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   28942篇
  免费   3099篇
  国内免费   2199篇
电工技术   2288篇
技术理论   7篇
综合类   3868篇
化学工业   740篇
金属工艺   267篇
机械仪表   1185篇
建筑科学   11089篇
矿业工程   1649篇
能源动力   494篇
轻工业   359篇
水利工程   971篇
石油天然气   588篇
武器工业   243篇
无线电   2530篇
一般工业技术   1678篇
冶金工业   471篇
原子能技术   189篇
自动化技术   5624篇
  2024年   90篇
  2023年   307篇
  2022年   664篇
  2021年   758篇
  2020年   787篇
  2019年   640篇
  2018年   641篇
  2017年   752篇
  2016年   957篇
  2015年   1122篇
  2014年   2147篇
  2013年   1680篇
  2012年   2381篇
  2011年   2512篇
  2010年   2142篇
  2009年   2059篇
  2008年   1989篇
  2007年   2211篇
  2006年   1935篇
  2005年   1527篇
  2004年   1245篇
  2003年   1049篇
  2002年   839篇
  2001年   730篇
  2000年   655篇
  1999年   493篇
  1998年   367篇
  1997年   271篇
  1996年   234篇
  1995年   212篇
  1994年   172篇
  1993年   130篇
  1992年   130篇
  1991年   77篇
  1990年   60篇
  1989年   57篇
  1988年   47篇
  1987年   28篇
  1986年   25篇
  1985年   15篇
  1984年   11篇
  1983年   10篇
  1982年   12篇
  1981年   13篇
  1980年   8篇
  1979年   12篇
  1978年   5篇
  1977年   6篇
  1976年   3篇
  1959年   8篇
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
991.
This article presents a design, modeling, simulation, and measurements of a hybrid photocurrent-to-digital converter integrated together with photo-diodes in a 130 nm CMOS process, without any additional process steps. Photo-currents of integrated photo-diodes with different responsivities to different wavelength of the light and light intensity are converted into 22-bits digital results in 2 ms. The results can then be converted into CIE XYZ or RGB color luminosity space using dedicated DSP algorithm. A high resolution, hybrid, ADC converts light induced photo-currents into 22-bit digital results, canceling the dark current of the photodiodes and 1/f noise and offset voltage of the input stage of the modulator. The whole converter consumes on average less than current at supply voltage at 10 conversions per second. It occupies approx. 0.8 mm2 of silicon area, including the three photodiodes, a multiplexer, and the ΣΔ modulator.  相似文献   
992.
Cinema as an influential mass medium continuously represents different spaces, environments, events, and symbols, and through which it reproduces viewers’ social reminiscence and merges imagination and reality in a constant manner. This paper attempts to illuminate the outlook of Iranian cinema on urban spaces (In this paper, urban space means “outdoor space” or “open space.” However, our purpose of applying the term “urban space” is an emphasis on the word “urban.” This includes what is connected with a city and its spaces and buildings, residents, and even social, economic, and political issues.), and to analyze the quality of their representation during the last two decades (1979–2006). Identifying displayed urban spaces and determining their strength and limitations, this endeavor not only offers guidelines on urban design pedagogy but also examines impacts of cinema on audiences’ visual literacy and perception, thereby exploring their expectations of urban environment.Based on content analysis of selected movies, we find that the Iranian films only occasionally involve urban spaces, and if they do, this practice is confined to historical or cultural spaces. This failure could be attributed to the poverty of urban spaces and limitations facing the film industry in such spaces on the one hand, and lack of the directors’ appropriate understanding of contemporary urban spaces and their mere attention to nostalgic spaces on the other hand.  相似文献   
993.
To improve the performance of the standard particle swarm optimization (PSO) which suffers from premature convergence and slow convergence speed, many PSO variants introduce lots of stochastic or aimless strategies to overcome the convergence problem. However, the mutual learning between elites particles is omitted, although which might be benefit to the convergence speed and, prevent the premature convergence. In this paper, we introduce DSLPSO, which integrates three novel strategies, specifically, tabu detecting, shrinking and local learning strategies, into PSO to overcome the aforementioned shortcomings. In DSLPSO, search space of each dimension is divided into many equal subregions. Then the tabu detecting strategy, which has good ergodicity for search space, helps the global historical best particle to detect a more suitable subregion, and thus help it jump out of a local optimum. The shrinking strategy enables DSLPSO to take optimization in a smaller search space and obtain a higher convergence speed. In the local learning strategy, a differential between two elites particles is used to increase solution accuracy. The experimental results show that DSLPSO has a superior performance in comparison with several other participant PSOs on most of the tested functions, as well as offering faster convergence speed, higher solution accuracy and stronger reliability.  相似文献   
994.
