全文获取类型
收费全文 | 1043篇 |
免费 | 29篇 |
国内免费 | 1篇 |
专业分类
电工技术 | 12篇 |
化学工业 | 141篇 |
金属工艺 | 20篇 |
机械仪表 | 27篇 |
建筑科学 | 13篇 |
矿业工程 | 1篇 |
能源动力 | 148篇 |
轻工业 | 39篇 |
水利工程 | 4篇 |
石油天然气 | 3篇 |
无线电 | 144篇 |
一般工业技术 | 187篇 |
冶金工业 | 127篇 |
原子能技术 | 6篇 |
自动化技术 | 201篇 |
出版年
2023年 | 11篇 |
2022年 | 15篇 |
2021年 | 42篇 |
2020年 | 30篇 |
2019年 | 32篇 |
2018年 | 43篇 |
2017年 | 29篇 |
2016年 | 29篇 |
2015年 | 19篇 |
2014年 | 25篇 |
2013年 | 46篇 |
2012年 | 25篇 |
2011年 | 20篇 |
2010年 | 29篇 |
2009年 | 33篇 |
2008年 | 32篇 |
2007年 | 45篇 |
2006年 | 30篇 |
2005年 | 25篇 |
2004年 | 15篇 |
2003年 | 14篇 |
2002年 | 16篇 |
2001年 | 11篇 |
2000年 | 12篇 |
1999年 | 20篇 |
1998年 | 39篇 |
1997年 | 34篇 |
1996年 | 27篇 |
1995年 | 25篇 |
1994年 | 21篇 |
1993年 | 17篇 |
1992年 | 17篇 |
1991年 | 15篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 17篇 |
1987年 | 9篇 |
1986年 | 14篇 |
1985年 | 38篇 |
1984年 | 17篇 |
1983年 | 20篇 |
1982年 | 17篇 |
1981年 | 14篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1977年 | 9篇 |
1976年 | 7篇 |
1975年 | 7篇 |
1973年 | 6篇 |
1971年 | 4篇 |
排序方式: 共有1073条查询结果,搜索用时 15 毫秒
1.
2.
As an aid towards improving the treatment of exchange and correlation effects in electronic structure calculations, it is
desirable to have a clear picture of the errors introduced by currently popular approximate exchange-correlation functionals.
We have performed ab initio density functional theory and density functional perturbation theory calculations to investigate
the thermal properties of bulk Cu, using both the local density approximation (LDA) and the generalized gradient approximation
(GGA). Thermal effects are treated within the quasiharmonic approximation. We find that the LDA and GGA errors for anharmonic
quantities are an order of magnitude smaller than for harmonic quantities; we argue that this might be a general feature.
We also obtain much closer agreement with experiment than earlier, more approximate calculations. 相似文献
3.
4.
5.
6.
While seeds ofCucurbita maxima contain both Δ5- and Δ7-sterols, the former, which have been described earlier, now have been found to disappear during germination. This suggests
that a function exists for the Δ5-compounds only in the early part of the life cycle ofC. maxima, unlike most of the other higher plants studied. In contrast to the Δ5-sterols, the level of Δ7-sterols increased during germination as well as during seedling development and maturation. The period of transition between
germination and seedling development appeared to be of special importance in terms of sterol changes. This period represented
a surge of sterol biosynthesis with an ontogenetic shift in sterol composition from approximately equal amounts of 24α- and
24β-ethyl stereochemistry to a predominance of the former. The sterol composition of the mature plants included only about
5% of the 24β-ethylsterols. The configurational relationships were demonstrated by high resolution1H-NMR. The sterols of the mature plants were: 25(27)-dehydrochondrillasterol, 24β-ethyl-25(27)-dehydrolathosterol, avenasterol,
spinasterol, 22-dihydrospinasterol and 24ξ-methyllathosterol. Based on the changes which occurred in the relative amounts
of the Δ7-sterols, it did not appear that the Δ5-components were being converted to their Δ7-analogs.
A portion of this work was presented at the meeting of the American Oil Chemists' Society in May, 1985 in Philadelphia. 相似文献
7.
Hari B. Goyal M. O. Garg K. R. Rao R. D. Srivastava 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1985,35(2):49-56
The kinetics of the reaction of acetic acid and acetylene over zinc acetate-activated carbon catalyst was investigated over a wide range of process variables in a pilot reactor. Although various catalytic reaction mechanisms were postulated, the rate of reaction was most satisfactorily correlated by a mechanism of surface reaction between charged adsorbed acetic acid and acetylene, which assumes that the rate controlling step was the irreversible charged adsorption of acetylene and acetic acid. 相似文献
8.
The medium coking coal fines of − 0.5 mm from Jharia coal field were taken for this investigation. The release analysis of the composite coal reveals that yield is very low at 10.0% ash, about 25% at 14% ash and 50% at 17% ash level. The low yield is caused by the presence of high ash finer fraction. The size-wise ash analysis of − 0.5 mm coal indicated that − 0.5 + 0.15 mm fraction contains less ash than − 0.15 mm fraction. Thus, the composite feed was split into − 0.5 + 0.15 mm and − 0.15 mm fractions and subjected to flotation separately. The low ash bearing fraction (− 0.5 + 0.15 mm) was subjected to two stages collectorless flotation to achieve the concentrate with 10% ash. The cleaner concentrate (18.9%) with 10% ash was recovered which has an application in metallurgical industries. The concentrate of 30.2% yield with 12.5% ash could be achieved in one stage collectorless flotation which is suitable for use in coke making as sweetener. As the − 0.15 mm fraction contains relatively high ash, collector aided flotation using sodium silicate was performed to get a concentrate of 23.6% yield with about 17% ash. The blending of this product with cleaner tail obtained from − 0.5 + 0.15 mm produces about 35.0% yield with 17% ash and that can be utilized for coke making. The reject from the two fractions can be used for conventional thermal power plant or cement industries using a 23.5% ash after one stage collector aided flotation and the final tailings produced content ash of 61.6% can be used for fluidization combustion bed (FBC). This eventually leads to complete utilization of coal. 相似文献
9.
H.P. Garg A.R. Shukla Indrajit Madhuri R.C. Agnihotri S. Chakravertty 《Applied Energy》1985,21(1):43-54
Indoor test methods for solar collectors are widely accepted and recommended by ASHRAE. The development of a solar simulator for indoor testing and the certification procedure for photo-thermal solar devices is discussed in this paper. The system consists of 14 quartz halogen lamps and provides a testing area of about 1 × 1 m. The irradiance can be varied from 400 to 1500 W/m2. This is achieved by varying the input power supplied to individual lamps. The radiation output characteristics of a single lamp have been studied. The distribution of intensity over the covered area of 1·20 × 1·20 m has been recorded using a precision Eppley pyranometer.A variety of collectors—evacuated tubular collectors and flat-plate collectors of both liquid and air heating types—has been tested under sufficiently stable insolation conditions. Results for a conventional solar air heater are presented together with suggestions for further improvements. 相似文献
10.
Rice husk generated as a by-product of rice processing is an important energy resource. The availability of this resource in India has been assessed and the technologies for exploitation of its energy potential in rice processing industry discussed. Nomographs have been developed for estimation of the husk required to meet the energy demand of parboiling, drying and milling operations. The unit cost of electricity using rice husk gasifier-based power generation systems has been calculated and its financial feasibility assessed in comparison with utility-supplied and diesel-generated electricity. With the cost and efficiency data assumed here, the unit cost of electricity produced by rice husk gasifier-dual fuel engine-generator system varies between Rs 2/kWh and Rs 7/kWh. (Note: 35 Rs approximates to $US 1.) 相似文献