supply chains. The growing demand of minimally or unprocessed packaged fruits has further aggravated the safety concerns which fuelled in extensive research with objectives to develop novel techniques of food processing, preservation, and packaging as well as for rapid, accurate, and early detection of contaminant products/microbes. Nevertheless, fruits and fruit-based products have yet to observe a panoramic introduction. Tropics and subtropics are the stellar producers of a variety of fruits; majority if not all is perishable and prone to postharvest decay. This evoked the opportunity to critically review the global scenario of emerging and novel techniques for fruit preservation and packaging, hence providing insight for their future implementation. This review would survey key nanotechnology innovations applied in preservation, packaging, safety, and storage of fruits and fruit-based products. The challenges and pros and cons of wider application of these innovative techniques, their commercial potential, and consumer acceptability have also been discussed.  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