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   228943篇
  免费   17467篇
  国内免费   9143篇
电工技术   12463篇
技术理论   24篇
综合类   14150篇
化学工业   38796篇
金属工艺   13145篇
机械仪表   14519篇
建筑科学   17573篇
矿业工程   7502篇
能源动力   6421篇
轻工业   13457篇
水利工程   3606篇
石油天然气   16626篇
武器工业   1647篇
无线电   25145篇
一般工业技术   27344篇
冶金工业   12809篇
原子能技术   2247篇
自动化技术   28079篇
  2024年   995篇
  2023年   3801篇
  2022年   6480篇
  2021年   9108篇
  2020年   7086篇
  2019年   6018篇
  2018年   6736篇
  2017年   7538篇
  2016年   6751篇
  2015年   8862篇
  2014年   11248篇
  2013年   13280篇
  2012年   14211篇
  2011年   15449篇
  2010年   13422篇
  2009年   12679篇
  2008年   12347篇
  2007年   11855篇
  2006年   12343篇
  2005年   10756篇
  2004年   7263篇
  2003年   6227篇
  2002年   5466篇
  2001年   4887篇
  2000年   5434篇
  1999年   6441篇
  1998年   5434篇
  1997年   4453篇
  1996年   4188篇
  1995年   3501篇
  1994年   2811篇
  1993年   1965篇
  1992年   1538篇
  1991年   1226篇
  1990年   933篇
  1989年   741篇
  1988年   537篇
  1987年   336篇
  1986年   278篇
  1985年   196篇
  1984年   139篇
  1983年   114篇
  1982年   124篇
  1981年   98篇
  1980年   70篇
  1979年   36篇
  1978年   26篇
  1977年   20篇
  1976年   35篇
  1973年   13篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
基于OpenGL和MFC的石油井管道的绘制   总被引:1,自引:0,他引:1  
介绍了O penGL的知识和石油井的基本概念,利用O penGL实现石油井管道的绘制,包括石油井数据的变换和管道起始点的跟踪和角度的旋转。纹理光照效果增强图形生动性,交互操作改变图形视角。并且利用DAO数据库和L istv iew控件实现数据保存和修改。该程序能够完成石油井的管道绘制和数据保存。  相似文献   
92.
A 3-D Enlarged Cell Technique (ECT) for the Conformal FDTD Method   总被引:1,自引:0,他引:1  
In this paper, we present an enlarged cell technique (ECT) to avoid the time step reduction encountered in the conformal finite-difference time-domain (CFDTD) method due to small irregular cells truncated by metallic boundaries. We focus our efforts on the discussion of the accuracy and stability of the ECT and its comparison with other conformal methods, especially the one called the uniformly stable conformal (USC) method. We also provide a simplified ECT, which is much easier to implement. In the ECT, a stability criterion is first constructed to identify instable irregular cells, i.e., those having so small an area to cause instability. Those instable cells are then enlarged into their adjacent cells to obtain a large, stable area. Careful treatment is performed on the communication between the intruding and intruded cells in terms of electromotive force by keeping the total electromotive force conservative. This technique is verified by several 3-D numerical experiments. Results show that the ECT is second-order accurate and numerically stable at the regular Courant time step limit.  相似文献   
93.
基于XML的基金会现场总线设备描述技术   总被引:2,自引:0,他引:2  
本文简单介绍了基金会现场总线FF的设备描述和新一代稳定、可靠、通用的网络标记语言XML的特点,提出了一种用XML语言实现设备描述的方法。  相似文献   
94.
Water treatment using TiO2 semiconductor as a durable heterogeneous photocatalyst has been the focus of environmentalists in recent years. Currently, we developed an inexpensive and highly efficient approach for synthesizing nitrogen-doped TiO2 with lower band-gap energy that can respond to visible light. Doping on the molecular scale led to an enhanced nitrogen concentration of up to 21.8%. Reflectance measurements showed the synthesized N-doped TiO2 nanoparticles are catalytically active with the absorbance that extends into the visible region up to 600 nm. The water purification potential of this new class of compound was evaluated by studying the photodegradation of Acid Orange 7 (AO7) and E. coli. Experiments were conducted to compare the photocatalytic activities of N-doped TiO2 nanocatalysts and commercially available Degussa P25 power under identical solar light exposure. N-doped TiO2 demonstrated superior photocatalytic activities in both chemical compound degradation and bactericidal reactions. The result of this study shows the potential of applying new generations of catalyst for wastewater purification and disinfection.  相似文献   
95.
We present the results from a user study looking at the ability of observers to mentally integrate wind direction and magnitude over a vector field. The data set chosen for the study is an MM5 (PSU/NCAR Mesoscale Model) simulation of Hurricane Lili over the Gulf of Mexico as it approaches the southeastern United States. Nine observers participated in the study. This study investigates the effect of layering on the observer's ability to determine the magnitude and direction of a vector field. We found a tendency for observers to underestimate the magnitude of the vectors and a counter‐clockwise bias when determining the average direction of a vector field. We completed an additional study with two observers to try to uncover the source of the counter‐clockwise bias. These results have direct implications to atmospheric scientists, but may also be able to be applied to other fields that use 2D vector fields.  相似文献   
96.
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   
97.
Stable social foraging swarms in a noisy environment   总被引:2,自引:0,他引:2  
Bacteria, bees, and birds often work together in groups to find food. A group of robots can be designed to coordinate their activities to search for and collect objects. Networked cooperative uninhabited autonomous vehicles are being developed for commercial and military applications. Suppose that we refer to all such groups of entities as "social foraging swarms". In order for such multiagent systems to succeed it is often critical that they can both maintain cohesive behaviors and appropriately respond to environmental stimuli (e.g., by optimizing the acquisition of nutrients in foraging for food). In this paper, we characterize swarm cohesiveness as a stability property and use a Lyapunov approach to develop conditions under which local agent actions will lead to cohesive foraging even in the presence of "noise" characterized by uncertainty on sensing other agent's position and velocity, and in sensing nutrients that each agent is foraging for. The results quantify earlier claims that social foraging is in a certain sense superior to individual foraging when noise is present, and provide clear connections between local agent-agent interactions and emergent group behavior. Moreover, the simulations show that very complicated but orderly group behaviors, reminiscent of those seen in biology, emerge in the presence of noise.  相似文献   
98.
对分置式牛津型斯特林制冷机进行了数值计算 ,介绍了计算模型考虑到的众多不可逆因素。通过对计算结果与实验结果的对比 ,验证了本文数值计算的准确性 ,说明本文计算模型与数值处理方法是切实可行的  相似文献   
99.
相对于传统的数字滤波器实现方法,符号的2次幂和(SPT)滤波器用移位寄存器替代乘法器,因而资源消耗少、速度快,更加适于专用集成电路(ASIC)设计.介绍了一种适用于宽带码分多址(WCDMA)前向信道中给定基带成形滤波器单位脉冲响应后设计SPT滤波器的方法.相对于传统的理想SPT系数优化方法,此方法更适于给定单位脉冲响应后SPT滤波器的设计,计算复杂度低;仿真结果显示,相对于更加简单的四舍五入方法,此算法在性能上又有可观的增益.  相似文献   
100.
高可用度的冗余UPS   总被引:1,自引:0,他引:1  
简述通信行业标准《通信局(站)电源系统总技术要求》(YD/T1051)对UPS可用度的要求,介绍适用于电信系统的高可用度冗余UPS。  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