全文获取类型
收费全文 | 13946篇 |
免费 | 1032篇 |
国内免费 | 9篇 |
专业分类
电工技术 | 94篇 |
综合类 | 8篇 |
化学工业 | 5257篇 |
金属工艺 | 195篇 |
机械仪表 | 315篇 |
建筑科学 | 510篇 |
矿业工程 | 17篇 |
能源动力 | 360篇 |
轻工业 | 3262篇 |
水利工程 | 113篇 |
石油天然气 | 73篇 |
无线电 | 614篇 |
一般工业技术 | 1894篇 |
冶金工业 | 880篇 |
原子能技术 | 40篇 |
自动化技术 | 1355篇 |
出版年
2024年 | 41篇 |
2023年 | 184篇 |
2022年 | 910篇 |
2021年 | 1033篇 |
2020年 | 424篇 |
2019年 | 433篇 |
2018年 | 486篇 |
2017年 | 517篇 |
2016年 | 558篇 |
2015年 | 468篇 |
2014年 | 601篇 |
2013年 | 918篇 |
2012年 | 865篇 |
2011年 | 998篇 |
2010年 | 758篇 |
2009年 | 711篇 |
2008年 | 656篇 |
2007年 | 626篇 |
2006年 | 480篇 |
2005年 | 375篇 |
2004年 | 322篇 |
2003年 | 294篇 |
2002年 | 276篇 |
2001年 | 172篇 |
2000年 | 120篇 |
1999年 | 173篇 |
1998年 | 213篇 |
1997年 | 169篇 |
1996年 | 159篇 |
1995年 | 121篇 |
1994年 | 117篇 |
1993年 | 93篇 |
1992年 | 79篇 |
1991年 | 59篇 |
1990年 | 61篇 |
1989年 | 48篇 |
1988年 | 44篇 |
1987年 | 41篇 |
1986年 | 46篇 |
1985年 | 46篇 |
1984年 | 36篇 |
1983年 | 25篇 |
1982年 | 21篇 |
1981年 | 24篇 |
1980年 | 24篇 |
1979年 | 26篇 |
1978年 | 25篇 |
1977年 | 19篇 |
1976年 | 25篇 |
1975年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
41.
Sandra Aparecida de Assis Pedro Fernandes Bruno Sommer Ferreira Joaquim MS Cabral Olga Maria Mascarenhas Faria Oliveira 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2004,79(3):277-280
A partially purified extract of pectinmethylesterase (PME) from acerola fruit was immobilized on various supports: glass, celite, chrysotile, agarose, concanavalin A Sepharose 4B, egg shell, polyacrylamide and gelatin. In addition, reticulation with glutaraldehyde was assessed, as well as the use of gelatin in the presence of celite, glass and silica. The highest immobilization yields were obtained when the pectinmethylesterase was immobilized in concanavalin A Sepharose 4B (81.7%) and in gelatin‐water (78.0%). Copyright © 2004 Society of Chemical Industry 相似文献
42.
Daniela D'Amato Maria Rosaria Corbo Matteo Alessandro Del Nobile & Milena Sinigaglia 《International Journal of Food Science & Technology》2006,41(10):1152-1157
In enology, alcoholic fermentation is a complex process involving several mechanisms. Slow and incomplete alcoholic fermentation is a chronic problem for the wine industry and factors leading to sluggish and stuck fermentations have been extensively studied and reviewed. The most studied cause of sluggish and stuck fermentation is the nitrogen content limitation. Nevertheless, other factors, such as temperature of fermentation and sugar concentration can affect the growth of yeasts. In this study we modelled the yeast growth‐cycle in wine model system as a function of temperature, sugar and ammonium concentrations; the individual effects and the interaction of these factors were analysed by means of a quadratic response surface methodology. Cell concentrations and weight loss were monitored in the whole wine fermentation process. The results of central composite design show that lower is the availability of nitrogen, higher is the cell growth rate; moreover, initial nitrogen concentration also influences survival time of Saccharomyces cerevisiae. 相似文献
43.
Generation and transmission of millimeter-wave data-modulated optical signals using an optical injection phase-lock loop 总被引:1,自引:0,他引:1
Generation and transmission of millimeter-wave data-modulated optical signals is presented using an optical injection phase-lock loop (OIPLL). Millimeter-wave signal generation is demonstrated with wide locking range, 30-GHz low phase noise level, -93 dBc/Hz, and a wide frequency tuning range, 4-60 GHz generation demonstrated using optical injection locking only, verified by using OIPLL in the 26-40 GHz range. The OIPLL is also used to transmit error-free 140-Mb/s amplitude shift keying and 68-Mb/s differential phase-shift keying (DPSK) modulated millimeter-wave signals over up to 65 km of uncompensated standard singlemode fiber. The DPSK system uses reference frequency modulation, eliminating the need for optical amplification. 相似文献
44.
