全文获取类型
收费全文 | 228116篇 |
免费 | 26389篇 |
国内免费 | 19707篇 |
专业分类
电工技术 | 15548篇 |
技术理论 | 9篇 |
综合类 | 23254篇 |
化学工业 | 35084篇 |
金属工艺 | 11842篇 |
机械仪表 | 14411篇 |
建筑科学 | 16591篇 |
矿业工程 | 6984篇 |
能源动力 | 8357篇 |
轻工业 | 10189篇 |
水利工程 | 9766篇 |
石油天然气 | 10306篇 |
武器工业 | 2713篇 |
无线电 | 22301篇 |
一般工业技术 | 27644篇 |
冶金工业 | 8398篇 |
原子能技术 | 2509篇 |
自动化技术 | 48306篇 |
出版年
2024年 | 1083篇 |
2023年 | 3880篇 |
2022年 | 6868篇 |
2021年 | 8060篇 |
2020年 | 8010篇 |
2019年 | 7160篇 |
2018年 | 6632篇 |
2017年 | 8205篇 |
2016年 | 9292篇 |
2015年 | 9700篇 |
2014年 | 13115篇 |
2013年 | 13940篇 |
2012年 | 15572篇 |
2011年 | 18216篇 |
2010年 | 14078篇 |
2009年 | 15089篇 |
2008年 | 14189篇 |
2007年 | 16046篇 |
2006年 | 13992篇 |
2005年 | 12323篇 |
2004年 | 10033篇 |
2003年 | 8943篇 |
2002年 | 7348篇 |
2001年 | 5584篇 |
2000年 | 4999篇 |
1999年 | 3920篇 |
1998年 | 3194篇 |
1997年 | 2610篇 |
1996年 | 2405篇 |
1995年 | 2026篇 |
1994年 | 1719篇 |
1993年 | 1247篇 |
1992年 | 1001篇 |
1991年 | 804篇 |
1990年 | 616篇 |
1989年 | 526篇 |
1988年 | 334篇 |
1987年 | 241篇 |
1986年 | 223篇 |
1985年 | 166篇 |
1984年 | 151篇 |
1983年 | 96篇 |
1982年 | 119篇 |
1981年 | 66篇 |
1980年 | 91篇 |
1979年 | 80篇 |
1978年 | 32篇 |
1977年 | 25篇 |
1976年 | 21篇 |
1959年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Quenching with gases rather than oil or other liquid media has the advantages of reducing the risks concerning health and environment, while simultaneously homogenizing the quenching results and minimizing distortion due to a wide range of possible process parameter variations and the pure convective heat transfer. In this contribution, a coupled solution for increasing homogenization of quenching results within high pressure gas quenching will be presented. In the first stage, an experimental test facility was set up for flow investigations and in the second stage a numerical simulation model was generated. The numerical and experimental results of the flow through the chamber were compared for several boundary conditions. Finally, after complete verification of the simulation, the model may be used to assist in parameter variation for optimization of homogeneous high pressure gas quenching. 相似文献
102.
A Cd analogue of the Tl and Hgn =3 series with nominal composition CdBa2Ca2Cu3Oy has been synthesized. The samples were superconducting according to magnetic susceptibility measurements. The critical temperature was 103 or 107 K depending on the preparation conditions. The EDX analysis revealed the presence of Cd-1111, Cd-1121, and Cd-2333 as minor phases. The observed diamagnetic effects were attributed to the differentT
c of these phases. 相似文献
103.
Tan Guang-ming Wang Zhen-zhong Wuhan University of Hydraulic Electric Engineering Wuhan P.R.China 《水动力学研究与进展(B辑)》1992,(1)
It is mentioned in this paper that the adjustment of flow structure occurs when themain-flow swings.The changes of turbulence structure and flow energy loss in the indoor rivermodel are measured.The experimental data are presented for the first time for the further studyof complicated river flow structure. 相似文献
104.
In this paper, we employ a nonlinear adaptive mechanism to globally stabilize nth-order reactions. 相似文献
105.
H.Honda T.Fukuda Institute of Advanced Material Study Kyushyu University Kasuga Fukuoka Japan 《热科学学报(英文版)》1992,1(2):123-129
A theoretical study has been made to optimize the fin geometry of a horizontal finned tube which is to be usedfor condensers that handle the vapor load of a liquid phase change cooling module.Systematic numerical calcu-lations of the vapor to coolant heat transfer have been performed for parametric values of fin height,fin spacing,vertical bundle depth and tubeside heat transfer coefficient.Three dielectric fluids (R-113,FC-72,and FC-87)at atmospheric pressure were selected as the working fluids.For a single tube with optimized fin geometry,theaverage heat flux increased in the order of FC-87,R-113 and FC-72.Both the optimum fin height and optimumfin spacing increased with increasing vertical bundle depth. 相似文献
106.
