全文获取类型
收费全文 | 17608篇 |
免费 | 2453篇 |
国内免费 | 1666篇 |
专业分类
电工技术 | 1724篇 |
综合类 | 1907篇 |
化学工业 | 519篇 |
金属工艺 | 461篇 |
机械仪表 | 1624篇 |
建筑科学 | 591篇 |
矿业工程 | 282篇 |
能源动力 | 435篇 |
轻工业 | 319篇 |
水利工程 | 155篇 |
石油天然气 | 606篇 |
武器工业 | 342篇 |
无线电 | 5329篇 |
一般工业技术 | 2423篇 |
冶金工业 | 262篇 |
原子能技术 | 234篇 |
自动化技术 | 4514篇 |
出版年
2024年 | 66篇 |
2023年 | 225篇 |
2022年 | 352篇 |
2021年 | 441篇 |
2020年 | 497篇 |
2019年 | 471篇 |
2018年 | 435篇 |
2017年 | 609篇 |
2016年 | 713篇 |
2015年 | 799篇 |
2014年 | 1235篇 |
2013年 | 1204篇 |
2012年 | 1396篇 |
2011年 | 1496篇 |
2010年 | 1179篇 |
2009年 | 1254篇 |
2008年 | 1094篇 |
2007年 | 1342篇 |
2006年 | 1229篇 |
2005年 | 960篇 |
2004年 | 817篇 |
2003年 | 777篇 |
2002年 | 547篇 |
2001年 | 444篇 |
2000年 | 394篇 |
1999年 | 315篇 |
1998年 | 216篇 |
1997年 | 246篇 |
1996年 | 157篇 |
1995年 | 187篇 |
1994年 | 106篇 |
1993年 | 109篇 |
1992年 | 74篇 |
1991年 | 75篇 |
1990年 | 54篇 |
1989年 | 52篇 |
1988年 | 37篇 |
1987年 | 22篇 |
1986年 | 14篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 12篇 |
1980年 | 3篇 |
1978年 | 4篇 |
1966年 | 5篇 |
1962年 | 4篇 |
1959年 | 3篇 |
1958年 | 3篇 |
1957年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
Sánchez-Meca Julio; Marín-Martínez Fulgencio; Chacón-Moscoso Salvador 《Canadian Metallurgical Quarterly》2003,8(4):448
It is very common to find meta-analyses in which some of the studies compare 2 groups on continuous dependent variables and others compare groups on dichotomized variables. Integrating all of them in a meta-analysis requires an effect-size index in the same metric that can be applied to both types of outcomes. In this article, the performance in terms of bias and sampling variance of 7 different effect-size indices for estimating the population standardized mean difference from a 2 × 2 table is examined by Monte Carlo simulation, assuming normal and nonnormal distributions. The results show good performance for 2 indices, one based on the probit transformation and the other based on the logistic distribution. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
62.
根据有线电视的数字化、光纤化发展趋势,现在的有线电视网络必须经过改造,以便为今后数字电视的传输和双向传输打下基础,进一步拓展有线电视的功能,为此提供一个城网改造的方案供参考。 相似文献
63.
64.
It is necessary to determine the accurate reflectance of painted surfaces for the review of paint finishes by computer graphics (CG) before actual painting of the exterior color of automobiles, and for quality control during production and inspection processes. We have optimized a method for measuring reflectance by using a statistical technique. We have found that the reflectance of a painted surface is best measured at an incident angle of 60° and at five aspecular angles of 10°, 18°, 28°, 40°, and 90°. Our method makes it possible to accurately reproduce reflection characteristics of paint finishes containing special flake pigments, such as pearl mica. Also it was proved that our method can apply not only to solid and metallic coatings but to all painted surfaces. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 275–282, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20125 相似文献
65.
自振空化射流提高钻井速度的实验研究 总被引:7,自引:0,他引:7
空化射流用于提高钻井速度的可行性研究结果表明,在钻进作业中,利用空泡破裂产生强大破坏作用来提高钻探的效率,其效果显著,可行性高。室内实验表明,自振空化射流在比普通喷嘴射流更深的井底或更高的围压条件下,有更大的起始空化数和更强的空化能力。自振空化喷嘴起始空化数大都在1.0以上,最高达到1.67,而锥形喷嘴最高仅为0.43,围压下其冲蚀效率是锥形喷嘴的1~2倍。现场试验同样证实设计的自振空化射流喷嘴在保护钻头、减少钻头磨损及增加进尺、提高机械钻速方面有显著作用。 相似文献
66.
Ahmed Helmy Khaled Sharaf Hani Ragai 《Analog Integrated Circuits and Signal Processing》2003,37(3):139-148
A noise analysis of bipolar harmonic mixers (BHM) used for direct-conversion receivers is presented in this paper. Analytical and simulated results for the transfer function of the mixer are presented. Simple analytical expressions describing noise contribution from all sources are derived. Estimation of flicker noise quite agrees with harmonic-balance simulation results. Based on the derived expressions, total time average noise power spectral density (PSD) at the output is compared with simulation results. For the recommended regions of operation, error is less than 20%. The overall BHM noise figure (NF) is calculated and optimized based on a simple extracted formula. Errors introduced by analysis remain within a 1.5-dB margin with respect to simulation results. The validity of analysis for high frequencies is justified. The effect of flicker noise coefficient on the overall mixer NF is compared for different available processes. 相似文献
67.
Wang Tian-kui Lu Fang Fan Xiao-bing Shi Xiao-jun China Ship Scientific Research Center Wuxi China 《水动力学研究与进展(B辑)》2003,15(4)
1 . INTRODUCTIONIntherecentdecades ,itisrealizedthatitisquitenecessarytocarryouttestsathighReynoldsnumberwithalowbackgroundnoiselevelinordertomeetmoreandmoreurgentneedsofmodernnavyandmaritimeindustry .Anewlargecavita tionchannelisdevelopedinCSSRCfortestingcompletehull/ propulsor/appendagesarrange ments[1] .Itrepresentsoneofthelatestintechno logicallyadvancedlargecavitationtestfacilities.Inthefollowingsections ,thefeaturesandthefirsttestresultsofthechannelwillbedescribed .2 . DICRIP… 相似文献
69.
The cross-spectral estimation methods are efficient in estimating the parameters of sinusoidal signals embedded in colored noise. But up to now, only FPT and cross-periodogram methods are used in this field, the modern auto-spectral estimation method is introduced into cross-spectral estimation in this paper, meanwhile the cross-correlation based Yule-Walker equation is proposed theoretically and the moment and singular-value decomposition (SVD)) algorithms for cross-spectral estimation have been developed. Finally, a numerical example is given for comparing the presented methods with the well-known Cadzow's SVD method. 相似文献
70.