全文获取类型
收费全文 | 5782篇 |
免费 | 515篇 |
国内免费 | 17篇 |
专业分类
电工技术 | 65篇 |
综合类 | 6篇 |
化学工业 | 1590篇 |
金属工艺 | 99篇 |
机械仪表 | 121篇 |
建筑科学 | 255篇 |
矿业工程 | 13篇 |
能源动力 | 148篇 |
轻工业 | 756篇 |
水利工程 | 38篇 |
石油天然气 | 13篇 |
无线电 | 566篇 |
一般工业技术 | 992篇 |
冶金工业 | 686篇 |
原子能技术 | 49篇 |
自动化技术 | 917篇 |
出版年
2022年 | 51篇 |
2021年 | 87篇 |
2020年 | 84篇 |
2019年 | 125篇 |
2018年 | 162篇 |
2017年 | 167篇 |
2016年 | 202篇 |
2015年 | 172篇 |
2014年 | 253篇 |
2013年 | 399篇 |
2012年 | 321篇 |
2011年 | 346篇 |
2010年 | 297篇 |
2009年 | 280篇 |
2008年 | 305篇 |
2007年 | 239篇 |
2006年 | 242篇 |
2005年 | 201篇 |
2004年 | 180篇 |
2003年 | 166篇 |
2002年 | 157篇 |
2001年 | 120篇 |
2000年 | 123篇 |
1999年 | 97篇 |
1998年 | 119篇 |
1997年 | 93篇 |
1996年 | 96篇 |
1995年 | 82篇 |
1994年 | 91篇 |
1993年 | 74篇 |
1992年 | 66篇 |
1991年 | 36篇 |
1990年 | 63篇 |
1989年 | 56篇 |
1988年 | 38篇 |
1987年 | 39篇 |
1986年 | 34篇 |
1985年 | 51篇 |
1984年 | 54篇 |
1983年 | 43篇 |
1982年 | 41篇 |
1981年 | 43篇 |
1980年 | 38篇 |
1979年 | 46篇 |
1978年 | 18篇 |
1977年 | 46篇 |
1976年 | 31篇 |
1975年 | 23篇 |
1974年 | 23篇 |
1973年 | 25篇 |
排序方式: 共有6314条查询结果,搜索用时 31 毫秒
71.
Sergey V. Ushakov Alexandra Navrotsky Jean A. Tangeman Katheryn B. Helean 《Journal of the American Ceramic Society》2007,90(4):1171-1176
Aerodynamic levitation combined with laser heating was used to prepare melts in the HfO2 –La2 O3 (–Gd2 O3 ) systems. All melts crystallized upon quenching in oxygen. Hf2 La2 O7 pyrochlore and Gd0.5 Hf0.5 O1.75 fluorite phases were identified. Gd0.5 Hf0.5 O1.75 fluorite was transformed into the pyrochlore structure by annealing at 1450°C. Pyrochlore that crystallized from HfO2 - La2 O3 melts contained 31.6–34.2 mol% La2 O3 . The unit cell parameter increased linearly with La content from 10.736 to 10.789 Å. Drop solution calorimetric experiments were performed in 3Na2 O·4MoO3 melt at 702°C. The enthalpies of formation from the oxides for pyrochlore phases are −107.0±5.0 kJ/mol for Hf2 La2 O7 and −48.8±4.7 kJ/mol for Hf2 Gd2 O7 . The enthalpy of the pyrochlore–fluorite phase transition in Hf2 Gd2 O7 is 23.6±3.1 kJ/mol. 相似文献
72.
Jozsef M. Berty Sunggyu Lee Ferenc Szeifert Jean B. Cropley 《Chemical Engineering Communications》1989,76(1):9-33
Testing kinetic models against a “true” and detailed kinetic expression was the aim of the Workshop on Kinetic Model Development at the Denver AIChE Meeting in August, 1983. For this purpose an artificial reaction mechanism was created, based on the known thermodynamics of the methanol synthesis as a framework. The kinetic rate laws, that were derived from this mechanism, were made thermodynamically consistent by achieving agreement between equilibrium constants calculated at various temperatures from the given, real original thermodynamic relationship and those calculated from the detailed reversible kinetic expressions.
Using the artificial kinetics as the "true" one, CSTR experiments were simulated. The results of a statistically designed set of experiments were published after 5% random error was added to the data. Participation was invited for all interested to correlate the data, develop kinetic models and to calculate the performance of the specified reactor.
