全文获取类型
收费全文 | 1229篇 |
免费 | 28篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 141篇 |
综合类 | 2篇 |
化学工业 | 314篇 |
金属工艺 | 32篇 |
机械仪表 | 55篇 |
建筑科学 | 27篇 |
能源动力 | 88篇 |
轻工业 | 99篇 |
水利工程 | 1篇 |
石油天然气 | 2篇 |
无线电 | 72篇 |
一般工业技术 | 199篇 |
冶金工业 | 93篇 |
原子能技术 | 43篇 |
自动化技术 | 92篇 |
出版年
2023年 | 4篇 |
2022年 | 5篇 |
2021年 | 17篇 |
2020年 | 8篇 |
2019年 | 10篇 |
2018年 | 11篇 |
2017年 | 24篇 |
2016年 | 23篇 |
2015年 | 16篇 |
2014年 | 41篇 |
2013年 | 93篇 |
2012年 | 44篇 |
2011年 | 66篇 |
2010年 | 51篇 |
2009年 | 54篇 |
2008年 | 61篇 |
2007年 | 57篇 |
2006年 | 40篇 |
2005年 | 39篇 |
2004年 | 42篇 |
2003年 | 54篇 |
2002年 | 32篇 |
2001年 | 24篇 |
2000年 | 24篇 |
1999年 | 37篇 |
1998年 | 39篇 |
1997年 | 38篇 |
1996年 | 21篇 |
1995年 | 22篇 |
1994年 | 19篇 |
1993年 | 13篇 |
1992年 | 12篇 |
1991年 | 13篇 |
1990年 | 16篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 19篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 16篇 |
1983年 | 13篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 16篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1973年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有1260条查询结果,搜索用时 15 毫秒
41.
To clarify the role of phosphate in the formation of corrosion products, the transformation of GRI(Cl−) with the addition of phosphate was characterized through XRD, TEM, and solution analysis. Electrochemical analysis showed that the transformation of GRI(Cl−) was delayed and the size of the final products, i.e., γ-FeOOH was reduced in the phosphate added case. X-ray absorption spectroscopy indicated that the neighboring Fe–Fe coordination number of FeO6 octahedral unit in γ-FeOOH was decreased. These effects of phosphate are attributed to its adsorption on GRI(Cl−) and nucleated γ-FeOOH that prevented particle growth during oxidation process. 相似文献
42.
Shigeru Kohtani Eito Yoshioka Kenji Saito Akihiko Kudo Hideto Miyabe 《Catalysis communications》2010,11(13):1049-1053
In the absence of molecular oxygen, various aromatic ketones such as acetophenone derivatives and diaryl ketones were photocatalytically hydrogenated on polycrystalline titanium dioxide (Degussa P25) under UV light irradiation (> 340 nm). The desired secondary alcohols were obtained with excellent chemical efficiency (almost 100% yields for 10 examples) by choosing ethanol as a sacrificial hole scavenger, which was oxidized into acetaldehyde. 相似文献
43.
Dual throat nozzle (DTN) is fast becoming a popular technique for thrust vectoring. The DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze the performance of a dual throat nozzle at various mass flow rates of secondary flow and nozzle pressure ratios (NPR). Two-dimensional, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. The present computational results were validated with available experimental data. Based on the present results, the control effectiveness of thrust-vectoring is discussed in terms of the thrust coefficient and the coefficient of discharge. 相似文献
44.
45.
T. Katsumi H. Kodama T. Matsuo H. Ogawa N. Tsuboi K. Hori 《Combustion, Explosion, and Shock Waves》2009,45(4):442-453
A new composition of hydroxylammonium nitrate based solution containing ammonium nitrate, methanol, and water was developed
for monopropellant in a reaction control system (RCS) as an alternative to conventional hydrazine. In comparison with hydrazine,
this solution has a 20% higher specific impulse, 1.4 times higher density, and lower freezing point and toxicity. The linear
burning rate of the solution is moderate at the operating pressures of RCS thrusters. It was found that the linear burning
rate had some characteristics whose mechanisms had not been understood. The combustion mechanism of this solution was investigated.
The burning behavior was observed using a medium speed camera, and a temperature profile for the combustion wave was measured
with a 2.5 μm diameter thermocouple. From these results, the instability of the liquid-gas interface may trigger a sudden
increase in the burning rate, and methanol was found to be effective in reducing the bubble growth rate in the solution. The
reactivity of several catalysts was evaluated in an open-cup test, and the S405 catalyst for hydrazine showed the best performance
among them. Thruster tests were conducted using the S405 catalyst with variation in the propellant mass flow rate, catalyst
bed configuration, and length-to-diameter ratio of the combustor. As a result, parameters were determined that ensured long
operating time. The model thruster operated stably for up to 100 sec with a specific impulse I
sp = 240 sec, which corresponds to a 90% efficiency.
__________
Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 4, pp. 109–120, July–August, 2009.
An erratum to this article can be found at 相似文献
46.
The decreased availability of economic resources requires the use of methods to assess hospital efficiency. The aim of our study was to retrospectively evaluate the applicability to the Italian reality of a catalogue of medical acts (CdAM-champs beta) set up for the French Health System. We wanted to evaluate the amount of resource utilization of a Cardiothoracic Operating Room of a IRCCS regional general hospital. The study included 83 admissions, occurring in October 1996, to the cardiac surgery department. Medical acts were recorded for all admissions taking into account both the number of acts and the weight of acts expressed as standard cost index or ICR. This takes into account the use of human (medical and nursing staff) and technical resources. Calculation of ICR beta scores was achieved by means of two different expressions. We observed a lack of correlation between the two values of each ICR. The previous formula (1991) gives more emphasis on the different conditions in which the operation was carried out (American Society of Anesthesiology score), duration of anesthesia and patients disease with a statistical significant difference. The last formula (1995) only evaluate patients' disease. None of the two formula of ICR beta turns out to be completely appropriate index of resource utilization during anesthesia; therefore this analysis still remains a difficult problem. Yet it must be recognized that this system deserves the merit of having evaluated the anesthesiological duties, by separating them from the surgical ones. 相似文献
47.
48.
The method has been developed to improve the bitumen product which incorporates an evaporator concentrate from a BWR, with respect to the swelling and leaching. The leachability of the product has been measured by the method recommended by the IAEA. The swelling of the product is successfully prevented by the addition of calcium chloride. The specimen containing the waste up to Wa/B (Weight ratio of Na2SO4 + CaCl2 and bitumen) = 60:40 shows no pronounced swelling, when it is immersed in water. The cumulative fractions of 137Cs and 60Co leached from a specimen which does not contain CaCl2 are 0.65 and 0.2 at the leaching time of 30 days. On the hand, the corresponding value at 100 days for the specimen with calcium chloride addition is 5 × 10?4 for 137Cs and 1 × 10?4 for 60Co. The coating of the specimen surface with a fresh bitumen (5 mm thickness) reduces the leachability further. These results indicate that this method is effective to improve the bitumen product incorporating BWR's evaporator concentrate. 相似文献
49.
50.