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   1611171篇
  免费   25022篇
  国内免费   7122篇
电工技术   35433篇
综合类   6503篇
化学工业   278402篇
金属工艺   66779篇
机械仪表   47266篇
建筑科学   48524篇
矿业工程   11952篇
能源动力   50622篇
轻工业   124828篇
水利工程   16413篇
石油天然气   38510篇
武器工业   151篇
无线电   200954篇
一般工业技术   302981篇
冶金工业   203961篇
原子能技术   34766篇
自动化技术   175270篇
  2021年   15738篇
  2020年   12046篇
  2019年   14821篇
  2018年   19428篇
  2017年   19210篇
  2016年   23299篇
  2015年   17788篇
  2014年   28918篇
  2013年   88559篇
  2012年   38607篇
  2011年   54126篇
  2010年   46529篇
  2009年   54236篇
  2008年   49586篇
  2007年   47738篇
  2006年   46961篇
  2005年   43055篇
  2004年   44030篇
  2003年   43646篇
  2002年   42329篇
  2001年   39042篇
  2000年   37173篇
  1999年   36742篇
  1998年   56616篇
  1997年   46656篇
  1996年   40148篇
  1995年   33694篇
  1994年   31107篇
  1993年   30916篇
  1992年   26971篇
  1991年   24247篇
  1990年   24531篇
  1989年   23684篇
  1988年   22211篇
  1987年   20341篇
  1986年   19738篇
  1985年   23092篇
  1984年   22830篇
  1983年   20826篇
  1982年   19636篇
  1981年   19751篇
  1980年   18424篇
  1979年   18825篇
  1978年   18076篇
  1977年   18557篇
  1976年   20635篇
  1975年   16312篇
  1974年   15717篇
  1973年   15848篇
  1972年   13320篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The performance of a home made MIS–p-Si solar cell was experimentally studied under various gamma irradiation doses (up to 500 Mrad). The effect of radiation dose on the IV and CV characteristics was investigated in this work. The obtained results showed that all the output parameters of the cells under investigation were degraded with gamma radiation exposure. In addition, the effects of fabrication conditions (metal thickness and adding of antireflection coating) on the cell output parameters were also investigated.  相似文献   
992.
993.
994.
简单介绍了碳氧比测井的原理及通常的数据处理方法。分析了由常规数据处理所得曲线仍然存在的问题及可能的成因 ,并给出了可行的修正办法。讨论了另一种可行的曲线异常数据的检测、剔除方法。实践表明 :文章讨论的两点建议都是可行的 ,并且在提高测量曲线质量的同时也提高了地层含油饱和度的解释精度。  相似文献   
995.
介绍了质量流量计的工作原理有应用效果。这种新型质量流量计精度高,稳定性好,示值计量简便,可直接显示质量、流量、介质温度、密度等,维护量低,但必须正确安装、使用,才能发挥其应有的作用。  相似文献   
996.
Theoretical analysis of heat transfer in laminar pulsating flow   总被引:2,自引:0,他引:2  
Pulsation effect on heat transfer in laminar incompressible flow, which led to contradictory results in previous studies, is theoretically investigated in this work starting from basic principles in an attempt to eliminate existing confusion at various levels. First, the analytical solution of the fully developed thermal and hydraulic profiles under constant wall heat flux is obtained. It eliminates the confusion resulting from a previously published erroneous solution. The physical implications of the solution are discussed. Also, a new time average heat transfer coefficient for pulsating flow is carefully defined such as to produce results that are both useful from the engineering point of view, and compliant with the energy balance. This rationally derived average is compared with intuitive averages used in the literature. New results are numerically obtained for the thermally developing region with a fully developed velocity profile. Different types of thermal boundary conditions are considered, including the effect of wall thermal inertia. The effects of Reynold and Prandtl numbers, as well as pulsation amplitude and frequency on heat transfer are investigated. The mechanism by which pulsation affects the developing region, by creating damped oscillations along the tube length of the time average Nusselt number, is explained.  相似文献   
997.
Mass transport in pulsating flow devices using either moving boundaries or oscillating imposed pressure drops are compared with each other by means of a calculation using a simple model. We conclude that there is no difference between the two configurations as long as one is interested only in the power required to move the fluid for the convective mass transport achieved. However, the boundary driven configuration is more efficient if the power is divided by the total mass transport where both the diffusive and convective parts are taken into account, the boundary driven configuration is more efficient. The amplitude of the piston stroke in the pressure driven configuration and the amplitude in the boundary driven case are assumed to be the same, and the inertia of the moving devices themselves are ignored in this calculation.  相似文献   
998.
J. Perahia comments on the paper by J. S. Hsu (see ibid., vol.16, p.192-7, 2001) and expands on the case of a two stator three phase squirrel cage induction machine where one stator housing is stationary and other stator housing is mounted on a worm gear assembly. The original author replies to the comments  相似文献   
999.
A quantum chemical study of the binding of Li+ cation to polyalkyloxides has been carried out. The lithium cation interaction with three polyalkyloxides (polyethylene oxide (PEO), polytrimethylene oxide (PTMO), and polypropylene oxide (PPO)) has been investigated using ab initio molecular orbital theory at the HF/6-31G* level with molecular models for the polymers. Coordination by one to six oxygens was considered. In addition, higher level calculations were carried out using G3(MP2) theory for coordination of Li+ by one oxygen. For coordination of lithium by one oxygen, the binding energy ordering is PTMO>PPO>PEO, with PTMO having the largest lithium cation affinity. The same ordering is found for larger coordination numbers with the exception of coordination by six oxygens, where the ordering changes due to the steric interactions.  相似文献   
1000.
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