全文获取类型
收费全文 | 53241篇 |
免费 | 5693篇 |
国内免费 | 2617篇 |
专业分类
电工技术 | 4286篇 |
技术理论 | 2篇 |
综合类 | 3612篇 |
化学工业 | 8385篇 |
金属工艺 | 2952篇 |
机械仪表 | 3364篇 |
建筑科学 | 4231篇 |
矿业工程 | 1669篇 |
能源动力 | 1715篇 |
轻工业 | 3521篇 |
水利工程 | 1043篇 |
石油天然气 | 2410篇 |
武器工业 | 522篇 |
无线电 | 6652篇 |
一般工业技术 | 6279篇 |
冶金工业 | 2473篇 |
原子能技术 | 687篇 |
自动化技术 | 7748篇 |
出版年
2024年 | 298篇 |
2023年 | 1014篇 |
2022年 | 2008篇 |
2021年 | 2923篇 |
2020年 | 2031篇 |
2019年 | 1630篇 |
2018年 | 1814篇 |
2017年 | 1921篇 |
2016年 | 1864篇 |
2015年 | 2567篇 |
2014年 | 3042篇 |
2013年 | 3742篇 |
2012年 | 3907篇 |
2011年 | 4060篇 |
2010年 | 3419篇 |
2009年 | 3337篇 |
2008年 | 3060篇 |
2007年 | 2854篇 |
2006年 | 2724篇 |
2005年 | 2237篇 |
2004年 | 1596篇 |
2003年 | 1354篇 |
2002年 | 1344篇 |
2001年 | 999篇 |
2000年 | 891篇 |
1999年 | 859篇 |
1998年 | 757篇 |
1997年 | 608篇 |
1996年 | 563篇 |
1995年 | 455篇 |
1994年 | 337篇 |
1993年 | 240篇 |
1992年 | 224篇 |
1991年 | 139篇 |
1990年 | 114篇 |
1989年 | 111篇 |
1988年 | 104篇 |
1987年 | 62篇 |
1986年 | 65篇 |
1985年 | 43篇 |
1984年 | 42篇 |
1983年 | 24篇 |
1982年 | 34篇 |
1981年 | 20篇 |
1980年 | 20篇 |
1979年 | 22篇 |
1978年 | 8篇 |
1977年 | 8篇 |
1976年 | 11篇 |
1959年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
严峻的能源短缺、居高不下的原油价格、日益严重的环境问题已经成为制约中国经济、社会发展的瓶颈。改变现有的以化石能源为主的能源结构, 相似文献
92.
新增探明储量的经济可采储量计算方法 总被引:5,自引:0,他引:5
提出了新增探明储量有无经济可采储量的判别方法。在此基础上,通过对立已开发油田技术可采储量经济转化率与油藏空气渗透率的相关关系式和图版,根据储层的空气渗透率,计算新增探明储量的经济转化率和经济可采储量。该方法参数易取,计算简便,对于快速、准确计算新增探明储量的经济可采储量具有重要意义。 相似文献
93.
94.
Kai Kang 《Fire Technology》2007,43(4):331-346
This paper presents an emergency evacuation analysis during a mid-platform train fire in an underground rail station. A time-based
evacuation scenario is developed taking into account the stairway inaccessibility due to smoke blockage. The calculation approach
in NFPA 130 is then applied to a parametric study of this time-based scenario and its reliability is examined using a micro-simulation
model. Both methods give consistent predictions of the exiting times. The results demonstrate that with the division of the
station into two zones, the exiting time could not meet the code requirements, whereas it does meet the required exiting time
without the division. Such division is due to smoke blockage and creates an uneven ratio of the occupant load to the available
exiting capacity. This shows that appropriate consideration of the fire and smoke effects is important for station egress
evaluation. Other issues such as the fire growth rate and the pre-evacuation time are also discussed. 相似文献
95.
