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   51248篇
  免费   2873篇
  国内免费   159篇
电工技术   727篇
综合类   69篇
化学工业   10820篇
金属工艺   2188篇
机械仪表   3280篇
建筑科学   1180篇
矿业工程   33篇
能源动力   2191篇
轻工业   4082篇
水利工程   281篇
石油天然气   98篇
武器工业   2篇
无线电   8170篇
一般工业技术   11024篇
冶金工业   4080篇
原子能技术   672篇
自动化技术   5383篇
  2024年   26篇
  2023年   578篇
  2022年   739篇
  2021年   1595篇
  2020年   1147篇
  2019年   1279篇
  2018年   1520篇
  2017年   1500篇
  2016年   1883篇
  2015年   1355篇
  2014年   2181篇
  2013年   3147篇
  2012年   3371篇
  2011年   4025篇
  2010年   2913篇
  2009年   3019篇
  2008年   2902篇
  2007年   2248篇
  2006年   2079篇
  2005年   1777篇
  2004年   1605篇
  2003年   1548篇
  2002年   1367篇
  2001年   1162篇
  2000年   1026篇
  1999年   952篇
  1998年   1628篇
  1997年   1039篇
  1996年   829篇
  1995年   577篇
  1994年   478篇
  1993年   424篇
  1992年   308篇
  1991年   284篇
  1990年   273篇
  1989年   247篇
  1988年   213篇
  1987年   178篇
  1986年   126篇
  1985年   123篇
  1984年   99篇
  1983年   73篇
  1982年   51篇
  1981年   47篇
  1980年   32篇
  1979年   38篇
  1978年   37篇
  1977年   44篇
  1976年   65篇
  1973年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
A multi-channel continuous toxicity monitoring system developed in our laboratory, based on two-stage mini-bioreactors, was successfully implemented in the form of computer-based data acquisition. The multi-channel system consists of a series of a two-stage minibioreactor systems connected by a fiber optic probe to a luminometer, and uses genetically engineered bioluminescent bacteria for the detection of the potential toxicity from the soluble chemicals. This system can be stably and continuously operated due to the separation of the culture reactor from the test reactor and accomplish easy and long-term monitoring without system shut down by abrupt inflows of severe polluting chemicals. Four different recombinant bioluminescent bacteria were used in different channels so that the modes of the samples toxicities can be reasonably identified and evaluated based upon the response signature of each channel. The bioluminescent signatures were delivered from four channels by switching one at once, while the data is automatically logged to an IBM compatible computer. We also achieved the enhancement of the system through the manipulation of the dilution rate and the use of thermo-lux fusion strains. Finally, this system is now being implemented to a drinking water reservoir and river for remote sensing as an early warning system.  相似文献   
142.
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   
143.
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   
144.
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   
145.
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   
146.
电动汽车常被喻作“归来的孩子”,因为这项技术在多年前进入市场后便一直沉寂,直至最近才再次活跃起来。其实,电动汽车早于1835年首次于美国出现,到1899年,纽约市接近90%的出租车都是由电力驱动。然而,当电力启动器和内燃机变得完善时,电动汽车的使用就迅速衰退。随着如今对环境保护的关注,由燃烧碳氢化合物造成的污染,加之汽油成本高升的影响,再次  相似文献   
147.
148.
149.
150.
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