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   3207篇
  免费   30篇
  国内免费   2篇
电工技术   8篇
化学工业   183篇
金属工艺   8篇
机械仪表   16篇
建筑科学   36篇
矿业工程   3篇
能源动力   19篇
轻工业   90篇
水利工程   9篇
石油天然气   6篇
无线电   77篇
一般工业技术   189篇
冶金工业   2487篇
原子能技术   4篇
自动化技术   104篇
  2022年   10篇
  2021年   16篇
  2020年   6篇
  2019年   6篇
  2018年   19篇
  2017年   17篇
  2016年   16篇
  2015年   14篇
  2014年   14篇
  2013年   37篇
  2012年   29篇
  2011年   50篇
  2010年   34篇
  2009年   20篇
  2008年   55篇
  2007年   40篇
  2006年   35篇
  2005年   41篇
  2004年   23篇
  2003年   37篇
  2002年   23篇
  2001年   36篇
  2000年   21篇
  1999年   88篇
  1998年   673篇
  1997年   422篇
  1996年   285篇
  1995年   173篇
  1994年   120篇
  1993年   155篇
  1992年   31篇
  1991年   42篇
  1990年   48篇
  1989年   40篇
  1988年   47篇
  1987年   35篇
  1986年   38篇
  1985年   31篇
  1983年   13篇
  1982年   14篇
  1981年   22篇
  1980年   26篇
  1979年   11篇
  1978年   5篇
  1977年   84篇
  1976年   168篇
  1975年   5篇
  1971年   7篇
  1970年   8篇
  1969年   5篇
排序方式: 共有3239条查询结果,搜索用时 17 毫秒
101.
We have examined the effects of the recently described heptadecapeptide nocistatin on K+-evoked glutamate release from rat cerebrocortical slices in vitro. In vivo, nocistatin reverses the action of nociceptin. Nocistatin (100 nM, n = 7) did not inhibit K+-evoked glutamate release alone. Nociceptin (100 nM) inhibited glutamate release by 51.7 +/- 8.3% (P < 0.05, n = 6) and this was fully reversed by nocistatin (100 nM). Nocistatin also appears to be an antagonist of nociceptin action in vitro.  相似文献   
102.
Full-scale field acoustic Doppler velocimeter measurements of the radial, axial, and tangential flow components were undertaken in a large-diameter turbulent swirling jet generated by a raft-mounted axial flow-mixing propeller discharging through a draft tube during isothermal and stratified conditions. The results were compared with classical jet theory and showed significant differences in the zone of flow establishment though similar behavior in the zone where established flow was found. It was concluded that the efflux from the axial flow-mixing propeller could not be described adequately by conventional jet theory due to the jet size and swirling characteristics.  相似文献   
103.
The kinetics of fuse regrowth during temperature humidity bias (THB) stresses were modeled with a power law for relative humidity (exponent /spl sim/2.3) and a power law for bias voltage (exponent /spl sim/1.7). Using these results we determined the optimal laser cut parameters to maximize product reliability.  相似文献   
104.
Materials that can switch from stiff to soft or from brittle to tough by slightly changing the temperature, pH, electric, or magnetic fields of their environments, can have a pronounced impact on many applications, including sensors, biomedical materials for less invasive surgeries, and packaging materials. In this work, temperature‐sensitive poly(N‐isopropyl acrylamide) grafts and low molar mass polyethylene glycol were incorporated in the interfacial region between clay nanoparticles and a bacteria‐derived polyhydroxybutyrate matrix to determine if the application of an external stimulus, such as small changes in temperature, could increase the toughness of the nanocomposites. The obtained materials were characterized by using thermal analysis, infrared spectroscopy, dynamic light scattering and dynamic mechanical tests. Mechanical properties were also evaluated at different temperatures and showed that small changes in temperature, such as from 25°C to 40°C, led to a pronounced increase in strain at break of the nanocomposites containing the modified interface. The external stimulus associated with the increase in temperature from 25°C to 40°C can reduce the interfacial interactions between clay and polymer matrix and create a highly plasticized polymer layer between the components of the nanocomposite, which favored the sliding of the interface and ultimately led to high values of elongation. POLYM. COMPOS., 37:1342–1349, 2016. © 2014 Society of Plastics Engineers  相似文献   
105.
