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   75039篇
  免费   726篇
  国内免费   689篇
电工技术   1430篇
综合类   47篇
化学工业   11228篇
金属工艺   3451篇
机械仪表   2648篇
建筑科学   1652篇
矿业工程   503篇
能源动力   1867篇
轻工业   6415篇
水利工程   846篇
石油天然气   2306篇
武器工业   41篇
无线电   7208篇
一般工业技术   16477篇
冶金工业   12467篇
原子能技术   2635篇
自动化技术   5233篇
  2022年   579篇
  2021年   908篇
  2020年   704篇
  2019年   784篇
  2018年   1552篇
  2017年   1568篇
  2016年   1772篇
  2015年   954篇
  2014年   1564篇
  2013年   3580篇
  2012年   2362篇
  2011年   2838篇
  2010年   2381篇
  2009年   2654篇
  2008年   2624篇
  2007年   2560篇
  2006年   2199篇
  2005年   1921篇
  2004年   1843篇
  2003年   1789篇
  2002年   1711篇
  2001年   1681篇
  2000年   1678篇
  1999年   1570篇
  1998年   3691篇
  1997年   2611篇
  1996年   1945篇
  1995年   1527篇
  1994年   1325篇
  1993年   1354篇
  1992年   996篇
  1991年   1050篇
  1990年   1075篇
  1989年   1055篇
  1988年   942篇
  1987年   875篇
  1986年   878篇
  1985年   934篇
  1984年   778篇
  1983年   767篇
  1982年   676篇
  1981年   689篇
  1980年   661篇
  1979年   646篇
  1978年   621篇
  1977年   773篇
  1976年   933篇
  1975年   580篇
  1974年   551篇
  1973年   543篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
This paper proposes a new feature extraction technique using wavelet based sub-band parameters (WBSP) for classification of unaspirated Hindi stop consonants. The extracted acoustic parameters show marked deviation from the values reported for English and other languages, Hindi having distinguishing manner based features. Since acoustic parameters are difficult to be extracted automatically for speech recognition. Mel Frequency Cepstral Coefficient (MFCC) based features are usually used. MFCC are based on short time Fourier transform (STFT) which assumes the speech signal to be stationary over a short period. This assumption is specifically violated in case of stop consonants. In WBSP, from acoustic study, the features derived from CV syllables have different weighting factors with the middle segment having the maximum. The wavelet transform has been applied to splitting of signal into 8 sub-bands of different bandwidths and the variation of energy in different sub-bands is also taken into account. WBSP gives improved classification scores. The number of filters used (8) for feature extraction in WBSP is less compared to the number (24) used for MFCC. Its classification performance has been compared with four other techniques using linear classifier. Further, Principal components analysis (PCA) has also been applied to reduce dimensionality.  相似文献   
992.
The EU-supported TeDUB (Technical Drawings Understanding for the Blind) project is developing a software system that aims to make technical diagrams accessible to blind and visually impaired people. It consists of two separate modules: one that analyses drawings either semi-automatically or automatically, and one that presents the results of this analysis to blind people and allows them to interact with it. The system is capable of analysing and presenting diagrams from a number of formally defined domains. A diagram enters the system as one of two types: first, diagrams contained in bitmap images, which do not explicitly contain the semantic structure of their content and thus have to be interpreted by the system, and second, diagrams obtained in a semantically enriched format that already yields this structure. The TeDUB system provides blind users with an interface to navigate and annotate these diagrams using a number of input and output devices. Extensive user evaluations have been carried out and an overall positive response from the participants has shown the effectiveness of the approach.  相似文献   
993.
With the emergence of new media, interactive film projects have mainly struggled to resolve the contradiction between dramatic structures and interaction. Dramatic film presents identification with the main character, where the viewer is constantly oppressed by the narrative, and therefore lost in illusion. In this context, when we bring on the scene interaction, the drama apparently starts to lose its power.

