全文获取类型
收费全文 | 2174篇 |
免费 | 85篇 |
国内免费 | 33篇 |
专业分类
电工技术 | 161篇 |
综合类 | 20篇 |
化学工业 | 320篇 |
金属工艺 | 56篇 |
机械仪表 | 48篇 |
建筑科学 | 59篇 |
矿业工程 | 10篇 |
能源动力 | 53篇 |
轻工业 | 181篇 |
水利工程 | 17篇 |
石油天然气 | 41篇 |
武器工业 | 32篇 |
无线电 | 262篇 |
一般工业技术 | 265篇 |
冶金工业 | 556篇 |
原子能技术 | 41篇 |
自动化技术 | 170篇 |
出版年
2023年 | 19篇 |
2022年 | 42篇 |
2021年 | 52篇 |
2020年 | 35篇 |
2019年 | 19篇 |
2018年 | 44篇 |
2017年 | 33篇 |
2016年 | 39篇 |
2015年 | 35篇 |
2014年 | 59篇 |
2013年 | 79篇 |
2012年 | 60篇 |
2011年 | 87篇 |
2010年 | 69篇 |
2009年 | 80篇 |
2008年 | 83篇 |
2007年 | 67篇 |
2006年 | 57篇 |
2005年 | 65篇 |
2004年 | 54篇 |
2003年 | 36篇 |
2002年 | 57篇 |
2001年 | 32篇 |
2000年 | 47篇 |
1999年 | 57篇 |
1998年 | 209篇 |
1997年 | 132篇 |
1996年 | 98篇 |
1995年 | 70篇 |
1994年 | 59篇 |
1993年 | 65篇 |
1992年 | 36篇 |
1991年 | 27篇 |
1990年 | 18篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 12篇 |
1986年 | 11篇 |
1985年 | 22篇 |
1984年 | 20篇 |
1983年 | 15篇 |
1982年 | 18篇 |
1981年 | 16篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 7篇 |
1977年 | 18篇 |
1976年 | 16篇 |
1975年 | 7篇 |
1967年 | 6篇 |
排序方式: 共有2292条查询结果,搜索用时 15 毫秒
71.
Four tufted capuchin monkeys (Cebus apella) were trained to choose from 2 hook-like tools, 1 of which successfully led to collecting food, whereas the other did not because of inappropriate spatial arrangement of the tool and the food. In Experiment 1, all of the monkeys successfully learned the basic task. The monkeys performed successfully with tools of novel colors and shapes in Experiments 2-5. These results demonstrate that the monkeys used the spatial arrangement of the tool and the food as a cue. However, they failed when there were obstacles (Experiment 6) or traps (Experiment 7) on the path along which she monkeys dragged tools. These results may suggest that capuchin monkeys understand the spatial relationship between 2 items, namely, food and. the tool, but do not understand the spatial relationship among 3 items, namely, food, tool, and the environmental condition. The possible role of stimulus generalization is also considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
72.
Infant death certificates were linked with birth certificates for infants born to residents of Tohoku, Tokai and Kyushu regions in 1989 (n = 409, 679, or about one-third of all births in Japan), to examine the effects of variables, as reported on birth certificates, on cause-specific infant mortality. "Certain conditions originating in the perinatal period" and "congenital anomalies" accounted for nearly 90 percent of neonatal deaths, while "congenital anomalies", "injuries and poisoning" and "sudden infant death" were responsible for about 65 percent of postneonatal deaths. Mortality rates for almost all causes of infant deaths, except injuries and poisonings, increased as birth weight decreased not only in the neonatal period but also in the postneonatal period. This suggests that low birth weight places some infants at higher risk of death, and conditions that lead to low birth weight independently contribute to the risk of infant death. Cox's proportional hazards linear model was used to assess the effects of variables on infant mortalities by causes of death. An extremely strong birth weight effect was noted for "certain conditions originating in the perinatal period" and "congenital anomalies". Being a male infant and late order of birth in multiparity were other risk factors for deaths from "congenital anomalies", while being a male infant, resident of Tohoku region and maternal stillbirth experience related to deaths from "certain conditions originating in the perinatal period". Elevated risks of sudden infant death syndrome (SIDS), of which mortality rate in Japan was considerably lower than those in most developed Western countries, i.e. 0.23 per 1,000 live births in 1989, were associated with low birth weight, being a male infant, low maternal age, late order of birth in multiparity and illegitimacy. Low maternal age, late order of birth in multiparity and illegitimacy, also, related significantly to increased risk of infant deaths for "injuries and poisoning". These results suggest the independent contributions of socioeconomic factors to infant mortality, especially postneonatal mortality, from SIDS, "injuries and poisonings". 相似文献
73.
