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1.
Boron nitride (BN) of low crystallinity was synthesized from triammoniadecaborane (TAD) and hydrazine at 125 MPa below 650° C. TAD itself was pyrolysed at 600° C and 125 MPa to form a mixture of amorphous boron and boron nitride containing BH and NH bonds. The infrared spectrum of the pyrolysed product of TAD itself at 600° C and 125 MPa showed the BNB absorption at 800cm–1 due to the formation of B3N3 structures. The X-ray diffraction (XRD) of the reaction product from TAD and hydrazine at 600° C had broad diffractions centred at 2=25.5° and 43.0° (CuK). The BH absorption at 2500cm–1 decreased in intensity on increasing the N/B ratio from 0.3 to 0.85, and disappeared finally at a ratio of N/B=1.3. The reaction product at 125 MPa had a porous structure. The electron diffraction of the specimen changed from faint rings to spots on circular rings after heat treatment at 800° C for 10 h. The heat-treated specimen, however, did not give sharp reflections corresponding to hexagonal BN in the XRD profile. BN of low crystallinity was transferred to cubic BN at 1200° C and 6.5 GPa in a 90% yield, which was higher than that of well-crystallized BN in the presence of AIN. 相似文献
2.
Hideaki Itoh Shigeharu Naka Tsuneaki Matsudaira Hiroshi Hamamoto 《Journal of Materials Science》1990,25(1):533-536
A sintered compact of titanium diboride (TiB2) was prepared by hot pressing of the synthesized TiB2 powder, which was obtained by a solid-state reaction between TiN and amorphous boron. Densification of the sintered compact occurred at 20 MPa and 1800° C for 5 to 60 min with the aid of a reaction sintering, including the TiB2 formation reaction between excess 20 at % amorphous boron in the as-synthesized powder (TiB2 + 0.2B) and intentionally added 10 at % titanium metal. A homogeneous sintered compact of a single phase of TiB2, which was prepared by hot pressing for 30 min from the starting powder composition [(TiB2 + 0.2B) + 0.1 Ti], had a fine-grained microstructure composed of TiB2 grains with diameters of 2 to 3 m. The bulk density was 4.47 g cm–3, i.e. 98% of the theoretical density. The microhardness, transverse rupture strength and fracture toughness of the TiB2 sintered compact were 2850 kg mm–2, 48 kg mm–2 and 2.4 MN m–3/2, respectively. The thermal expansion coefficient increased with increasing temperature up to 400° C and had a constant value of 8.8 x 10–6 deg–1 above 500° C. 相似文献
3.
Hideaki Itoh Tsuneaki Matsudaira Shigeharu Naka Hiroshi Hamamoto 《Journal of Materials Science》1989,24(2):420-424
TiB2 powder was synthesized by a controlled formation reaction from titanium metal and amorphous boron. Precursory TiB2 formed by the pretreatment of the mixed powder (mole ratio: B/Ti=2.0) at 600° C for 60 min in an argon stream. Hollow TiB2 powder with an average grain size of 15m was obtained by subsequent heat treatment above 900° C for more than 60 min in an argon stream. The formation reaction of TiB2 powder was further controlled by pretreatment of the mixed powder at 600° C for 60 min in a hydrogen and argon stream and subsequent heat treatment at 1000° C for 360 min in an argon stream, when hollow-free TiB2 powder was formed by a milder formation reaction between amorphous boron and the reformed titanium metal with hydrogen diffused lattice. 相似文献
4.
Shin-ichi Hirano Akira Fujii Toshinobu Yogo Shigeharu Naka 《Journal of the American Ceramic Society》1990,73(8):2238-2241
Cubic BN was synthesized under high-temperature and -pressure conditions from BN powder formed by pressure pyrolysis of borazine below 700°C and 100 MPa. The conversion of BN powder to cubic BN was strongly influenced by the residual hydrogen identified by the BH/BN ratio of IR absorption band. The activation energy for cubic BN synthesis from BN powder-20 mol% AIN was 46 kJ/mol, when the starting BN was synthesized at 250°C. A mixture of BN powder and cubic BN particles was converted to cubic BN in a 100% yield by heat treatment at 1800°C and 6.5 GPa without any catalyst. The presence of cubic BN particles does enhance the conversion to cubic BN from BN powder. The energy required for the transformation of starting BN to cubic BN in the presence of cubic BN seed was 355 kJ/mol. 相似文献
5.
Bong-Kuk Sea Suek-Yuel Choo Tae-Jong Lee Shigeharu Morooka Seung-Koo Song 《Korean Journal of Chemical Engineering》1995,12(4):416-420
SiC-coated film onto carbon fibers as a barrier of oxidation resistance and reaction between carbon fibers and metals was
investigated. The chemical vapor deposition of silicon carbide onto carbon fibers was performed at various temperatures ranging
from 700 to 1000°C using triisopropylsilane vapor carried by hydrogen gas. The strength of the SiC-coated carbon fibers was
decreased due to deterioration of fibers and chemical attack of hydrogen on the surface of carbon fibers during the coating
process. The oxidation and the thermal resistance of the SiC-coated carbon fibers compared to the uncoated carbon fibers were
improved at temperature range of 600–800°C and 1000–1200°C, respectively. Morphological change by air oxidation at temperature
range of 500–800‡C was also investigated for the SiC-coated and the uncoated carbon fibers, respectively. The SiC-coated film
between carbon fiber and aluminum was sufficient as a barrier of reaction on carbon fiber reinforced aluminum at temperature
of above 1000°C. 相似文献
6.