In this article, a new interactive film model based on Brechtian film theory is proposed. This model presents a new way of spatiotemporal construction where different audiovisual combinations can be viewed successively, and this way the viewer can actively construct his/her own story. Theoretical framework of the Brechtian interactive film model is supported by an interactive film application, named Academia. The main feature of the model is that, while interaction is very simple, the continuity of the narrative is preserved and the film requiring an intellectual level of interpretation.  相似文献   
994.
995.
The effect of alkaline pretreatment of waste-activated sludge, using two models to study the sequential hydrolysis rates of suspended (Sanders' surface model) and dissolved (Goel's saturation model) solids, on the mesophilic and thermophilic anaerobic digestion rate is evaluated. The pretreatment, which reduces the size of the solids, increases the reaction rate by increasing the surface area and the specific surface hydrolysis constant (K(SBK)); at thermophilic conditions from 0.45 x 10(-3) kg m(-2) d(-1) for the fresh sludge to 0.74 x 10(-3) kg m(-2) d(-1) for the pretreated sludge and at mesophilic conditions these values are 0.28 x 10(-3) kg m(-2) d(-1) and 0.47 x 10(-3) kg m(-2) d(-1) confirming the usefulness of a pretreatment for solids reduction. But for soluble solids, the thermoalkaline pretreatment decreases the reaction rates by inducing a competitive inhibition on the thermophilic anaerobic digestion rate while in the mesophilic range, a non-competitive inhibition is observed. A mathematical simulation of the consecutive reactions, suspended solids to dissolved solids and to methane in staged anaerobic thermophilic-mesophilic digestion, shows that with 4% suspended solids concentration it is better not to use a thermoalkaline pretreatment because overall solids reduction and total methane production are not as good as without pretreatment.  相似文献   
996.
A laboratory-scale aerobic activated sludge reactor (AASR) system was employed to investigate the effects of sludge retention time (SRT) on the removal of three polyaromatic hydrocarbons (PAHs) with low benzene rings [(acenaphthene (ACT), fluorene (FLN) and phenanthrene (PHE)] and six PAHs with high benzene rings [(benzo[b]fluoranthene (BbF), benzo[k]fluoranthene (BkF), benzo[a]pyrene (BaP), indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene (DahA), benzo[g,h,i]perylene (BghiP)] in the presence of rhamnolipid (RD), emulsan (EM) and surfactine (SR) biosurfactants. This study showed that biosurfactants enhance the PAH biodegradation by increasing the biomass growth. RD exhibits a better performance than the other biosurfactants in the removal of the chemical oxygen demand (COD) and PAHs. At a RD concentration of 15 mg/L aerobic treatment for 25 days, SRT was enough to remove over 95% of total PAHs, and COD(dis). Under the same conditions 75% of COD originating from the inert organics (COD(inert)) and 96% of COD originating from the inert soluble microbial products (COD(imp)) were removed. At 25 days SRT and 15 mg/L RD concentration, about 88% of PAHs were biodegraded by the AASR system, 4% were accumulated in the system, 3% were released in the effluent, and 5% remained in the waste sludge.  相似文献   
997.
The objective of this study was to assess workers' exposure to bioaerosols in sludge drying units. Simultaneous collection of inhalable dust and airborne biological agents was carried out using rotating cup samplers (CIP 10, Arelco). Sixteen stationary and 30 personal measurements were performed in three drying plants, during summer and winter. Microbial content of air was characterized by high amounts of Gram-negative bacteria, endotoxin, and thermophilic actinomycetes. High differences between exposure levels were observed with regard to workplaces and tasks. Dryers and conveyors in operation were closed, and the monitoring task in the dryer room was associated with low levels of personal exposure, close to background levels. Conversely, cleaning and maintenance of the dryer and conveyors required the equipment to be opened, giving significantly higher task-based personal exposure levels. The fall of dried sludge into indoor containers resulted in high emission and spreading of dust. Mean personal exposure levels to fungi were moderate or low for all tasks. Based on the results of this study, appropriate means of operational control and personal protection are being developed and implemented on sites.  相似文献   
998.
In order to characterize the pollution discharged into the Moselle River and some of its tributaries, spectroscopic techniques, namely UV-vis spectroscopy and synchronous fluorescence spectroscopy, have been combined. UV-visible spectra were analysed using the maximum of the second derivative at 225 nm (related to nitrates), the SUVA254 and E2/E3 indices (related to the nature of organic matter). Synchronous fluorescence spectra (delta lambda = 50 nm) presented different shapes depending upon the type of pollution. The pollution results from anthropogenic activities: untreated domestic sewage due to misconnections in a periurban river, effluent from urban WWTPS, agricultural runoff (nitrates) in several streams, discharge from a paper mill (humic-like substances due to wood processing) and from steel mills (PAHs).  相似文献   
999.
A vast amount of valuable human knowledge is recorded in documents. The rapid growth in the number of machine-readable documents for public or private access necessitates the use of automatic text classification. While a lot of effort has been put into Western languages—mostly English—minimal experimentation has been done with Arabic. This paper presents, first, an up-to-date review of the work done in the field of Arabic text classification and, second, a large and diverse dataset that can be used for benchmarking Arabic text classification algorithms. The different techniques derived from the literature review are illustrated by their application to the proposed dataset. The results of various feature selections, weighting methods, and classification algorithms show, on average, the superiority of support vector machine, followed by the decision tree algorithm (C4.5) and Naïve Bayes. The best classification accuracy was 97 % for the Islamic Topics dataset, and the least accurate was 61 % for the Arabic Poems dataset.  相似文献   
1000.
We describe a numerical model of an internal pellet target to study the beam dynamics in storage rings, where the nuclear experiments with such type of target are planned. In this model the Monte Carlo algorithm is applied to evaluate the particle coordinates and momentum deviation depending on time and parameters of the target. One has to mention that due to statistical character of the pellet distribution in the target the analytical techniques are not applicable. This is also true for the particle distribution in the stored beam, which is influenced by various effects (such as a cooling process, intra-beam scattering, betatron oscillation, space charge effect). In this case only the Monte Carlo technique to model energy straggling in combination with the pellet distribution in the target should be considered.

Program summary

Program title: PETAG01Catalogue identifier: ADZV_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADZV_v1_0.htmlProgram obtainable from: CPC Program Library, Queen's University, Belfast, N. IrelandLicensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.htmlNo. of lines in distributed program, including test data, etc.: 1068No. of bytes in distributed program, including test data, etc.: 11 314Distribution format: tar.gzProgramming language: Fortran 77, C/C++Computer: Platform independentOperating system: MS Windows 95/2000/XP, Linux (Unix)RAM: 128 MBClassification: 11.10Nature of problem: Particle beam dynamics with use of the pellet target.Solution method: Monte Carlo with analytical approximation.Running time: dozens of seconds  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