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161.
This study was conducted to determine the effect of clay content in GFRP (glass‐fiber‐reinforced polymer) composite samples as they were aged in an alkaline solution. Two kinds of GFRP composite samples were prepared. One was E‐glass‐fiber‐reinforced vinyl ester polymer, and the other was nano‐GFRP composites prepared with the addition of 1 and 2 wt% of montmorillonite clay to the polymer matrix. These samples were aged in alkaline solution of pH 13.2 with and without sustained load. The load was 1335 N or 18.7% of the tensile strength of the composite samples. The aging was evaluated by measuring the reduction in tensile strength after 6 months. Also, absorption of alkaline solution into the plain and nano‐GFRP samples was investigated so as to elucidate the diffusion behaviors. It was found that for a short exposure time (e.g. 1 month) and without sustained load, dispersing 2 wt% of the nanoclay in the polymer matrix of the GFRP samples reduces the diffusivity by 39%. However, with the application of sustained load, the glass fiber composite samples deteriorate more with increasing clay content. The reduction in tensile strength was 7.1%, 12.1%, and 18.1% for the samples containing 0, 1, and 2 wt% of clay, respectively. J. VINYL. ADDIT. TECHNOL., 12:25–32, 2006. © 2006 Society of Plastics Engineers 相似文献
162.
A chemical additive method using sol–gel reactions was used to modify the composition and resultant properties of a commercially available 0.96(0.91Pb(Mg1/3Nb2/3)O3–0.09PbTiO3)–0.04 BaTiO3 (PMN–PT–BT) ceramic. Without an additional ball-mixing process, several combinations of minor additives such as Fe, Ba, Sr, Zn, and Ti were incorporated by the chemical method. Weak- and high-field characteristics including dielectric properties, induced strain and polarization, and associated hystereses were evaluated for the samples sintered at 1200 °C for 4 h. All properties were found to depend on the chemical additives and temperature. Especially, the temperature dependence of high-field characteristics revealed different behavior from that reported for conventionally prepared samples. For example, the samples containing 0.5 wt.% SrO, 0.5 wt.% ZnO, and 0.5 wt.% TiO2 did not exhibit a transition to piezoelectric behavior at the temperature expected from the dielectric measurements. Overall, the coating process has been successfully used to modify, and in some cases, enhance the high-field characteristics of PMN-based ceramics for electromechanical uses. 相似文献
163.
A thermally labile polymer, poly(propylene glycol), was modified to obtain PPG having an amino end group. PPG was incorporated into a partially aliphatic polyimide based on an alicyclic dianhydride, and this afforded triblock copolymers containing various amounts of PPG blocks. The thermal properties of the copolymers were investigated by thermogravimetric analysis and differential scanning calorimetry. The thermal decomposition of the PPG block in the copolymers was carried out at 240°C under various pressures to obtain porous polyimide films. The pores remained during the thermolysis under a reduced pressure of 710 mmHg, whereas they collapsed under (near) atmospheric pressure. The pore size increased as the amount of the PPG block in the copolymers increased. The dielectric constants of the porous polyimides varied from 2.60 to 2.42 with the original copolymer composition. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 532–538, 2006 相似文献
164.
Shengfang Shi Sunghun Cho Tomoyo Goto Tohru Sekino 《Journal of the American Ceramic Society》2021,104(6):2753-2766
To further improve the mechanical performance and reduce the percolation threshold by controlling microstructures, Al2O3-TiC composites containing 0-20 vol% TiC were fabricated via in situ reaction synthesis. Graphite (ATC) and carbon nanotubes (ATCT) were used as carbon sources. The composites were also fabricated via a conventional process using a TiC starting powder (AT). X-ray diffraction analysis and scanning electron microscopy observation results indicated successful fabrication of the composites with various microstructures. TiC particles in ATCT were completely dispersed at grain boundaries, whereas in ATC and AT, these particles were either intragranular or intergranular dispersed. The composites could be listed as follows, ATCT > ATC > AT, that is, in descending order of the reinforcing flexural strength and fracture toughness. The nanoindentation measurement indicated the optimum hardening effect of ATCT. The ATCT composite also exhibited the highest fracture toughness, which was 49% higher than that of the monolithic Al2O3. Crack deflection was considered as the main toughening mechanism while crack bridging behavior also occurred in ATCT. For a given TiC content, ATCT exhibited the lowest electrical resistivity, owing mainly to the complete grain-boundary dispersion of the relatively large TiC particles. The similarity of the Al2O3 grain size and TiC particle size of ATCT contributed to the lowest percolation threshold achieved (11.2%), which (to date) is the lowest value that has been reported for the Al2O3-TiC system. 相似文献
165.
