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   9736篇
  免费   720篇
  国内免费   136篇
电工技术   331篇
综合类   131篇
化学工业   1856篇
金属工艺   447篇
机械仪表   549篇
建筑科学   322篇
矿业工程   105篇
能源动力   359篇
轻工业   767篇
水利工程   79篇
石油天然气   102篇
武器工业   49篇
无线电   1661篇
一般工业技术   1567篇
冶金工业   799篇
原子能技术   97篇
自动化技术   1371篇
  2024年   35篇
  2023年   134篇
  2022年   225篇
  2021年   315篇
  2020年   231篇
  2019年   224篇
  2018年   239篇
  2017年   248篇
  2016年   298篇
  2015年   325篇
  2014年   455篇
  2013年   679篇
  2012年   603篇
  2011年   641篇
  2010年   446篇
  2009年   512篇
  2008年   463篇
  2007年   405篇
  2006年   411篇
  2005年   368篇
  2004年   322篇
  2003年   283篇
  2002年   312篇
  2001年   230篇
  2000年   218篇
  1999年   199篇
  1998年   385篇
  1997年   236篇
  1996年   169篇
  1995年   140篇
  1994年   118篇
  1993年   118篇
  1992年   63篇
  1991年   72篇
  1990年   56篇
  1989年   60篇
  1988年   40篇
  1987年   45篇
  1986年   39篇
  1985年   31篇
  1984年   29篇
  1983年   20篇
  1982年   14篇
  1981年   25篇
  1980年   17篇
  1979年   9篇
  1978年   15篇
  1977年   14篇
  1976年   21篇
  1973年   8篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Currently relational databases are widely used, while object-oriented databases are emerging as a new generation of database technology. This paper presents a methodology to provide effective sharing of information in object-oriented databases and relational databases. The object-oriented data model is selected as a common data model to build an integrated view of the diverse databases. An object-oriented query language is used as a standard query language. A method is developed to transform a relational data definition to an equivalent object-oriented data definition and to integrate local data definitions. Two distributed query processing methods are derived. One is for general queries and the other for a special class of restricted queries. Using the methods developed, it is possible to access distributed object-oriented databases and relational databases such that the locations and the structural differences of the databases are transparent to users.  相似文献   
82.
Uniaxial tensile tests in various directions following uniaxial extension, equibiaxial stretching or plane strain rolling have been performed to study the effects of changes in strain path on the anisotropy of yield stresses of aluminium-killed low-carbon steel and 70-30 brass sheets. The anisotropy could be predicted from the specimen textures, if dislocation structure were equiaxed, as in the case of equibiaxial stretching. However, elongated dislocation cell structures, developed in the steel specimens prestrained in uniaxial tension or plane strain rolling, gave rise to the second-stage yield stresses higher than predicted from textures in the directions different from the maximum prestrain direction. Planar dislocation structures in the brass specimens prestrained in uniaxial tension or plane strain rolling gave the second-stage yield stresses lower than predicted from the textures in the directions different from the maximum prestrain direction. The phenomena are discussed based on textures and dislocation structures.  相似文献   
83.
The efficacy of corticosteroids in asthma has been recognized over 40 years ago. Since that time, the advent of inhaled forms has further improved the therapeutic of these drugs which are now recognized as the fundamental treatment for asthma, and described in detail by national and international consensus. Based on a large body of literature, it can now be recommended to prescribe inhaled corticosteroids for symptomatic asthma patients. Long-term treatment is required and dosage not exceeding 1000 micrograms/d (beclometasone dipropionate equivalent) in adults are safe. Differences in the pharmacological characteristics of the various systematic and inhaled corticosteroids can be used to adapt treatment and administration route to each patient and achieve good patient compliance with optimal therapeutic efficacy.  相似文献   
84.
This paper describes a simple and effective way to modify an existing hard-switched flyback power converter into a circuit with zero-voltage switching (ZVS) and zero-current switching (ZCS). The key improvement is to turn the unattractive features of the coupled inductor leakage inductance and snubber capacitor into attractive ones. The coupled inductor leakage inductance and snubber are used to form a quasi-resonant circuit to facilitate ZVS/ZCS of all power devices. The operating principles of the power converter and experimental results are presented  相似文献   
85.
Studies the anomalous variations of the OFF-state leakage current (IOFF) in n-channel poly-Si thin-film transistors (TFTs) under static stress. The dominant mechanisms for the anomalous IOFF can be attributed to (1) IOFF increases due to channel hot electrons trapping at the gate oxide/channel interface and silicon grain boundaries and (2) IOFF decreases due to hot holes accumulated/trapped near the channel/bottom oxide interface near the source region. Under the stress of high drain bias, serious impact ionization effect will occur to generate hot electrons and hot holes near the drain region. Some of holes will be injected into the gate oxide due to the vertical field (~(V_Gstress V_Dstress)/T OX) near the drain and the others will be migrated from drain to source along the channel due to lateral electric field (~V_Dstress/LCH)  相似文献   
86.
A novel reconfigurable microstrip patch antenna with frequency and polarization diversities is proposed. A U‐slot is incorporated into a square patch, and a PIN diode is utilized to switch the slot on and off, which realizes the frequency diversity characteristic. The polarization diversities among linear polarization (LP), right‐hand circular polarization (RHCP), and left‐hand circular polarization (LHCP) are also obtained by switching three PIN diodes on the slot and the truncating corners of a square patch on and off. The antenna design and experimental results are presented.  相似文献   
87.
88.
Motion vector plays one significant feature in moving object segmentation. However, the motion vector in this application is required to represent the actual motion displacement, rather than regions of visually significant similarity. In this paper, region-based selective optical flow back-projection (RSOFB) which back-projects optical flows in a region to restore the region's motion vector from gradient-based optical flows, is proposed to obtain genuine motion displacement. The back-projection is performed based on minimizing the projection mean square errors of the motion vector on gradient directions. As optical flows of various magnitudes and directions provide various degrees of reliability in the genuine motion restoration, the optical flows to be used in the RSOFB are optimally selected based on their sensitivity to noises and their tendency in causing motion estimation errors. In this paper a deterministic solution is also derived for performing the minimization and obtaining the genuine motion magnitude and motion direction.  相似文献   
89.
Drawing Power Law Graphs Using a Local/Global Decomposition   总被引:1,自引:0,他引:1  
  相似文献   
90.
This paper describes the development strategy of a prototype expert system, called RViES, for the reactor vessel integrity. The main objectives of the system are to assist engineers to perform fatigue and fracture mechanics analyses of reactor vessels quickly and accurately. The system consists of three parts; user interface, knowledge base and inference engine. Various rules recommended in codes and standards are stored in the knowledge base. Several case studies were performed to check the usefulness of the system.  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