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   313182篇
  免费   3773篇
  国内免费   720篇
电工技术   6225篇
综合类   561篇
化学工业   47279篇
金属工艺   10375篇
机械仪表   8905篇
建筑科学   8022篇
矿业工程   890篇
能源动力   8630篇
轻工业   31394篇
水利工程   2558篇
石油天然气   3670篇
武器工业   8篇
无线电   39937篇
一般工业技术   58865篇
冶金工业   57776篇
原子能技术   5486篇
自动化技术   27094篇
  2021年   2307篇
  2019年   2164篇
  2018年   3646篇
  2017年   3481篇
  2016年   3572篇
  2015年   2570篇
  2014年   4481篇
  2013年   14449篇
  2012年   7451篇
  2011年   10226篇
  2010年   8000篇
  2009年   9226篇
  2008年   9731篇
  2007年   9705篇
  2006年   8611篇
  2005年   8008篇
  2004年   7854篇
  2003年   7602篇
  2002年   7412篇
  2001年   7608篇
  2000年   7273篇
  1999年   7632篇
  1998年   17887篇
  1997年   12953篇
  1996年   10218篇
  1995年   7960篇
  1994年   7272篇
  1993年   6973篇
  1992年   5329篇
  1991年   5107篇
  1990年   4980篇
  1989年   4826篇
  1988年   4727篇
  1987年   3938篇
  1986年   4043篇
  1985年   4760篇
  1984年   4314篇
  1983年   4064篇
  1982年   3648篇
  1981年   3799篇
  1980年   3484篇
  1979年   3453篇
  1978年   3263篇
  1977年   3854篇
  1976年   4912篇
  1975年   2812篇
  1974年   2686篇
  1973年   2714篇
  1972年   2228篇
  1971年   1982篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Nanorod field-effect transistors (FETs) that use multiple Mg-doped ZnO nanorods and a SiO2 gate insulator were fabricated and characterized. The use of multiple nanorods provides higher on-currents without significant degradation in threshold voltage shift and subthreshold slopes. It has been observed that the on-currents of the multiple ZnO nanorod FETs increase approximately linearly with the number of nanorods, with on-currents of ~1 muA per nanorod and little change in off-current (~4times10-12). The subthreshold slopes and on-off ratios typically improve as the number of nanorods within the device channel is increased, reflecting good uniformity of properties from nanorod to nanorod. It is expected that Mg dopants contribute to high n-type semiconductor characteristics during ZnO nanorod growth. For comparison, nonintentionally doped ZnO nanorod FETs are fabricated, and show low conductivity to compare with Mg-doped ZnO nanorods. In addition, temperature-dependent current-voltage characteristics of single ZnO nanorod FETs indicate that the activation energy of the drain current is very low (0.05-0.16 eV) at gate voltages both above and below threshold  相似文献   
992.
993.
Multishell Carrier Transport in Multiwalled Carbon Nanotubes   总被引:1,自引:0,他引:1  
Understanding carrier transport in carbon nanotubes (CNTs) and their networks is important for harnessing CNTs for device applications. Here, we report multishell carrier transport in individual multiwalled CNTs, and films of randomly dispersed multiwalled CNTs, as a function of electric field and temperature. Electrical measurements and first-principles density functional theory calculations indicate transport across CNT shells. Intershell conduction occurs across an energy barrier range of 60-250 meV in individual CNTs, and ~ 60 meV in CNT networks. In both cases, the conductance behavior can be explained based upon field-enhanced carrier injection and defect-enhanced transport, as described by the Poole-Frenkel model.  相似文献   
994.
995.
Achieving an innovative integrated sensor fusion architecture with a robust vehicle navigation and localization using an extended Kalman filter, interval analysis and covariance intersection that can overcome the uncertainty in the system model and sensor noise statistics. There are various approaches to the problem, but here the focus is on an approach which can guaranteed performance of sensor-based navigation. The guaranteed performance is quantified by explicit bounds of position estimate of a ground vehicle. Ground vehicles generally carry dead reckoning sensors such as wheel encoders and inertial sensors, to measure acceleration and angle rate, while obstacle detection and mapmaking is done with time-of-flight ultrasonic sensors. Most of these sensors give overlapping or complementary information and sometimes are redundant as well, which offers scope for exploiting data fusion. The purpose here is to achieve data fusion for ground vehicles with low-cost sensors by forming an intelligent sensor system. This is accomplished by combining the sensors' measurements and processing these measurements with data fusion algorithms. The algorithms are complementary in the sense that they compensate for each other's limitations, so that the resulting performance of the sensor system is better than its individual components.  相似文献   
996.
997.
Fericean  S. Droxler  R. 《IEEE sensors journal》2007,7(11):1538-1545
Noncontacting inductive sensors are applicable on a large scale for position detection or travel measurement in industrial applications. Reasons for such broad acceptance in many sectors of industry are noncontact and wear-free sensing of the target (any metal object), reliability and robustness, resistance to fouling, water tightness and compact size. The present work is intended to be a systematic, complete, and consistent presentation of the technological innovations, recent implementations and current trends regarding the analog distance and travel sensing offered by noncontacting inductive sensors for industrial applications. It starts with the fundamentals of inductive sensing and presents the physical basics gained by modern analytic and simulation methods, as well as high-level integrated circuits for inductive sensors. The following sections deal with present-day inductive analog proximity sensors and with the distinctive technological innovation offered by the new inductive linear displacement sensors and with miniaturization results achieved through consistent integration.  相似文献   
998.
R. Mujoo    P.K.W. Ng 《Journal of food science》2003,68(8):2448-2452
ABSTRACT: Grain of the soft white wheat cultivar Harus was harvested weekly from anthesis to maturity and fructooligosaccharides (FOS) contents were determined by reversed-phase high-performance liquid chromatography. Tests were carried out to determine the effect of adding immature wheat meal to a base flour of cultivar Russ (hard red spring) on the quality characteristics of bread. FOS content was also analyzed in baked bread, and the effect of transglutaminase in improving bread quality was examined. Marked decreases in FOS contents, such as 1-kestose and nystose, were observed with grain maturation. The overall quality of bread appeared to be acceptable, and the added FOS were retained after baking.  相似文献   
999.
Thrombin from Atlantic salmon (Salmo salar) was purified and characterized as a potential new binding agent for the food industry. Purification was performed avoiding inhibitors, using BaSO4 adsorption and heparin‐Sepharose affinity chromatography. Prothrombin activation was performed using a mixture of eggs and gills from salmon. Optimized conditions for the adsorption, elution, and the activation step are presented. The purified thrombin clotted bovine fibrinogen with a specific activity of 1423 U/mg. Sequence data are presented and compared with other species. This method of nontoxic activation and purification will allow salmon thrombin to be used in the food industry.  相似文献   
1000.
This study examined organizational family-responsive policies, perceptions of the organization as family supportive, and supervisor support as issues that may be salient to the experience of conflict between paid employment (work) and family roles. Data were collected from 355 managerial personnel in New Zealand. Although work-family conflict and psychological strain were strongly linked, the availability of organizational policies had no significant association with levels of conflict or strain, whereas policy usage was related only to work-to-family interference and not to family-to-work interference. On the other hand, perceptions of the organization as family supportive and supervisor support for work-family balance displayed significant relationships with key variables, highlighting the importance of these variables for interventions designed to ameliorate the negative impact of work-family conflict on managerial well-being. Implications for the effective implementation of family-responsive interventions are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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