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31.
Laser-Sintered Barium Titanate 总被引:1,自引:0,他引:1
Toshihiro Kasai Yoshiharu Ozaki Hideki Noda Kenji Kawasaki Kei Tanemoto 《Journal of the American Ceramic Society》1989,72(9):1716-1718
Laser sintering of alkoxy-derived ultrafine BaTiO3 powders was investigated. The temperature increases of the sample with laser irradiation were measured with a thermocouple. It was found that laser irradiation could generate enough heat to sinter ceramics. A slurry was prepared by mixing an alkoxy-derived BaTiO3 powder, binder additives, solvent, and plasticizer. The slurry was tape cast and dried to give a green sheet. The green sheet was laser sintered and was then characterized by SEM, XRD, and density measurements. The effect of burnout before laser irradiation and the characteristic microstructure of laser-sintered BaTiO3 are described. 相似文献
32.
In Situ Observation of Phase Separation of a Barium Borate Melt in a Stable Immiscibility Region under Microgravity 总被引:1,自引:0,他引:1
Satoru Inoue Akio Makishima Hiroyuki Inoue Kohei Soga Tomoya Konishi Tomoyoshi Asano Yuu Ishii Masato Koyama 《Journal of the American Ceramic Society》1997,80(9):2413-2417
The precipitation of droplets was directly observed on a BaO–B2 O3 melt in a drop shaft experiment. This is the first time that precipitation of droplets has been observed in a 4.5 s drop test. The melt film of 4BaOz96B2 O3 (mol%) held on a platinum wire loop was heated above the critical tem-perature to produce uniformity and was cooled down to the phase separation temperature range. Phase separation of the melt was observed directly with a video camera. The IR image of the melt was simultaneously detected with a CCD array and was converted into a two-dimensional thermograph. 相似文献
33.
Sn-incorporated folded sheets mesoporous materials (Sn-FSM-16) with various contents of Sn were synthesized by using a mixture of water glass, SnCl4 and NaOH as starting materials. Hexadecyltrimethyl-ammonium chloride (surfactant) was used to intercalate into the layered silicate. The reaction process was followed by measurements of XRD patterns of intermediates. The Sn-FSM-16 was formed via the following mechanism: (1) layered silicates such as - - and -Na2Si2O5 were formed as intermediates by the calcination of the mixture of the starting materials; (2) the surfactant was intercalated into the layered silicates; (3) the surfactant-silicate complex with hexagonal structure was obtained as a precursor of Sn-FSM-16; (4) the precursor was calcined to decompose the surfactant in the interlayer and was changed to Sn-FSM-16. The structural aspect of Sn in Sn-FSM-16 was studied by XPS profiles of Sn 3d
5/2 and Si2p, 29 Si MAS NMR and FTIR. The content of Sn in Sn-FSM increased with increasing concentrations of both Sn and NaOH in the starting materials. The surface area of Sn-FSM-16 decreased with an increase of Sn content in Sn-FSM (1160–620 m2/g). 相似文献
34.
Summary Polysilanes with an optically active alkoxy group, i.e., (S)-(+)-2-butoxy, (R)-(-)-2-butoxy, (S)-(-)-2-methyl-1-butoxy, and (S)-(+)-3,7-dimethyl-1-octoxy, at the terminal positions, the chiral carbon centers of which were located at the α, β, and γ
positions relative to the oxygen, respectively, were prepared, and the effect of the position of chiral center of the terminal
optically active group on the induction of optical activity in polysilanes was investigated. The circular dichroism (CD) spectra
of these polymers showed positive Cotton signals around 340 nm at temperatures below -20 °C, but the intensities were small,
indicating that the optically active groups at the terminal positions have some ability, albeit small, to induce optical activity
to the polysilanes. Further, the optically active (S)-(+)-2-butoxy and (R)-(-)-2-butoxy groups did not control the helical sense direction of the polymers, despite the different chiral stimuli from
the 2-butoxy groups introduced to the terminal positions. To control the helical structure of polysilanes by the use of optically
active terminal groups, appropriate optically active groups are required. 相似文献
35.
Mark I. Jones Hideki Hyuga Kiyoshi Hirao Yukihiko Yamauchi 《Journal of the American Ceramic Society》2004,87(4):714-716
Novel Lu-α-SiAlON ceramics were produced by hot pressing mixtures of Si3 N4 , Lu2 O3 , AlN, and Al2 O3 at 1950°C for 2 h in a nitrogen atmosphere. The resultant SiAlON was fully dense and possessed a uniform, equiaxed microstructure with a grain size of ∼1 μm, which resulted in a high hardness of >19 GPa. In addition to high hardness, the sample showed very high optical transparency in the visible light region, with >70% transmission at higher wavelengths. This high transparency was attributed to the uniform, dense microstructure and lack of residual grain-boundary phase. 相似文献
36.