Flooding phenomenon limits the stability and the flow of a liquid film falling along the walls of a channel in which a gas is flowing upwards.As known, the entrainment effect can completely prevent the liquid to fall from its natural flow. The present work proposes a new mechanistic model for the prediction of the onset of flooding in vertical and inclined pipes in the presence of obstructions, as well as taking into account the viscosity effect. The good performance of the model in the different geometrical conditions and for variable viscosities of the liquid component assesses the validity of the hypothesis that the instability of a wavelike disturbance limits the countercurrent flow in a channel. 相似文献
107.
锆(Ⅳ)-3,5-diBr-PADAP-安替比林三元配合物的分光光度研究与应用 总被引:1,自引:0,他引:1
本文提出在安替比林存在下,以3,5-diBr-PADAP为显色剂,分光光度测定微量锆的新方法。在pH1~2的HCl介质中,锆(W)与试剂和安替比林形成配合比为1:1:1的红色三元配合物,最大吸收值在615nm波长处,摩尔吸光系数ε=1.35×10~5。锆(Ⅳ)量在0~25μg/25ml范围内,遵守比尔定律。方法简单、快速、准确。若采用钽试剂—苯萃取法分离共存离子,可适用于钽铌矿和合金中痕量锆的测定。 相似文献
108.
109.
Solid solutions of the GdFeO3–GdInO3 system were prepared at 1550 °C by ceramic powder processing. The formulated composition was Gd(Fe1−xInx)O3 (GFI) with the indium contents at x = 0, 0.25, 0.5, 0.75, and 1.0. A stable phase of Gd(Fe1/3In2/3)O3 in our system was identified by X-ray diffraction and phase composition analysis. Multi-phase morphologies were observed for GFI bulks with x = 0.5 and 0.75. Dielectric and electrical properties of the GFI bulks were investigated. The addition of 25% In3+ in GdFeO3 had an obvious enhancement in polarization and led to an elevated resonance frequency. Dielectric properties of GFI bulks except GdInO3 were strongly dependent upon the test frequency, which corresponded to the response of polarization mechanism. GdInO3 displayed as a stable dielectric, which was frequency- and temperature-insensitive. GdInO3 was thermally activated and became leaky until above 600 °C. 相似文献
110.
Guanghui Wang Lei Huang Rong Yu Nansheng Deng 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(5):601-608
BACKGROUND: Endocrine disruptors in the aquatic environment and their potential adverse effects are currently issues of concern. One of these endocrine disruptors is 2,2‐bis(4‐hydroxy‐3‐methylphenyl)propane (BPP). In this work the molecular recognition interaction of BPP with β‐cyclodextrin (β‐CD) was studied using IR spectroscopy and steady state fluorescence spectroscopy, and the photocatalytic degradation behaviour of BPP based on molecular recognition interaction was investigated in a TiO2/UV–visible (λmax = 365 nm) system. This might provide a new method for the treatment of some organic pollutants in wastewater. RESULTS: β‐CD reacts with BPP to form a 1:1 inclusion complex, the formation constant of which is 4.94 × 103 L mol?1. The photodegradation rate constant of BPP after molecular recognition by β‐CD showed a 1.42‐fold increase in the TiO2/UV–visible (λmax = 365 nm) system. The photodegradation of BPP depended on the concentration of β‐CD, the pH value, the gaseous medium and the initial concentration of BPP. The photodegradation efficiency of BPP with molecular recognition was higher than that without molecular recognition. After 100 min of irradiation the mineralisation efficiency of BPP after molecular recognition by β‐CD reached 94.8%, whereas the mineralisation efficiency of BPP before molecular recognition by β‐CD was only 40.6%. CONCLUSION: The photocatalytic degradation of BPP after molecular recognition by β‐CD can be enhanced in the TiO2/UV‐visible (λmax = 365 nm) system. This enhancement is dependent on the enhancement of the adsorption of BPP, the moderate inclusion depth of BPP in the β‐CD cavity and the increase in the frontier electron density of BPP after molecular recognition. Copyright © 2008 Society of Chemical Industry 相似文献