Seong-Joong Kim Yeojin Ahn Jeong F. Kim Seung-Eun Nam Hosik Park Young Hoon Cho Kyung-youl Baek You-In Park 《应用聚合物科学杂志》2021,138(7):49860
To overcome the plasticization effect in polyimide membranes, many researchers have proposed crosslinking method. This can reduce an inter-segmental mobility by tightening and rigidifying the polymer chains. However, it is difficult to modify the whole polymer chains throughout the membrane because the reaction can be hindered by the diffusion rate of the crosslinker. In particular, it is hard for bulky crosslinker to penetrate a dense membrane with a small d-spacing. This study investigated the effect of crosslinking a dense Matrimid membrane with p-phenylenediamine (p-PDA) via two different crosslinking methods (i.e., methanol-swelling crosslinking process [M-SCP] and liquid-phase crosslinking process [L-PCP]). Most of the crosslinking reaction in M-SCP occurs on the membrane surface due to difficulty in penetration of the bulky p-PDA into the Matrimid dense membrane. In contrast, the L-PCP allows uniform crosslinking across the membrane. The membranes crosslinked using L-PCP showed excellent chemical resistance. Furthermore, the plasticization phenomenon was not observed in the membranes crosslinked using L-PCP with p-PDA more than 15%. Meanwhile, the membrane crosslinked using M-SCP exhibited poor plasticization and chemical resistance properties. These results showed that the L-PCP method can be more effective for the crosslinking of dense membrane to deliver both high plasticization and chemical resistance. 相似文献
166.
Ahn Kyu-Hong Hwang Jong-Hyuk Song Kyung-Guen Jung Yong-Ho Cho Eul-Saeng Lim Byung-Ran Kim Kwang-Soo 《Metals and Materials International》2004,10(2):167-170
The performance of an attached growth wastewater treatment process was investigated in an effort to improve nitrogen removal
efficiency. Recycled Yakult (lactic acid fermentation drink) bottles made of polystyrene were used as a biofilm media. The
use of Yakult bottles as a biofilm media has been attempted by numerous researchers in Japan for the removal of solids and
organics. However, these studies focused only on the removal of solids and organics. This study extended their application
to the removal of nitrogen for domestic sewage treatment. Yakult media was placed in a reactor with 70% apparent reactor volume
in a conventional A/O process. The bottom of the Yakult media was removed, and randomly filled Yakult media were effectively
able to reduce the flow in tanks, resulting in an increase in the contact time between pollutants and microorganisms. With
higher HRT, the nitrogen removal efficiency was increased by up to 83% with 12 hr of HRT. Nitrification appeared to be the
limiting factor of nitrogen removal at an HRT that is less than 12 hr, indicating that the Yakult process requires more retention
time to achieve nitrification compared to other biofilm processes. The removal efficiencies of organics and solids were high
regardless of the change of operational parameters.
This article is based on a presentation in “The 7th Korea-China Workshop On Advanced Materials” organized by the Korea-China
Advanced Materials Cooperation Center and the China-Korea Advanced Materials Cooperation Center, held at Ramada Plaza Jeju
Hotel, Jeju Island, Korea on August 24–27, 2003. 相似文献
167.
Tae-Sik Kim Young-Je An Kwang Ho Kim Won-Sub Chung Young-Rae Cho 《Metals and Materials International》2006,12(4):339-343
The effect of the dielectric constant (k) of bonding materials in a screen-printed carbon nanotube (CNT) cathode on the field
enhancement factor was investigated for high-efficiency CNT cathodes using the ANSYS software. The values obtained by a simulation
study were compared to the experimental results obtained for screen-printed CNT cathodes. The field enhancement factor increased
as the dielectric constant decreased, reaching a maximum value at a dielectric constant of 1, the value for a vacuum. The
findings indicate that the larger sheet resistance of the bonding materials, after the firing process, can be attributed to
the larger emission current of the CNT cathode. From these results, it was concluded that the best bonding materials for screen-printed
CNT cathodes should have a low dielectric constant and a high sheet resistance. This finding can be used as criteria for selecting
bonding materials for use in CNT pastes for highly efficient CNT cathodes. 相似文献
168.
Kyung-Man Moon Hwang-Rae Cho Myung-Hoon Lee Sung-Kyu Shin Sung-Cheol Koh 《Metals and Materials International》2007,13(3):211-216
The differences between the general corrosion and microbiologically influenced corrosion (MIC) of steels were investigated
in terms of its electrochemical behavior and surface phenomena. The corrosion potential of steels in the absence of SRB (sulfate-reducing
bacteria) shifted to a negative value with the immersion time. However, the potential of the presence of SRB shifted to a
positive value after 30 days' incubation, indicating the growth of SRB biofilms on the test metal specimens and the formation
of corrosion products. In addition, the color of a medium inoculated with SRB changed from gray to black. The change in color
appeared to be caused by the formation of pyrites (FeS) as a corrosion product, while no significant change in color was observed
in a medium without SRB inoculation. Moreover, corrosion rates of various steels tested for MIC were higher compared to those
of steels in the absence of SRB. In particular, the corrosion current density of TMCP steels in the presence of SRB was larger
than that of other steels. Pitting corrosion was also observed at the surface of all steels in the SRB-inoculated medium.
The pitting corrosion likely occurred due to SRB that was associated with the increasing corrosion rates through increasing
cathodic reactions, which caused a reduction of sulfate to sulfide as well as the formation of an oxygen concentration cell. 相似文献
169.
Numerical simulation technology was applied for optimizing the casting design and conditions in large cast iron castings for marine engine. By the simulation of mold filling and solidification sequences the problems of the previous casting conditions were analyzed and marked improvements for large cylinder liner parts were derived from these results. Especially the amount and positions of chills were optimized to increase the mechanical properties and to minimize the shrinkage and microporosity in the castings. Ultrasonic testing, penetration testing and mechanical property testing were carried out for the parts with the modified casting conditions. It showed that no defects in the castings were found and the productivity could be distinctly increased. The mechanical properties satisfied also the specification demanded. 相似文献
170.