The results of 19 submitted entries are summarized with the conclusion that the models had more differences than were expected, but their predictive values were not as different as was anticipated, if the extreme high production rates due to thermal runaways are not considered. This in turn points out the necessity to check models experimentally, in pilot plant, not only for predicted optimum, but also for calculated runaway conditions. Models which did not capture the true character of this reaction failed to predict the onset of runaway reactions. 相似文献
Using the artificial kinetics as the "true" one, CSTR experiments were simulated. The results of a statistically designed set of experiments were published after 5% random error was added to the data. Participation was invited for all interested to correlate the data, develop kinetic models and to calculate the performance of the specified reactor.
The results of 19 submitted entries are summarized with the conclusion that the models had more differences than were expected, but their predictive values were not as different as was anticipated, if the extreme high production rates due to thermal runaways are not considered. This in turn points out the necessity to check models experimentally, in pilot plant, not only for predicted optimum, but also for calculated runaway conditions. Models which did not capture the true character of this reaction failed to predict the onset of runaway reactions. 相似文献
73.
Xiaohong Gu Tinh Nguyen Mounira Oudina David Martin Bouchra Kidah Joan Jasmin Aziz Rezig Lipiin Sung Eric Byrd Jonathan W. Martin Derek L. Ho Y. C. Jean 《Journal of Coatings Technology and Research》2005,2(7):547-556
Atomic force microscopy (AFM) has been used to study the morphology and microstructure of an amine-cured epoxy before and
after outdoor exposure. Measurements were made from samples prepared in an essentially CO2-free, H2O-free glove box and from samples prepared in ambient conditions. For those prepared in a CO2-free glove box, AFM imaging was conducted on (1) an unexposed air/coating surface, (2) an unexposed coating bulk, (3) an
unexposed coating/substrate interface, and (4) a field exposed air/coating surface. For samples prepared in ambient conditions,
only the unexposed air/coating surface was investigated. The same regions of the exposed samples were scanned periodically
by the AFM to monitor changes in the surface morphology of the coating as UV exposure progressed. Small angle neutron scattering
and Fourier transform infrared spectroscopy (FTIR) studies were performed to verify the microstructure and to follow chemical
changes during outdoor exposure, respectively. The results have shown that amine blushing, which occurs only under ambient
conditions, had a significant effect on the surface morphology and microstructure of the epoxy. The surface morphology of
the samples prepared under CO2-free, dry conditions was generally smooth and homogeneous. However, the interface and the bulk samples clearly revealed a
two-phase structure consisting of bright nodular domains and dark interstitial regions, indicating an inhomogeneous microstructure.
Such heterogeneous structure of the bulk was in good agreement with results obtained by small angle neutron scattering of
unexposed samples and by AFM phase imaging of the degraded sample surface. The relationship between submicrometer physical
changes and molecular chemical degradation is discussed.
Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004, in Chicago,
IL. 相似文献
74.
Effect of dietary n−3 and n−6 polyunsaturated fatty acids on lipid-metabolizing enzymes in obese rat liver 总被引:2,自引:0,他引:2
Isabelle Niot Joseph Gresti Jacqueline Boichot Georges Semporé Georges Durand Jean Bézard Pierre Clouet 《Lipids》1994,29(7):481-489
This study was designed to examine whether n−3 and n−6 polyunsaturated fatty acids at a very low dietary level (about 0.2%)
would alter liver activities in respect to fatty acid oxidation. Obese Zucker rats were used because of their low level of
fatty acid oxidation, which would make increases easier to detect. Zucker rats were fed diets containing different oil mixtures
(5%, w/w) with the same ratio of n−6/n−3 fatty acids supplied either as fish oil or arachidonic acid concentrate. Decreased
hepatic triacylglycerol levels were observed only with the diet containing fish oil. In mitochondrial outer membranes, which
support carnitine palmitoyltransferase I activity, cholesterol content was similar for all diets, while the percentage of
22∶6n−3 and 20∶4n−6 in phospholipids was enhanced about by 6 and 3% with the diets containing fish oil and arachidonic acid,
respectively. With the fish oil diet, the only difference found in activities related to fatty acid oxidation was the lower
sensitivity of carnitine palmitoyltransferase I to malonyl-CoA inhibition. With the diet containing arachidonic acid, peroxisomal
fatty acid oxidation and carnitine palmitoyltransferase I activity were markedly depressed. Compared with the control diet,
the diets enriched in fish oil and in arachidonic acid gave rise to a higher specific activity of aryl-ester hydrolase in
microsomal fractions. We suggest that slight changes in composition of n−3 or n−6 polyunsaturated fatty acids in mitochondrial
outer membranes may alter carnitine palmitoyltransferase I activity. 相似文献
75.
