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   29134篇
  免费   2568篇
  国内免费   1496篇
电工技术   1821篇
技术理论   3篇
综合类   2086篇
化学工业   4827篇
金属工艺   1535篇
机械仪表   1867篇
建筑科学   2214篇
矿业工程   946篇
能源动力   817篇
轻工业   2512篇
水利工程   556篇
石油天然气   1902篇
武器工业   225篇
无线电   2932篇
一般工业技术   3069篇
冶金工业   1375篇
原子能技术   343篇
自动化技术   4168篇
  2024年   150篇
  2023年   530篇
  2022年   944篇
  2021年   1261篇
  2020年   914篇
  2019年   771篇
  2018年   876篇
  2017年   987篇
  2016年   860篇
  2015年   1149篇
  2014年   1544篇
  2013年   1865篇
  2012年   1931篇
  2011年   2236篇
  2010年   1911篇
  2009年   1834篇
  2008年   1846篇
  2007年   1661篇
  2006年   1586篇
  2005年   1419篇
  2004年   954篇
  2003年   792篇
  2002年   736篇
  2001年   647篇
  2000年   624篇
  1999年   622篇
  1998年   480篇
  1997年   436篇
  1996年   371篇
  1995年   302篇
  1994年   270篇
  1993年   178篇
  1992年   151篇
  1991年   90篇
  1990年   71篇
  1989年   44篇
  1988年   50篇
  1987年   31篇
  1986年   16篇
  1985年   8篇
  1984年   14篇
  1983年   8篇
  1982年   8篇
  1981年   8篇
  1980年   7篇
  1979年   2篇
  1959年   2篇
  1951年   1篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
一种新型准分子激光器循环系统中的密封传动技术,具有可耐高气压,不失耦,不使用昂贵强磁材料,结构简单等优点,虽有涡流损失过大之不足,但能很好地适用于小功率下运行。  相似文献   
52.
熔喷生产最终产品质量的控制,对于过程优化具有重要的意义。产品质量的在线检测是过程监测与质量控制必不可少的。本文首次在熔喷系统中引入人工智能的研究方法,对熔喷非织造布的厚度与纤维直径进行在线预测。实测数据与人工神经网络的预测结果吻合较好,从而证实了人工神经网络用于模拟熔喷过程的可行性。网络的输入包括:挤出机温度、喷头温度、熔融体挤出速率、空气流率及接收距离。神经元计算的输出是纤维直径与熔喷非织布的厚度。文中进一步提出了将神经网络与专家系统相结合的研究路线,以实现熔喷过程的优化控制。  相似文献   
53.
BACKGROUND: The efficacy of breast self-examination in helping to reduce mortality from breast cancer has not been rigorously demonstrated. PURPOSE: To assess efficacy, a large, randomized trial was initiated in Shanghai, China. METHODS: From October 1989 to October 1991, 267040 current and retired female employees associated with 520 factories in the Shanghai Textile Industry Bureau were randomly assigned on the basis of factory to either a self-examination instruction group (133375 women) or a control group (133665 women). The women were born within the period from 1925 through 1958. Women in the instruction group were given intensive training in breast self-examination, including the use of silicone breast models and personalized instruction, plus two subsequent reinforcement sessions and multiple reminders to practice the technique. Women in the control group were asked to attend training sessions on the prevention of low back pain. All women have been followed for the development of breast diseases and for death from breast cancer. RESULTS: A high level of participation during the first 4-5 years of the trial was documented among women in the instruction group. Randomly sampled women in this group demonstrated greater proficiency in detecting lumps in breast models than did randomly sampled women in the control group. Approximately equal numbers of breast cancers were detected in the two groups (331 in the instruction group and 322 in the control group) through 1994, which is the last year for which case-finding efforts have been completed. The breast cancers detected in the instruction group were not diagnosed at an appreciably earlier stage or smaller size than those in the control group. More benign breast lesions were detected in the instruction group than in the control group (1457 versus 623, respectively), suggesting a higher index of suspicion for women who received training. Cumulative breast cancer mortality rates through 5 years from entry into the study were nearly equivalent for the two groups. CONCLUSIONS: Breast self-examination has not led to a reduction in mortality from breast cancer in this study cohort in the first several years since the trial began. A shift toward the diagnosis of disease at a less advanced stage in women given instruction has also not been demonstrated. Longer follow-up of participants in this trial is required before final assessment can be made of the efficacy of breast self-examination. IMPLICATIONS: At this time, there is insufficient evidence to recommend for or against the teaching of breast self-examination.  相似文献   
54.
随着计算机技术的发展和水平的提高,图像,声音,图形等多媒体信息逐步应用于管理信息系统之中。文章中提出了图文数据库系统设计中存在的三个基本问题。讨论了介绍了图文数据库系统的设计方法和实现技术。  相似文献   
55.
由电压型运算放大器组成的精密整流电路要严格地匹配电阻才能获得精密全波整流波形.本文给出一种具有CCⅡ电路特性由运算放大器AD844所构成的电流模精密整流电路.无需匹配电阻就可输出良好的精密全波整流波形.且具有输入电压范围大,频带宽等特点.  相似文献   
56.
The synthesis of rare-earth perovskite-type composition thin films of LaNiO3 by means of the inorganic-sol-gel (ISG) method was studied. The structural stability under high temperature in reducing atmospheres and the oxygen-sensitivity mechanism of the LaNiO3 thin films were examined. It is shown that under the experimental conditions, LaNiO3 decomposes and the valance states of nickel are +2 and +3.  相似文献   
57.
在枪口脉冲噪声的测试过程中,传声器(即话筒)的选择具有至关重要的作用.本文主要依据国家军用标准中对枪口脉冲噪声的测试要求,分析枪口脉冲噪声的特性,介绍枪口脉冲噪声测试中几种不同原理的传声器,研究和探讨几种常用电容传声器的特性及应用范围.  相似文献   
58.
This paper redefines three measures of element s-importance for 2-state systems regardless of s-coherence, presents the calculation methods of these measures, and gives a new method to calculate the system time-specific failure and recovery frequencies. A poor point in the literature in extending methods for evaluating the s-importance of elements of s-coherent system to non-coherent system is pointed out. An example illustrates these definitions and calculation methods.  相似文献   
59.
本文简单地回顾了提高VLSI测试效率所采用的一些手段,讨论了在ASIC测试问题研究中出现的一些新观点、新方法、新动向,以及所取得的成果。在此基础上,文章阐明了ASIC测试技术的发展方向,并着重论述了可望在未来得到发展的,针对ASIC的功能测试方法。  相似文献   
60.
Laguerre Functional Model has many advantages such as good approximation capability for the variances of system time‐delay, order and other structural parameters, low computational complexity, and the facility of online parameter identification, etc., so this model is suitable for complex industrial process control. A series of successful applications have been gained in linear and non‐linear predictive control fields by the control algorithm based on Laguerre Functional Model, however, former researchers have not systemically brought forward the theoretical analyses of the stability, robustness, and steady‐state performance of this algorithm, which are the keys to guarantee the feasibility of the control algorithm fundamentally. Aimed at this problem, we introduce the principles of the Incremental Mode Linear Laguerre Predictive Control (IMLLPC) algorithm, and then systemically propose the theoretical analyses and proofs of the stability and robustness of the algorithm, in addition, we also put forward the steady‐state performance analysis. At last, the control performances of this algorithm on two different physical industrial plants are presented in detail, and a number of experimental results validate the feasibility and superiority of IMLLPC algorithm. Copyright © 2005 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