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   8550篇
  免费   216篇
  国内免费   1篇
电工技术   10篇
综合类   3篇
化学工业   719篇
金属工艺   26篇
机械仪表   20篇
建筑科学   94篇
矿业工程   77篇
能源动力   33篇
轻工业   456篇
水利工程   20篇
石油天然气   9篇
无线电   135篇
一般工业技术   334篇
冶金工业   6589篇
原子能技术   13篇
自动化技术   229篇
  2023年   33篇
  2022年   65篇
  2021年   93篇
  2020年   56篇
  2019年   54篇
  2018年   62篇
  2017年   94篇
  2016年   119篇
  2015年   102篇
  2014年   104篇
  2013年   185篇
  2012年   128篇
  2011年   138篇
  2010年   122篇
  2009年   97篇
  2008年   118篇
  2007年   120篇
  2006年   75篇
  2005年   72篇
  2004年   68篇
  2003年   50篇
  2002年   53篇
  2001年   41篇
  2000年   32篇
  1999年   207篇
  1998年   2058篇
  1997年   1169篇
  1996年   743篇
  1995年   391篇
  1994年   350篇
  1993年   402篇
  1992年   52篇
  1991年   100篇
  1990年   75篇
  1989年   81篇
  1988年   90篇
  1987年   95篇
  1986年   77篇
  1985年   73篇
  1984年   12篇
  1983年   23篇
  1982年   42篇
  1981年   50篇
  1980年   43篇
  1979年   10篇
  1978年   18篇
  1977年   163篇
  1976年   318篇
  1975年   19篇
  1955年   7篇
排序方式: 共有8767条查询结果,搜索用时 15 毫秒
31.
Increasing evidence links the RAGE (receptor for advanced glycation end products)/DIAPH1 (Diaphanous 1) signaling axis to the pathogenesis of diabetic complications. RAGE is a multi-ligand receptor and through these ligand–receptor interactions, extensive maladaptive effects are exerted on cell types and tissues targeted for dysfunction in hyperglycemia observed in both type 1 and type 2 diabetes. Recent evidence indicates that RAGE ligands, acting as damage-associated molecular patterns molecules, or DAMPs, through RAGE may impact interferon signaling pathways, specifically through upregulation of IRF7 (interferon regulatory factor 7), thereby heralding and evoking pro-inflammatory effects on vulnerable tissues. Although successful targeting of RAGE in the clinical milieu has, to date, not been met with success, recent approaches to target RAGE intracellular signaling may hold promise to fill this critical gap. This review focuses on recent examples of highlights and updates to the pathobiology of RAGE and DIAPH1 in diabetic complications.  相似文献   
32.
Aspects of reconfigurable and flexible fixtures   总被引:1,自引:0,他引:1  
The design and manufacture of fixtures and other dedicated tooling for positioning of workpieces are among the major cost drivers in product industrialization. This has spurred research and commercial interest towards other fixturing solutions like reconfigurable fixtures, with the ability to be changed, or “reconfigured”, to suit different parts and products. When reconfiguring, the product interface not only has to be moved but moved to a desired position and orientation. Several different approaches have been used to move and position these devices, all with their own advantages and disadvantages. This article presents different methods used to position and reconfigure flexible fixture devices using a parallel kinematic device as a case. Discussing the different ways to reconfigure a flexible device, the article aims to arrange the techniques according to their key features.  相似文献   
33.
This paper proposes a complete compression and coding scheme for on-board satellite applications considering the main on-board constraints: low computational power and easy bit rate control. The proposed coding scheme improves the performance of the current Consultative Committee for Space Data Systems (CCSDS) recommendation for a low additional complexity. We consider post-transforms in the wavelet domain, select the best representation for each block of wavelet coefficients, and encode it into an embedded bit stream. After applying a classical wavelet transform of the image, several concurrent representations of blocks of wavelet coefficients are generated. The best representations are then selected according to a rate-distortion criterion. Finally, a specific bit-plane encoder derived from the CCSDS recommendation produces an embedded bit stream ensuring the easy rate control required. In this article, both the post-transforms and the best representation selection have been adapted to the low complexity constraint, and the CCSDS coder has been modified to compress post-transformed representations.  相似文献   
34.
Remote‐controlled drug depots represent a highly valuable tool for the timely controlled administration of pharmaceuticals in a patient compliant manner. Here, the first pharmacologically controlled material that allows for the scheduled induction of a medical response in mice is described. To this aim, a novel, humanized biohybrid material that releases its cargo in response to a small‐molecule stimulus licensed for human use is developed. The functionality of the material in mice is demonstrated by the remote‐controlled delivery of a vaccine against the oncogenic human papillomavirus type 16. It is shown that the biohybrid depot‐mediated immunoprotection is equivalent to the classical multi‐injection‐based vaccination. These results indicate that this material can be used as a universal remote‐controlled vehicle for the patient‐compliant delivery of vaccines and pharmaceuticals.  相似文献   
35.
