全文获取类型
收费全文 | 121271篇 |
免费 | 3941篇 |
国内免费 | 1889篇 |
专业分类
电工技术 | 2772篇 |
技术理论 | 2篇 |
综合类 | 4523篇 |
化学工业 | 17764篇 |
金属工艺 | 6892篇 |
机械仪表 | 5378篇 |
建筑科学 | 5203篇 |
矿业工程 | 1507篇 |
能源动力 | 2024篇 |
轻工业 | 5899篇 |
水利工程 | 1796篇 |
石油天然气 | 2955篇 |
武器工业 | 213篇 |
无线电 | 13756篇 |
一般工业技术 | 20931篇 |
冶金工业 | 4743篇 |
原子能技术 | 681篇 |
自动化技术 | 30062篇 |
出版年
2024年 | 125篇 |
2023年 | 626篇 |
2022年 | 970篇 |
2021年 | 1452篇 |
2020年 | 1085篇 |
2019年 | 910篇 |
2018年 | 15269篇 |
2017年 | 14371篇 |
2016年 | 10909篇 |
2015年 | 1985篇 |
2014年 | 1992篇 |
2013年 | 2454篇 |
2012年 | 5317篇 |
2011年 | 11854篇 |
2010年 | 10459篇 |
2009年 | 7563篇 |
2008年 | 8787篇 |
2007年 | 9774篇 |
2006年 | 2205篇 |
2005年 | 3010篇 |
2004年 | 2352篇 |
2003年 | 2241篇 |
2002年 | 1572篇 |
2001年 | 976篇 |
2000年 | 1093篇 |
1999年 | 1178篇 |
1998年 | 1020篇 |
1997年 | 869篇 |
1996年 | 882篇 |
1995年 | 647篇 |
1994年 | 565篇 |
1993年 | 392篇 |
1992年 | 352篇 |
1991年 | 283篇 |
1990年 | 195篇 |
1989年 | 167篇 |
1988年 | 145篇 |
1987年 | 106篇 |
1986年 | 76篇 |
1985年 | 56篇 |
1984年 | 57篇 |
1968年 | 45篇 |
1967年 | 36篇 |
1966年 | 44篇 |
1965年 | 46篇 |
1959年 | 37篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 63篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
101.
随着集成电路技术的发展及计算机性能的不断提高,计算机组装结构设计在计算机,总体设计中的地位越来越重要,它直接影响到计算机性能的提高。本文针对一个基于工作站和EUCLID-IS软件的电子计算机组结构CAD系统,从软、硬件平台,系统功能及实现等方面进行了讨论,旨在为电子计算机组装结构设计提供一种强有力的、方便的设计工具,有利于增强国产计算机的市场竞争能力。 相似文献
102.
本地七号公共信令网实施的若干问题 总被引:1,自引:1,他引:0
本文主要讨论本地七号公共信令网实施的若干问题,如信令转发点的设置,链路设置和路由选择,话路网和信令网的关系,不同制式七号公共信令的互通问题等。 相似文献
103.
Kosslyn Stephen M.; Koenig Olivier; Barrett Anna; Cave Carolyn Backer; Tang Joyce; Gabrieli John D. E. 《Canadian Metallurgical Quarterly》1989,15(4):723
Analyses of human object recognition abilities led to the hypothesis that 2 kinds of spatial relation representations are used in human vision. Evidence for the distinction between abstract categorical spatial relation representations and specific coordinate spatial relation representations was provided in 4 experiments. These results indicate that Ss make categorical judgments—on/off, left/right, and above/below—faster when stimuli are initially presented to the left cerebral hemisphere, whereas they make evaluations of distance—in relation to 2 mm, 3 mm, or 1 in. (2.54 cm)—faster when stimuli are initially presented to the right cerebral hemisphere. In addition, there was evidence that categorical representations developed with practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
104.
Certain new sulfide-smelting processes and coal-gasification processes generate high-strength sulfur dioxide streams, for
which a new process for converting sulfur dioxide to elemental sulfur needs to be developed because no process exists that
is generally and economically applicable to the treatment of such streams. A thermodynamic and experimental investigation
to develop a new process for converting sulfur dioxide to elemental sulfur by a cyclic process involving calcium sulfide and
calcium sulfate without generating secondary pollutants was carried out. In this process, the starting raw material, calcium
sulfate, is reduced by a suitable reducing agent, such as hydrogen, to produce calcium sulfide, which is used to reduce sulfur
dioxide to elemental sulfur vapor and calcium sulfate. The latter is, in turn, reduced to regenerate calcium sulfide. In this
Part I, detailed experimental results are presented on the kinetics of the reaction between sulfur dioxide and calcium-sulfide
pellets, which produces elemental sulfur and calcium sulfate. The experiments were carried out at temperatures between 1023
and 1088 K and sulfur-dioxide partial pressures between 9 and 60 kPa by the use of a thermogravimetric analysis (TGA) technique.
