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   616篇
  免费   21篇
  国内免费   1篇
电工技术   5篇
化学工业   125篇
金属工艺   2篇
机械仪表   7篇
建筑科学   25篇
能源动力   15篇
轻工业   74篇
水利工程   3篇
无线电   111篇
一般工业技术   85篇
冶金工业   111篇
自动化技术   75篇
  2023年   3篇
  2022年   5篇
  2021年   22篇
  2020年   7篇
  2019年   15篇
  2018年   18篇
  2017年   7篇
  2016年   16篇
  2015年   13篇
  2014年   15篇
  2013年   25篇
  2012年   36篇
  2011年   26篇
  2010年   27篇
  2009年   21篇
  2008年   30篇
  2007年   29篇
  2006年   24篇
  2005年   25篇
  2004年   9篇
  2003年   15篇
  2002年   11篇
  2001年   10篇
  2000年   12篇
  1999年   16篇
  1998年   54篇
  1997年   29篇
  1996年   29篇
  1995年   13篇
  1994年   10篇
  1993年   9篇
  1992年   8篇
  1991年   4篇
  1990年   6篇
  1989年   3篇
  1988年   3篇
  1986年   4篇
  1985年   4篇
  1982年   2篇
  1981年   2篇
  1979年   1篇
  1978年   2篇
  1977年   4篇
  1976年   2篇
  1975年   1篇
  1973年   1篇
  1972年   2篇
  1970年   2篇
  1969年   1篇
  1968年   1篇
排序方式: 共有638条查询结果,搜索用时 218 毫秒
51.
We report the palladium(II)‐catalyzed aerobic oxidative coupling of isocyanides with various (2‐aminophenyl)azoles using air as the stoichiometric oxidant. A diverse range of medicinally valuable azolo[c]quinazolines was obtained by this new approach.

  相似文献   

52.
The objectives of this observational study were (1) to assess the time from the appearance of the amniotic sac (AS) or feet outside the vulva to birth in Holstein cows (primiparous and multiparous) with (dystocia) or without assistance (eutocia) at calving, and (2) to estimate reference times to be used as guidelines for obstetric intervention in Holstein cows that need assistance during difficult births. Cows (n = 92) from 1 commercial dairy operation were used in this study. Periparturient dairy cows (primiparous, n = 58; multiparous, n = 34) were placed in a maternity pen and constantly monitored until birth. The calving ease of cows, time from AS or feet appearance to birth, calving progress from a subset of 15 cows (frequency and duration of abdominal contractions during labor), calf birth weight, calf sex, and stillbirths (born dead or died within 24 h after birth) were recorded. The reference times for obstetric intervention during dystocia were estimated based on values from unassisted births (normal). The normal range of times from the appearance of AS or feet outside the vulva to birth was estimated based on the mean + 2 standard deviations (SD) of unassisted births. According to farm protocol, assistance was provided to cows without calving progress 80 min after AS appearance or earlier (e.g., to correct malpositions). Cows with dystocic births had a longer time from AS appearance to birth and increased incidence of stillbirth compared with cows with eutocic calvings. After the appearance of the AS, calving progress was evident every 15 min for eutocic births. The estimated reference times (mean + 2 SD) from AS appearance to birth were 69.7 min and from feet appearance to birth were 64.6 min for eutocic births. Findings from this study suggested that calving personnel should start assisting cows 70 min after AS appearance (or 65 min after feet appearance) outside the vulva. The time spent in labor (straining) combined with the time from the appearance of the AS or feet to birth, and the assessment of calving progress (as described for eutocic births) should be used as guidelines for obstetric intervention during difficult births under field conditions. These reference times should be interpreted in combination with adequate obstetrical knowledge and examination.  相似文献   
53.
In this paper we present our work in the design of ubiquitous social experiences, aiming to foster group participation and spontaneous playful behaviours in a city environment. We outline our approach of design for emergence: to provide just enough of a game context and challenge for people to be creative, to extend and enrich the experience of play through their interaction in the real world. CitiTag is our mixed reality testbed, a wireless location-based multiplayer game based on the concept of playground ‘tag’. We describe the design and implementation of CitiTag and discuss results from two user studies.  相似文献   
54.
