全文获取类型
收费全文 | 2560篇 |
免费 | 195篇 |
国内免费 | 5篇 |
专业分类
电工技术 | 37篇 |
综合类 | 1篇 |
化学工业 | 675篇 |
金属工艺 | 51篇 |
机械仪表 | 46篇 |
建筑科学 | 68篇 |
矿业工程 | 4篇 |
能源动力 | 90篇 |
轻工业 | 245篇 |
水利工程 | 21篇 |
石油天然气 | 2篇 |
无线电 | 230篇 |
一般工业技术 | 540篇 |
冶金工业 | 142篇 |
原子能技术 | 18篇 |
自动化技术 | 590篇 |
出版年
2024年 | 5篇 |
2023年 | 39篇 |
2022年 | 83篇 |
2021年 | 113篇 |
2020年 | 85篇 |
2019年 | 77篇 |
2018年 | 80篇 |
2017年 | 84篇 |
2016年 | 108篇 |
2015年 | 94篇 |
2014年 | 123篇 |
2013年 | 170篇 |
2012年 | 204篇 |
2011年 | 229篇 |
2010年 | 171篇 |
2009年 | 149篇 |
2008年 | 153篇 |
2007年 | 127篇 |
2006年 | 127篇 |
2005年 | 79篇 |
2004年 | 72篇 |
2003年 | 60篇 |
2002年 | 42篇 |
2001年 | 25篇 |
2000年 | 20篇 |
1999年 | 23篇 |
1998年 | 44篇 |
1997年 | 31篇 |
1996年 | 16篇 |
1995年 | 14篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 5篇 |
1991年 | 15篇 |
1990年 | 4篇 |
1989年 | 3篇 |
1988年 | 3篇 |
1987年 | 6篇 |
1986年 | 4篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1982年 | 5篇 |
1981年 | 5篇 |
1979年 | 6篇 |
1975年 | 3篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1967年 | 1篇 |
1931年 | 1篇 |
排序方式: 共有2760条查询结果,搜索用时 15 毫秒
951.
952.
Didier Saury Nicolas RougerFrancis Djanna François Penot 《International Communications in Heat and Mass Transfer》2011,38(6):679-687
A large-scale experimental setup is built and instrumented. It consists in a 4 m-high cavity with a horizontal cross-section equal to 0.86 × 1.00 m². Two opposite vertical walls are heated and cooled down; other walls (lateral walls, ceiling and floor) are made of insulating medium covered with a thin and low-emissivity film designed to minimize radiative effects into the cavity. The temperatures of active walls are imposed, constant and equally distributed around the ambient temperature in order to reduce heat losses. The temperature difference between the hot and cold walls is chosen to respect the Boussinesq approximation. Under these assumptions, Rayleigh number values up to 1.2 × 1011 (ΔT = 20 °C) can be obtained. The centre-symmetry is verified on the thermal stratification. Influence of the temperature difference and of wall emissivities on the stratification parameter (dimensionless vertical temperature gradient) is discussed. Velocity measurements allow the velocity field to be obtained and provide information on flows encountered in the cavity. Temperature measurements are also carried out in the whole cavity. In the paper, a complete experimental characterization is provided: airflow inside the cavity is analyzed and the Nusselt number along the hot and the cold wall is presented. 相似文献
953.
Chang HS Um W Rod K Serne RJ Thompson A Perdrial N Steefel CI Chorover J 《Environmental science & technology》2011,45(19):8313-8320
Leaching behavior of Sr and Cs in the vadose zone of Hanford site (Washington) was studied with laboratory-weathered sediments mimicking realistic conditions beneath the leaking radioactive waste storage tanks. Unsaturated column leaching experiments were conducted using background Hanford pore water focused on first 200 pore volumes. The weathered sediments were prepared by 6 months reaction with a synthetic Hanford tank waste leachate containing Sr and Cs (10(-5) and 10(-3) molal representative of LO- and HI-sediment, respectively) as surrogates for (90)Sr and (137)Cs. The mineral composition of the weathered sediments showed that zeolite (chabazite-type) and feldspathoid (sodalite-type) were the major byproducts but different contents depending on the weathering conditions. Reactive transport modeling indicated that Cs leaching was controlled by ion-exchange, while Sr release was affected primarily by dissolution of the secondary minerals. The later release of K, Al, and Si from the HI-column indicated the additional dissolution of a more crystalline mineral (cancrinite-type). A two-site ion-exchange model successfully simulated the Cs release from the LO-column. However, a three-site ion-exchange model was needed for the HI-column. The study implied that the weathering conditions greatly impact the speciation of the secondary minerals and leaching behavior of sequestrated Sr and Cs. 相似文献
954.