Summary
In this paper thermal behavior of some HNBR blends with CPE, PVC, CR and NBR at three temperatures, 150, 170 and 190°C is
presented. Changes in characteristic IR bands, gel fraction, and chlorine content were assessed. Some mechanistic differences
between the studied systems, regarding the involvement the depletion of chlorine and modification in gel content, were pointed
out. Cyclization of nitrile structure was also observed by means of 2240 cm−1 band ascribed to >C=NH. Kinetic considerations are presented.
Received: 3 June 2002/Revised version: 14 November 2002/ Accepted 20 November 2002
Correspondence to Traian Zaharescu 相似文献
45.
The influence of NaCl and CO2 on the atmospheric corrosion of magnesium alloy AZ91 is studied in the laboratory. Samples were exposed under carefully controlled air and flow conditions; the relative humidity was 95%, the temperature was 22.0°C and the concentration of CO2 was < 1 ppm or 350 ppm. Different amounts of sodium chloride (0–70 μg/cm2) were added before exposure. The corrosion products were analyzed by gravimetry, ion chromatography, X‐ray diffraction and scanning electron microscopy. Mass gain and metal loss results are reported. The combination of high humidity and NaCl is very corrosive towards AZ91. However, the NaCl‐induced corrosion is inhibited by ambient concentrations of CO2. Exposure in the absence of CO2 gives rise to heavy pitting, with brucite, Mg(OH)2, being the dominant corrosion product. In the presence of CO2 a layer of hydrated magnesium hydroxy carbonate, Mg5(CO3)4(OH)2 · 5 H2O forms. A tentative corrosion mechanism is presented that explains the behavior in the two environments. 相似文献
46.
Johansson H. Lowenborg P. 《Circuits and Systems II: Express Briefs, IEEE Transactions on》2004,51(4):181-184
Recently, a particular structure for linear-phase finite-impulse response (FIR) filters with a variable bandwidth has received attention. In this structure, the overall transfer function is a weighted linear combination of fixed subfilters, with the weights being directly determined by the bandwidth. An advantage of this structure is that there are only a few adjustable parameters (weights), which results in a simple updating routine. However, in this paper, it is demonstrated that the use of a number of fixed regular overdesigned filters, each taking care of a part of the frequency region, in fact results in a lower overall arithmetic complexity. The price to pay is an increased group and phase delay. 相似文献
47.
48.
Kerstin Skog Åsa Eneroth & Maria Svanberg 《International Journal of Food Science & Technology》2003,38(3):313-323
Hamburgers and chicken fillets were cooked in convection ovens, deep‐fried or contact fried and analysed for mutagenic activity using the Ames test. For the three different convection ovens, the cooking parameters studied included the presence of steam, air velocity, air temperature and holding time. For deep‐frying and contact frying, the cooking parameters included cooking temperature and cooking time. In cooked hamburgers, mutagenic activity was only detected in those that had been deep‐fried. In chicken fillets, mutagenic activity was detected in samples prepared with all cooking methods, being highest in the deep‐fried samples. Factorial analysis indicated that heat transfer was the most important factor affecting mutagenic activity. High temperature and high air velocity in the convection ovens enhanced mutagenic activity. The presence of steam reduced the mutagenic activity, except when high temperature was used in combination with high air velocity. In chicken fillets, high mutagenic activity correlated to high weight loss during cooking. Pan‐fried chicken fillets were analysed using high performance liquid chromatography (HPLC) and the mutagenic/carcinogenic heterocyclic amines 2‐amino‐3,8‐dimethylimidazo[4,5‐f ]‐quinoxaline (MeIQx), 2‐amino‐1‐methyl‐6‐phenylimidazo‐[4,5‐b]‐pyridine (PhIP) and the co‐mutagenic heterocyclic amine Norharman (9H‐pyrido[3,4‐b]‐indole) were identified. The HPLC fractions were tested for mutagenic activity and, apart from the mutagenic fractions corresponding to MeIQx and PhIP, several mutagenic fractions were detected that did not correspond to known heterocyclic amines. 相似文献
49.
Maria E. Nadal Edward A. Early Will Weber Robert Bousquet 《Color research and application》2008,33(2):94-99
The NIST 0:45 reflectometer measures the spectral reflectance factor at an influx angle of 0° and an efflux angle of 45° of colored, nonfluorescent specimens at room temperature, with widths ranging from 3 to 10 cm and heights from 3 to 20 cm and with an uncertainty of less than 0.5 in color difference units. Published in 2008 by John Wiley & Sons, Inc. Col Res Appl, 33, 94–99, 2008 相似文献
50.
Sets of color tiles are available from the National Institute of Standards and Technology calibrated using the NIST 0:45 Reflectometer. The uncertainties associated with the measured values for the color tiles are an indispensable component of the calibration report that accompanies these tiles. A systematic, analytical approach developed previously was applied to the particular case of the reference instrument and color tile set, taking into account the operation and characteristics of the instrument and the spectral properties of the set. The primary sources of uncertainty were identified, and the resulting uncertainties in the color space values L*, a*, and b* were determined. In general, the uncertainties are lowest for those color tiles whose reflectance factors are nearly constant with wavelength. Published in 2008 by John Wiley & Sons, Inc. Col Res Appl, 33, 100–107, 2008 相似文献