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   4377篇
  免费   47篇
  国内免费   3篇
电工技术   12篇
综合类   3篇
化学工业   318篇
金属工艺   93篇
机械仪表   64篇
建筑科学   105篇
矿业工程   10篇
能源动力   50篇
轻工业   172篇
水利工程   19篇
石油天然气   11篇
无线电   134篇
一般工业技术   341篇
冶金工业   2811篇
原子能技术   13篇
自动化技术   271篇
  2022年   14篇
  2021年   16篇
  2020年   11篇
  2018年   25篇
  2017年   21篇
  2016年   29篇
  2015年   24篇
  2014年   27篇
  2013年   91篇
  2012年   61篇
  2011年   83篇
  2010年   61篇
  2009年   53篇
  2008年   66篇
  2007年   79篇
  2006年   80篇
  2005年   56篇
  2004年   64篇
  2003年   70篇
  2002年   74篇
  2001年   45篇
  2000年   51篇
  1999年   124篇
  1998年   818篇
  1997年   476篇
  1996年   307篇
  1995年   188篇
  1994年   157篇
  1993年   180篇
  1992年   55篇
  1991年   47篇
  1990年   60篇
  1989年   45篇
  1988年   56篇
  1987年   58篇
  1986年   55篇
  1985年   47篇
  1984年   37篇
  1983年   38篇
  1982年   41篇
  1981年   47篇
  1980年   31篇
  1979年   23篇
  1978年   32篇
  1977年   78篇
  1976年   152篇
  1975年   23篇
  1974年   17篇
  1973年   20篇
  1972年   19篇
排序方式: 共有4427条查询结果,搜索用时 15 毫秒
21.
Previous research in this laboratory has shown that preweaning and postweaning juvenile meadow voles, Microtus pennsylvanicus, can acquire a spatial task, the Morris water-maze task. The present study examined the influence of age of juvenile acquisition ("before weaning" (BW; Day 10 and 15 after birth) and "after weaning" (AW; Day 20 and 25 after birth)) of a spatial task on subsequent re-acquisition of the same hidden-platform spatial water-maze task. This study also compared sex differences and litter sex-ratio effects on reacquisition performance. Fifteen litters of adults were re-tested in the same water maze 6 weeks after being initially tested as juveniles. All analyses were conducted using a covariate that removed the group differences in the original task performance. Adult voles from female-biased litters, that had previously learned the task at an older juvenile age (AW), reacquired the same task faster than adults that had previously learned the task at a younger juvenile age (BW). In the adult BW group there was also a significant litter sex-ratio effect such that voles born into a female-biased litter re-acquired the task more slowly than did voles born into a male-biased litter. There were no significant sex or litter sex-ratio effects on spatial learning in the AW group. These results show that adult meadow voles can require a spatial task more quickly if they initially learned the task at an older juvenile age, suggestive of a period of infantile amnesia. In addition, these results indicate that the litter sex-ratio can affect adult spatial performance, suggesting that the relative amount of androgens in utero may influence the development of sexually-dimorphic spatial ability in adulthood.  相似文献   
22.
23.
Murray R 《Architectural record》1993,181(11):48-51, 120-3
Constrained by the excesses of the previous decade and tepid performance in the general economy, the rebound by construction from its 1990-91 downturn could best be described as subdued and selective. Single-family housing led the way before faltering this year, and only scattered help has come from the industry's other sectors. The big question facing construction at the end of 1993 is whether the current recovery is in danger of stalling or, put differently, does it have the stamina to become more broad-based?  相似文献   
24.
The it Imperative in Business Transformation   总被引:2,自引:0,他引:2  
The IT imperative is to construct enterprisewide systems and capabilities needed by business to compete. For IS managers, this means embracing the viewpoint that IT plays a crucial role in building the business of the future. IS and business management must act as true partners, each supporting the other in creating an optimally performing company.  相似文献   
25.
Murray AM  Melton LA 《Applied optics》1985,24(17):2783-2787
Fluorescent additives which allow the determination of droplet temperatures in hydrocarbon fuel sprays have been developed. These systems, which exploit the chemistry of organic exciplexes; should make possible the determination of droplet temperatures within 1 degree C. Two specific systems are described: 3,10-dicyanophenanthrene/diethylaniline over the 20-135 degrees C range, and naphthalene/tetramethyl-p-phenylene diamine over the 140-265 degrees C range. These additives should allow 2-D real-time nonintrusive visualization of the droplet temperatures in an evolving fuel spray.  相似文献   
26.
The application of r.f.-sputter etching techniques to the fabrication of grooves in the surface of quartz is reported. This process has been used for the construction of devices which employ the interaction of surface acoustic waves with arrays of well-defined parallel grooves. Devices have been produced with grooves up to 2.5 m deep, which have substantially rectangular profiles and controllable mark-to-space ratios. The groove geometries have been characterized using Talysurf, optical microscopy, SEM and TEM techniques.  相似文献   
27.
Since 2009, the Spallation Neutron Source (SNS) has been producing neutrons with ion beam powers near 1 MW, which requires the extraction of ~50 mA H(-) ions from the ion source with a ~5% duty factor. The 50 mA are achieved after an initial dose of ~3 mg of Cs and heating the Cs collar to ~170 °C. The 50 mA normally persist for the entire 4-week source service cycles. Fundamental processes are reviewed to elucidate the persistence of the SNS H(-) beams without a steady feed of Cs and why the Cs collar temperature may have to be kept near 170 °C.  相似文献   
28.
Despite its impressive rate of growth in the past decades, an increasing amount if dissatisfaction with the area of psychosomatic medicine is reflected in recent literature. The discipline's failures relate to concepts of pathogenesis and therapeutic application of research findings. These failures are explained as a necessary consequence of the philosophical tenet of mind-body dualism which underlies medical theory. It is urged that advocates of psychosomatic medicine give the concept of "holism" meaning at the most fundamental level by establishing a rational basis for theory, or else forsake this line of research for others which yield causal relationships conductive to effective therapy.  相似文献   
29.
Column-based dynamic power supply has been integrated into a high-frequency 70-Mb SRAM design that is fabricated on a high-performance 65-nm CMOS technology. The fully synchronized design achieves a 3-GHz operating frequency at 1.1-V power supply. The power supply at SRAM cell array is dynamically switched between two different voltage levels during READ and WRITE operations. Silicon measurement has proven this method to be effective in achieving both good cell READ and WRITE margins, while lowering the overall SRAM leakage power consumption.  相似文献   
30.
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