全文获取类型
收费全文 | 328207篇 |
免费 | 3180篇 |
国内免费 | 873篇 |
专业分类
电工技术 | 5571篇 |
综合类 | 215篇 |
化学工业 | 51722篇 |
金属工艺 | 16324篇 |
机械仪表 | 10283篇 |
建筑科学 | 7163篇 |
矿业工程 | 2599篇 |
能源动力 | 7096篇 |
轻工业 | 24107篇 |
水利工程 | 4169篇 |
石油天然气 | 10802篇 |
武器工业 | 14篇 |
无线电 | 32856篇 |
一般工业技术 | 68005篇 |
冶金工业 | 57861篇 |
原子能技术 | 10244篇 |
自动化技术 | 23229篇 |
出版年
2021年 | 2720篇 |
2019年 | 2668篇 |
2018年 | 4806篇 |
2017年 | 4889篇 |
2016年 | 5225篇 |
2015年 | 3092篇 |
2014年 | 5367篇 |
2013年 | 13529篇 |
2012年 | 8374篇 |
2011年 | 11176篇 |
2010年 | 8988篇 |
2009年 | 10267篇 |
2008年 | 10303篇 |
2007年 | 10183篇 |
2006年 | 8688篇 |
2005年 | 8108篇 |
2004年 | 7762篇 |
2003年 | 7316篇 |
2002年 | 7256篇 |
2001年 | 7252篇 |
2000年 | 6981篇 |
1999年 | 6941篇 |
1998年 | 16620篇 |
1997年 | 11997篇 |
1996年 | 9077篇 |
1995年 | 6888篇 |
1994年 | 6026篇 |
1993年 | 6026篇 |
1992年 | 4637篇 |
1991年 | 4590篇 |
1990年 | 4599篇 |
1989年 | 4536篇 |
1988年 | 4433篇 |
1987年 | 4056篇 |
1986年 | 4066篇 |
1985年 | 4428篇 |
1984年 | 4180篇 |
1983年 | 3952篇 |
1982年 | 3658篇 |
1981年 | 3894篇 |
1980年 | 3636篇 |
1979年 | 3848篇 |
1978年 | 3962篇 |
1977年 | 4270篇 |
1976年 | 5474篇 |
1975年 | 3541篇 |
1974年 | 3571篇 |
1973年 | 3676篇 |
1972年 | 3276篇 |
1971年 | 2926篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Lithium-ion batteries are becoming more and more important not only for portable electronic devices, but also in prevision of high power electric vehicles. In such an optic, deep studies regarding all the components of a secondary battery are in development. In this study, high voltage cathode materials have been selected. Crystals with spinel structure have a 3D vacancy pathway suitable for Li-ions transport. The material under study was LiNi0.5Mn1.5O4 doped with magnesium replacing the nickel. Various samples were synthesized via three different routes: a solid-state method, a modified sol–gel method and a xerogel method. The structure and morphology of the powders were analyzed with HRTEM and XRD. Electrochemical tests were also performed. A wide range of particle sizes (from micro to nanosize) was the result of the different synthesis routes. Unfortunately pure materials were not always obtained. The electrochemical tests showed improvement of the material's cyclability, by reducing the particle size. The electrochemical tests further confirmed the existence of a Li1+dMn2−dO4 impurity. The results are quite promising, however, further improvement of the purity of the electrode composition are needed. 相似文献
992.
Measurements of frequencies and spatial correlations of coherent structures in rod bundle flows 总被引:2,自引:2,他引:0
Cross-wire anemometry was used to identify and characterize coherent flow pulsations in isothermal air flow near the gap regions of a five-rod bundle with a design pitch-to-diameter ratio of 1.149 and contained in a quasi-trapezoidal duct. It was confirmed that such pulsations are quasi-periodic and contribute significantly to the velocity fluctuations across the gap. The frequency of pulsations was found to decrease with diminishing rod–wall gap size in the range between 0.015D and 0.250D, where D is the rod diameter. The pulsations in a rod–wall gap and an adjacent rod–rod gap were strongly coupled and occurred at the same frequency as one rod was displaced towards the duct wall. 相似文献
993.
The blast furnace in the blast-furnace shop at the West Slovakian Metallurgical Combine is charged by means of a complex system
that usually includes the following: an ore yard with a hopper gantry; a system to collect, weigh, and transport the charge
materials to the top of the furnace; the charging apparatus of the furnace; a system that controls the charging operation.
The use of continuous-acting mechanisms facilitates charging of the ore-bearing materials in the charge while minimizing the
content of the −5-mm fraction of these components and the number of coke particles smaller than 25 mm. The productivity of
the furnace could be increased further, which would allow the addition of an efficient aspiration system and make it easier
to fully automate the furnace.
__________
Translated from Metallurg, No. 7, pp. 45–46, July, 2006. 相似文献
994.
995.
O. A. Teplov I. G. Voropaev V. G. Dyubanov L. I. Leont’ev 《Russian Metallurgy (Metally)》2007,(4):268-275
The interaction of hydrogen with the zinc-containing electrometallurgical slime of the Severstal’ metallurgical works has been studied. The sequence of transformations in the slime heated to 1100°C in hydrogen or air has been established. The experimental and calculated weight losses coincide. Some of the carbonates are shown to decompose in the temperature range 300–700°C, and most iron and zinc oxides are reduced to a metal. In the temperature range 650–850°C, zinc is almost completely sublimated. At temperatures above 800°C, complex oxides are reduced and calcium and magnesium carbonates and sulfates are likely to decompose. Experimental digital data on the zinc sublimation rate are processed by the least squares method with approximating equations used in thermal analysis. The kinetics of nonisothermal zinc sublimation is comprehensively analyzed using a unique procedure developed for taking into account the background of a peak and the effect of accompanying processes. An equation for the calculation of the zinc sublimation rate under experimental conditions (fluidized bed) is given and tested. 相似文献
996.
V. A. Borodulya Yu. S. Teplitskii Yu. G. Epanov I. I. Markevich 《Journal of Engineering Physics and Thermophysics》1987,53(6):1393-1396
Experimental data was obtained on external heat transfer in infiltrated granular beds of coarse particles. It was determined that calcualtions with the proposed model agree satisfactorily with the experimental results.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 53, No. 6, pp. 919–923, December, 1988. 相似文献
997.
I. E. Gorbatkina L. D. Konoval'chikov B. K. Nefedov B. L. Khusid 《Chemistry and Technology of Fuels and Oils》1989,25(3):127-130
Translated from Khimiya i Tekhnoloyiya Topliv i Masel, No. 3, pp. 3–5, March, 1989. 相似文献
998.
999.
1000.
G. F. Molokanov 《Journal of Computer and Systems Sciences International》2006,45(2):331-335
The year 2006 marks the ninetieth anniversary of the air navigation (later called navigation) service of the Air Forces of this country. The history of air navigation is investigated, and an opinion about its modern state and directions of further development is presented. 相似文献