Yu-Ping Zeng Jian-Feng Yang Naoki Kondo Tatsuki Ohji Hideki Kita Shuzo Kanzaki 《Journal of the American Ceramic Society》2005,88(6):1622-1624
The fracture energies of the tape-cast silicon nitride with and without 3 wt% rod-like β-Si3 N4 seed addition were investigated by a chevron-notched-beam technique. The material was doped with Lu2 O3 –SiO2 as sintering additives for giving rigid grain boundaries and good heat resistance. The seeded and tape-cast silicon nitride has anisotropic microstructure, where the fibrous grains grown from seeds were preferentially aligned parallel to the casting direction. When a stress was applied parallel to the fibrous grain alignment direction, the strength measured at 1500°C was 738 MPa, which was almost the same as room temperature strength 739 MPa. The fracture energy of the tape-cast Si3 N4 without seed addition was 109 and 454 J/m2 at room temperature and 1500°C, respectively. On the contrary, the fracture energy of the seeded and tape-cast Si3 N4 was 301 and 781 J/m2 at room temperature and 1500°C, respectively, when a stress was applied parallel to the fibrous gain alignment. The large fracture energies were attributable primarily to the unidirectional alignment fibrous Si3 N4 grains. 相似文献
37.
This paper deals with the epoxide treatment of silk fabrics by the pad/batch method. The optimum reaction conditions, i.e., NaOH concentration, and reaction temperature were 2.5 g/L and 30°C, respectively. A weight gain of 8.5% was attained at a reaction time of 6 h. This value slightly increased to 10% after 24 h. The reactivity of tyrosine and basic amino acid residues was dependent on the reaction time and did not significantly differ from the results of epoxide-treated silk fiber by the conventional method in tetrachloroethylene. The moisture regain slightly decreased at 4% weight gain and then increased with the epoxide content, exceeding the value of the untreated control. The crease recovery of the epoxide-treated silk fabrics measured in the wet state was significantly improved, whereas that in the dry state was almost unchanged. The rate of photoyellowing of the epoxide-treated silk fabrics by the pad/batch method was reduced significantly compared with that of the untreated control. Among the mechanical properties, elongation at break and tensile modulus remained unchanged, whereas the tensile strength slightly increased following the epoxide reaction. The thermal properties were evaluated by DSC and TGA and on the basis of the dynamic viscoelastic measurements. The DSC curve of the epoxide-treated sample showed a slight increase of the decomposition temperature of silk fibroin. The rate of weight loss determined by TGA remained unchanged regardless of the chemical modification, whereas the peak of loss modulus became broader and shifted to lower temperature. The X-ray diffractograms showed that the crystalline structure of silk fibers was not affected by the reaction with epoxides. © 1993 John Wiley & Sons, Inc. 相似文献
38.
Hideki Ishida Kaori Sasaki Yoshihiko Okada Takeshi Mitsuda 《Journal of the American Ceramic Society》1992,75(9):2541-2546
The effect of curing temperature (40°, 60°, 80°C) on the hydration behavior of β-dicalcium silicate (β-C2 S) was investigated. The β-C2 S was obtained by decomposition of hillebrandite, Ca2 (SiO3 )(OH)2 , at 600°C, has a specific surface area of about 7 m2 /g, and is in the form of fibrous crystals. The dependence of the hydration reaction on temperature continues until the reaction is completed. The hydration is completed in 1 day at 80°C and in 14 days at 14°C. The hydration mechanism is different above and below 60°C, but at a given temperature, the reaction mechanism and the silicate anion structures of C-S-H do not change significantly from the initial to the late stages of the reaction. High curing temperature and long curing times after completion of reaction promote silicate polymerization. The Ca/Si ratio of C-S-H shows high values, being almost 2.0 above 60°C and 1.95 below 40°C. 相似文献
39.
Tateoki Iizuka Hideki Kita Hideki Hyuga Takene Hirai Kazuo Osumi 《Journal of the American Ceramic Society》2004,87(3):337-341
A W2 C-nanoparticle-reinforced Si3 N4 -matrix composite was fabricated by sintering porous Si3 N4 that had been infiltrated with a tungsten solution. During the sintering procedure, nanometer-sized W2 C particles grew in situ from the reaction between the tungsten and carbon sources considered to originate mainly from residual binder. The W2 C particles resided in the grain-boundary junctions of the Si3 N4 , had an average diameter of ∼60 nm, and were polyhedral in shape. Because the residual carbon, which normally would obstruct sintering, reacted with the tungsten to form W2 C particles in the composite, the sinterability of the Si3 N4 was improved, and a W2 C–Si3 N4 composite with almost full density was obtained. The flexural strength of the W2 C–Si3 N4 composite was 1212 MPa, ∼34% higher than that of standard sintered Si3 N4 . 相似文献
40.
William Leobandung Hideki Ichikawa Yoshinobu Fukumori Nicholas A. Peppas 《应用聚合物科学杂志》2003,87(10):1678-1684
Poly(ethylene glycol)‐based nanoparticles have received significant attention in the field of biomedicine. When they are copolymerized with pH‐ or temperature‐sensitive comonomers, their small size allows them to respond very quickly to changes in the environment, including changes in the pH, ionic strength, and temperature. In addition, the high surface‐to‐volume ratio makes them highly functionalized. In this work, nanoparticles composed of temperature‐sensitive poly(N‐isopropylacrylamide), poly(ethylene glycol) 400 dimethacrylate, and poly(ethylene glycol) 1000 methacrylate were prepared by a thermally initiated, free‐radical dispersion polymerization method. The temperature‐responsive behavior of the hydrogel nanoparticles was characterized by the study of their particle size with photon correlation spectroscopy. The size of the nanoparticles varied from 200 to 1100 nm and was a strong function of the temperature of the system, from 5 to 40°C. The thermal, structural, and morphological characteristics were also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1678–1684, 2003 相似文献