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   1008篇
  免费   30篇
  国内免费   3篇
电工技术   16篇
化学工业   198篇
金属工艺   29篇
机械仪表   27篇
建筑科学   18篇
矿业工程   3篇
能源动力   41篇
轻工业   78篇
水利工程   7篇
石油天然气   1篇
无线电   76篇
一般工业技术   270篇
冶金工业   155篇
原子能技术   5篇
自动化技术   117篇
  2024年   4篇
  2023年   8篇
  2022年   23篇
  2021年   41篇
  2020年   38篇
  2019年   42篇
  2018年   36篇
  2017年   31篇
  2016年   24篇
  2015年   26篇
  2014年   34篇
  2013年   64篇
  2012年   30篇
  2011年   41篇
  2010年   48篇
  2009年   44篇
  2008年   32篇
  2007年   28篇
  2006年   18篇
  2005年   21篇
  2004年   12篇
  2003年   18篇
  2002年   21篇
  2001年   14篇
  2000年   12篇
  1999年   12篇
  1998年   44篇
  1997年   24篇
  1996年   21篇
  1995年   10篇
  1994年   14篇
  1993年   16篇
  1992年   8篇
  1990年   14篇
  1989年   11篇
  1988年   10篇
  1987年   10篇
  1986年   6篇
  1985年   20篇
  1984年   11篇
  1983年   9篇
  1982年   10篇
  1981年   12篇
  1980年   15篇
  1979年   11篇
  1977年   5篇
  1976年   11篇
  1975年   3篇
  1974年   3篇
  1973年   3篇
排序方式: 共有1041条查询结果,搜索用时 31 毫秒
111.
Focal and segmental, but not generalized, myoclonus have been described with human immunodeficiency virus (HIV) infection. We describe three patients with generalized myoclonus and acquired immunodeficiency syndrome (AIDS) dementia complex. In each, myoclonus persisted until death, invariably after a course of a few months. In two patients, myoclonus was elicited by sudden auditory stimuli and resembled a startle response. This form of myoclonus may be subcortical in origin. We suggest that the AIDS dementia complex be included among the causes of myoclonic dementia.  相似文献   
112.
The development of smoking cessation and relapse prevention interventions for pregnant and postpartum women is a public health priority. However, researchers have consistently reported substantial difficulty in recruiting this population into clinical trials. The problem is particularly acute for relapse prevention studies, which must recruit women who have already quit smoking because of their pregnancy. Although these individuals are an important target for tobacco control efforts, they represent an extremely small subgroup of the general population. This paper describes multiple recruitment strategies used for a clinical trial of a self-help relapse prevention program for pregnant women. The effectiveness of the strategies and the direct expense per participant recruited are provided. A proactive recruitment strategy (telephoning women whose phone numbers were purchased from a marketing firm) was ultimately much more successful than a variety of reactive strategies (advertisements, press releases, direct mail, Web placement, health care provider outreach). We found few differences between proactively and reactively recruited participants on baseline variables. The primary difference was that the former had smoked fewer cigarettes per day and reported lower nicotine dependence prior to quitting. Strengths and limitations of the recruitment strategies are discussed.  相似文献   
113.
Designed 2 studies to investigate the forbidden fruit effect in 83 3rd and 4th graders. Results indicate (a) no support for a forbidden fruit effect, (b) that procedural aspects other than the prohibition in the forbidden toy paradigm influenced the child's valuation of the entire toy set, and (c) that there is a necessity for an appropriate comparison condition when using the forbidden toy paradigm. These results are extended to the previous research on the sour grapes effect. (4 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
114.
115.
The tensile yield stress is compared with the uniaxial compression yield stress for specimens of polycarbonate tested at constant strain rate from −120 to + 120°C. The strain rate dependence of the tensile yield stress is also studied from − 140 to + 20°C. The yield behaviour is described by a modification of the Eyring theory of non-Newtonian viscosity where the deformation is supposed to involve two different flow processes. The validity of a yield criterion previously established by one of us, is checked throughout the range of temperatures explored; the proposed equation gives a good fit to the data provided it is applied separately to each flow process. Then the present investigation, combining the yield condition with the modified Eyring theory, provides a formalism which agrees with the data and accurately renders the temperature, strain rate and pressure dependence of the yield stress of polycarbonate.  相似文献   
116.
The flow, heat and mass transfer on the unsteady laminar incompressible boundary layer in micropolar fluid at the stagnation point of a 2-dimensional and an axisymmetric body have been studied when the free stream velocity and the wall temperature vary arbitrarily with time. The partial defferential equations governing the flow have been solved numerically using a quasilinear finite-difference scheme. The skin friction, microrotation gradient and heat transfer parameters are found to be strongly dependent on the coupling parameter, mass transfer and time, whereas the effect of the microrotation parameter on the skin friction and heat transfer is rather weak, but microrotation gradient is strongly affected by it. The Prandtl number and the variation of the wall temperature with time affect the heat-transfer very significantly but the skin friction and micrortation gradient are unaffected by them.  相似文献   
117.
118.
119.
120.
Step voltage transient current studies have been made in cellulose acetate films as a function of filed and thickness. A logarithmic plot (Scherr-Montroll plot) of the transient current vs. time gives a knee at a time tT, which is interpreted as the transit time of the charge carrier. The value of the carrier mobility has been estimated to be 3.9 × 10?9 cm2.V?1.S?1 in cellulose acetate film. The carrier mobility in iodine-doped (2% w/w) cellulose acetate film has also been determined from Scher-Montroll plot and is found to be 3.3 × 10?7 cm2.V?1.S?1.  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