全文获取类型
收费全文 | 233篇 |
免费 | 3篇 |
专业分类
电工技术 | 13篇 |
化学工业 | 50篇 |
金属工艺 | 6篇 |
机械仪表 | 2篇 |
能源动力 | 6篇 |
轻工业 | 11篇 |
水利工程 | 4篇 |
无线电 | 21篇 |
一般工业技术 | 45篇 |
冶金工业 | 68篇 |
原子能技术 | 4篇 |
自动化技术 | 6篇 |
出版年
2023年 | 1篇 |
2021年 | 2篇 |
2016年 | 3篇 |
2015年 | 2篇 |
2014年 | 2篇 |
2013年 | 11篇 |
2012年 | 7篇 |
2011年 | 12篇 |
2010年 | 5篇 |
2009年 | 3篇 |
2008年 | 5篇 |
2007年 | 11篇 |
2006年 | 3篇 |
2005年 | 3篇 |
2004年 | 6篇 |
2003年 | 8篇 |
2002年 | 4篇 |
2001年 | 4篇 |
2000年 | 3篇 |
1999年 | 4篇 |
1998年 | 25篇 |
1997年 | 16篇 |
1996年 | 15篇 |
1995年 | 8篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 5篇 |
1991年 | 1篇 |
1990年 | 5篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1987年 | 3篇 |
1986年 | 5篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1976年 | 4篇 |
1975年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1967年 | 1篇 |
排序方式: 共有236条查询结果,搜索用时 15 毫秒
51.
The reaction hot-pressing at 1700 and 1750° C of a number of compositions in the system Al-Si-N-O corresponding to points spanning the-sialon phase line in the region of z=0.8 has been studied. Measurements have been made of densification rate and of the rate of conversion of-Si3N4 to-sialon. The densification process for these compositions may be described in terms of a liquid-phase assisted fast particle rearrangement process succeeded by Coble creep. The rates of these processes are sensitive to the volume of grain-boundary liquid phase present, which in turn is determined by the position of the compositional point in relation to the-sialon line. For systems containing very little grain-boundary phase, the vapour-phase transport of material may become important. 相似文献
52.
A curious resistivity anomaly in high-Curie-point barium-lead titanate materials with positive temperature coefficients of resistivity (PTCR) has been observed just below the Curie point (∼420°C), besides the normal PTCR anomaly. The additional resistivity anomaly was observed in the resistivity-temperature characteristics, especially on cooling, and shewed a significant dependence on the cooling rate. 相似文献
53.
Influence of Interaction between Neighboring Oxygen Ions on Phase Stability in Cubic Zirconia 总被引:1,自引:0,他引:1
Akihide Kuwabara Junji Katamura Yuichi Ikuhara Taketo Sakuma 《Journal of the American Ceramic Society》2002,85(10):2557-2561
The electronic structures of undoped c - and t -ZrO2 were calculated by a first-principles molecular orbital method. A preliminary analysis revealed that experimental energy-loss near-edge structure profiles obtained in ZrO2 –8 mol% Y2 O3 could be satisfactorily explained from the present theoretical calculation. The calculation suggests that the stability of t -ZrO2 could be described by the interaction between neighboring oxygen ions rather than the covalency of Zr—O bonds. The effect of dopant cations on the stability of cubic-zirconia solid solutions can be estimated semiquantitatively in terms of the repulsive Coulomb force between neighboring oxygen ions. 相似文献
54.
55.
Hatsujiro Hashimoto Masago Kuwabara Yoshizo Takai Sumiyuki Tsubokawa Yasuhiro Yokota 《Microscopy research and technique》1989,12(3):180-200
Four kinds of works on the detection of displacement of atoms in crystals are shown. The irregular small displacement of atoms has been detected, with an accuracy of about 0.1 Å around dislocations and stacking faults in Au crystals as shown by their electron microscope images. The displacement of the atomic images is recorded by aberration-free focus (AFF). Even when the periodic displacement of atoms in SiC and TaS2 crystals is around 0.1% of the lattice constant, this displacement has been revealed as the weak-contrast anomaly in the images. Using in situ observations by a TV system attached to an electron microscope, the rapid movements of atoms that have taken place within 1/30 sec have been recorded. Using the technique of successive subtraction of the images by TV system and image sigma, only the images of moving atoms in Au crystal have been recorded each 1/10 sec. 相似文献
56.
