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   3123篇
  免费   137篇
  国内免费   1篇
电工技术   11篇
化学工业   748篇
金属工艺   25篇
机械仪表   53篇
建筑科学   117篇
矿业工程   8篇
能源动力   43篇
轻工业   578篇
水利工程   40篇
石油天然气   8篇
无线电   91篇
一般工业技术   281篇
冶金工业   939篇
原子能技术   3篇
自动化技术   316篇
  2023年   22篇
  2022年   89篇
  2021年   82篇
  2020年   65篇
  2019年   50篇
  2018年   68篇
  2017年   63篇
  2016年   66篇
  2015年   66篇
  2014年   82篇
  2013年   216篇
  2012年   147篇
  2011年   174篇
  2010年   133篇
  2009年   153篇
  2008年   128篇
  2007年   142篇
  2006年   107篇
  2005年   117篇
  2004年   100篇
  2003年   93篇
  2002年   74篇
  2001年   54篇
  2000年   46篇
  1999年   41篇
  1998年   49篇
  1997年   46篇
  1996年   47篇
  1995年   41篇
  1994年   42篇
  1993年   38篇
  1992年   44篇
  1991年   13篇
  1990年   38篇
  1989年   48篇
  1988年   28篇
  1987年   47篇
  1986年   41篇
  1985年   39篇
  1984年   31篇
  1983年   19篇
  1982年   42篇
  1981年   22篇
  1980年   22篇
  1979年   14篇
  1978年   26篇
  1977年   16篇
  1975年   15篇
  1974年   13篇
  1973年   10篇
排序方式: 共有3261条查询结果,搜索用时 31 毫秒
981.
In this study we examined the rhenium electrodeposition process onto p-Si(100) from acidic media. The study was carried out by means of cyclic voltammetry and the potential-steps method from which the corresponding nucleation and growth mechanism were determined. Both methods were performed under illumination using a solar simulator for electron photogeneration. A 3D progressive nucleation, diffusion-controlled growth of rhenium films was found. Likewise, a morphologic analysis was completed for the deposits obtained at different potential values by means of atomic force microscopy. An energetic characterization through capacitance measurements (Mott–Schottky plots and parallel capacitance) of the p-Si/NO3 and p-Si/Re/NO3 interfaces was done.The photoelectrochemical reduction of nitrate ions, PERN, on the different p-Si/Re electrode systems synthesized was studied. An overpotential decrease of 0.3 V and a photocurrent increase for the PERN on p-Si(100)/Re electrode systems compared with p-Si(100) and metallic Re was found. Finally, the kinetic parameters of the cathodic reactions in the p-Si and p-Si/Re acidic media were estimated using intensity modulated photocurrent spectroscopy. A brief analysis from this technique was done. According to these results, the p-Si/Re electrode system could be a potential photoelectrocatalyst for the PERN.  相似文献   
982.
This paper describes the use of a genetic algorithm (GA) for the problem of offline point-to-point autonomous mobile robot path planning. The problem consists of generating “valid” paths or trajectories, for an Holonomic Robot to use to move from a starting position to a destination across a flat map of a terrain, represented by a two-dimensional grid, with obstacles and dangerous ground that the Robot must evade. This means that the GA optimizes possible paths based on two criteria: length and difficulty. First, we decided to use a conventional GA to evaluate its ability to solve this problem (using only one criteria for optimization). Due to the fact that we also wanted to optimize paths under two criteria or objectives, then we extended the conventional GA to implement the ideas of Pareto optimality, making it a multi-objective genetic algorithm (MOGA). We describe useful performance measures and simulation results of the conventional GA and of the MOGA that show that both types of GAs are effective tools for solving the point-to-point path-planning problem.  相似文献   
983.
In phoneme recognition experiments, it was found that approximately 75% of misclassified frames were assigned labels within the same broad phonetic group (BPG). While the phoneme can be described as the smallest distinguishable unit of speech, phonemes within BPGs contain very similar characteristics and can be easily confused. However, different BPGs, such as vowels and stops, possess very different spectral and temporal characteristics. In order to accommodate the full range of phonemes, acoustic models of speech recognition systems calculate input features from all frequencies over a large temporal context window. A new phoneme classifier is proposed consisting of a modular arrangement of experts, with one expert assigned to each BPG and focused on discriminating between phonemes within that BPG. Due to the different temporal and spectral structure of each BPG, novel feature sets are extracted using mutual information, to select a relevant time-frequency (TF) feature set for each expert. To construct a phone recognition system, the output of each expert is combined with a baseline classifier under the guidance of a separate BPG detector. Considering phoneme recognition experiments using the TIMIT continuous speech corpus, the proposed architecture afforded significant error rate reductions up to 5% relative  相似文献   
984.
