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991.
V. A. Lavrenko L. A. Glebov A. P. Pomitkin V. G. Chuprina T. G. Protsenko 《Oxidation of Metals》1975,9(2):171-179
The kinetics of titanium carbide oxidation in oxygen over the temperature range of 600–1200°C and oxygen pressure from 0.1 to 740 Torr have been studied with a vacuum microbalance. Layer-by-layer x-ray analysis, petrography, metallography, and gas chromatography have been used to analyze the oxidation products. A paralinear nature of the oxidation of material was established, and the rate constants of the process were calculated for the corresponding parabolic and linear portions of the kinetic curves. It was shown that a gaseous product, CO2, formed, as well as a solid product, TiO2 (rutile), both stoichiometric and nonstoichiometric. The lower oxides, Ti3O5, Ti2O3, TiO, were noted in the scale at temperatures from 700 to 800° and low oxygen pressures, their relative quantity rising with decreasing pressure. Based on x-ray analysis and microhardness measurements, it was concluded that titanium oxicarbides formed in the TiC, directly adjacent to the scale. A possible oxidation mechanism of titanium carbide is proposed. 相似文献
992.
Martin Friis Christer Persson Per Nylén Jan Wigren 《Journal of Thermal Spray Technology》2001,10(2):301-310
A detailed investigation of the relationship between the parameters of the spray process and the in-flight properties of the
particles was carried out using a multivariate statistical approach. A full factorial designed experiment concerning the spray
process was performed, the spray gun parameters’ current, argon flow rate, hydrogen flow rate, and powder feed rate being
selected to control the process. The particle properties, viz. velocity, temperature, and diameter, were determined using an optical measurement system, DPV 2000. In addition, the standard
deviations of, and the correlations between, the measured particle properties were analyzed. The results showed current to
have the strongest impact on particle velocity and particle temperature and argon flow rate to be the only parameter with
an inverse effect on velocity and temperature. 相似文献
993.
Polycarbonate (PC) nanofibers are prepared using the air blowing‐assisted electrospinning process. The effects of air blowing pressure and PC solution concentration on the physical properties of fibers and the filtration performance of the nanofiber web are investigated. The air blowing‐assisted electrospinning process produces fewer beads and smaller nanofiber diameters compared with those obtained without air blowing. Uniform PC nanofibers with an average fiber diameter of about 0.170 μm are obtained using an applied voltage of 40 kV, an air blowing pressure of 0.3 MPa, a PC solution concentration of 16%, and a tip‐to‐collection‐screen distance (TCD) of 25 cm. The filtration efficiency improvement of the air blowing‐assisted electrospun web can be attributed to the narrow distribution of fiber diameter and small mean flow pore size of the electrospun web. Performance results show that the air blowing‐assisted electrospinning process can be applied to produce PC nanofiber mats with high‐quality filtration. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
994.
《分离科学与技术》2012,47(6):813-819
The flow patterns in the annular region of a 50 mm annular centrifugal extractor (ACE) were studied using phase particle image velocimetry (PIV), by which the distributions of radial velocity, axial velocity, vorticity, turbulent kinetic energy (TKE), and micromixing time of a fluid under different rotating Reynolds numbers were investigated. In the center of the annular region, both the radial and axial velocities of the fluid are close to zero, regardless of the rotating Reynolds number changes. The TKE of the fluid along the radial direction is small at center and large on the edge. The results show that the mixing process mainly occurs at the region near the outer cylinder’s sidewall, and the mixing time in this region is less than that in the internal annular region. Besides, the whole mixing efficiency is proportional to the rotational speed when the speed is below a certain level, and then gradually reaches a plateau when the speed is further increased. 相似文献
995.
Catherine A. Fromen Tammy W. Shen Abigail E. Larus Peter Mack Benjamin W. Maynor J. Christopher Luft Joseph M. DeSimone 《American Institute of Chemical Engineers》2013,59(9):3184-3194
The top‐down, micromolding technique, referred to as Particle Replication in Nonwetting Templates (PRINT®), affords a new opportunity for the generation of inhalation therapeutics. Powders were fabricated with predetermined particle size and shape; when dispersed with a collision jet nebulizer, these particles resulted in monodisperse aerosols with geometric standard deviations well below 1.2. Dynamic shape factors for this novel set of uniformly shaped particles were determined by correcting the drag of nonspherical particles in the ultra‐Stokesian flow conditions of the aerodynamic particle sizer (APS). This convenient approach for shape factor determination agreed well with current literature approaches and allowed for the correction of APS results for particles with known volumes. Determined shape factor values of PRINT geometries were used to estimate the theoretical median aerodynamic diameters of individual aerosols, which were then compared to actual inhalation powders. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3184–3194, 2013 相似文献
996.
