全文获取类型
收费全文 | 27228篇 |
免费 | 2138篇 |
国内免费 | 1271篇 |
专业分类
电工技术 | 3360篇 |
技术理论 | 1篇 |
综合类 | 2666篇 |
化学工业 | 2933篇 |
金属工艺 | 1025篇 |
机械仪表 | 2464篇 |
建筑科学 | 2160篇 |
矿业工程 | 901篇 |
能源动力 | 1669篇 |
轻工业 | 1614篇 |
水利工程 | 999篇 |
石油天然气 | 1851篇 |
武器工业 | 246篇 |
无线电 | 1541篇 |
一般工业技术 | 1858篇 |
冶金工业 | 1194篇 |
原子能技术 | 465篇 |
自动化技术 | 3690篇 |
出版年
2024年 | 68篇 |
2023年 | 320篇 |
2022年 | 547篇 |
2021年 | 708篇 |
2020年 | 716篇 |
2019年 | 625篇 |
2018年 | 574篇 |
2017年 | 722篇 |
2016年 | 870篇 |
2015年 | 874篇 |
2014年 | 1474篇 |
2013年 | 1523篇 |
2012年 | 1736篇 |
2011年 | 2023篇 |
2010年 | 1426篇 |
2009年 | 1573篇 |
2008年 | 1494篇 |
2007年 | 1946篇 |
2006年 | 1735篇 |
2005年 | 1586篇 |
2004年 | 1270篇 |
2003年 | 1190篇 |
2002年 | 1005篇 |
2001年 | 813篇 |
2000年 | 696篇 |
1999年 | 617篇 |
1998年 | 478篇 |
1997年 | 407篇 |
1996年 | 321篇 |
1995年 | 289篇 |
1994年 | 194篇 |
1993年 | 172篇 |
1992年 | 138篇 |
1991年 | 122篇 |
1990年 | 74篇 |
1989年 | 85篇 |
1988年 | 77篇 |
1987年 | 29篇 |
1986年 | 16篇 |
1985年 | 14篇 |
1984年 | 12篇 |
1983年 | 15篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 3篇 |
1977年 | 7篇 |
1976年 | 5篇 |
1959年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
《低温学》2015
The development of a high cooling power and high efficiency 4.2 K two stage G-M cryocooler is critically important given its broad applications in low temperature superconductors, MRI, infrared detector and cryogenic electronics. A high efficiency 1.5 W/4.2 K pneumatic-drive G-M cryocooler has recently been designed and developed by ARS. The effect of expansion volume rate and operation conditions on the cooling performance has been experimentally investigated. A typical cooling performance of 1.5 W/4.2 K has been achieved, and the minimum temperature of the second stage is 2.46 K. The steady input power of the compressor at 60 Hz is 6.8 kW, while the operation speed of the rotary valve is 30 rpm. A maximum cooling power of 1.75 W/4.2 K has been obtained in test runs. 相似文献
2.
The heat transfer and flow characteristics of MWCNT-R141b nanorefrigerant with different mass fractions have been studied through experiments. Experimental results were compared with existing correlations. A two-step method was used to prepare the nanorefrigerants. Span-80 was used as surfactant with an average particle diameter of 20 nm. Transmittance method was used to evaluate the stability of nanorefrigerants. Results showed that the stability of MWCNT-R141b nanorefrigerant, which is the added dispersant, was good during the experiments. The 0.3 wt% MWCNT-R141b nanorefrigerants had optimal heat transfer enhancement effects compared with pure refrigerants. The maximum Nusselt number increased by 40%. The specific pressure drop of nanorefrigerant increased as the Reynolds number (Re) increased, and the specific pressure drop of the pure refrigerant was minimum, which is similar to R141b. 相似文献
3.
This paper presents a model of shell and tube evaporator with micro-fin tubes using R1234yf and R134a. The model developed for this evaporator uses the ε-NTU method to predict the evaporating pressure, the refrigerant outlet enthalpy and the outlet temperature of the secondary fluid. The model accuracy is evaluated using different two-phase flow boiling correlations for micro-fin tubes and comparing predicted and experimental data. The experimental tests were carried out for a wide range of operating conditions using R134a and R1234yf as working fluids. The predicted parameter with maximum deviations, between the predicted and experimental data, is the evaporating pressure. The correlation of Akhavan– Behabadi et al. was used to predict flow boiling heat transfer, with an error on cooling capacity prediction below 5%. Simulations, carried out with this validated model, show that the overall heat transfer coefficient of R1234yf has a maximum decrease of 10% compared with R134a. 相似文献
4.
含动力学抑制剂的天然气水合物相平衡研究对新型低剂量抑制剂的开发具有指导作用。在283.6 ~ 290.9 K和7.51 MPa ~ 15.97 MPa的温压范围内研究了抑制剂Inhibex501及其溶剂2-乙二醇单丁醚对甲烷水合物相平衡条件的影响。实验结果显示,0.5wt%和2.0wt%浓度的Inhibex501对甲烷水合物形成的热力学条件具有促进作用,能使甲烷水合物形成移向更高的温度或者更低的压力,而2-乙二醇单丁醚在浓度0.2wt% ~ 1.0wt%范围几乎不改变甲烷水合物形成的热力学条件,N-乙烯基己内酰胺与N-乙烯基吡咯烷酮的共聚物对水合物形成热力学条件的改变起主要作用。 相似文献
5.
6.
7.
The activation of safety valves causes the development of flow reaction forces that have to be transferred in an adequate way via the piping to the steel structure or via the connected vessel into the foundation. If the safety valve outlet piping is connected to a blowdown system or, in case of blowing off into the atmosphere, are equipped with a T‐piece at the outlet, the stationary reaction forces are compensated completely. The transient opening process, however, develops flow reaction forces which culminate in peaks of short duration. In this article, a simple method will be proposed for the estimation of the resulting reaction forces as a function of the length of the pipe at the safety valve outlet. CFD calculations and blowdown tests executed with a full‐lift safety valve have confirmed this method on principle. Special importance is attributed to the short duration of the effect of the reaction forces which seems to have only a negligible impact on the supporting steel structure. 相似文献
8.
9.
10.
腐蚀阴极尖端的新方法 总被引:1,自引:0,他引:1
给出一种腐蚀阴极尖端的新方法,使得对阴极常用金属材料(W,Mo,Ir,Ta等)制作的阴极尖端的腐蚀效果明显,针尖对称性和重复性都很好,成品率和质量都有所提高. 相似文献