全文获取类型
收费全文 | 199340篇 |
免费 | 2636篇 |
国内免费 | 611篇 |
专业分类
电工技术 | 3468篇 |
综合类 | 149篇 |
化学工业 | 28960篇 |
金属工艺 | 8049篇 |
机械仪表 | 6068篇 |
建筑科学 | 4811篇 |
矿业工程 | 1303篇 |
能源动力 | 5127篇 |
轻工业 | 17116篇 |
水利工程 | 2297篇 |
石油天然气 | 4040篇 |
武器工业 | 8篇 |
无线电 | 23066篇 |
一般工业技术 | 40011篇 |
冶金工业 | 37227篇 |
原子能技术 | 5086篇 |
自动化技术 | 15801篇 |
出版年
2021年 | 1604篇 |
2019年 | 1569篇 |
2018年 | 2573篇 |
2017年 | 2645篇 |
2016年 | 2775篇 |
2015年 | 1794篇 |
2014年 | 3074篇 |
2013年 | 8939篇 |
2012年 | 5050篇 |
2011年 | 7021篇 |
2010年 | 5589篇 |
2009年 | 6350篇 |
2008年 | 6443篇 |
2007年 | 6511篇 |
2006年 | 5579篇 |
2005年 | 5228篇 |
2004年 | 5005篇 |
2003年 | 4887篇 |
2002年 | 4525篇 |
2001年 | 4656篇 |
2000年 | 4578篇 |
1999年 | 4726篇 |
1998年 | 11373篇 |
1997年 | 8120篇 |
1996年 | 6408篇 |
1995年 | 4673篇 |
1994年 | 4271篇 |
1993年 | 4073篇 |
1992年 | 3223篇 |
1991年 | 3076篇 |
1990年 | 2870篇 |
1989年 | 2951篇 |
1988年 | 2826篇 |
1987年 | 2398篇 |
1986年 | 2308篇 |
1985年 | 2715篇 |
1984年 | 2505篇 |
1983年 | 2345篇 |
1982年 | 2090篇 |
1981年 | 2203篇 |
1980年 | 2029篇 |
1979年 | 2124篇 |
1978年 | 2120篇 |
1977年 | 2366篇 |
1976年 | 3188篇 |
1975年 | 1833篇 |
1974年 | 1761篇 |
1973年 | 1772篇 |
1972年 | 1443篇 |
1971年 | 1339篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
961.
The applicability of fluidised-bed reactor (FBR) based sulphate reducing bioprocess was investigated for the treatment of iron containing (40-90 mg/L) acidic wastewater at 65 degrees C. The FBR was inoculated with sulphate-reducing bacteria (SRB) originally enriched from a hot mining environment. Ethanol or acetate was supplemented as carbon and electron source for the SRB. A rapid startup with 99.9, 46 and 29% ethanol, sulphate and acetate removals, in respective order, was observed even after 6 days. Iron was almost completely removed with a rate of 90 mg/L.d. The feed pH was decreased gradually from its initial value of 6 to around 3.7 during 100 days of operation. The wastewater pH of 4.3-4.4 was neutralised by the alkalinity produced in acetate oxidation and the average effluent pH was 7.8 +/- 0.8. Although ethanol removal was complete, acetate accumulated. Later the FBR was fed with acetate only. Although acetate was present in the reactor for 295 days, its oxidation rates did not improve, which may be due to low growth rate and poor attachment ability of acetate oxidising SRB. Hence, the oxidation of acetate is the rate limiting step in the sulphidogenic ethanol oxidation by the thermophilic SRB. 相似文献
962.
963.
964.
965.
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
966.
V. Erhardt B. Handreck C. Mitschka B. Seppelt 《Molecular nutrition & food research》1985,29(7):693-701
The milling industry faces the task of saving energy without impairing the quantity and quality of the products. By applying experimental plans for the optimization of several effect variables, approximations (compromise solutions) between the cause variables (conditioning parameters) and the effect variables (quantity and quality parameters) are sought, which satisfy the aims laid down. 相似文献
967.
968.
Most of the UK nuclear power reactors are gas-cooled and graphite moderated. As well as acting as a moderator the graphite also acts as a structural component providing channels for the coolant gas and control rods. For this reason the structural integrity assessments of nuclear graphite components is an essential element of reactor design. In order to perform graphite component stress analysis, the definition of the constitutive equation relating stress and strain for irradiated graphite is required. Apart from the usual elastic and thermal strains, irradiated graphite components are subject to additional strains due to fast neutron irradiation and radiolytic oxidation. In this paper a material model for nuclear graphite is presented along with an example of a stress analysis of a nuclear graphite moderator brick subject to both fast neutron irradiation and radiolytic oxidation. 相似文献
969.
The leaching of zinc concentrate obtained from the zinc ore located in the Ganesh-Himal region of Nepal has been carried out
in the presence of ammonium persulfate (APS) as an oxidant. Leaching variables such as time, temperature, acid, and oxidant
concentration, E
h
, and particle size of sphalerite concentrate were studied to optimize the condition and to understand the mechanism of the
reaction. The zinc extraction increased up to a temperature of 333 K and a further rise in the temperature to 343 K resulted
in lowering of metal extraction. A decrease in particle size and increase in oxidant concentration enhanced the dissolution
rate of zinc. The leaching data best fitted to the mixed controlled kinetic model. An activation energy of 43 kJ/mol was obtained
for the dissolution of zinc in the temperature range 303 to 333 K with APS. The leaching mechanism was further established
by characterizing the original concentrate and the leach residue by X-ray diffraction (XRD) phase identification and scanning
electron microscopy (SEM) studies. 相似文献
970.
Stormwater reuse is increasing in popularity as a technique for overcoming water shortages in urban Australia. However, technology for the reliable treatment of stormwater for reuse is still not fully developed. This paper presents the first steps in refining biofilters for stormwater reuse. Six different filter media were selected, to target specific stormwater pollutants, as well as support plant growth. They were tested in the laboratory, where the filters were dosed three times per week with semi-synthetic stormwater for five weeks. Pollutant removal performance was monitored, and revealed that all soil-based filters performed similarly (while sand filters behaved somewhat differently). All filters removed more than 80% of solids and greater than 90% of lead, copper, and zinc. Three filter types were able to remove some phosphorus (particularly in the top 30 cm of the media). Apart from sand, all filter media were net producers of nitrogen, leading to an important conclusion that non-vegetated, soil-based filters are not suitable for targeting nutrients. However, since heavy metals are the primary pollutant of concern with respect to stormwater reuse for irrigation (the most popular end-use), it was concluded that biofilters may be promising technologies for treatment of stormwater for reuse. 相似文献