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   2472篇
  免费   292篇
  国内免费   1篇
电工技术   23篇
综合类   3篇
化学工业   743篇
金属工艺   64篇
机械仪表   170篇
建筑科学   40篇
矿业工程   1篇
能源动力   112篇
轻工业   336篇
水利工程   3篇
石油天然气   1篇
无线电   458篇
一般工业技术   545篇
冶金工业   53篇
原子能技术   28篇
自动化技术   185篇
  2023年   34篇
  2022年   37篇
  2021年   76篇
  2020年   71篇
  2019年   60篇
  2018年   90篇
  2017年   103篇
  2016年   119篇
  2015年   107篇
  2014年   159篇
  2013年   183篇
  2012年   196篇
  2011年   219篇
  2010年   154篇
  2009年   137篇
  2008年   146篇
  2007年   111篇
  2006年   98篇
  2005年   77篇
  2004年   83篇
  2003年   81篇
  2002年   87篇
  2001年   49篇
  2000年   56篇
  1999年   37篇
  1998年   34篇
  1997年   22篇
  1996年   25篇
  1995年   19篇
  1994年   13篇
  1993年   7篇
  1992年   5篇
  1991年   7篇
  1990年   9篇
  1989年   7篇
  1988年   8篇
  1987年   7篇
  1986年   5篇
  1985年   10篇
  1984年   4篇
  1983年   4篇
  1981年   1篇
  1980年   2篇
  1979年   1篇
  1978年   1篇
  1977年   1篇
  1975年   2篇
  1974年   1篇
排序方式: 共有2765条查询结果,搜索用时 15 毫秒
71.
Electromagnetic shielding properties of soft magnetic metal alloy (Fe-Al-Si) flakes and Ni-Zn ferrite composites for effective suppression of broadband and high frequency noise were investigated. In the soft magnetic composites, the maxima of reflection loss were shifted to high frequency with increase in content of Ni-Zn ferrite. The composites with content of 50 and 70% ferrite exhibited broadband absorptive characteristics. The broadband character- istics might be caused by the extended resonance due to an overlap between imaginary permeability and permittivity of the two composites over the frequency range from 2 to 10 GHz.  相似文献   
72.
Hot band annealing is known to be a prerequisite for good magnetic properties irrespective of manufacturing methods in grain‐oriented Fe‐3 wt.% Si electrical steels. In this study, the effects of hot band annealing on magnetic properties were investigated in 3% grain‐oriented electrical steels of low soluble AI contents and one‐stage cold rolling. Microstructure and precipitate distribution were compared with hot band annealing conditions. Secondary recrystallization behaviour with hot band annealing condition was also discussed.  相似文献   
73.
Abstract— We studied the silicide‐mediated crystallization of a‐Si for low‐temperature polycrystalline‐silicon (LTPS) on glass. By controling the heating method and Ni density on the a‐Si, the grain size could be increased to 40 μm. Radial grain growth from a NiSi2 crystalline nucleus gives rise to a large‐grain poly‐Si without amorphous phase inside. A field‐effect mobility of over 200 cm2/V‐sec was achieved by using LTPS.  相似文献   
74.
This paper presents a nonlinear kinematic tolerance analysis algorithm for planar mechanical systems comprised of higher kinematic pairs. The part profiles consist of line and circle segments. Each part translates along a planar axis or rotates around an orthogonal axis. The part shapes and motion axes are parameterized by a vector of tolerance parameters with range limits. A system is analyzed in two steps. The first step constructs generalized configuration spaces, called contact zones, that bound the worst-case kinematic variation of the pairs over the tolerance parameter range. The zones specify the variation of the pairs at every contact configuration and reveal failure modes, such as jamming, due to changes in kinematic function. The second step bounds the worst-case system variation at selected configurations by composing the zones. Case studies show that the algorithm is effective, fast, and more accurate than a prior algorithm that constructs and composes linear approximations of contact zones.  相似文献   
75.
This hybrid dynamic simulation scheme implements part of the simulator in software running on a processor and maps the rest onto a programmable hardware accelerator. An algorithm for hardware synthesis of behavioral testbenches enables better partitions, resulting in lower communication costs between the two components. TPartition improves the performance of hardware accelerated simulation without a designer's remodeling effort and without losing compatibility with the original testbench.  相似文献   
76.
Today’s business environment is experiencing as a period of expansion and the globalization. Therefore, a distribution plan with low cost and high customer satisfaction in supply chain management (SCM) has been widely investigated. The purpose of this study is to establish optimal distribution planning in the supply chain. In this paper, a hybrid approach involving a genetic algorithm (GA) and simulation is presented to solve this problem. The GA is employed in order to quickly generate feasible distribution sequences. Considering uncertain factors such as queuing, breakdowns and repairing time in the supply chain, the simulation is used to minimize completion time for the distribution plan. The computational results for an example of a simple supply chain are given and discussed to validate the proposed approach. We obtained a more realistic distribution plan with optimal completion time by performing the iterative hybrid GA simulation procedure which reflects the stochastic nature of supply chains.  相似文献   
77.