76.
Frédéric Destaillats Jean B. Jean-Denis Joseph Arul Robert L. Wolff Paul Angers 《Journal of the American Oil Chemists' Society》2002,79(11):1091-1094
GC analysis was performed to determine regiospecific distribution and FA composition in seed oils of the Aceraceae species,
Acer saccharum and A. saccharinum. The oil content in the seeds was low at 5.0% in A. saccharum and 5.8% in A. saccharinum, and the main FA were linoleic (30.8 and 29.4%), oleic (21.3 and 27.6%), palmitic (10.1 and 10.5%), and cis-vaccenic (9.4 and 7.9%) acids, respectively. In addition, both oils contained long-chain monoenes of the n−9 and n−7 groups,
including 11-eicosenoic, 13-docosenoic, 15-tetracosenoic, 13-eicosenoic, and 15-docosenoic acids, whereas γ-linolenic acid
accounted for 0.8% of total FA in A. saccharum, and 0.5% in A. saccharinum. Regiospecific analysis, performed using the methodology of dibutyroyl derivatives of MAG, indicated that linoleic, oleic,
and linolenic acids were mainly esterified at the internal position of TAG in both seed oils, whereas long-chain monoenes
of the n−7 group were almost exclusively esterified on the external positions. 相似文献
77.
硅酮密封胶对阳极氧化铝的黏结质量千差万别.影响黏结性的关键因素是铝材表面的封孔程度、氧化层的着色情况、清洁剂的特性以及基材表面清洁与打胶之间允许的时间间隔.由于清洁剂将有机污染物从阳极氧化铝表面去除的效果不同,所以此效果并不和黏结质量有必然联系.据猜测,吸附在阳极氧化铝表面的清洁溶剂会改善基材表面从而提高硅酮胶的黏结性,但这种改善效果会随着清洁溶剂随时间的的挥发而降低.对于给定的溶剂,最佳的黏结效果取决于材料表面的封孔程度.依照ISO 2143酸刻蚀方法测量材料表面的封孔程度,可以预测未着色的阳极氧化铝基材的黏结性.对于着色的阳极氧化铝表面,依照ISO 2931的测试标准,用电相位漂移方法可以用来预测黏结质量.一种控制阳极氧化铝表面的方法被提了出来,此方法是测量不同频率下基材的电阻抗并将它成功地和硅酮密封胶与该材料表面的长期黏接性联系起来. 相似文献
78.
Summary The herbicide 2,4-D was microencapsulated using ethyl cellulose to develop controlled release formulations that protect it from photodegradation and evaporation and to reduce the environment pollution. Ethyl cellulose microspheres loaded with 2,4-D were prepared by the emulsion solvent-evaporation technique. We have obtained the desired microspheres with higher drug entrapment and encapsulation yield by varying certain conditions as stirring speed, polymer-solvent ratio, drug-polymer ratio, pH of continuous phase and organic phase solvent. The shape and size of microspheres were analysed by scanning electron microscopy. The herbicide release was studied at 25 °C and the release data were analysed according to Fick’s Law. The results demonstrate that we can control the release rate by modifying the process parameters. 相似文献
79.
Poly(p-tert-butoxycarbonyloxystyrene): a convenient precursor to p-hydroxystyrene resins 总被引:1,自引:0,他引:1
An efficient synthetic route to pure, high molecular weight poly(p-hydroxystyrene) is reported. The route involves synthesis of a new monomer, p-tert-butoxycarbonyloxystyrene, polymerization by radical initiation or by cationic initiation in liquid SO2, followed by thermolysis or acidolysis of the tert-butoxycarbonyl protecting group. Porous, crosslinked resin beads containing the nucleophilic, phenol pendant group have been prepared in a similar fashion from the precursor terpolymer of p-tert-butoxycarbonyloxystyrene, styrene and divinylbenzene. The utility of this resin for solid-phase synthesis has been demonstrated. 相似文献
80.
Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.