Yosuke Abe Tomohito Tsuru Shi Shi Naoko Oono Shigeharu Ukai 《Journal of Nuclear Science and Technology》2016,53(10):1528-1534
Various types of nanometric defects such as voids and helium (He) bubbles produced by high-energy neutron irradiations are known to degrade the mechanical properties of irradiated materials. In this study, we have evaluated the obstacle strength of He bubbles to the mobility of an edge dislocation in α-iron for 2 and 4 nm bubbles with He-to-vacancy (He/V) ratios ranging from 0 to 1 at 300 and 500 K, by molecular dynamics simulation. Results showed that as the He/V ratio increases, the obstacle strength needed for the release of a dislocation from the bubble becomes stronger up to a moderate He/V ratio (0.6 and 0.4 for 2 and 4 nm bubbles, respectively, at both temperatures), and a further increase in the He/V ratio leads to weakening of the obstacle strength. For He/V = 1, the obstacle strengths are 10–30% weaker than those at moderate He/V ratios depending on the bubble size and temperature. The extent of obstacle strength was found to be correlated with the dilation caused by He bubbles depending on the bubble size, He/V ratio, and temperature. 相似文献
7.
Yuta Shizukawa Shigenari Hayashi Suzue Yoneda Yasumitsu Kondo Hiroshi Tanei Shigeharu Ukai 《Oxidation of Metals》2016,86(3-4):315-326
The phase transformation behavior of a thermally grown oxide scale of FeO on pure-Fe and an Fe–2wt%Au alloy was investigated. Particular attention was paid to formation of a magnetite seam, which is the Fe3O4 layer formed at the FeO/alloy interface at an initial stage of the phase transformation, since it has important effects on the overall phase transformation of FeO scale. A thin Au(Fe) layer was found to develop on the Fe–Au alloy at the FeO/alloy interface after 32 min of oxidation at 750 °C in air. This Au(Fe) layer prevented formation of a magnetite seam and accelerated the FeO eutectoid reaction. The Au(Fe) layer acted as a “chemical diffusion barrier” for inward diffusion of Fe from the FeO to the alloy substrate across the FeO/alloy interface and prevented magnetite seam formation. 相似文献
8.
The formation of solid solution in the Co3−xMnxO4 system in atmospheres of oxygen, air and argon was examined at a constant temperature of 1000 °C. In oxygen, a small amount
of the NaCl-type compound was found to co-exist with the cubic spinel in the composition rangex≤0.1. A single phase of the cubic spinel was found in the range 0.1 to 1.3 and the tetragonal spinel above 1.9. In the rangex=1.3 to 1.9 where the cubic and tetragonal spinels co-exist they both have very broadened diffraction line profiles. In air,
the identified phases and the changes in their lattice constants with composition were very similar to those in oxygen, except
that the NaCl-type compound and the cubic spinel co-existed over a larger range. In argon, the cubic spinel was not observed
over any of the composition range and the NaCI-type compound and the tetragonal spinel co-existed in the wide range of 1.1
to 2.3. The experimental results are discussed with regard to the cation distribution in the spinel and also to the relative
stability of Co3+- and Mn3+-ions under the low partial pressure of oxygen. 相似文献
9.
Synthesis and properties of carbons dispersed with α-iron particles from divinylbenzene-vinylferrocene 总被引:1,自引:0,他引:1
α-Iron-dispersed carbon was synthesized, through pressure pyrolysis of divinylbenzene-vinylferrocene above 750°C, and by reduction
of magnetite-dispersed carbon. Divinylbenzenevinylferrocene copolymer was pyrolysed at 125 MPa above 750°C to yield carbons
dispersed with α-iron accompanied by cementite. Magnetite in the carbon matrix was reduced to α-iron after heat treatments
at 500°C in a flow of hydrogen. Carbons synthesized by the pressure pyrolysis of divinylbenzene-vinylferrocene at 800°C and
125 MPa contained iron-compound particles up to 200 nm, whereas the median diameter of α-iron particles in the carbon matrix
after reduction treatments was 20 nm. α-Iron-dispersed carbon had a Curie temperature of 770°C. The saturation magnetization
of iron-dispersed carbon increased with increasing the pyrolysis temperature of divinylbenzene-vinylferrocene copolymer, and
reached a constant value of 183 e.m.u.g−1 at 800°C. The saturation magnetization of α-iron-dispersed carbon after the reduction treatment revealed practically the
theoretical value of α-iron. Carbons finely dispersed with only α-iron particles were synthesized successfully by reduction
of magnetitedispersed carbons. 相似文献
10.
Yamamoto T Mukai K Yamashita H Kubota M Fukuda S Kurimoto M Tsujisaka Y 《Journal of Bioscience and Bioengineering》2005,100(2):212-215
Random mutation by error-prone PCR was introduced into kojibiose phosphorylase from Thermoanaerobacter brockii ATCC35047. One thermostable mutant enzyme, D513N, was isolated. The D513N mutant enzyme showed an optimum temperature of 67.5-70 degrees C (the wild type, 65 degrees C), and thermostability up to 67.5 degrees C (the wild type, up to 60 degrees C). The half-lives of D513N were estimated to be 135 h at 60 degrees C, 110 min at 70 degrees C and 6 min at 75 degrees C, respectively. They were about 1.6-fold, 7-fold and 6-fold longer than those of the wild-type enzyme, respectively. 相似文献