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   51403篇
  免费   2927篇
  国内免费   159篇
电工技术   735篇
综合类   70篇
化学工业   11078篇
金属工艺   2229篇
机械仪表   3411篇
建筑科学   1151篇
矿业工程   25篇
能源动力   2218篇
轻工业   3996篇
水利工程   272篇
石油天然气   88篇
武器工业   2篇
无线电   8152篇
一般工业技术   11154篇
冶金工业   3962篇
原子能技术   681篇
自动化技术   5265篇
  2024年   50篇
  2023年   584篇
  2022年   911篇
  2021年   1522篇
  2020年   1116篇
  2019年   1235篇
  2018年   1495篇
  2017年   1496篇
  2016年   1814篇
  2015年   1377篇
  2014年   2197篇
  2013年   3156篇
  2012年   3408篇
  2011年   4087篇
  2010年   2959篇
  2009年   3061篇
  2008年   2909篇
  2007年   2265篇
  2006年   2112篇
  2005年   1791篇
  2004年   1627篇
  2003年   1582篇
  2002年   1390篇
  2001年   1173篇
  2000年   1043篇
  1999年   970篇
  1998年   1594篇
  1997年   1014篇
  1996年   820篇
  1995年   568篇
  1994年   473篇
  1993年   422篇
  1992年   299篇
  1991年   280篇
  1990年   259篇
  1989年   246篇
  1988年   215篇
  1987年   174篇
  1986年   123篇
  1985年   119篇
  1984年   95篇
  1983年   66篇
  1982年   38篇
  1981年   40篇
  1980年   33篇
  1979年   31篇
  1978年   30篇
  1977年   40篇
  1976年   65篇
  1973年   20篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
Network direct attached storage (NDAS) is a network storage architecture that allows direct attachment of existing ATA/ATAPI devices to Ethernet without a separate server. Unlike other architectures such as NAS, SAN, and USB mass storage, no server computer intervenes between the storage and the client hosts. We describe an NDAS disk controller (NDC) amenable to low-cost single-chip implementation that processes a simplified L3/L4 protocol and converts commands between ATA/ATAPI and Ethernet, while the remaining complex tasks are performed by remote hosts. Unlike NAS architectures that use TCP/IP, NDAS uses a TCP-like lean protocol that lends itself well to high-performance hardware realization. Thanks to the simple NDAS architecture and protocol, an NDC implemented on a single 4 mm /spl times/ 4 mm chip in 0.18 /spl mu/m CMOS technology achieves a maximum throughput of 55 Mbytes/s on gigabit Ethernet, which is comparable to that of a high-performance disk locally attached to a host computer.  相似文献   
142.
Optimal ensemble construction via meta-evolutionary ensembles   总被引:1,自引:0,他引:1  
In this paper, we propose a meta-evolutionary approach to improve on the performance of individual classifiers. In the proposed system, individual classifiers evolve, competing to correctly classify test points, and are given extra rewards for getting difficult points right. Ensembles consisting of multiple classifiers also compete for member classifiers, and are rewarded based on their predictive performance. In this way we aim to build small-sized optimal ensembles rather than form large-sized ensembles of individually-optimized classifiers. Experimental results on 15 data sets suggest that our algorithms can generate ensembles that are more effective than single classifiers and traditional ensemble methods.  相似文献   
143.
Seasoned beef called Jangzorim in Korea is produced by boiling in soy sauce, and is a popular food in Korea. The aim of this study is to evaluate the microbial safety and physical qualities of sous vide processed seasoned beef, and the effect of nisin during storage. Sous vide processed packages with or without nisin (100 IU or 500 IU) were stored at 4 °C or 25 °C for 60 days, and samples measured for quality at regular intervals throughout this storage period. In the case of 25 °C storage, the number of mesophilic microorganisms in seasoned beef packages without nisin increased markedly, but with nisin there was no observed increase. Psychrotrophic microorganisms, anaerobic microorganisms, and B. cereus cells showed similar trends, although C. perfringens was not detected in all samples. At 25 °C storage, changes in the cutting force of packages containing nisin showed no significant change, packages without nisin decreased markedly. The colour of packages without nisin showed a drastic decrease in lightness (‘L’) while no changes were observed in packages with nisin.  相似文献   
144.
A direct adaptive control scheme is proposed for nonminimum-phase systems in which controller parameters are estimated from the recursive least-squares algorithm and additional auxiliary parameters are obtained from the proposed polynomial identity. A local convergence is guaranteed without any extra condition. Integral action is incorporated into the adaptive controller to eliminate the steady-state error and to satisfy a condition of the unique solution for the polynomial identity. The control law used in this scheme is based on the set-point-on-I-only proportional-integral-derivative (PID) structure  相似文献   
145.
146.
147.
148.
149.
LiFePO4 is a potential candidate for the cathode material of the lithium secondary batteries. A co-precipitation method was adopted to prepare LiFePO4 because it is simple and cheap. Nitrogen gas was needed to prevent oxidation of Fe2+ in the aqueous solution. The co-precipitated precursor shows the high reactivity with the reductive gas, and the single phase of LiFePO4 is successfully synthesized with the aid of carbon under less reductive conditions. LiFePO4 fine powder prepared by co-precipitation method shows high rate capability, impressive specific capacity and cycle property.  相似文献   
150.
Physical modeling of gas/liquid mass transfer in a gas stirred ladle   总被引:3,自引:0,他引:3  
The absorption of gas through the plume eye and of an injected gas in a steelmaking ladle process was investigated, using a physical model of CO2 absorption into a NaOH solution. The results show that the inert gas escaping through the plume eye is ineffective in protecting the bath from the atmosphere, and placing an oil layer (simulated slag) decreases the absorption rate significantly. Increasing the flow rate of the inert gas not only exposes more of the liquid surface to the CO2 atmosphere, but also increases the mass transfer coefficient at the surface. The overall mass transfer between an injected CO2 gas and NaOH solution includes the mass transfer through the surface of the bath as well as the mass transfer in the bubble dispersion zone. The difference between the mass transfer in the bubble dispersion zone and the overall mass transfer was found to be significant for relatively low gas flow rates. The mass transfer coefficient of CO2 in the bubble dispersion zone was estimated using available information regarding the bubble size and velocity. Mass transfer coefficient estimated for the constant bubble frequency regime shows a dependence on gas flow rate. However, if a constant characteristic size of bubbles is assumed as an alternative approach, the mass transfer coefficient is independent of the gas flow rate.  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