全文获取类型
收费全文 | 7144篇 |
免费 | 1140篇 |
国内免费 | 206篇 |
专业分类
电工技术 | 36篇 |
综合类 | 348篇 |
化学工业 | 2330篇 |
金属工艺 | 103篇 |
机械仪表 | 806篇 |
建筑科学 | 81篇 |
矿业工程 | 79篇 |
能源动力 | 81篇 |
轻工业 | 1182篇 |
水利工程 | 23篇 |
石油天然气 | 243篇 |
武器工业 | 9篇 |
无线电 | 967篇 |
一般工业技术 | 1057篇 |
冶金工业 | 750篇 |
原子能技术 | 220篇 |
自动化技术 | 175篇 |
出版年
2024年 | 34篇 |
2023年 | 164篇 |
2022年 | 296篇 |
2021年 | 398篇 |
2020年 | 315篇 |
2019年 | 313篇 |
2018年 | 266篇 |
2017年 | 337篇 |
2016年 | 322篇 |
2015年 | 324篇 |
2014年 | 471篇 |
2013年 | 456篇 |
2012年 | 595篇 |
2011年 | 537篇 |
2010年 | 384篇 |
2009年 | 382篇 |
2008年 | 340篇 |
2007年 | 385篇 |
2006年 | 341篇 |
2005年 | 264篇 |
2004年 | 217篇 |
2003年 | 216篇 |
2002年 | 174篇 |
2001年 | 122篇 |
2000年 | 111篇 |
1999年 | 80篇 |
1998年 | 87篇 |
1997年 | 69篇 |
1996年 | 77篇 |
1995年 | 60篇 |
1994年 | 52篇 |
1993年 | 38篇 |
1992年 | 50篇 |
1991年 | 41篇 |
1990年 | 33篇 |
1989年 | 20篇 |
1988年 | 14篇 |
1987年 | 17篇 |
1986年 | 13篇 |
1985年 | 15篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 7篇 |
1981年 | 10篇 |
1980年 | 3篇 |
1976年 | 3篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1959年 | 1篇 |
1951年 | 2篇 |
排序方式: 共有8490条查询结果,搜索用时 15 毫秒
1.
2.
光纤荧光传感器衰减寿命的加权对数拟合法 总被引:2,自引:0,他引:2
荧光寿命的检测是荧光光学传感器的核心内容,国际上尝试了多种方法来拟合这种理论上为单指数衰减信号的荧光衰减曲线。这些方法包括非线性函数标准拟合方法。即Levenburg-Marquardt方法,以及Prony方法、FFT方法,对数拟合法等等。为了克服在实际应用中发生的信号退化,需要在测量信号衰减寿命的同时测量信号的初始强度。文章介绍了一种加权的对数拟合法,经计算机仿真及实际数据测试均可以得到和Levenburg-Marquardt方法非常接近的结果,且拟合时间大大缩短,测量稳定性大大提高。仿真测试及具体实验测试结果显示了这种方法的有效性。该方法不仅与Levenburg-Marquardt方法的偏差曲线非常相似,而且实验测得的荧光寿命与Levenburg-Marquardt方法偏差在0.2%以内。 相似文献
3.
4.
References: 《中国炼油与石油化工》2007,(3):35-42
The proton nuclear magnetic resonance spectroscopy (1H-NMR), the synchronous fluorescence spectrometry (SFS) and the ruthenium ions catalyzed oxidation (RICO) method were used to determine the chemical structure of polyaromatic nucleus in Oman residue fractions. The results of 1H-NMR analyses showed that the average numbers of aromatic rings in the aromatics, resins and asphaltenes units were 3.2, 5.6 and 8.2, respectively. SFS was used to investigate the distribution of aromatic rings in residue fractions, the main distribution range of aromatic rings in aromatics, resins and asphaltenes were 3 4 rings, 3--5 rings and more than 5 rings, respectively. The aromatic network in residue fractions was oxidized to produce numerous carboxylic acids. The types and content of benzenepolycarboxylic acids, such as phthalic acid, benzenetricarboxylic acids, benzenetetracarboxylic acids, benzenepentacarboxylic acid and benzenehexacarboxylic acid disclosed the condensed types of aromatic nuclei in the core. The biphenyl fraction (BIPH), the cata-condensed fraction (CATA), the peri-condensed fraction (PERI) and the condensed index (BCI) were calculated based on the benzenepolycarboxylic acids formed. The results implied that there was less biphenyl type structures in all residue fractions. The aromatics fraction was almost composed of the cata-condensed type system, and the asphaltenes fraction was wholly composed of the peri-condensed type system, while in the resins fraction co-existed the two types, herein the peri-con- densed type was predominant over the cata-condensed type. Based on the analytical results obtained in the study, the components --aromatics, resins and asphaltenes -- were given the likely structural models. 相似文献
5.
