全文获取类型
收费全文 | 366篇 |
免费 | 5篇 |
专业分类
电工技术 | 14篇 |
综合类 | 2篇 |
化学工业 | 92篇 |
金属工艺 | 3篇 |
机械仪表 | 7篇 |
建筑科学 | 10篇 |
能源动力 | 5篇 |
轻工业 | 51篇 |
石油天然气 | 2篇 |
无线电 | 54篇 |
一般工业技术 | 58篇 |
冶金工业 | 50篇 |
原子能技术 | 7篇 |
自动化技术 | 16篇 |
出版年
2023年 | 2篇 |
2021年 | 4篇 |
2020年 | 1篇 |
2019年 | 4篇 |
2018年 | 3篇 |
2017年 | 3篇 |
2016年 | 8篇 |
2015年 | 7篇 |
2014年 | 11篇 |
2013年 | 13篇 |
2012年 | 16篇 |
2011年 | 20篇 |
2010年 | 18篇 |
2009年 | 11篇 |
2008年 | 23篇 |
2007年 | 13篇 |
2006年 | 10篇 |
2005年 | 13篇 |
2004年 | 10篇 |
2003年 | 9篇 |
2002年 | 9篇 |
2001年 | 12篇 |
2000年 | 9篇 |
1999年 | 12篇 |
1998年 | 21篇 |
1997年 | 17篇 |
1996年 | 10篇 |
1995年 | 14篇 |
1994年 | 11篇 |
1993年 | 7篇 |
1992年 | 8篇 |
1991年 | 6篇 |
1990年 | 2篇 |
1989年 | 7篇 |
1988年 | 2篇 |
1987年 | 2篇 |
1986年 | 4篇 |
1985年 | 2篇 |
1984年 | 3篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 2篇 |
排序方式: 共有371条查询结果,搜索用时 15 毫秒
31.
32.
Positive temperature coefficient of resistivity (PTCR) materials have become very important components, and among these materials
barium titanate compounds make up the most important group. When properly processed these compounds show a high PTCR at the
Curie temperature (the transition temperature from the ferroelectric tetragonal phase to the paraelectric cube phase). In
the first half of this paper literature related to the resistivity-temperature behaviour is discussed. As explained by the
well established Heywang model, the PTCR effect is caused by trapped electrons at the grain boundaries. From reviewing experimental
results in the literature it is clear that the PTCR effect can not be explained by assuming only one kind of electron trap.
It is concluded that as well as barium vacancies, adsorbed oxygen as 3d-elements can act as electron traps. In the second
half of this paper, the influence of the processing parameters on the PTCR related properties is discussed. Special emphasis
is placed on the phenomenon that the conductivity and grain size decrease abruptly with increasing donor concentration above
∼ 0.3 at%. Several models explaining this phenomenon are discussed and apparent discrepancies in experimental data are explained. 相似文献
33.
Nepheline solid solutions having high thermal expansion coefficients ranging from 1.2 to 1.8×10−5°C−1 were prepared from the systems NaAlSiO4-LiAlSiO4 and NaAlSi4-KAlSiO4. The thermal expansion coefficient decreased by substituting Li+ for Na+, and increased by substituting K+ for Na+. By forming a series of the nepheline solid solutions in a single ceramic body, a functionally gradient material with respect
to thermal expansion was prepared. The thermal expansion coefficient should gradually vary with position according to the
composition x in Na1−x MxAlSiCO4 (M=Li and K). 相似文献
34.
35.
Akira Miyazaki Takayuki Yamazaki Taikan Suehara Toshio Namba Shoji Asai Tomio Kobayashi Haruo Saito Toshitaka Idehara Isamu Ogawa Yoshinori Tatematsu 《Journal of Infrared, Millimeter and Terahertz Waves》2014,35(1):91-100
Positronium is an ideal system for research on Quantum Electrodynamics (QED), especially in a bound state. A discrepancy of 3.9 standard deviations has been found between the measured hyperfine structure (Ps-HFS) and the QED predictions. This may be due to the contribution of unknown new physics or common systematic effects in previous measurements, in all of which the Zeeman effect was used. We propose a new method to directly measure the Ps-HFS using a high power gyrotron. We compare two resonators which have been developed to supply sufficient power to drive the direct transition, a Fabry-Pérot resonator and a ring resonator with a diffraction grating. We plan to perform first direct measurement of Ps-HFS within the next six months. 相似文献
36.
