全文获取类型
收费全文 | 4822篇 |
免费 | 184篇 |
国内免费 | 85篇 |
专业分类
电工技术 | 89篇 |
技术理论 | 2篇 |
综合类 | 345篇 |
化学工业 | 772篇 |
金属工艺 | 278篇 |
机械仪表 | 283篇 |
建筑科学 | 347篇 |
矿业工程 | 26篇 |
能源动力 | 93篇 |
轻工业 | 283篇 |
水利工程 | 37篇 |
石油天然气 | 31篇 |
武器工业 | 9篇 |
无线电 | 127篇 |
一般工业技术 | 552篇 |
冶金工业 | 1090篇 |
原子能技术 | 37篇 |
自动化技术 | 690篇 |
出版年
2024年 | 8篇 |
2023年 | 47篇 |
2022年 | 129篇 |
2021年 | 164篇 |
2020年 | 107篇 |
2019年 | 96篇 |
2018年 | 98篇 |
2017年 | 91篇 |
2016年 | 97篇 |
2015年 | 106篇 |
2014年 | 187篇 |
2013年 | 327篇 |
2012年 | 197篇 |
2011年 | 361篇 |
2010年 | 294篇 |
2009年 | 324篇 |
2008年 | 283篇 |
2007年 | 300篇 |
2006年 | 318篇 |
2005年 | 259篇 |
2004年 | 210篇 |
2003年 | 166篇 |
2002年 | 138篇 |
2001年 | 120篇 |
2000年 | 75篇 |
1999年 | 59篇 |
1998年 | 39篇 |
1997年 | 53篇 |
1996年 | 48篇 |
1995年 | 32篇 |
1994年 | 46篇 |
1993年 | 35篇 |
1992年 | 30篇 |
1991年 | 15篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 25篇 |
1986年 | 15篇 |
1985年 | 11篇 |
1984年 | 11篇 |
1983年 | 6篇 |
1982年 | 8篇 |
1981年 | 6篇 |
1979年 | 5篇 |
1971年 | 6篇 |
1965年 | 5篇 |
1963年 | 6篇 |
1961年 | 6篇 |
1955年 | 4篇 |
排序方式: 共有5091条查询结果,搜索用时 15 毫秒
51.
V Chandrasekaran Ch Sreerama Murthy P Subrahmaniam G Venkateswarlu 《Bulletin of Materials Science》1986,8(1):39-48
Iron-chromium-cobalt alloys possess attractive magnetic properties combined with good formability and hence are identified as technologically important magnetic materials. Alloys with compositions Fe-28·9 Cr-15·6 Co and Fe-28·4 Cr-20·1Co (weight percent) have been studied. Heat-treatment parameters during thermomagnetic treatment viz temperature, time and external magnetic field were optimized with reference to magnetic properties. The fully treated anisotropic alloys develop remanence=11·5–12·0 kilo Gauss, coercivity=600–650 Oersted and energy product=4–4·5 million Gauss Oersted. Electron microscopic and Mössbauer spectroscopic techniques were used to identify the original and transformed phases. During the various stages of the development of the alloy, the changes in mechanical hardness were correlated with magnetic hardness. 相似文献
52.
Controlled experiments to study corrosion effects due to external varying fields in embedded pipelines 总被引:1,自引:0,他引:1
We present controlled laboratory tests carried out to study corrosion effects due to induction currents on pipes embedded in environments with electrical resistance lateral discontinuities. Sacrificial anodes were connected to underground pipes, and corrosion rates were estimated by measuring the mass loss in each anode. We considered 1 Hz and 50 Hz inducting fields, and the effects produced on the pipes were compared with cases without an external field. The results indicated an increase in the corrosion rate when the pipe was under the effect of induction currents, particularly where there was a change of electrical resistance in the soil. 相似文献
53.
基于家族基因的网格信任模型 总被引:1,自引:0,他引:1
针对现有基于PKI (Public Key Infrastructure)的网格信任系统的不足,证书主体信息不明确, 认证过程复杂等缺陷提出了一种新颖的基于家族基因的网格信任模型。该模型解决了传统信任模型存在的问题,如采用将用户的全部身份信息放在用户的基因里方法解决了证书主体信息的不明确,用基因检测解决了认证过程的复杂,用基因指派解决了访问控制的繁琐,并且给出了网格家族、家族基因、基因指派、基因鉴别和信任等概念,并建立了模型的形式化描述,理论分析和实验结果表明这种模型是网格信任领域一种较好的解决方案。 相似文献
54.