The objectives of this study were to develop a predictive statistical model for low-fill-weight capsule filling of inhalation products with dosator nozzles via the quality by design (QbD) approach and based on that to create refined models that include quadratic terms for significant parameters. Various controllable process parameters and uncontrolled material attributes of 12 powders were initially screened using a linear model with partial least square (PLS) regression to determine their effect on the critical quality attributes (CQA; fill weight and weight variability). After identifying critical material attributes (CMAs) and critical process parameters (CPPs) that influenced the CQA, model refinement was performed to study if interactions or quadratic terms influence the model. Based on the assessment of the effects of the CPPs and CMAs on fill weight and weight variability for low-fill-weight inhalation products, we developed an excellent linear predictive model for fill weight (R2?=?0.96, Q2?=?0.96 for powders with good flow properties and R2?=?0.94, Q2?=?0.93 for cohesive powders) and a model that provides a good approximation of the fill weight variability for each powder group. We validated the model, established a design space for the performance of different types of inhalation grade lactose on low-fill weight capsule filling and successfully used the CMAs and CPPs to predict fill weight of powders that were not included in the development set.  相似文献   
995.
《工程(英文)》2018,4(1):103-111
Given the increasingly notable segmentation of underground space by existing subway tunnels, it is difficult to effectively and adequately develop and utilize underground space in busy parts of a city. This study presents a combined construction technology that has been developed for use in underground spaces; it includes a deformation buffer layer, a special grouting technique, jump excavation by compartment, back-pressure portal frame technology, a reinforcement technique, and the technology of a steel portioning drum or plate. These technologies have been successfully used in practical engineering. The combined construction technology presented in this paper provides a new method of solving key technical problems in underground spaces in effectively used cross-subway tunnels. As this technology has achieved significant economic and social benefits, it has valuable future applications.  相似文献   
996.
Abstract

A numerical technique for integrating the full Navier‐Stokes and diffusion equations through an initial value problem has been used to investigate the time development of a line buoyant source issuing in a density‐stratified environment. The basic physical features and some structures of the interactions of the motion at the intermediate mixing region are obtained. Results show that the stratification tends to inhibit the flow development of the buoyant source and to encourage the formation of a recirculatory vortex on the lower region near the source and the upper region.  相似文献   
997.
Many methods for multinational License Plate Detection (LPD) have been proposed in recent times but most of them are not sophisticated enough to handle complex backgrounds. Moreover, their ability to handle various environmental and illumination conditions has been limited and still needs improvement. In this paper, we propose a novel technique to detect license plates of vehicles regardless of their color, size, and content. As the rear vehicle lights are an essential part of any vehicle, we reduce the image processing area to eliminate the complex background by detecting the rear-lights as the license plates are in a certain range of these lights. Heuristic Energy Map (HEM) of the vertical edge information in the Region of Interest (ROI) is calculated and area with the dense edges is selected using a unique histogram approach which is considered to be the license plate. The proposed algorithm is tested on 855 images from various countries including China, Pakistan, Serbia, Italy and various states of America. Experimental results show that the proposed method is able to detect license plates 90.4% of times despite of complex backgrounds in 0.25 s on average that can achieve real time performance.  相似文献   
998.
特殊教育是九年制义务教育不可分割的一部分,培智学校是特殊教育学校中占比最大的学校。目前我国培智学校普通教学空间的设计基本遵照普通中小学教学空间,对智力障碍学生的针对性不足。文章基于调研得出的培智学校教学空间的现状,分析得出教学发展对功能空间的需求,据此提出教学空间的功能组成、空间规模和组合模式。认为培智学校的建设应与时代发展相吻合,不宜保守但也不能不计国情过度超前。  相似文献   
999.
导线不均匀覆冰和不同期脱冰会使线路发生跳跃,导致相间短路[1]。防脱冰改造施工中新型相间间隔棒可以有效地抑制脱冰跳跃。文中主要介绍了防脱冰改造施工中新型相间间隔棒的施工新工艺,运用此施工新工艺可以有效缩短停电施工改造时间,且对类似工程技术改进具有一定的参考价值。  相似文献   
1000.
隧道通风过程中空气湿热状态变化研究   总被引:1,自引:1,他引:0  
隧道及巷道等地下工程在施工及运营阶段需要以自然或机械通风设施等方式进行通风,以保持充足的新鲜空气量,并维持其内人员的舒适感。当前大多研究集中在隧道通风过程中的空气质量以及烟雾透过率,而较少关注通风过程中空气的湿热状态的变化。以热力学及流体力学的基本理论为基础,研究地下隧道长距离、大规模地下输送新鲜空气过程中,隧道内空气湿热状态的变化。通过论证,在经过隧道长距离输送后,空气湿热状态参数发生较大变化。这说明,空气在地下输送过程中,尽管有风机做功以及摩擦生热过程,但在恒温层的保温作用下,温度只会略有上升;而湿度则会升至饱和状态。这将对地下储库、地下采矿等地下工程的空气调节系统设计研究工作有一定指导意义。  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