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   60533篇
  免费   2477篇
  国内免费   198篇
电工技术   867篇
综合类   93篇
化学工业   10842篇
金属工艺   2067篇
机械仪表   3065篇
建筑科学   1236篇
矿业工程   52篇
能源动力   2156篇
轻工业   4073篇
水利工程   252篇
石油天然气   212篇
武器工业   1篇
无线电   10019篇
一般工业技术   11226篇
冶金工业   9578篇
原子能技术   630篇
自动化技术   6839篇
  2023年   533篇
  2022年   833篇
  2021年   1402篇
  2020年   991篇
  2019年   1009篇
  2018年   1333篇
  2017年   1326篇
  2016年   1649篇
  2015年   1302篇
  2014年   2032篇
  2013年   3481篇
  2012年   3192篇
  2011年   3903篇
  2010年   2970篇
  2009年   3163篇
  2008年   2917篇
  2007年   2462篇
  2006年   2244篇
  2005年   1940篇
  2004年   1852篇
  2003年   1707篇
  2002年   1650篇
  2001年   1290篇
  2000年   1205篇
  1999年   1296篇
  1998年   3433篇
  1997年   2158篇
  1996年   1665篇
  1995年   1195篇
  1994年   886篇
  1993年   900篇
  1992年   509篇
  1991年   537篇
  1990年   459篇
  1989年   444篇
  1988年   368篇
  1987年   302篇
  1986年   289篇
  1985年   262篇
  1984年   199篇
  1983年   157篇
  1982年   163篇
  1981年   143篇
  1980年   158篇
  1979年   105篇
  1978年   100篇
  1977年   197篇
  1976年   336篇
  1975年   83篇
  1974年   74篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Fast DCT algorithm with fewer multiplication stages   总被引:1,自引:0,他引:1  
A novel fast DCT scheme with reduced multiplication stages and fewer additions and multiplications is proposed. The proposed algorithm is structured so that most multiplications tend to be performed at the final stage, which reduces the propagation error that could occur in the fixed-point computation. Minimisation of the multiplication stages can further decrease the error  相似文献   
82.
The authors suggest a novel virtual circuit connection method based on the reverse traversing technique to minimise the waste of network bandwidth resources, when the Internet protocol multicast is interoperated using the resource reservation protocol over an asynchronous transfer mode network. Simulation results show that, as the number of receivers increases, the bandwidth requirements on all links of the network of the proposed scheme become more advantageous than those of other conventional methods  相似文献   
83.
We propose a hybrid ARQ scheme which uses QPSK modulation for the first transmission and BPSK modulation for retransmissions. The throughput performance of the proposed ARQ scheme is better that those of ARQ schemes purely using QPSK modulation or purely using BPSK modulation for transmissions. Furthermore, the proposed scheme does not require any operation of error correction as usually required in hybrid ARQ schemes. Therefore, the ARQ scheme proposed in this paper can be easily implemented  相似文献   
84.
Four hundred forty-six patients with Tourette Syndrome (TS) and/or their parents completed a 52-item self-report survey about vocal and motor tics, and the frequency of associated co-morbid conditions of aggression, obsessions and compulsions, attentional problems, sleep disturbance, mood disturbance, anxiety, and self-mutilative behaviours which have been frequently reported in the literature on TS. Respondents also responded to an open-ended question regarding the most disabling aspects of TS. Results were analyzed within two age groups; under 18 years of age (N = 245) and 18 years of age or older (N = 177). Tics and associated conditions were the most frequently reported disabling aspect by both age groups. Subjects under age 18, however, reported significantly more frequent problems with hyperactivity, temper control, aggressive behaviours and sleepwalking than adults with TS.  相似文献   
85.
86.
Polyvinylpyrrolidone (PVP) in aqueous solution was used as a binding agent in a fluidized-bed system to agglomerate acetaminophen powder into directly compressible granules. It was found that a minimal amount of 5% w/w PVP in a concentration of 7.5% w/v or less was needed to produce granules with an acceptable flow and the corresponding tablets having enough hardness without capping. There was a strong correlation between the time for 80% dissolved (T80) and the logarithm of granule volume-surface mean diameter. A directly compressible acetaminophen composition to manufacture tablets having a T80 value less than 30 min can be prepared simply by adding an appropriate amount of disintegrant (crospovidone, sodium starch glycolate, or pregelatinized starch) to the agglomerated granules.  相似文献   
87.
88.
OBJECTIVE: The purpose of this study was to evaluate ERCP and CT findings of ectopic drainage of the common bile duct into the duodenal bulb. CONCLUSION: Although rare, the diagnosis of ectopic drainage of the common bile duct into the duodenal bulb is important to prevent inadvertent damage during biliary tract or gastric surgery and to clarify the cause of chronic peptic ulcers.  相似文献   
89.
In a high-resolution flat panel system, a conventional interface that directly connects a liquid crystal display (LCD) controller to a flat panel cannot overcome the problems of excess EMI (electromagnetic interference) and power caused by full-swing transmission signals in parallel lines. This paper presents a high-speed digital video interface system implemented with a low-cost standard CMOS (complimentary metal-oxide-semiconductor) technology that can mitigate EMI and power problems in high-resolution flat panel display systems. The combined architecture of the high-speed, small number of parallel lines and low-voltage swing serial interface can support resolutions from VGA (640×480 pixels) up to XGA (1024×768 pixels) with significant power improvement and drastic EMI reduction. To support high-speed, low-voltage swing signaling and overcome channel-to-channel skew problems, a robust data recovery system is required. The proposed digital phase-locked loop enables robust skew-insensitive data recovery of up to 1.04 GBd  相似文献   
90.
This study analyses the relationship between the use of rotating instruments, the production of a smear layer and the presence of alterations to enamel microstructures. The rotating instruments used were carbide (8-12 blade) and diamond tipped (30-15 m) cutters. Cavities were made in extracted teeth. Subsequently, half the sample was analysed using the rugosimeter before and after the application of ortophosphoric acid at 35% for 15 and the other half suing a Scansion Electronic microscope (SEM). The results obtained showed on the one hand that carbide cutters leave a smoother surfacer than diamond tipped cutters, and on the other that the smear layer is eliminated better by carbide cutters compared to diamond tipped cutters. Moreover, there are no major traumatic-type alterations at the level of the enamel affecting the microstructure after the use of carbide cutters.  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