全文获取类型
收费全文 | 30132篇 |
免费 | 6491篇 |
国内免费 | 2025篇 |
专业分类
电工技术 | 2601篇 |
综合类 | 3240篇 |
化学工业 | 6670篇 |
金属工艺 | 741篇 |
机械仪表 | 2379篇 |
建筑科学 | 1331篇 |
矿业工程 | 294篇 |
能源动力 | 1470篇 |
轻工业 | 1673篇 |
水利工程 | 384篇 |
石油天然气 | 611篇 |
武器工业 | 341篇 |
无线电 | 4143篇 |
一般工业技术 | 2023篇 |
冶金工业 | 777篇 |
原子能技术 | 1340篇 |
自动化技术 | 8630篇 |
出版年
2024年 | 78篇 |
2023年 | 264篇 |
2022年 | 707篇 |
2021年 | 810篇 |
2020年 | 830篇 |
2019年 | 775篇 |
2018年 | 872篇 |
2017年 | 845篇 |
2016年 | 946篇 |
2015年 | 758篇 |
2014年 | 4307篇 |
2013年 | 3260篇 |
2012年 | 4146篇 |
2011年 | 4546篇 |
2010年 | 3787篇 |
2009年 | 3461篇 |
2008年 | 1646篇 |
2007年 | 1080篇 |
2006年 | 838篇 |
2005年 | 735篇 |
2004年 | 653篇 |
2003年 | 533篇 |
2002年 | 412篇 |
2001年 | 408篇 |
2000年 | 331篇 |
1999年 | 269篇 |
1998年 | 226篇 |
1997年 | 215篇 |
1996年 | 178篇 |
1995年 | 131篇 |
1994年 | 106篇 |
1993年 | 113篇 |
1992年 | 82篇 |
1991年 | 58篇 |
1990年 | 43篇 |
1989年 | 39篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 25篇 |
1985年 | 16篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 5篇 |
1981年 | 18篇 |
1980年 | 4篇 |
1974年 | 1篇 |
1966年 | 1篇 |
1959年 | 6篇 |
1957年 | 1篇 |
1951年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 134 毫秒
41.
J.M Mäkynen J.K Jokiniemi P.P Ahonen E.I Kauppinen R Zilliacus 《Nuclear Engineering and Design》1997,178(1):74
Hygroscopic NaOH, CsI, CsOH and inert Ag aerosol behaviour at different temperatures and relative humidities (RH) has been studied in a well instrumented and controlled vessel of 1.81 m3 total free volume. Homogeneous thermal-hydraulic conditions for aerosol measurement in the vessel were achieved. The aerosol number and mass concentration were measured continuously during the experiments using a Condensation Nucleus Counter and a Tapered Element Oscillating Microbalance. The particle size distribution and chemical composition in the test conditions were measured by Berner low pressure impactors. In the case of NaOH the half life of the aerosol mass concentration was more than four times longer at low RH (22%) as compared to high RH (96%). The half lives of the CsOH and CsI aerosols were only twice as long at low RH as compared to high RH. Thus at high RH (96–97%) the half lives of CsOH and CsI were twice as long as the half life for the NaOH aerosol. The faster decay of the NaOH aerosol is due to the smaller density decrease of NaOH during water condensation. CsOH particles grew rapidly to their equilibrium size at all humidities. The measured equilibrium size for CsOH aerosol agree well with the calculated particle size at different RHs. Experimental results were also compared with calculations obtained by severe accident computer codes. These calculated results will be presented in a later paper. 相似文献
42.
关于彩色火焰蜡烛的研制 总被引:1,自引:0,他引:1
本文阐述了利用焰色反应的原理研制彩色火焰蜡烛,着重分析并解决了在研制工作中出现的几个技术关键,如主燃剂的选取、蜡烛成型和强度、发色剂的选择与用量等. 相似文献
43.
分析了磷-溴(P-Br)阻燃剂的特性及阻燃机理。应用P-Br阻燃剂进行了阻燃涤纶切片的开发研制试验,结果表明:P-Br阻燃剂阻燃效果好、能高度分散并有良好的热稳定性,其所制阻燃涤纶切片有良好的可纺性。 相似文献
44.
高发泡聚乙烯阻燃初探 总被引:1,自引:0,他引:1
徐明宇 《现代塑料加工应用》1994,6(5):14-16
根据聚合物燃烧现象和一般阻燃机理寻求研究高发泡聚乙烯的阻燃方法和阻燃剂。研究结果表明:只有对添加型阻燃剂三元并用,方能不降低高发泡聚乙烯的物性,制得较为理想的高发泡聚乙烯自熄型制品。 相似文献
45.
测定环境中钚的新方法 总被引:2,自引:2,他引:0
提出了TOPO萃取,大面积有机相制原与平行板屏栅电离室α谱仪结合,测定草、土壤等环境中钚的新方法。土壤和草灰的化学回收率分别为72%和97%,最低探测限为4×10^-2Bq/kg。分析了I-AEA和NIST的标准物质,结果与标准值相符。操作程序简单、快速,适用于核事故应急分析和环境监测。 相似文献
46.
47.
K.F. Chan C.K. Wan K.N. Yu 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2007,262(1):128-134
In the present work, we have studied the feasibility of a method based on polyallyldiglycol-carbonate (PADC) films to investigate the effects of alpha particles on HeLa cervix cancer cells. Thin PADC films with thickness of about 20 μm were prepared from commercially available CR-39 films by chemical etching to fabricate custom-made petri dishes for cell culture, which could accurately record alpha particle hit positions. A special method involving “base tracks” for aligning the images of cell nuclei and alpha particle hits has been proposed, so that alpha particle transversals of cell nuclei can be visually counted. Radiobiological experiments were carried out to induce DNA damages, with the TdT-mediated dUTP Nick-End Labeling (TUNEL) fluorescence method employed to detect DNA strand breaks. The staining results were investigated by flow cytometer. The preliminary results showed that more strand breaks occurred in cells hit by alpha particles with lower energies. Moreover, large TUNEL positive signals were obtained even with small percentages of cells irradiated and TUNEL signals were also obtained from non-targeted cells. These provided evidence for the bystander effect. 相似文献
48.
杜永泰 《电气电子教学学报》2002,24(6):37-39,52
本文讨论了调幅系数为任意值的调幅波,给出了它的表达式,频谱与调幅系数,调制效率和信噪比增益的计算公式。 相似文献
49.
本文介绍了由微道板构成的透射型定时探测器,得到的飞行时间系统的时间分辨为280ps。并对进一步改善时间特性作了讨论。 相似文献
50.
J. HEJNA 《Journal of microscopy》2008,232(2):276-281
A discrete dynode electron multiplier with radial flux of electrons was built and tested in the range of low‐voltage scanning electron microscopy as a backscattered electron detector of topographic contrast. The multiplier collects backscattered electron emitted in a specific range of take‐off angles and over the whole azimuth angular range enabling large solid collection angle. Multipliers with different dynode shapes were studied theoretically with the use of the software for particle optics and three assemblies were built and tested experimentally. The gain estimation, assessment of the type of detected electrons (secondary electron or backscattered electron), imaging the spatial collection efficiency and signal‐to‐noise measurements were performed. 相似文献