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   8237篇
  免费   961篇
  国内免费   693篇
电工技术   382篇
综合类   739篇
化学工业   1064篇
金属工艺   1064篇
机械仪表   423篇
建筑科学   367篇
矿业工程   110篇
能源动力   235篇
轻工业   124篇
水利工程   73篇
石油天然气   233篇
武器工业   57篇
无线电   2455篇
一般工业技术   1186篇
冶金工业   231篇
原子能技术   66篇
自动化技术   1082篇
  2024年   59篇
  2023年   153篇
  2022年   222篇
  2021年   231篇
  2020年   293篇
  2019年   309篇
  2018年   239篇
  2017年   300篇
  2016年   327篇
  2015年   339篇
  2014年   499篇
  2013年   554篇
  2012年   590篇
  2011年   631篇
  2010年   447篇
  2009年   483篇
  2008年   488篇
  2007年   525篇
  2006年   453篇
  2005年   433篇
  2004年   381篇
  2003年   294篇
  2002年   228篇
  2001年   206篇
  2000年   205篇
  1999年   165篇
  1998年   120篇
  1997年   130篇
  1996年   102篇
  1995年   96篇
  1994年   76篇
  1993年   48篇
  1992年   51篇
  1991年   37篇
  1990年   31篇
  1989年   26篇
  1988年   21篇
  1987年   13篇
  1986年   20篇
  1985年   12篇
  1984年   12篇
  1983年   12篇
  1982年   11篇
  1981年   3篇
  1979年   2篇
  1977年   3篇
  1976年   2篇
  1963年   2篇
  1957年   1篇
  1956年   3篇
排序方式: 共有9891条查询结果,搜索用时 0 毫秒
1.
By using scanning polarization force microscopy,the deliquescence process and the atomic steps on the cleavage surface of CaCO3 in air were studied in situ.Under an exposure to medium umidity(-57%),the sloiw step movement has been observed.  相似文献   
2.
3.
Using the photonic band gap in photonic crystals, the fundamental waveguide structures for the light wavelength range have been developed. Based on the fine structure of these many functional devices have been proposed by analytical or numerical simulation methods and the experiments of trial manufacture. In this paper, the treatment of chiral dielectric in the Condensed Node Spatial Network for the vector potential is explained, and we show the polarization plane rotation property in air‐hole and pillar type photonic crystal waveguide structures with the chiral medium substrate. Then, we show the fundamental advantage of the air‐hole type photonic crystal waveguide structure in application to a mode converter. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(1): 7–14, 2005; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20098  相似文献   
4.
A hybrid mathematic model for pervaporation is proposed which incorporates the concepts of solution-diffusion model and pore model. The model allows performance prediction as well as the establishment of the internal concentration and pressure profiles within the membrane. The model parameters specific to the particular membrane and mixture system are determined using liquid sorption and pervaporation experimental data. The model is experimentally examined using ethanol–water mixtures and poly(dimethyl siloxane)–poly(vinyldiene fluoride) (PDMS–PVDF) composite membranes. The characteristics of flux and separation factor predicted using the model are in fair agreement with the experimental data under various feed concentrations and downstream pressures for different membrane arrangements, including single-layer, reverse single-layer and double-layer PDMS–PVDF composite membranes. Internal profiles of pressure, concentration and component mole fraction can be established using the model. Concentration polarization phenomena for ethanol and water are located at membrane interfaces and vapor–liquid interfaces, respectively. Performances of several different membrane designs are compared using the model.  相似文献   
5.
In recent years, polymer amines have been studied as an efficient corrosion inhibitor for iron in acid media. In this article, the performance of water soluble polyaniline as corrosion inhibitor for iron in 0.5M H2SO4 has been evaluated by potentiodynamic polarization, linear polarization, and electrochemical impedance spectroscopy and compared with the performance of the aniline monomer. It has been found that polyaniline is an efficient inhibitor, since the maximum efficiency of 84% has been observed at a concentration of 100 ppm, whereas the monomer has accelerated the corrosion. FTIR studies have shown that the polyaniline is strongly adsorbed on the iron surface and inhibits the corrosion effectively. However, aniline has been found to improve the passivation tendency of iron at higher concentrations. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2144–2153, 2006  相似文献   
6.
High fidelity repeater false-target badly affects a radar system’s detecting, tracking, and data processing. It is an available approach of confronting false-target for radar that discriminates firstly and then eliminates. Whereas for the technique progress about the repeater false-target jam, it is more and more difficult to discriminate this jam in the time-domain, frequency-domain, or space-domain. The technique using polarization information to discriminate the target and false-target is discussed in th...  相似文献   
7.
王现彬  赵正平 《材料导报》2016,30(6):133-136
建立了氮极性(N-polar)GaN基HEMT器件的准二维(Quasi-2-D)电荷传输模型,仿真研究了N-polar GaN基HEMT的直流特性。仿真结果表明,不同的极化效应会对输出特性曲线和转移特性曲线产生不同的影响,考虑自发极化效应(Psp)+压电极化效应(Ppe)、只考虑Ppe和只考虑Psp三种情况下的阈值电压分别为:-3.96V、-2.29V和-2.47V,而其对应的峰值跨导则分别为44mS/mm、41.2mS/mm和41.3mS/mm。该模型为N-polar GaN基HEMT器件仿真提供了理论参考。  相似文献   
8.
Collision and intersection detection of surfaces is an important problem in computer graphics and robotic engineering. A key idea of our paper is to use the bracket method to derive the necessary and sufficient conditions for the collision of two ruled surfaces. Then the numerical intersection curve can be characterized. The cases for two bounded ruled surfaces are also discussed.  相似文献   
9.
The model-based human body motion analysis system   总被引:3,自引:0,他引:3  
In this paper, we propose a model-based method to analyze the human walking motion. This system consists of three phases: the preprocessing phase, the model construction phase, and the motion analysis phase. In the experimental results, we show that our system not only analyzes the motion characteristics of the human body, but also recognizes the motion type of the input image sequences. Finally, the synthesized motion sequences are illustrated for verification. The major contributions of this research are: (1) developing a skeleton-based method to analyze the human motion; (2) using Hidden Markov Model (HMM) and posture patterns to describe the motion type.  相似文献   
10.
We show how the study of the geometry of the nine flex tangents to a cubic produces pseudo-parameterizations, including the ones given by Icart, Kammerer, Lercier, Renault and Farashahi, and infinitely many new ones.  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