Nakano S Maeshima H Matsumura A Ohno K Ueda S Kuwabara Y Yamada T 《Journal of food protection》2004,67(8):1694-1701
A PCR assay for the detection of Bacillus cereus strains able to produce an emetic toxin (cereulide) was developed in this study based on a sequence-characterized amplified region (SCAR) derived from a random amplified polymorphic DNA (RAPD) fragment. One of the RAPD fragments generated was selected, cloned, and sequenced. A set of PCR primers was newly designed from the SCAR obtained (the sequence of the cloned RAPD fragment) and used in this assay. To determine the specificity of the assay, 30 different B. cereus strains, 8 other Bacillus strains (of six species), and 16 other non-Bacillus strains (from 16 genera) were tested. Results were positive for every emetic B. cereus strain and for only one nonemetic B. cereus strain. For all other bacterial strains, results were negative. Bacterial DNA for PCR was prepared by a simple procedure using Chelex 100 resin from the bacterial colony on the agar plate or from culture after growth in brain heart infusion medium. This PCR assay enabled us to detect the bacteria of emetic B. cereus grown on agar plates but not the bacteria of nonemetic B. cereus. To test this PCR assay for the monitoring of the emetic bacteria, 10 to 70 CFU of B. cereus DSM 4312 (emetic) per g of food was inoculated into several foods as an indicator, followed by a 7-h enrichment culture step. Because this PCR assay based on the SCAR derived from the RAPD fragment was able to detect bacterial cells, this assay should be useful for rapid and specific detection of emetic B. cereus. 相似文献
57.
Extremely large piezoresistive effects with a gage factor (elastoresistance) of > 1 × 106 in single grain boundaries of thin ceramic bars of semiconducting barium titanate have been observed at room temperature. Thin barium titanate ceramic bars with a diameter in the range of 10 to 20 μm were prepared to consist of single grains joined together in series. Large piezoresistive effects were observed for some of the single grain boundaries in the present samples under compressive stresses, but no distinct piezoresistance was observed in the grain bulk. A giant piezoresistive effect with a gage factor of 3 × 107 was observed for a single grain boundary which exhibited a saw-tooth type PTCR (positive temperature coefficient of resistivity) characteristic with a significantly large bias dependence of it. This demonstrates that the piezoresistive phenomenon may be interpreted in terms of the change of the potential barrier height due to the change of ferroelectric domain morphologies in the vicinity of grain boundaries under mechanical and electric stresses. 相似文献
58.
59.
Copoly(vinyl alcohol–styrenesulfonic acid) resin was prepared by a two-step polymerization, consisting of a suspension polymerization of styrene containing divinylbenzene using tetraethylthiuram disulfide as an initiator and a subsequent block copolymerization of vinyl acetate to the crosslinked polystyrene obtained, followed by sulfonation and saponification. Some reaction conditions in the polymerization of styrene were investigated to obtain copolymer containing more vinyl alcohol units. The catalytic activity of the copolymer on the hydrolysis of dextrin was investigated and found to be increased with increasing amount of vinyl alcohol units and with a lowering degree of crosslinking of the copolymer. The maximum acceleration of rate obtained in the presence of the copolymer was about six times that in the presence of Amberlite 120B. Catalytic activity of the copolymer on hydrolysis of sucrose and methyl acetate were also investigated and found to be comparable each other and lower than that for dextrin. The difference between the activities for dextrin and for sucrose and methyl acetate increased with an increasing amount of vinyl alcohol units in the copolymer. 相似文献
60.
Varistor characteristics in PTCR-type (Ba,Sr)TiO3 ceramics prepared by single-step firing in air 总被引:3,自引:0,他引:3
This paper deals with donor, acceptor-codoped (Ba0.4Sr.6)TiO3 ceramics with distinct varistor characteristics at room temperature, which were prepared by single-step firing in air. The materials, with the Curie point at around –90 °C, exhibited a large PTCR (positive temperature coefficient of resistivity) effect of more than seven orders of magnitude in the temperature range –90 °C (the resistivity 103 · cm) to room temperature ( > 1010 · cm). An apparent dielectric constant of >20000 and tan < 0.05 (at 100 kHz) were observed for the present materials at room temperature, and moreover, the materials exhibited nonlinear current-voltage characteristics with the nonlinear coefficient, , in the range 7–12 and the varistor field, Ev, in the range 0.3–1.0 kV/cm. The value of in the present materials increased systematically with increasing in their PTCR temperature range. It has been found that there exists a close correlation between and the grain-boundary potential barrier height, e, obtained from the -T characteristic of the materials. An almost linear relationship was also found to exist between and log Ev for the present materials. 相似文献