全文获取类型
收费全文 | 81187篇 |
免费 | 9330篇 |
国内免费 | 5663篇 |
专业分类
电工技术 | 6790篇 |
技术理论 | 5篇 |
综合类 | 6851篇 |
化学工业 | 11217篇 |
金属工艺 | 4823篇 |
机械仪表 | 5669篇 |
建筑科学 | 6876篇 |
矿业工程 | 2962篇 |
能源动力 | 2394篇 |
轻工业 | 6368篇 |
水利工程 | 2144篇 |
石油天然气 | 3747篇 |
武器工业 | 1109篇 |
无线电 | 10257篇 |
一般工业技术 | 7962篇 |
冶金工业 | 3068篇 |
原子能技术 | 1165篇 |
自动化技术 | 12773篇 |
出版年
2024年 | 521篇 |
2023年 | 1545篇 |
2022年 | 3285篇 |
2021年 | 4544篇 |
2020年 | 3358篇 |
2019年 | 2511篇 |
2018年 | 2765篇 |
2017年 | 3081篇 |
2016年 | 2706篇 |
2015年 | 4185篇 |
2014年 | 5250篇 |
2013年 | 6063篇 |
2012年 | 7158篇 |
2011年 | 7387篇 |
2010年 | 6646篇 |
2009年 | 6070篇 |
2008年 | 5777篇 |
2007年 | 5184篇 |
2006年 | 4378篇 |
2005年 | 3489篇 |
2004年 | 2295篇 |
2003年 | 1543篇 |
2002年 | 1380篇 |
2001年 | 1083篇 |
2000年 | 918篇 |
1999年 | 730篇 |
1998年 | 433篇 |
1997年 | 379篇 |
1996年 | 329篇 |
1995年 | 275篇 |
1994年 | 218篇 |
1993年 | 148篇 |
1992年 | 106篇 |
1991年 | 100篇 |
1990年 | 68篇 |
1989年 | 50篇 |
1988年 | 49篇 |
1987年 | 27篇 |
1986年 | 24篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 3篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 24篇 |
1979年 | 16篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1959年 | 15篇 |
1951年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
一种新的图像水印方案 总被引:1,自引:0,他引:1
目标区域是图像中视觉上最重要的部分。针对现有的水印算法很少考虑图像中确定的目标区域这一问题,提出了一种基于目标区域的水印方案(WIOR)。方案首先利用小波变换分析图像的目标特征,并依据图像的小波高频系数特征对其进行聚类,获得水印的嵌入域,在此嵌入域中,选择小波系数并对其进行量化调制来嵌入二值扩谱水印;同时,通过只在图像的局部区域内嵌入较少的水印信息来改善水印的隐蔽性。实验结果表明,该方案对于一类具有突出目标特征的图像具有较好的效果。嵌入的水印主要优势在于真正把水印嵌入图像的视觉重要部分,从而能有效地抵御剪切攻击,而且可以实现盲检测。 相似文献
72.
73.
An account is given of some principal observations made from a series of experiments in which three-span pipe beams were subjected to central impact by indenters with different nose shapes. These pipes were filled and pre-pressurized with water in order to identify the main effects produced by the fluid–structure interaction. In comparison, the impact experiments of the pipes with no water were also carried out. The perforation failure modes and corresponding critical impact energies were obtained in different test conditions. The experimental results indicated that the critical perforation energy and the deformation of the wall of the pipe were significantly influenced by the presence of the water and the pressure. 相似文献
74.
75.
76.
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
77.
78.
杨雷 《石油化工安全环保技术》2006,22(3):9-10
根据胜利油田建立实施HSE管理体系工作的现状,提出现阶段推行HSE管理体系要做好五方面的工作。在日常管理工作中,要做到高标准、高质量、严要求、严考核。 相似文献
79.
Xianfu Lei Pingzhi Fan 《Communications Letters, IEEE》2008,12(10):720-721
We point out that a simpler expression could be derived for the outage probability considered by Chalise and Vandendorpe (2008). As a result, the computation of confluent hypergeometric function of two variables is not needed and the required computational effort is significantly reduced. 相似文献
80.
In CFD simulation of diesel combustion, the predictive capabilities of the spray model play the most important role. Consequently, under the strict guidelines of the V&V, a method to adjust parameters of diesel spray model WAVE to accompany with the in-cylinder physical progress has been investigated in this paper. Moreover, the simulation of the spray has been validated by high-speed photography experiments and verified by the equation proposed by Hiroyasu. Finally, a modified setup for the WAVE spray model has been proposed and applied in the spray and combustion simulation for Deutz1013 diesel in different engine speed. 相似文献