Yang Wei 《Materials Letters》2007,61(6):1337-1340
Well-crystallized LaF3:Yb,Er nanoparticles were prepared by the polyol method and three kinds of polyols (glycol, diethylene glycol and glycerol) were chosen as the reaction medium respectively. All of the obtained LaF3:Yb,Er nanoparticles have roughly spherical shapes, and the average sizes of these nanoparticles ranged from 5 to 7 nm. These nanoparticles could be well dispersed in water or ethanol to form colloidal solutions. When these nanoparticles were excited by the 980 nm laser, several upconversion emissions were observed. 相似文献
6.
7.
本文介绍了降秩因子分析(RAFA)方法,它是从一个多组分混合物中直接定量计算其中某一组分,而不必知道其它组分的物种及含量的一种定量分析的数学方法。它适用于双线性的数据。本实验首先将荧光分光光度计与外接计算机相连,以获得样品的激发-发射矩阵(EEM),再用RAFA方法对蒽、萘、菲、芘、芴、(艹屈)六种标样的一至五组分的混合物进行定量分析,获得满意的结果。 相似文献
8.
J. Sieber D. Broton C. Fales S. Leigh B. MacDonald A. Marlow S. Nettles J. Yen 《Cement and Concrete Research》2002,32(12):1899-1906
The eight portland cements and two calcium aluminate cements in the Standard Reference Material (SRM) 1880 series are among the most popular SRMs in the catalog of the National Institute of Standards and Technology (NIST) Standard Reference Materials Program. Numerous laboratories rely on them for elemental analysis and qualification for ASTM C 114-00 Standard Test Methods for Chemical Analysis of Hydraulic Cement. NIST has collected new candidate materials from around the world and partnered with Construction Technology Laboratories (CTL) in their preparation and certification. This paper describes the procedures taken at NIST and CTL to prepare and test materials for certification including the homogeneity testing, the X-ray fluorescence methods and the statistical data analysis performed for value assignment. 相似文献
9.
Kenji Imura 《Color research and application》2007,32(3):195-200
In this article, a new method for measuring a total spectral radiance factor of a FWA‐treated sample illuminated by a specific standard illuminant is introduced. The method replaces an unstable real fluorescent standard by a bi‐spectral luminescent radiance factor data, which works as a virtual fluorescent standard (VFS) by knowing spectral intensity distributions of illuminations applied to the sample. The method utilizes two illuminations I1 and I2 whose relative spectral intensity distributions are different from each other and synthesizes a virtual illumination presenting the identical fluorescent spectral radiance factor to that presented by the standard illuminant with the VFS of the specific bi‐spectral luminescent radiance factor by linearly combining I1 and I2 with the suitable weighting factors. The applicability of the method is examined in principle by comparing ISO brightness and CIE whiteness index of fluorescent standard paper as a test sample obtained by this new method to the assigned values. © 2007 Wiley Periodicals, Inc. Col Res Appl, 32, 195–200, 2007 相似文献
10.
New HPLC Method to Determine Ethyl Carbamate in Alcoholic Beverages Using Fluorescence Detection 总被引:2,自引:0,他引:2
ABSTRACT: A new methodology to the quantification of ethyl carbamate (EC) has been developed. This method allows the analysis by HPLC of ethyl carbamate in samples of wine, fortified wine, and wine brandy, by a pre-column derivatization with 9-xanthydrol, and fluorescence detection. This does not require previous sample extraction or concentration. The method presents an average recovery of 96% among samples studied, a detection limit of 4.2μg/L, and an average intermediate precision of 6.3%. The comparison of the results obtained for EC analysis on the same wine brandy samples by GC/MS and HPLC are statistically indistinguishable with 97.5% probability. The results of the analysis of 42 samples are presented. 相似文献