A series of Pd/-Al2O3 catalysts with a designed loading of 1 wt % were prepared by the sol-gel method using boehmite (AlOOH) sols and various palladium compounds. These materials were developed for later use as inorganic membranes. The samples were calcined at 400 °C in flowing O2 to decompose the Pd complex and change the phase of the support to -Al2O3. H2 pulse chemisorption was used to determine the average Pd particle sizes, while particle size distributions were obtained from TEM micrographs. XRD was used to determine the crystallinity of the -Al2O3 support after extended treatments at 650 °C in O2 and H2 atmospheres. The physical properties of the support were studied using nitrogen adsorption-desorption at 77 K. Initial BET surface areas were about 350 m2/g. Pore size distributions were very narrow and centered at 3.6 nm, but broadened and became bimodal during the 650 °C treatments. An ion-exchanged sample prepared by traditional methods was used as a basis for comparison to the sol-gel samples.  相似文献   
106.
Mobile learning is increasing in popularity, but not all university students have mobile devices to support it. Our study investigated cross-platform software that has the potential to allow education practitioners to provide mobile support to their students’ learning, while offering similar functionality to non-mobile users via more traditional computing platforms. Undergraduate students were trained in the use of multi-platform cloud-based note-taking software (Evernote), and used the software in independent study for 8 weeks. Data show adoption for a range of functions, particularly gathering and managing information, organisation and planning, and the recording of ideas. Multimedia functions were also adopted innovatively by some students. Use for reflection was rare. Non-adopters were in a minority, giving low utility appraisals and difficulty in changing habits as reasons. Subjective evaluations and recommendations showed that a majority of students felt positive about the software and found it quick and easy to use. Mobile and non-mobile users only differed on the number of locations in which they used the software, and the proportion of notes classified as ideas, both being higher in mobile users. The data provide decision support for education practitioners who wish to provide mobile learning to their students alongside traditional platforms.  相似文献   
107.
Reliability centered maintenance (RCM) incorporates sound guidance for managers who wish to attain high standards of maintenance at their operating plants. Since the amount and type of maintenance which is applied depend strongly on the machine or components age (DFR, CFR or IFR), on its replacement cost as well as on the cost and safety consequences of system failure, a careful analysis of the system components based on their reliability data should be done in order to optimize the maintenance program. This paper describes the methodology which was used at an aluminum plant in order to select critical machines and to develop an optimal maintenance policy based on reliability data of each machine, safety consequences of system failure, lead time and repair time, and components criticality.  相似文献   
108.
109.
Bilateral electrolytic lesions of the anteroventral nucleus of the thalamus given after training impaired retention performance (extinction and reacquisition) of 12 male New Zealand White rabbits in a differential avoidance conditioning task. In addition, the lesions abolished the excitatory, discriminative multiple-unit discharges that had developed in the cingulate and retrosplenial cortices to the auditory CSs during the course of behavioral acquisition, prior to the induction of the lesions. The excitatory discharges were supplanted in the Ss with lesions by CS-elicited reduction of neuronal firing to levels below the prestimulus baseline. Lesions given to 8 Ss before training did not disrupt behavioral acquisition, but they did eliminate the excitatory tone-elicited neuronal discharges that normally occur in the cortex before and during training. The CS-elicited reduction of neuronal firing did not occur at the beginning of training in the Ss given lesions before training, but it developed during the course of training. The lesions did not eliminate the excitatory and discriminative neuronal activity of the prefrontal cortex. Results demonstrate the excitatory and discriminative neuronal discharges in the cingulate and retrosplenial cortices are critically dependent on the connections of these areas with the anterior thalamic nuclei. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
110.
Multimedia Tools and Applications - Recording videos with smartphones at large-scale events such as concerts and festivals is very common nowadays. These videos register the atmosphere of the event...  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