利用透射电镜和场发射扫描电镜研究了两种不同Ru含量(3%和5%,质量分数)的第四代镍基单晶高温合金DD22在1130℃长期时效过程中γ′相形貌演化、TCP相析出和界面位错网的演化情况。研究结果表明:在完全热处理后5Ru合金比3Ru合金的γ′相尺寸更小,形状更规则,γ/γ′相界面的错配度更大,高Ru含量使合金Re,Mo等元素出现反分配现象;5Ru合金在1130℃长期时效过程中γ′相粗化速率、溶解速率和形筏速率均低于3Ru合金;5Ru合金在长期时效1000 h后仍没有TCP相析出,而3Ru合金在时效50 h后便析出TCP相,随着长期时效时间延长,TCP相数量增多,尺寸增大;与3Ru合金相比,长期时效1000 h后5Ru合金γ′/γ界面位错网更加致密和规则;综上所述,Ru的元素反分配作用和低的扩散系数使5Ru合金比3Ru合金表现出更高的组织稳定性。 相似文献
74.
Hydrogen sulfide (H2S) was introduced into a microwave plasma chemical vapor deposition of microcrystalline diamond thin film. Secondary-ion mass spectroscopy showed that sulfur concentration was controlled from 2 × 1015 to 9 × 1017 cm− 3 by controlling the H2S/CH4 ratio, while that of hydrogen concentration was around 5 × 1020 cm− 3 and was independent of the H2S/CH4 ratio. Electrical conductance increased linearly as the S concentration increased from 2 × 1015 to 3 × 1016 cm− 3 without significant deterioration of film crystallinity, i.e., the amount of sp2 phase did not increase. Non-ohmic conduction was converted to ohmic conduction when the S concentration reached 9 × 1017 cm− 3 by increasing the H2S/CH4 ratio to 30,000 ppm. This modification was consistent to the formation of a graphitic phase by heavy S-doping, which was identified by Raman spectra and surface morphology. 相似文献
75.
城市防洪工程中临河堤防设计一般存在施工场地小、施工导流困难、需考虑城市景观要求等问题。基于抛石碾压基床的台阶式岸线具有施工场地要求小、无需施工导流、可结合城市景观灵活布置等优点,本文介绍了台阶式岸线在富大有堤遗留问题(岸线整治)工程中的应用,可供类似的城市防洪工程参考和借鉴。 相似文献
76.
77.
Chienru Lung Shota Miyake Hiroaki Kakigano Yushi Miura Toshifumi Ise Toshinari Momose Hideki Hayakawa 《Electrical Engineering in Japan》2013,182(4):29-46
For the past few years, hybrid generation systems including solar panel and gas cogeneration have been used for residential houses. Solar panels can generate electronic power at daytime but not at night. But the power consumption of residential houses usually peaks in the evening. The gas engine cogeneration system can generate electronic power without such a restriction, and it also can generate heat power to warm up a house or to produce hot water. In this paper we propose a solar panel and gas engine cogeneration hybrid system with an energy storage device, combined by a DC bus. If a blackout occurs, the system still can supply electronic power for special house loads. We propose a control scheme for the system related to the charging level of the energy storage device and the voltage of the utility grid, which can be applied to both grid‐connected and standalone operation. Finally, we report experiments designed to demonstrate system operation and calculations for loss estimation. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(4): 29–46, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ).DOI 10.1002/eej.22321 相似文献
78.
在传统的三段式继电保护离线整定的定值性能分析过程中,常因定值选择不合理而导致定值计算准确度低。为此,在确定影响分支系数大小的因素的基础上,将分支系数看作为预计算变量,建立故障分析模型,计算三段式继电保护过程后备保护定值;设定三段式继电保护离线整定定值优化约束条件,采用滑膜变结构控制方法设定控制策略,结合惩罚函数的形式将约束条件添加到目标函数中,将定值性能分析问题转化为无约束优化问题,实现基于滑模变结构控制的三段式继电保护离线整定的定值性能分析。实验结果表明,相比于传统方法,该方法的定值准确度更高,定值性能更好。 相似文献
79.
Mike Tien-Chien Lee Yu-Chin Hsu Ben Chen Masahiro Fujita 《Design Automation for Embedded Systems》1997,2(3-4):319-338
ATM switch, the core technology of an ATM networking system, is one of the major products in Fujitsu telecommunication business. However, current gate–level design methodology can no longer satisfy its stringent time–to–market requirement. It becomes necessary to exploit high–level methodology to specify and synthesize the design at an abstraction level higher than logic gates. This paper presents our prototyping experience on domain–specific high–level modeling and synthesis for Fujitsu ATM switch design. We propose a high–level design methodology using VHDL, where ATM switch architectural features are considered during behavior modeling, and a high–level synthesis compiler, MEBS, is prototyped to synthesize the behavior model down to a gate–level implementation. Since the specific ATM switch architecture is incorporated into both modeling and synthesis phases, a high–quality design is efficiently derived. The synthesis results shows that given the design constraints, the proposed high–level design methodology can produce a gate–level implementation by MEBS with about 15 percent area reduction in shorter design cycle when compared with manual design. 相似文献
80.