Yu Yang Hugo Bender Kai Arstila Bart Swinnen Bert Verlinden Ingrid De Wolf 《Microelectronics Reliability》2008,48(8-9):1517-1520
Focused ion beam (FIB) and nano-probing were applied for failure analysis of three-dimensional stacked circuits with copper through-silicon-vias between the stacked chips. The failure analysis was done after high temperature storage and thermal cycling tests. Passive voltage contrast in FIB allowed to pinpoint the open sites. FIB cross-sections showed the presence of opens at the bottom of the copper vias. The failure cause was suspected to be an interlayer particle, which was confirmed by optical profilometry. Nano-probing was used on another sample to pinpoint the failure location through the measurement of the local resistance within the daisy chains. The failure was traced out to be related with surface contamination. 相似文献
96.
薄板坯连铸连轧工艺对铌微合金化高强度钢组织和性能的影响 总被引:1,自引:0,他引:1
首先建立薄板坯连铸连轧工艺的试验室模拟技术,并运用该模拟技术,研究薄板坯连铸连轧工艺(CSP)和传统板坯再加热工艺(TRP)两种工艺对铌微合金化高强度钢的显微组织和力学性能的影响。研究结果表明:CSP钢的晶粒细化效果不如TRP钢,两者的平均铁素体晶粒尺寸分别为8.17μm和6.30μm。在CSP试验钢板中铌的析出量较大,特别是在铁素体中细小颗粒的铌的析出物较多,沉淀强化效果较强。CSP试验钢的σ0.5和σb分别较TRP工艺低约40MPa和约25MPa,同时其低温冲击韧性较好,FATT温度较低。 相似文献
97.
Peter Su Adrian Gerlich Motomichi Yamamoto Thomas H. North 《Journal of Materials Science》2007,42(24):9954-9965
The formation of local melted films during friction stir spot welding of as-cast AZ91D and thixomolded AZ91 material is investigated.
The average temperatures close to the tip of the rotating pin vary from 438 to 454 °C during the dwell period in friction
stir spot welding. These measured temperature values are higher than the melting temperature of α-Mg + Mg17Al12 eutectic (437 °C). It is suggested that the temperature in the stir zone during the dwell period is determined by the relative
proportions of α-Mg and (α-Mg + Mg17Al12) eutectic material, which are incorporated during friction stir spot welding. Based on the stir zone temperature measurements
and a detailed examination of material located at the root of the pin thread it is suggested that material is moved downwards
via the pin thread and into the stir zone during the dwell period in friction stir spot welding. Evidence of local melted
film formation is observed in the stir zone of AZ91 spot welds. It is suggested that melted films are retained since their
dissolution rate is much slower in the high temperature stir zone than it is when melted films is formed in the stir zone
during Al 7075-T6 friction stir spot welding. The spontaneous melting temperature, solute diffusion rate and the thermodynamic
driving force for droplet dissolution are much higher during Al 7075-T6 friction stir spot welding. 相似文献
98.
合成2,4-二叔丁基苯酚工业试验 总被引:2,自引:0,他引:2
以离子交换树脂为催化剂,苯酚和甲基叔丁基醚为原料合成2,4-二叔丁基苯酚(简称2,4酚),合成产物经过滤再经间歇真空精馏精制提纯,得到高纯度的2,4酚成品。成品精馏后釜中残液在酸性白土催化剂的作用下通过歧化反应生成对叔丁基苯酚,再经精馏提纯得到成品对叔丁基苯酚。通过工艺优化,使2,4酚、对叔丁基苯酚形成联产生产工艺,降低了生产原料消耗和成本。 相似文献
99.
Yi Kai Zhou Sung Woo Choi Shigeya Kimura Shuichi Emura Shigehiko Hasegawa Hajime Asahi 《Journal of Superconductivity and Novel Magnetism》2007,20(6):429-432
GaGdN layers were grown at temperatures below 300°C by radio-frequency plasma-assisted molecular beam epitaxy on sapphire
substrates. GaGdN samples with high Gd concentration as high as 12.5% were obtained by lowering the growth temperature. X-ray
diffraction results showed no obvious secondary phase, which means that the phase separation can be suppressed by the growth
at low temperatures. All samples, including those grown at room temperature, showed ferromagnetic characteristics. Photoluminescence
emission was observed, though spectra exhibit broad and sharp luminescence bands related to many kinds of defects. It is suggested
that electrons coming from defects, especially, nitrogen vacancy, stabilize ferromagnetism, and that the carrier-induced ferromagnetism
occurs in the low-temperature-growth GaGdN. 相似文献