Root Cause of Charge Loss in a Nitride-Based Localized Trapping Memory Cell   总被引:1,自引:0,他引:1  
Data retention loss mechanisms in nitride-based localized trapping memory devices are investigated with various electrical measurements and Medici simulations. First, the effect of program and erase cycles on device behavior is determined in terms of bottom oxide degradation and nitride charge profile evolution. Even if a strong degradation of the interface is observed, there is no important impact of this degradation on the cell behavior. However, the nitride charge profile evolves with cycling and leads to a three-pole electron-hole-electron profile over the channel region. Second, the interface trap annealing, the tunneling through the bottom oxide, and the lateral redistribution are studied in order to determine which mechanism plays the main role in the threshold voltage shift after cycling. The retention performance is dominated by a lateral redistribution of charges in the nitride layer.  相似文献   
55.
In this paper, an in-depth analysis is presented of the write/erase degradation in Source Side Injection Flash EEPROM cells, using the HIMOS cell as a typical example. The different mechanisms governing the degradation are studied and quantified by combining UV erasure and I-V measurements with a charge pumping analysis. Both procedures are shown to disclose two effects contributing to the change of the threshold voltage window: a change in the amount of charge on the floating gate due to a decrease in the injection current, accompanied by the series effect of oxide and interface charges locally trapped above the channel. By correlating the results from charge pumping and I-V measurements, an estimate is made of the spatial extent of the damaged region  相似文献   
56.
The paper is focused on the evolution of the watermarking schemes from pixel-based approaches to content based methods. Firstly, the field of watermarking is presented, its implication in the real word is outlined. The second section gives a brief overview of different approaches in the spatial and the frequential domain. We then present different content-based approaches used to improve the invisibility or the synchronisation of the mark. The last section describes our content-based scheme; the synchronisation of the mark after image processing lies in the use of feature point detectors. The image is decomposed into a set of triangles and each triangle is individually marked.  相似文献   
57.
58.
This paper proposes and describes a new technique in the design and implementation of stand-alone programmable controllers which implement complex control algorithms for complex systems in general and time-critical systems in particular. Unlike other existing commercially available controllers, the proposed controller is capable of implementing all kinds of simple and complex control algorithm techniques such as PIDs, adaptive, optimal, etc. The controller is designed to handle timed events accurately due to the utilization of a new software approach based on Petri net technique as well as the use of an optimized simulation language designed for control and data acquisition applications. The most significant aspects of the proposed controller are its low cost, high speed, and easy implementation. Using the new approach, it is possible to effortlessly and efficiently simulate any controller algorithm and controlled plant, verify results if they meet pre-defined system specifications and then immediately generate and save codes on EPROMs to be placed on the controller board. The proposed controller system consists of a hardware portion and a software package. The software package is written in C and assembly languages and consists of four different programs. A prototype of the proposed controller was designed, constructed and successfully tested to implement various control algorithms. The data obtained suggest that the proposed technique will significantly aid engineers to simplify the task of implementing complex algorithms industry such as robotics.  相似文献   
59.
60.
In this work we have studied soft breakdown (SBD) in capacitors and nMOSFET's with 4.5-nm oxide thickness. It is shown that for larger area devices gate current and substrate current as a function of the gate voltage after SBD are stable and unique curves, but for smaller area devices both currents become lower and unstable. This difference can be explained by the different energy available for discharging in the SBD path. It is shown that the SBD detection strongly depends on the test structure area. In nMOSFET's for positive gate polarity, the large increase in the substrate current at the SBD moment is proposed as a sensitive SBD detector. Two level fluctuations in the gate current are investigated at different voltages and are explained by means of a model where electron capture-emission in the traps of the SBD path induces local field fluctuations causing variations in the tunneling rate across the oxide. In the substrate current directly correlated two-level fluctuations are observed  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