全文获取类型
收费全文 | 259550篇 |
免费 | 3499篇 |
国内免费 | 968篇 |
专业分类
电工技术 | 5015篇 |
综合类 | 381篇 |
化学工业 | 37493篇 |
金属工艺 | 9751篇 |
机械仪表 | 7806篇 |
建筑科学 | 6374篇 |
矿业工程 | 981篇 |
能源动力 | 7480篇 |
轻工业 | 21575篇 |
水利工程 | 2300篇 |
石油天然气 | 3378篇 |
武器工业 | 31篇 |
无线电 | 35085篇 |
一般工业技术 | 51366篇 |
冶金工业 | 49400篇 |
原子能技术 | 5128篇 |
自动化技术 | 20473篇 |
出版年
2022年 | 1594篇 |
2021年 | 2354篇 |
2020年 | 1722篇 |
2019年 | 2047篇 |
2018年 | 3475篇 |
2017年 | 3462篇 |
2016年 | 3568篇 |
2015年 | 2393篇 |
2014年 | 4181篇 |
2013年 | 11892篇 |
2012年 | 6541篇 |
2011年 | 8934篇 |
2010年 | 7207篇 |
2009年 | 8163篇 |
2008年 | 8681篇 |
2007年 | 8549篇 |
2006年 | 7589篇 |
2005年 | 6706篇 |
2004年 | 6457篇 |
2003年 | 6706篇 |
2002年 | 6184篇 |
2001年 | 6645篇 |
2000年 | 6129篇 |
1999年 | 6557篇 |
1998年 | 16732篇 |
1997年 | 11608篇 |
1996年 | 8975篇 |
1995年 | 6739篇 |
1994年 | 6032篇 |
1993年 | 5959篇 |
1992年 | 4239篇 |
1991年 | 4110篇 |
1990年 | 3927篇 |
1989年 | 3723篇 |
1988年 | 3620篇 |
1987年 | 3074篇 |
1986年 | 3000篇 |
1985年 | 3279篇 |
1984年 | 2992篇 |
1983年 | 2900篇 |
1982年 | 2682篇 |
1981年 | 2598篇 |
1980年 | 2514篇 |
1979年 | 2351篇 |
1978年 | 2155篇 |
1977年 | 2654篇 |
1976年 | 3614篇 |
1975年 | 1805篇 |
1974年 | 1767篇 |
1973年 | 1695篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
102.
J. Grune K. Sempert M. Kuznetsov T. Jordan 《International Journal of Hydrogen Energy》2021,46(23):12487-12496
This paper presents results of experimental investigations on spherical and cylindrical flame propagation in pre-mixed H2/air-mixtures in unconfined and semi-confined geometries. The experiments were performed in a facility consisting of two transparent solid walls with 1 m2 area and four weak side walls made from thin plastic film. The gap size between the solid walls was varied stepwise from thin layer geometry (6 mm) to cube geometry (1 m). A wide range of H2/air-mixtures with volumetric hydrogen concentrations from 10% to 45% H2 was ignited between the transparent solid walls. The propagating flame front and its structure was observed with a large scale high speed shadow system. Results of spherical and cylindrical flame propagation up to a radius of 0.5 m were analyzed. The presented spherical burning velocity model is used to discuss the self-acceleration phenomena in unconfined and unobstructed pre-mixed H2/air flames. 相似文献
103.
104.
105.
106.
107.
108.
In this study, further analysis of the osmotic drying process was conducted to identify the optimum combination of parameters for drying rectangular alumina-gelatin beams. This study was designed to determine the effect of three variables related to the osmotic drying process (osmotic pressure, molecular weight, and immersion time) on the interaction between the liquid desiccant and the submerged alumina-gelatin samples. The water loss from the alumina-gelatin samples was positively correlated with the molecular weight, osmotic pressure, and immersion time. Up to 40% by weight of the initial water content was removed during the osmotic drying process. The samples also experienced solids gain due to the counterflow of solute from the liquid desiccant. The least amount of solids gain resulted from drying for the shortest immersion time at low osmotic pressure and high molecular weight. Evidence of possible interactions between variables was noted for the sintered density metric. Statistical methods were used to form regression equations for the measured responses (water loss, solids gain, bulk density). A verification experiment was conducted to compare the experimental outcomes to the predicted outcomes. The responses were simultaneously optimized to identify the combination of variable settings required to meet specified goals. In order to maximize water loss, minimize solids gain, and maximize bulk density, the ceramic-gelatin object should be immersed for approximately 60?min in an aqueous solution of 100,000?g/mol poly(ethylene oxide) at an osmotic pressure of 2.50?MPa. These values are valid for the range of parameter settings tested and the sample fabrication and drying methods used. 相似文献
109.
O.N. Kondrateva G.E. Nikiforova A.V. Tyurin M.A. Ryumin V.M. Gurevich A.P. Kritskaya K.S. Gavrichev 《Ceramics International》2018,44(15):18103-18107
The heat capacity of ytterbium orthovanadate was first measured by adiabatic calorimetry in the temperature range T?=?12.28–344.06?K. No obvious anomalies were observed on the curve obtained. The values of standard thermodynamic functions in the temperature range T?=?0–400 K were calculated. Based on low-temperature calorimetry data obtained, previously published data on the high-temperature heat capacity of ytterbium orthovanadate were corrected. The anomalous contribution to heat capacity for YbVO4 was compared with the data known for YbPO4. 相似文献
110.
Mohan B. Ponnuchamy G. Mohan Muralikrishna Venkateswara Rao Mannava G. Srinivas Reddy 《Ceramics International》2018,44(13):15019-15023
Nanocrystalline nickel oxide (NiO) was prepared from nickel hydroxide by Spark plasma sintering (SPS) and the mechanisms involved in the densification of NiO were studied. Reverse precipitated nickel hydroxide powders were SPS processed at 400, 600 and 700?°C with 70?MPa pressure. Pure NiO with 12?nm crystallite size formed after 400?°C sintering process. However NiO grains had grown to 18 and 38?nm after 600 and 700?°C sintering respectively. NiO pellets prepared using 600 and 700?°C SPS sintering schedules had relative densities of 83% and 94% respectively. Two displacement rate regimes were observed during densification of NiO in both 600 and 700?°C sintering processes. Decomposition of nickel hydroxide and particle sliding of NiO led to first displacement rate maximum while inverse Hall-Petch based plastic deformation facilitated densification during the constant second displacement rate regime. No densification occurred during sintering holding times indicating the limited role that diffusion played during densification. 相似文献