Research on semiconductor photocatalysts for the conversion of solar energy into chemical fuels has been at the forefront of renewable energy technologies. Water splitting to produce H2 and CO2 reduction to hydrocarbons are the two prominent approaches. A lesser‐known process, the conversion of solar energy into the versatile high‐energy product H2O2 via reduction of O2 has been proposed as an alternative concept. Semiconductor photoelectrodes for the direct photosynthesis of H2O2 from O2 have not been applied up to now. Photoelectrocatalytic oxygen reduction to peroxides in aqueous electrolytes by hydrogen‐bonded organic semiconductor is observed photoelectrodes. These materials have been found to be remarkably stable operating in a photoelectrochemical cell converting light into H2O2 under constant illumination for at least several days, functioning in a pH range from 1 to 12. This is the first report of a semiconductor photoelectrode for H2O2 production, with catalytic performance exceeding prior reports on photocatalysts by one to two orders of magnitude in terms of peroxide yield/catalyst amount/time. The combination of a strongly reducing conduction band energy level with stability in aqueous electrolytes opens new avenues for this widely available materials class in the field of photo(electro) catalysis.  相似文献   
36.
37.
Although filamentous fungi live in physically and chemically complex natural environments that require optimal survival strategies, both at colony and individual cell level, their growth dynamics are usually studied on homogenous media. This study proposes a new research methodology based on the purposeful design, fabrication and operation of microfluidics structures to examine the temporal and spatial responses of filamentous fungi. Two model fungal strains, the wild type of Neurospora crassa – a commonly used model organisms – and the ro-1 mutant strain of this species impaired in hyphal growth and morphology, have been chosen to demonstrate the potential of this new methodology. Time-lapse observations of both species show that filamentous fungi respond rapidly to the physically microstructured environment without any detectable temporal or spatial adjustment period. Despite their genetic differences, and consequently different growth behaviour, both strains present efficient space-search strategies enabling them to solve the microsized networks successfully and in similar periods, thus demonstrating that the space-searching algorithms are robust and mutation-independent. Additionally, the use of the proposed methodology could put in evidence new biological mechanisms responsible for the apical extension of filamentous fungi, beyond the classical theory based on the central role of Spitzenkörper.  相似文献   
38.
当设计者用光电晶体管将一个调制后的光信号转换成电信号时,如果有高亮度的背光使光电晶体管饱和,就会遇到麻烦.当光电晶体管基极端悬浮时,其集电极/射极电压只取决于信号与背光重叠而产生的光电流.光电晶体管增益及其作用区范围由R1阻值(见图1)确定.R1阻值较高时,电路的增益增加,但光电晶体管会很快饱和.图1中没有背光照射时,晶体管工作在其线性区的偏置点φ2,Q1的集电极电压围绕VCE作线性变化.其输出VOUT准确地重复使调制光信号产生幅度波动.当施加外部稳定的背光照明时,电路的工作点移至偏置点φ3,输出电压被压缩并出现失真.  相似文献   
39.
Printed image multiplexing based on the design of metasurfaces has attracted much interest in the past decade. Optical switching between different images displayed directly on the metasurface is performed by altering the parameters of the incident light such as polarization, wavelength, or incidence angle. When using white light, only two-image multiplexing is implemented with polarization switching. Such metasurfaces are made of nanostructures perfectly controlled individually, which provide high-resolution pixels but small images and involve long fabrication processes. Here, it is demonstrated that laser processing of nanocomposites offers a versatile low-cost, high-speed method with large area processing capabilities for controlling the statistical properties of random metasurfaces, allowing up to three-image multiplexing under white light illumination. By independently controlling absorption and interference effects, colors in reflection and transmission can be varied independently yielding two-image multiplexing under white light. Using anisotropy of plasmonic nanoparticles, a third image can be multiplexed and revealed through polarization changes. The design strategy, the fundamental properties, and the versatility of implementation of these laser-empowered random metasurfaces are discussed. The technique, applied on flexible substrate, can find applications in information encryption or functional switchable optical devices, and offers many advantages for visual security and anticounterfeiting.  相似文献   
40.
This paper proposes new transmission schemes for the delivery of satellite services. In the proposed scenarios, mobile terminals are allowed to forward the signal received from the satellite. This scheme provides spatial diversity just like MIMO transmission schemes. Moreover, the coverage area is extended because masked terminals have an additional opportunity to get the service from neighboring terminals. We use the paradigm of cooperative communications to compare the advantages and limitations of several scenarios in hybrid terrestrial/satellite systems. In particular, we study the following basic transmission scheme: in a first time slot, the satellite sends its signal and, in a second time slot, mobile terrestrial terminals are relaying the satellite signal. An analysis framework is proposed and applied to this cooperation scenario at the destination terminal. The framework is modeling the cooperation process and clearly separates the control part from the data user part. The paper outlines the importance of the control part by evaluating the relay selection policy on a basic hybrid satellite/ad hoc system. Copyright © 2011 John Wiley & Sons, Ltd.  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