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   317724篇
  免费   26105篇
  国内免费   14315篇
电工技术   18265篇
技术理论   30篇
综合类   21323篇
化学工业   52568篇
金属工艺   18369篇
机械仪表   20023篇
建筑科学   25030篇
矿业工程   10080篇
能源动力   9172篇
轻工业   20454篇
水利工程   5611篇
石油天然气   20975篇
武器工业   2373篇
无线电   35292篇
一般工业技术   36934篇
冶金工业   16738篇
原子能技术   3471篇
自动化技术   41436篇
  2024年   1467篇
  2023年   5355篇
  2022年   9277篇
  2021年   12795篇
  2020年   9926篇
  2019年   8625篇
  2018年   9457篇
  2017年   10563篇
  2016年   9488篇
  2015年   12645篇
  2014年   15917篇
  2013年   18616篇
  2012年   19871篇
  2011年   21365篇
  2010年   18872篇
  2009年   17717篇
  2008年   17229篇
  2007年   16530篇
  2006年   16872篇
  2005年   14522篇
  2004年   10323篇
  2003年   9792篇
  2002年   10101篇
  2001年   8829篇
  2000年   7767篇
  1999年   8318篇
  1998年   6615篇
  1997年   5505篇
  1996年   5216篇
  1995年   4331篇
  1994年   3461篇
  1993年   2408篇
  1992年   1946篇
  1991年   1481篇
  1990年   1156篇
  1989年   900篇
  1988年   683篇
  1987年   430篇
  1986年   371篇
  1985年   255篇
  1984年   189篇
  1983年   146篇
  1982年   157篇
  1981年   129篇
  1980年   100篇
  1979年   61篇
  1978年   35篇
  1977年   31篇
  1976年   61篇
  1974年   27篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control).  相似文献   
32.
Discovering unknown adverse drug reactions (ADRs) in postmarketing surveillance as early as possible is highly desirable. Nevertheless, current postmarketing surveillance methods largely rely on spontaneous reports that suffer from serious underreporting, latency, and inconsistent reporting. Thus these methods are not ideal for rapidly identifying rare ADRs. The multiagent systems paradigm is an emerging and effective approach to tackling distributed problems, especially when data sources and knowledge are geographically located in different places and coordination and collaboration are necessary for decision making. In this article, we propose an active, multiagent framework for early detection of ADRs by utilizing electronic patient data distributed across many different sources and locations. In this framework, intelligent agents assist a team of experts based on the well‐known human decision‐making model called Recognition‐Primed Decision (RPD). We generalize the RPD model to a fuzzy RPD model and utilize fuzzy logic technology to not only represent, interpret, and compute imprecise and subjective cues that are commonly encountered in the ADR problem but also to retrieve prior experiences by evaluating the extent of matching between the current situation and a past experience. We describe our preliminary multiagent system design and illustrate its potential benefits for assisting expert teams in early detection of previously unknown ADRs. © 2007 Wiley Periodicals, Inc. Int J Int Syst 22: 827–845, 2007.  相似文献   
33.
阿笑 《食品与药品》2005,7(9B):68-69
我国幅员辽阔,产物众多,各地的饮食习惯也不同。非常有趣的是,特别的饮食习惯不仅影响了各地人的生活,甚至还塑造了他们的性格。正所谓“一方水土养一方人”。  相似文献   
34.
35.
哈尔滨炼油厂MTBE装置试生产   总被引:4,自引:0,他引:4  
介绍了哈尔滨炼油厂MTBE装置的工艺路线、新技术的应用及特点;催化剂的装填及应用情况;总结了生产过程中遇到的一系列问题及解决办法;探索了平稳生产的新徐径,以保证装置安全、平稳、长周期运行;同时对反应器操作温度、催化蒸馏塔操作压力、原料中醇烯比等因素对异丁烯转化率及MTBE产品的影响做了简单的总结。  相似文献   
36.
DC resistivity, dielectric constant, dielectric loss and positron annihilation spectra of (Ba1−x Ho x )TiO3 ceramics have been measured as a function of holmium concentration x. It has been found that the DC resistivity of (Ba1−x Ho x )TiO3 is strongly dependent on the Ho content: it decreases three orders of magnitude and reaches a minimum at x = 0.4%. Doping with 0.6% holmium increases the permittivity of BaTiO3 by approximately three times (from ∼1,300 to ∼4,000), with only a slight increase in the corresponding dielectric loss. The local electron density and defect concentration estimated using positron annihilation technique conforms well to the features found in the dielectric and resistivity measurements. The results have been discussed in terms of a mixed compensation model.  相似文献   
37.
The laboratory scale anaerobic–anoxic–aerobic (A2O) process fed with synthetic brewage wastewater was designed to investigate the effects of changing feed C/P ratio on the performance of biological nutrient removal (BNR) processes. In the experiment, the influent chemical oxygen demand (COD) concentration was kept at approximately 300 mg L?1 while the total phosphorus concentration was varied to obtain the desired C/P ratio. Results showed that when the C/P ratio was lower than 32, phosphorus removal efficiency increased as C/P ratio increased linearly, while when the C/P ratio was higher than 32, the P removal efficiency was maintained at 90–98%, and effluent P concentration was lower than 0.5 mg L?1. However, regardless of the C/P ratio, excellent COD removal (90% or higher) and good total nitrogen removal (75–84%) were maintained throughout the experiments. It was also found that very good linear correlation was obtained between COD uptake per unit P released in the anaerobic zone and C/P ratio. In addition, the P content in the wasted activated sludge increased with the decrease in the C/P ratio. Based on the results, it was recommended that the wastewater C/P ratio and its effects be incorporated into BNR design and operational procedures, appropriate C/P ratios were used to achieve the effluent treatment goals. Copyright © 2005 Society of Chemical Industry  相似文献   
38.
We present a method to obtain complete information of femtosecond pulses. By measuring triple-optical autocorrelation directly with third-harmonic generation, without spectral information, a temporal pulse shape can be obtained by analytical calculation without direction-of-time ambiguity. Combining the resulting optical pulse shape with its corresponding optical spectrum, the exact phase and color variations in time can all be recovered with a Gerchberg-Saxton algorithm through an iterative calculation with an O(n) complexity.  相似文献   
39.
The deactivation characteristics of Pd/SiO2 in the selective hydrogenation of acetylene were correlated with changes in the amount of the C4 species produced. The amounts of butenes produced changed in parallel with the catalyst activity, indicating that the rate limiting step for butene production was the same as that for acetylene hydrogenation. On the other hand, the amount of 1,3-butadiene produced changed, showing a maximum with catalyst deactivation because 1,3-butadiene is an intermediate in the sequential reaction process which involves both the production and consumption of 1,3-butadiene. This was verified by a simultaneous TG/reaction experiment showing that 1,3-butadiene was a precursor of green oil. The catalyst showed a self-regenerative behavior in its activity and the amounts of C4 species produced during the early stage of deactivation because two opposite factors, which contributed to either the lowering or the promotion of activity, were involved in the process. A specific type of polymer species, produced during the initial period of deactivation, is proposed to be responsible for the promotion of catalyst activity.  相似文献   
40.
所开发的压水堆核燃料循环分析计算机经济程序包括12个子程序,代表着压水堆整个核燃料循环各种不同的工艺过程。本程序能算出压水堆核电站核燃料循环中燃料费用对发电成本的影响,给出各工艺过程对燃料成本的敏感度分析,并尽可能给出燃料循环中燃料材料及服务的价格数据.  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