采用扫描电子显微镜(SEM)和能谱仪(EDS),观察和分析了熟料中的矿物形貌和化学组成,探讨了碱在熟料中的存在形式.研究结果表明,在高碱熟料中可以观察到有明显的硫酸盐存在,如Na2SO4,K2SO4,CaSO4或CaSO4·K2SO4;高碱熟料中碱更易进入硅酸盐矿物和铝酸盐矿物中,分别形成KC23S12、NCBA3;熟料中的碱(R2O)有一部分固溶在硅酸盐矿物和铝酸盐矿物中. 相似文献
997.
采用炭黑和单甲基丙烯酸锌(ZMMA)并用作补强剂制备了氢化丁腈橡胶(HNBR)复合材料,使用X射线衍射法和透射电子显微镜法分析了ZMMA在HNBR硫化过程中的结构和形态变化,并研究了一段硫化时间对复合材料力学性能的影响。结果表明,在硫化过程中,ZMMA发生了复杂的化学反应;随着一段硫化时间的延长,氢化丁腈橡胶复合材料的拉伸强度和100%定伸应力变化都不大,而撕裂强度先增大后减小,拉断伸长率减小。X射线衍射结果表明,ZMMA由结晶态转变为非结晶态。透射电子显微镜分析结果表明,在硫化开始阶段,ZMMA聚合反应已经完成,有大量的纳米级粒子分布在橡胶基体中。 相似文献
998.
Jong Min Kim Sang Mok Chang Sung Min Kong Kyo-Seon Kim Jinsoo Kim Woo-Sik Kim 《Ceramics International》2009
This study investigated the control of hydroxyl groups, one of key factors determining the surface properties of silica particles synthesized by the sol-precipitation of tetraethyl orthosilicate (TEOS). Thus, a thermal gravity analysis (TGA) was used to facilitate quantitative measurements of the hydroxyl groups on the silica particles, while BET and FT-IR were used to analyze the specific surface area and functional silane groups on the silica particles, respectively. In the sol-precipitation process, silanes that include various hydroxyl groups are formed as intermediates based on the hydrolysis and condensation of TEOS. Thus, NH3, as a basic catalyst initiating the nucleophilic substitution of TEOS, was found to accelerate the hydrolysis and increase the hydroxyl group content on the silica particles. Plus, the hydroxyl group content was also increased when increasing the concentrations of TEOS and water as the hydrolysis reactants. However, the hydroxyl group content was reduced when increasing the temperature, due to the promotion of condensation. Based on the weight loss of the particles according to the thermal analysis, the hydroxyl group content on the silica particles varied from 5.6–42.7 OH/nm2 under the above reaction conditions. 相似文献
999.
1000.
T. Schalow B. Brandt D. E. Starr M. Laurin S. Schauermann Sh. K. Shaikhutdinov J. Libuda H.-J. Freund 《Catalysis Letters》2006,107(3-4):189-196
We have studied the influence of oxygen on the structure and morphology of a Pd/Fe3O4 model catalyst using molecular beam (MB) methods, IR reflection absorption spectroscopy (IRAS) and scanning tunneling microcopy
(STM). The model catalyst was prepared under ultrahigh vacuum (UHV) conditions by physical vapor deposition (PVD) and growth
of Pd nanoparticles on an ordered Fe3O4 thin film on Pt(111).
It is found that surface oxides are formed on the Pd nanoparticles even under mild oxidation conditions (temperatures of 500 K
and effective oxygen partial pressures of around 10−6 mbar). These surface oxides are initially generated at the Pd/Fe3O4 interface and, subsequently, are formed at the Pd/gas interface. The process of formation and reduction of surface and interface
oxides on the Pd particles is fully reversible in that all oxides formed can be fully reduced. As a result, the oxide phase
acts like a storage medium for oxygen during oxidation reactions, as probed via CO oxidation.
The process of surface and interface oxidation is directly connected with the onset of a non-reversible sintering process
of the Pd particles. It is suggested that this sintering process occurs via a mobile Pd oxide species, which is stabilized
by interaction with the Fe3O4 support. The restructuring is monitored via STM and IRAS using CO as a probe molecule. In addition to a decrease in particle
density and Pd surface area, a reshaping of the particles occurs, which is characterized by the formation of well-ordered
crystallites and with a relatively large fraction of (100) facets. After a few oxidation/reduction cycles at 500 K, the sintering
process becomes very slow and the system shows a stable behavior under conditions of CO oxidation. 相似文献