Objective: Examined the influence of mutual communal behaviors on the adjustment reported by persons with spinal cord injury (SCI) and their family caregivers. Previous research has found that persons who have a history of mutually communal behaviors in relationships may react differently to relationship changes after an acquired physical disability than dyads with few communal behaviors. Method: Family caregivers and persons with SCI were administered measures of mutual communal behaviors, depression, and life satisfaction. Structural equation modeling was used to test the relations among caregivers' communal behaviors and care recipients' communal behaviors, depression, and life satisfaction. Results: Caregiver and care recipient reports of communal behaviors were not significantly correlated. Significant paths indicated that care recipients' communal behavior scores were positively associated with their life satisfaction, and care recipients' depression was inversely associated with their life satisfaction. Caregivers' communal behavior scores were unrelated to their self-reported adjustment. Conclusions: Caregiver-care recipient dyads may differ in their perceptions of communal behaviors in their relationships. Although care recipient reports of communal behavior may be related to their life satisfaction, communal behaviors may not serve a similar function among caregivers of persons with SCI. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
985.
The Current Evaluation of Risk and Functioning-Revised (CERF-R), an assessment instrument designed for use with adults with severe and persistent mental illness (SPMI) delineates 18 areas of risk and functioning along with judgments regarding level of care needs. Consensus treatment team ratings were obtained on 736 state hospital patients and 2,607 clients receiving public sector mental health services in the community. Results indicate that the CERF-R exhibits a high level of internal consistency, test-retest, and interrater reliability. Concurrent validity was evident for the functional subscale. The functional and risk items successfully discriminate level of service needs. Factor analysis of the CERF-R is consistent with the three primary reasons persons with SPMI need public mental health services. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
986.
The application of type-2 fuzzy logic to the problem of automated quality control in sound speaker manufacturing is presented in this paper. Traditional quality control has been done by manually checking the quality of sound after production. This manual checking of the speakers is time consuming and occasionally was the cause of error in quality evaluation. For this reason, by applying type-2 fuzzy logic, an intelligent system for automated quality control in sound speaker manufacturing is developed. The intelligent system has a type-2 fuzzy rule base containing the knowledge of human experts in quality control. The parameters of the fuzzy system are tuned by applying neural networks using, as training data, a real time series of measured sounds produced by good sound speakers. The fractal dimension is used as a measure of the complexity of the sound signal.  相似文献   
987.
Before a Children's Court decision is reached, a clinical assessment may be ordered by the court. This assessment often occurs when tension is high for the family and when well-established defenses may falter, and it can provide a prime, critical opportunity to facilitate positive change. Comprehensive psychological assessment at the Children's Court Clinic in Melbourne, Australia, indicates the intervention value of a serious attempt to understand the complexity of the psychological issues facing a child and family. With the aid of illustrative case studies, this article discusses the therapeutic aspects and implications of such assessment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
988.
A method based on the Polanyi-Dubinin-Manes (PDM) model is presented to predict adsorption isotherms of aqueous organic contaminants on activated carbons. It was assumed that trace organic compound adsorption from aqueous solution is primarily controlled by nonspecific dispersive interactions while water adsorption is controlled by specific interactions with oxygen-containing functional groups on the activated carbon surface. Coefficients describing the affinity of water for the activated carbon surface were derived from aqueous-phase methyl tertiary-butyl ether (MTBE) and trichloroethene (TCE) adsorption isotherm data that were collected with 12 well-characterized activated carbons. Over the range of oxygen contents covered by the adsorbents (approximately 0.8-10 mmol O/g dry, ash-free activated carbon), a linear relationship between water affinity coefficients and adsorbent oxygen content was obtained. Incorporating water affinity coefficients calculated from the developed relationship into the PDM model, isotherm predictions resulted that agreed well with experimental data for three adsorbents and two adsorbates [tetrachloroethene (PCE), cis-1,2-dichloroethene (DCE)] that were not used to calibrate the model.  相似文献   
989.
Unfavorable aggregation and deposition of colloidal particles in natural and engineered systems is still a subject of debate. Complicating factors such as surface roughness, secondary minimum aggregation, and the nature of discrete surface charge and surface potential make it difficult to attribute a specific cause to these phenomena. The presence of surface charge heterogeneity and its influence on interaction forces, which are responsible for aggregation and deposition, are studied in this work through the application of atomic force microscopy (AFM). Force-volume-mode AFM was used to map interaction forces on a surface and relate them to surface charge heterogeneities. The experimental system consisted of a silica plate and a standard silicon nitride AFM tip. Copper ions were used for sorption on the silica surface in order to modify the surface charge and cause charge reversal. Different concentrations of copper ions were selected to identify conditions of partial coverage of the silica surface. The pH and ionic strength of the solutions were varied, and the extension of the surface charge modification and its influence on the resulting interaction forces were monitored via AFM force measurements. Depending on the pH and ionic strength, the interaction force was found to change at certain regions on the surface from attraction to either weak or strong repulsion. Force imaging allowed the visual localization of zones of strong repulsive interaction that diminished in size with increasing ionic strength. X-ray photoelectron spectroscopy analysis was used to confirm the presence of copper on the surface. Local charge differences on a surface result in local differences in surface forces, not only in magnitude but also in direction. This behavior may explain the aggregation, deposition, and transport of colloidal particles under unfavorable chemical conditions.  相似文献   
990.
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