Abstract: Addition of wheat bran to flours modifies their expansion properties after cooking extrusion. This can be attributed to changes in the melt shear viscosity at the die. The effect of wheat bran concentration added to achieve 2 levels of dietary fibers of 12. 6% and 24.4%, and process conditions on the shear viscosity of wheat flour was therefore assessed using an online twin‐slit rheometer. The shear viscosity measured at 30 s?1 ranged from 9.5 × 103 to 53.4 × 103 Pa s. Regardless of the process conditions and bran concentration, the extruded melts showed a pseudoplastic behavior with a power law index n ranging from 0.05 to 0.27. Increasing the barrel temperature of the extruder from 120 to 180 °C, the water content from 18% to 22% or the screw speed from 400 to 800 rpm significantly decreased the melt shear viscosity at the extruder exit. The addition of bran significantly increased the melt shear viscosity only at the highest bran concentration. The effect was process condition dependant. Mathematical interpretations, based upon observations, of the experimental data were carried out. They can be used to predict the effect of the process conditions on the melt shear viscosity at the die of extruded wheat flour with increasing bran concentration. The viscosity data will be applied in future works to study the expansion properties of extruded wheat flour supplemented with bran. Practical Application: Incorporation of wheat bran, a readily available and low cost by‐product, in extruded puffed foods is constrained due to its negative effect on the product texture. Understanding the effect of wheat bran on rheological properties of extruded melts, driving the final product properties, is essential to provide solutions to the food industry and enhance its use. 相似文献
955.
Dalmasso M Nicolas P Falentin H Valence F Tanskanen J Jatila H Salusjärvi T Thierry A 《International journal of food microbiology》2011,145(1):113-120
Propionibacterium freudenreichii is used as a ripening culture in Swiss cheese manufacture. This study investigates the molecular diversity and the population structure of this bacterium via multilocus sequence typing (MLST). Internal fragments of seven genes sequenced for 113 strains of different subspecies and origins allowed the resolution of 46 sequence types (STs) with occurrence frequencies ranging from 1 to 11. The core genome of the species harbours a low level of nucleotide polymorphism. In our data, single nucleotide polymorphisms account for only 2.28% of the concatenated sequences, and the average polymorphism rate in pairwise comparisons is 0.46%. The analyses reveal quantitatively comparable contributions of recombination and mutation in nucleotide changes at core genome loci along cell lineages. Remarkably, the STs exhibit little if any dairy biotope specialization. Phenotypic characterisation of the strains, based on their aptitude to use lactose and nitrate, shows that the two previously identified subspecies (freudenreichii and shermani) do not reflect the ancestral relationships in the P. freudenreichii population. The considerable phenotypic heterogeneity, found even at the ST level, suggests instead a history of recurrent switches between phenotypes. 相似文献
956.
The matched filter is a widely used detector in hyperspectral detection applications because of its simplicity and its efficiency in practical situations. We propose to estimate its performance with respect to the number of spectral bands. These spectral bands are selected thanks to a genetic algorithm in order to optimize the contrast between the target and the background in the detection plane. Our band selection method can be used to optimize not only the position but also the linewidth of the spectral bands. The optimized contrast always increases with the number of selected bands. However, in practical situations, the target spectral signature has to be estimated from the image. We show that in the presence of estimation error, the maximum number of bands may not always be the best choice in terms of detection performance. 相似文献
957.
Meier Beat; von Wartburg Philipp; Matter Sibylle; Rothen Nicolas; Reber Rolf 《Canadian Metallurgical Quarterly》2011,65(1):12
In retrospective memory, performance predictions have been found to enhance performance on subsequent memory tests. In prospective memory, the influence of metacognitive judgments on performance has not been investigated systematically. In the present study, 140 undergraduate students performed a complex short-term memory task that included a prospective memory task. Half of them gave performance predictions after the prospective memory task instructions. In addition, the specificity of the prospective memory task was manipulated by instructing participants either to perform an action when a word that belongs to the category of musical instruments was presented or to respond when the word “trumpet” was presented. The results showed that performance predictions enhanced performance, but only for the categorical task. Additional analyses of retrieval experience showed that performance predictions lead to an increase in search experiences while cue specificity was accompanied by an increase in pop up experiences. The results indicate that performance predictions can improve prospective performance and thus may be a valuable strategy for assisting prospective memory. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献
958.
Stéphane Reculusa Matthias Heim Feng Gao Nicolas Mano Serge Ravaine Alexander Kuhn 《Advanced functional materials》2011,21(4):691-698
Porous gold structures with a well‐defined pore size and thickness are obtained through electrochemical deposition of gold in a colloidal crystal template synthesized by the Langmuir–Blodgett (LB) technique. Cylindrical gold wires were used as substrates for the LB deposition of successive monolayers of silica particles of various sizes, and the electrodeposition of gold through this inorganic template led to a homogeneous, porous metal structure. These materials were characterized through typical electrochemical experiments and showed high surface‐to‐volume ratios with promising features for their further use in miniaturized electrocatalytic devices. 相似文献
959.
960.
Lafjah M Djafri F Bengueddach A Keller N Keller V 《Journal of hazardous materials》2011,186(2-3):1218-1225
Beta zeolite supported sol-gel TiO(2) photocatalytic materials were prepared according to a sol-gel route in which high specific surface area Beta zeolite powder was incorporated into the titanium isopropoxide sol during the course of the sol-gel process. This led to an intimate contact between the zeolite surface and the TiO(2) precursors, and resulted in the anchorage of large amounts of dispersed TiO(2) nanoparticles and in the stabilization of TiO(2) in its anatase form, even for high TiO(2) wt. contents and high calcination temperatures. Taking the UV-A photocatalytic oxidation of methanol as gas phase target reaction, high methanol conversions were obtained on the Beta zeolite supported TiO(2) photocatalysts when compared to bulk sol-gel TiO(2), despite lower amounts of TiO(2) within the photoactive materials. The methanol conversion was optimum for about 40 wt.% TiO(2) loading and calcination temperatures of 500-600°C. 相似文献