Francesca Piccotti Ilona Rybinska Elisabetta Scoccia Carlo Morasso Alessandra Ricciardi Lorena Signati Tiziana Triulzi Fabio Corsi Marta Truffi 《International journal of molecular sciences》2021,22(7)
Lipofilling (LF) is a largely employed technique in reconstructive and esthetic breast surgery. Over the years, it has demonstrated to be extremely useful for treatment of soft tissue defects after demolitive or conservative breast cancer surgery and different procedures have been developed to improve the survival of transplanted fat graft. The regenerative potential of LF is attributed to the multipotent stem cells found in large quantity in adipose tissue. However, a growing body of pre-clinical evidence shows that adipocytes and adipose-derived stromal cells may have pro-tumorigenic potential. Despite no clear indication from clinical studies has demonstrated an increased risk of cancer recurrence upon LF, these observations challenge the oncologic safety of the procedure. This review aims to provide an updated overview of both the clinical and the pre-clinical indications to the suitability and safety of LF in breast oncological surgery. Cellular and molecular players in the crosstalk between adipose tissue and cancer are described, and heterogeneous contradictory results are discussed, highlighting that important issues still remain to be solved to get a clear understanding of LF safety in breast cancer patients. 相似文献
55.
Effects of blending on surface characteristics of copper corrosion products in drinking water distribution systems 总被引:1,自引:0,他引:1
Copper scales formed over 6-months during exposure to ground, surface and saline waters were characterized by EDS, XRD and XPS. Scale color and hardness were light red-brown-black/hard for high alkalinity and blue-green/soft for high SO4 or Cl waters. Cl was present in surface or saline copper scales. The Cu/Cu2O ratio decreased with time indicating an e transfer copper corrosion mechanism. Cu2O, CuO, and Cu(OH)2 dominated the top 0.5-1 A° scale indicating continuous corrosion. Cu2O oxidation to CuO increased with alkalinity, and depended on time and pH. Total copper release was predicted using a Cu(OH)2 model. 相似文献
56.
57.
The effects of water pollution on the immersion corrosion of mild and low alloy steels 总被引:1,自引:0,他引:1
R.E. Melchers 《Corrosion Science》2007,49(8):3149-3167
The short-term immersion corrosion of mild and low alloy steels in seawaters is known to be proportional to the concentration of dissolved oxygen (DO) in the bulk water. Longer-term corrosion is a function of the activity of sulphate-reducing bacteria and is influenced by the concentration of nutrients in the bulk water. These influences are examined in more detail for the corrosion of steels in the brackish waters of the River Thames and for several immersion corrosion sites on the Eastern Australian seaboard and in the North Sea. The published data sources were supplemented with plausible assumptions about environmental conditions. New interpretations of the data are provided based on the previously published model for immersion corrosion. For waters with negligible salinity and sulphate levels early corrosion loss was shown to depend on the dissolved oxygen content of the waters, and later corrosion loss was a direct function of nitrogenous nutrient (pollution) levels. This also applies to longer-term corrosion. 相似文献
58.
在分析了网络化定制关键技术的基础上,针对性地对信息映射方法和产品族建进行了研究。提出了多层结构信息映射模型,以及综合类元件和参数化特征建模的双层复合产品族模型。结合本方法和以往网络化制造领域中所取得的成果,实现了较完整的基于Web的个性化定制过程。 相似文献
59.
L. Savary J. Saussey G. Costentin M. M. Bettahar M. Gubelmann-Bonneau J. C. Lavalley 《Catalysis Today》1996,32(1-4):57-61
A VPO/TiO2 catalyst tested in the oxydehydrogenation reaction (ODH) of propane between 300 and 400°C shows satisfactory performances (up to 80% of propene selectivity at 2% of propane conversion at 300°C or 56% of propene selectivity at 9% of propane conversion at 400°C). Addition of water or pyridine in the feed gas tends to decrease the propane conversion and enhances the propene selectivity. It is shown that water increases the number of Brönsted surface acid sites by dissociative adsorption which, in turn, enhances propene selectivity at the expense of the COx selectivity. These results are in good agreement with spectroscopic IR observations performed under catalytic conditions showing that the Lewis acid sites are linked to COxformation, whereas it seems that Brönsted sites would rather be linked to propene formation. 相似文献
60.