The rate of this reaction was demonstrated by the conversion of 40 pct calcium-sulfide pellets obtained from the hydrogen
reduction of fresh calcium sulfate in 10 minutes at 1073 K under a sulfur-dioxide partial pressure of 43 kPa. The reactivity
decreased somewhat during the first three cycles but remained largely unchanged thereafter up to the tenth cycle. This characteristic
of the pellets is important because the solids must be reusable for repeated cycles to avoid generating secondary pollutants.
A pore-blocking model was found to fit the reaction rate. The reaction is first order with respect to sulfur-dioxide partial
pressure and has an activation energy of 101 to 134 kJ/mol (24 to 32 kcal/mol) for calcium-sulfide pellets reacted and regenerated
several different times. Sulfur dioxide-containing streams from certain sources, such as the regenerator off-gas from an integrated-gasification,
combined-cycle, desulfurization unit and new sulfide-smelting plants, contain much higher partial pressures of SO2. In these cases, the rate of the first reaction is expected to be proportionally higher than in the test conditions reported
in this article. The reduction kinetics of calcium-sulfate pellets with hydrogen gas is reported in the accompanying Part
II. 相似文献
105.
Following up on recent studies of the Zn-rich corners of the Zn-Fe-Ni and Zn-Fe-Si ternary systems, a 450 °C isothermal section
of the Zn-Fe-Ni-Si quaternary phase diagram with the Zn composition being fixed at 93 at.% was determined experimentally using
optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDS), and x-ray
diffractometry (XRD). FeSi was found to be in equilibrium with almost all phases in the section, including the T, ζ, Ni-δ,
NiSi2, and FeSi2 phases, as well as the liquid phase (L). Silicon solubilities in the T, ζ, and Ni-δ phases were rather limited. However,
the solubilities of Fe and Zn in the NiSi2 phase, at 4.5 at.% and 7.2 at.%, respectively, were appreciable. The existence of the (L+NiSi2+Ni-δ) three-phase equilibrium state apparently prevents other Ni-Si compounds from entering equilibrium with the liquid at
450 °C. No true quaternary compound was found in the study. 相似文献
106.
Microbiological denitrification of red beet juice 总被引:1,自引:0,他引:1
Dorota Walkowiak-Tomczak 《European Food Research and Technology》2002,215(5):401-406
The purpose of study was the determination of optimal conditions for red beet juice denitrification by Paracoccus denitrificans bacteria as well as the evaluation of the usefulness of microbiologically treated juice for the production of a natural colouring preparation for foods. Total reduction of nitrates was found during bacterial culturing at 25 and 30 °C, at an initial pH of 7.0-8.0 and juice osmotic pressure of 900-1100 mOsm/kg. Microbiological denitrification procedure affected colour, taste and aroma of the juice. However, the use of juice as food colouring and component was made feasible by acidification and partial evaporation of water together with volatile substances. 相似文献
107.
108.
飞机液压系统污染及控制 总被引:2,自引:2,他引:0
本文全面分析了收音机液压系统污染的危害和主要原因,并在此基础上有针对性地提出了预防措施。 相似文献
109.
George Ter-Stepanian 《Bulletin of Engineering Geology and the Environment》2002,61(3):197-205
The paper discusses the postulated suspension force, by which it is possible to explain some enigmatic phenomena observed
in different types of mass movements. This force is generated in thick suspensions as a result of friction between sinking
solid particles and static water. The suspension force is related to the seepage force but they have opposite directions.
Both forces form flow networks. Having explained the suspension force, the paper describes how this influences the movement
of material, particularly in debris flows. Enigmatic features and the mechanism of debris flows and lahars are explained by
virtue of the suspension force.
Electronic Publication 相似文献
110.
We consider the problem of rescheduling trains in the case where one track of a railway section consisting of two tracks
in opposing directions is closed due to construction activities. After presenting an appropriate model for this situation
we derive a polynomial algorithm for the subproblem of finding an optimal schedule with minimal latenesss if the subsequences
of trains for both directions outside the construction site are fixed. Based on this algorithm we propose a local search procedure
for the general problem of finding good schedules and report test results for some real world instances.
Received: December 8, 1999 / Accepted: May 2, 2001 相似文献