首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   4110篇
  免费   357篇
  国内免费   177篇
电工技术   94篇
综合类   527篇
化学工业   310篇
金属工艺   284篇
机械仪表   199篇
建筑科学   436篇
矿业工程   47篇
能源动力   143篇
轻工业   253篇
水利工程   50篇
石油天然气   86篇
武器工业   7篇
无线电   162篇
一般工业技术   238篇
冶金工业   998篇
原子能技术   9篇
自动化技术   801篇
  2025年   40篇
  2024年   109篇
  2023年   96篇
  2022年   160篇
  2021年   129篇
  2020年   153篇
  2019年   90篇
  2018年   70篇
  2017年   61篇
  2016年   102篇
  2015年   92篇
  2014年   355篇
  2013年   370篇
  2012年   505篇
  2011年   574篇
  2010年   386篇
  2009年   442篇
  2008年   211篇
  2007年   286篇
  2006年   230篇
  2005年   61篇
  2004年   14篇
  2003年   9篇
  2002年   11篇
  2001年   16篇
  2000年   7篇
  1999年   6篇
  1998年   5篇
  1996年   3篇
  1995年   2篇
  1994年   3篇
  1992年   2篇
  1991年   3篇
  1990年   1篇
  1989年   1篇
  1988年   6篇
  1987年   11篇
  1986年   5篇
  1985年   3篇
  1984年   1篇
  1981年   1篇
  1980年   2篇
  1978年   1篇
  1968年   1篇
  1966年   1篇
  1965年   1篇
  1963年   2篇
  1962年   3篇
  1951年   1篇
排序方式: 共有4644条查询结果,搜索用时 15 毫秒
1.
《Pattern recognition letters》2007,28(10):1172-1175
A feasibility study on the potential of the electrocardiogram (ECG) for biometrical applications is presented. A test set of 234 ECG recordings from 74 subjects was compiled emulating a realistic scenario for ECG biometrics by using short measurements of 10 s length in combination with a practicable choice of ECG leads. The long-term stability of the individual ECG was investigated during time periods up to several years. Verification and identification was done by utilizing the heart vector and a simple distance measure. As a result, encouraging error rates were obtained; for verification, for instance, the achieved equal error rate was smaller than 3%.  相似文献   
2.
Understanding the TCP congestion control mechanism from a global optimization point of view is not only important in its own right, but also crucial to the design of other transport layer traffic control protocols with provable properties. In this paper, we derive a global utility function and the corresponding optimal control law, known as TCP control law, which maximizes the global utility. The TCP control law captures the essential behaviors of TCP, including slow start, congestion avoidance, and the binary nature of congestion feedback in TCP. We find that the utility function of TCP is linear in the slow start phase and is proportional to the additive increase rate and approaches the well-known logarithm function as the data rate becomes large in the congestion avoidance phase. We also find that understanding the slow start phase with a fixed threshold is critical to the design of new transport layer control protocols to enable quality of service features. Finally, as an application, we design a Minimum Rate Guaranteed (MRG) traffic control law that shares the same utility function as the TCP control law. Our simulation study of the MRG control law indicates that it is indeed TCP friendly and can provide minimum rate guarantee as long as the percentage of network resource consumed by the MRG flows is moderately small.  相似文献   
3.
In this paper, we address two important issues in the video concept detection problem: the insufficiency of labeled videos and the multiple labeling issue. Most existing solutions merely handle the two issues separately. We propose an integrated approach to handle them together, by presenting an effective transductive multi-label classification approach that simultaneously models the labeling consistency between the visually similar videos and the multi-label interdependence for each video. We compare the performance between the proposed approach and several representative transductive and supervised multi-label classification approaches for the video concept detection task over the widely used TRECVID data set. The comparative results demonstrate the superiority of the proposed approach.  相似文献   
4.
介绍表面化学改性活性炭研究进展,针对其特点和改性方法作了系统描述.在此基础上,对其去除水中有机物、重金属离子、亚硝酸盐等污染物质做了简要说明.  相似文献   
5.