J Ishizaki K Meguro H Ambo M Shimada S Yamaguchi C Hayasaka H Komatsu Y Sekita A Yamadori 《Canadian Metallurgical Quarterly》1998,53(6):P359-P363
We investigated community-based data of the Mini-Mental State Examination (MMSE) scores of elderly residents along with the effects of age and educational level. MMSE was planned for all residents over 65 years of age in a town in northern Japan. The number of elders who took the MMSE was 2,266 (90%). The score significantly declined with age and lower educational level, although no effect of sex was apparent. For the MMSE subitems, all the values except for that of naming showed effects of both age and educational level. Those screened by MMSE who fell in the range of cognitive impairment (< 24) accounted for 21.8% and those with severe cognitive impairment (< 18) constituted 6.0%. Despite the differences in language and culture, the mean scores are remarkably similar between Japan and other countries. This is the first normative, community-based study of MMSE among elderly adults in Japan. 相似文献
37.
38.
Wenzhong Hu Ping Xu Toshitaka Uchino 《Journal of the science of food and agriculture》2005,85(14):2475-2481
Fresh ginseng (Panax ginseng) was packaged with LDPE and PVC films. The respiration rates of fresh ginseng were determined in modified atmosphere packaging (MAP) at 0, 10 and 20 °C. The changes in chemical compositions were also measured before and after storage. The results showed that respiration rates of fresh ginseng were suppressed more effectively in MAP, especially in a poly(vinyl chloride) (PVC) package. The storage life of fresh ginseng was significantly extended with better appearance and firmness for 210 days. The decay rate was only 1.3% and 1.0% in both low density polyethylene (LDPE) and PVC film package after 210 days of storage at 0 °C, respectively. The results of saponin analysis indicated that the contents of total saponin were not changed much in all treatments. Reducing sugar was increased by 2.7 to 5.3 times, while pectin decreased by 1.1 to 1.4 times after 210 days of storage at the range of 0–20 °C. Total sugar content also increased during storage, especially in LDPE packages and high temperature. It was considered that MAP was very effective storage method for keeping quality better with minimal quality loss and lower decay rate at lower temperature. Copyright © 2005 Society of Chemical Industry 相似文献
39.
K Ishizaki S Kinbara N Miyazawa Y Takeuchi N Hirabayashi H Kasai T Araki 《Canadian Metallurgical Quarterly》1997,333(2-3):207-213
We investigated the effect of sodium tauroursodeoxycholate (UR-906) on cholestasis in common bile duct-ligated rats in comparison with the effect of dehydrocholic acid. UR-906 (30-180 mumol/kg) and dehydrocholic acid (180 mumol/kg) were intravenously given once daily for consecutive 20 days in rats and the common bile duct was ligated for the last 10 days. On the next day after the last test drug administration, serum biochemical and plasma hemostatic variables were determined. UR-906 significantly ameliorated the elevation of serum cholesterol, phospholipid, bilirubin and bile acid concentrations in bile duct-ligated rats. UR-906 significantly suppressed the prolongation of plasma prothrombin time and activated partial thromboplastin time. Furthermore, UR-906 significantly suppressed the decreases in plasma coagulation factor II and X activities. However, dehydrocholic acid did not cause significant changes in any of the variables examined in this model. These results suggest that UR-906 has a beneficial effect against cholestasis induced by bile duct ligation in rats and that this drug may be useful in the treatment of clinical cholestatic disorders. 相似文献
40.
A direct method of producing ultra-fine nitride and carbide powders of 20 to 40 nm by arc plasma in a controlled atmosphere
(with ammonia or methane gas) is described. The powders produced were SiC, TiC, WC (+W2C), AIN and Si3N4. Other nitrides and carbides may also be produced using this method. Special attention was paid to the production conditions
of silicon nitride. 相似文献