This paper reports a technique for measuring the velocity and dissolved oxygen concentration (DOC) fields simultaneously in a micro-scale water flow using oxygen-sensitive particles (OSP) and a conventional microparticle image velocimetry method. The OSP were fabricated using a dispersion polymerization method by synthesizing platinum (II) octaethyporphyrin (PtOEP) with polystyrene, and used as tracer particles and oxygen sensors. An ultraviolet light-emitting diode with a wavelength of 385 nm was used as the excitation light source, and phosphorescence images of OSP were captured on a CMOS high-speed camera. The interrogation window concept was used to measure the DOC in water from the dispersed phosphorescence intensity distribution of OSP. The Stern–Volmer equations in the interrogation windows were obtained from in situ calibration. Water containing OSP with DOC values of 0 and 100 % were injected into a Y-shaped microchannel using a double loading syringe pump. The velocity and DOC field over the entire channel area were quantified.  相似文献   
78.
Vapor phase carbon (C)‐reduction‐based syntheses of C nanotubes and graphene, which are highly functional solid C nanomaterials, have received extensive attention in the field of materials science. This study suggests a revolutionary method for precisely controlling the C structures by oxidizing solid C nanomaterials into gaseous products in the opposite manner of the conventional approach. This gaseous nanocarving enables the modulation of inherent metal assembly in metal/C hybrid nanomaterials because of the promoted C oxidation at the metal/C interface, which produces inner pores inside C nanomaterials. This phenomenon is revealed by investigating the aspects of structure formation with selective C oxidation in the metal/C nanofibers, and density functional theory calculation. Interestingly, the tendency of C oxidation and calculated oxygen binding energy at the metal surface plane is coincident with the order Co > Ni > Cu > Pt. The customizable control of the structural factors of metal/C nanomaterials through thermodynamic‐calculation‐derived processing parameters is reported for the first time in this work. This approach can open a new class of gas–solid reaction‐based synthetic routes that dramatically broaden the structure‐design range of metal/C hybrid nanomaterials. It represents an advancement toward overcoming the limitations of intrinsic activities in various applications.  相似文献   
79.
Hur JH  Kim KM  Chang M  Lee SR  Lee D  Lee CB  Lee MJ  Kim YB  Kim CJ  Chung UI 《Nanotechnology》2012,23(22):225702
We report a physical model for multilevel switching in oxide-based bipolar resistive memory (ReRAM). To confirm the validity of the model, we conduct experiments with tantalum-oxide-based ReRAM of which multi-resistance levels are obtained by reset voltage modifications. It is also noticeable that, in addition to multilevel switching capability, the ReRAM exhibits extremely different switching timescales, i.e. of the order of 10(-7)?s to 10(0)?s, with regard to reset voltages of only a few volts difference which can be well explained by our model. It is demonstrated that with this simple model, multilevel switching behavior in oxide bipolar ReRAM can be described not only qualitatively but also quantitatively.  相似文献   
80.
Plants are defended from attack by emission of volatile organic compounds (VOCs) that can act directly against pathogens and herbivores or indirectly by recruiting natural enemies of herbivores. However, microbial VOC have been less investigated as potential triggers of plant systemic defense responses against pathogens in the field. Bacillus amyloliquefaciens strain IN937a, a plant growth-promoting rhizobacterium that colonizes plant tissues, stimulates induced systemic resistance (ISR) via its emission of VOCs. We investigated the ISR capacity of VOCs and derivatives collected from strain IN937a against bacterial spot disease caused by Xanthomonas axonopodis pv. vesicatoria in pepper. Of 15 bacterial VOCs and their derivatives, 3-pentanol, which is a C8 amyl alcohol reported to be a component of sex pheromones in insects, was selected for further investigation. Pathogens were infiltrated into pepper leaves 10, 20, 30, and 40 days after treatment and transplantation to the field. Disease severity was assessed 7 days after transplantation. Treatment with 3-pentanol significantly reduced disease severity caused by X. axonopodis and naturally occurring Cucumber mosaic virus in field trials over 2 years. We used quantitative real-time polymerase chain analysis to examine Pathogenesis-Related genes associated with salicylic acid (SA), jasmonic acid (JA), and ethylene defense signaling. The expression of Capsicum annuum Pathogenesis-Related protein 1 (CaPR1), CaPR2, and Ca protease inhibitor2 (CaPIN2) increased in field-grown pepper plants treated with 3-pentanol. Taken together, our results show that 3-pentanol triggers induced resistance by priming SA and JA signaling in pepper under field conditions.  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