The effect of compression on the crystallization behavior and corrosion resistance of Al(86)Ni9La5 amorphous ribbons was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning elec-tron microscopy (SEM) and electrochemistry test. The XRD and TEM results reveal that the compressed Al(86)Ni9La5 ribbons spun with the circumferential speed (R) of 29.3 m/s are in fully amorphous state; however, the compressed ribbons spun with R=14.7 m/s have crystalline phases embedded in the amorphous matrix. The SEM images indicate that after compression, the toughness of the ribbons increases. Electrochemical results show that the compression decreases the stability of the passive film of the Al(86)Ni9La5 amorphous ribbons, because of the compression-introduced free volume, shear bands and crystalline phases; meanwhile, with R=14.7 m/s, the compression-induced crystalline phases in the Al(86)Ni9La5 ribbons increase the corrosion potential.  相似文献   
6.
运用CFD软件对卡鲁金热风炉和ZSD热风炉的气体燃烧和流动进行了数值模拟,得到燃烧室出口烟气速度的分布,并对卡鲁金热风炉燃烧室出口烟气的压力和温度分布进行了测试,分析了两种炉型燃烧室的结构特点。结果表明,卡鲁金热风炉燃烧室出口烟气分布的均匀程度大大高于传统的ZSD热风炉,其结构特点对ZSD热风炉的改造有很大的参考价值。  相似文献   
7.
Multifunctional properties of nanomaterials becomes a hot topic in nano research for the development of multifunctional devices, because modern devices need multifunctional platform for the high efficient plural performance on a single device. Here, we introduce a multifunctional π-conjugated poly (3-methylthiophene) (P3MT) nanotube (NT), showing controllable optical and electrical properties through the control of doping level. P3MT NTs were electrochemically synthesized in the low temperature (−40 °C) on the nanoporous template. The change of doping level by post cyclic voltammetry (CV) treatment on the P3MT lead the variance of polaron/bipolaron band, resulting into the drastic change of ultraviolet-visible absorption and photoluminescence properties. While P3MT NTs before CV treatment show an ohmic behavior in the current-voltage characteristics, those after CV treatment show high photocurrent. From the field emission experiment, the P3MT NTs before CV treatment have a relatively low turn-on electric field and stable electron emission property compared to the P3MT NTs after CV treatment. This shows that the π-conjugated polymers should be shed new light on their multifunctionality for the potential application to the multifunctional platform of opto-electronic nanodevices.  相似文献   
8.
This paper presents a new method of background segmentation for virtual background reconstruction in video-based virtual reality application. To aim at discounting the effect of non-uniform lightness on the diffuse and specular reflection background respectively, a background-colour measurement for diffuse as well as specular reflection is proposed based on Phong illumination model. This colour estimation has two steps: first, based on the colour invariance of diffuse reflection, the diffuse component of the model was estimated; second, the specular component was derived by using estimated diffuse factor and differerial laws. The experimental results of background segmentation show that the presented algorithm is considered robust to non-uniform lightness for diffuse reflection as well as the specular reflection and is also applicable for real-time vldeo-based virtual reality system.  相似文献   
9.
A thin film consisting of a disordered nanorod network of indium tin oxide (ITO) and conventional ITO films are fabricated on gallium nitride (GaN) based-light emitting diodes (LEDs) by electron beam evaporation. The surface morphologies are observed by scanning electron microscopy (SEM). The disordered nanorod network of ITO is grown in vacuum without oxygen. It can be applied directly on the LED as the current spreading film unlike other nanorods which require growth on a conductive layer. The transmittance, current–voltage characteristic, and the dependence of light output power on current are measured for disordered nanorod network ITO LEDs and conventional ITO LEDs, respectively. The measurement results indicate that the nanorod network provides a significant improvement in the light output power of GaN-based LEDs. The influence of the structure of ITO films on the light output power of GaN-based LEDs is discussed.  相似文献   
10.
目的建立HPLC测定盐酸奥洛他定滴眼液中苯扎氯铵含量的方法。方法以氰基键合硅胶为填充剂;乙腈-水-三乙胺为440∶560∶1,用磷酸调pH 3.4为流动相,流速1.0 mL/min;检测波长210 nm。结果苯扎氯铵在0.05~0.15 mg/mL范围内呈良好的线性关系(r=0.999 8);平均回收率99.7%(n=9,RSD=0.69%)。结论此方法简便灵敏准确,重复性好,可用于测定盐酸奥洛他定滴眼液中苯扎氯铵的含量。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号