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   2479篇
  免费   102篇
  国内免费   2篇
电工技术   17篇
综合类   7篇
化学工业   558篇
金属工艺   40篇
机械仪表   34篇
建筑科学   104篇
能源动力   25篇
轻工业   265篇
水利工程   10篇
石油天然气   4篇
无线电   220篇
一般工业技术   364篇
冶金工业   627篇
原子能技术   19篇
自动化技术   289篇
  2023年   8篇
  2022年   53篇
  2021年   61篇
  2020年   47篇
  2019年   31篇
  2018年   45篇
  2017年   52篇
  2016年   52篇
  2015年   67篇
  2014年   87篇
  2013年   123篇
  2012年   106篇
  2011年   119篇
  2010年   102篇
  2009年   103篇
  2008年   105篇
  2007年   97篇
  2006年   77篇
  2005年   92篇
  2004年   71篇
  2003年   59篇
  2002年   52篇
  2001年   37篇
  2000年   52篇
  1999年   52篇
  1998年   138篇
  1997年   93篇
  1996年   82篇
  1995年   53篇
  1994年   60篇
  1993年   50篇
  1992年   28篇
  1991年   19篇
  1990年   21篇
  1989年   21篇
  1988年   16篇
  1987年   15篇
  1986年   16篇
  1985年   19篇
  1984年   10篇
  1983年   10篇
  1982年   13篇
  1981年   14篇
  1980年   7篇
  1977年   32篇
  1976年   37篇
  1975年   8篇
  1974年   6篇
  1973年   13篇
  1972年   8篇
排序方式: 共有2583条查询结果,搜索用时 15 毫秒
91.
92.
Statistics on road traffic accidents (RTAs) mainly come from police records. The police reported RTA statistics however are known to have a large degree of under-registration, underestimating the true risk of being injured in traffic accidents. The use of medical based datasets can provide a more accurate estimate of the actual traffic accident health risk. Exposure-based rates of the actual burden from Flanders and Brussels were calculated, comparing differences between road user, age, gender and type of injury sustained. Minimal Clinical Data (MCD) was selected for the years 2003–2007, as well as data from the mortality statistics. Disability Adjusted Life Years (DALY) were calculated and put into perspective with the passenger kilometres travelled.  相似文献   
93.
The current trend toward producing lighter vehicles in the automotive industry is driven by the need to conform to the new exhaust emission control regulations. This objective presents a challenge to steel manufacturers. The difficulty lies in designing new alloys with an optimum strength/formability/cost balance for the various components. Here, the key to success lies in controlling the steel microstructure and especially the phase transformations at the smallest possible scale. Among the different alloying elements, light elements such as carbon and boron are of prime importance due to their major effects on the kinetics of phase transformations. Characterization tools combining high spatial and analytical resolution such as secondary ion mass spectrometry (SIMS) and field emission gun-transmission electron microscopy (TEM) were used. In this article, the examples presented are as follows. (1) Boron segregation and precipitation effects to control hardenability in martensitic steels. (2) Local carbon distribution in advanced high-strength steels, with a specific emphasis on martensite tempering. Links have been established between the boron and carbon distribution and the formability.  相似文献   
94.
This paper describes the establishment of an Internet gateway local to the University of Sussex, firstly as a Gopher and more recently as a World Wide Web server. There follows an account of a project currently underway to assess the practical value of Internet resources to research and the consequential training and support requirements. This assessment is planned to determine the value of a local gateway to academic researchers at Sussex and the roles specific to a local gateway that such comprehensive resources as Yahoo and BUBL cannot fulfil. The project is using an interview‐based methodology to gain an understanding of researchers’ views of Internet resource provision, and these interviews are being analysed with the help of the NUD*IST qualitative data analysis software package. The account is of research in progress, and hence does not conclude with the set of pragmatic policy proposals that forms its key objective. Instead, some indication is given of the broad early findings of the project  相似文献   
95.
96.
Uniform spherical beads were used to explore the scaling behavior of a granular system near its critical angle of repose on a conical 3D bead pile. We found two tuning parameters that could take the system to a critical point. The existence of those tuning parameters violates the fundamental assumption of self-organized criticality, which proposed that complex dynamical systems self-organize to a critical point without need for tuning. Our avalanche size distributions were well described by a simple power-law, as is characteristic of a critical point, with the power τ = 1.5 when dropping beads slowly onto the apex of a bead pile from a small height. However, we could also move the system from the critical point using either of two tuning parameters: the height from which the beads fell onto the top of the pile or the region over which the beads struck the pile. As the drop height increased, the system did not reach the critical point yet the resulting distributions were independent of the bead mass, coefficient of friction, or coefficient of restitution. All our apex-dropping distributions for any type of bead (glass, stainless steel, zirconium) showed universality by scaling onto a common curve with τ = 1.5 and σ =?1.0, where 1/σ is the power of the tuning parameter. From independent calculations using the moments of the distribution, we find values for τ = 1.6 ± 0.1 and σ =?0.91 ± 0.15. When beads were dropped across the surface of the pile instead of solely on the apex, then the system also moved from the critical point and again the avalanche size distributions fell on a common curve when scaled similarly using the same values of τ and σ. We also observed that an hcp structure on the base of the pile caused an emergent structure in the pile that had six faces with some fcc or hcp structure; this structure did not affect the distribution of avalanche sizes.  相似文献   
97.
Investigation of the thermal-resistive probe response in an AC scanning thermal microscope (SThM) as a function of the distance probe–material surface under ambient conditions and the current excitation frequency is presented. The analysis of temperature experimental results points out a phenomenon which can be interpreted as a thermal wave resonance. The modeling of the thermal response with the finite element method considering the surrounding medium as a thermally conducting medium tends to confirm this. This phenomenon is independent of the sample nature and is related to the thermal diffusion length of the air medium between the probe and the sample. An equivalent resonance factor is defined: it shows a linear dependence with the characteristic distance for which the thermal resonance phenomenon is an extremum. The system—probe/sample surface—behaves as a resonant cavity at the microscale. This configuration is not specific to a SThM and can occur within electronic devices.  相似文献   
98.
99.
A millimeter-wave Power Amplifier (PA) based on a 65nm CMOS technology from STMicroelectronics has been designed. The targeted feature is the unlicensed band around 60 GHz suitable for wireless personal area network application (WPAN). To optimize the linearity, the PA is designed under class A biasing to have an output compression point (OCP1) close to its saturated Power (P sat). S-parameters and large signal measurement results are demonstrated and compared with electromagnetic simulations. The PA offers a P sat of 8.3 dBm, an OCP1 of 6 dBm and a gain of 6.7 dB. The die area is 0.29 mm2 with pads. Considering those results, one-tone simulations are not sufficient to characterize the linearity performances of the PA in its real conditions of use. Consequently, two-tone simulations are firstly performed. After, linearity figures of merit (FoM) are discussed applying an orthogonal frequency-division multiplexing (OFDM) modulated signal. The PA offers an adjacent channel power ratio (ACPR) of 15 dB and an error vector magnitude (EVM) of 20% at PA compression operating mode.  相似文献   
100.
Sn-3wt%Pb alloy was directionally solidified without and with a 0.08T transverse magnetic field(TMF),and real-time recorded by in-situ synchrotron X-ray imaging.Results indicate that TMF shortened the distance from the location of nucleation to the advancing interface,and accelerated the growth rate of the equiaxed crystal,which caused the columnar-to-equiaxed transition(CET)finally.The thermoelectromagnetic convection(TEMC)in front of the interface and around the crystal’s dendritic branch should respond to changes of the distance and the growth rate.  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