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   5436篇
  免费   353篇
  国内免费   284篇
电工技术   262篇
综合类   279篇
化学工业   589篇
金属工艺   294篇
机械仪表   660篇
建筑科学   140篇
矿业工程   99篇
能源动力   225篇
轻工业   174篇
水利工程   18篇
石油天然气   56篇
武器工业   41篇
无线电   1007篇
一般工业技术   834篇
冶金工业   83篇
原子能技术   233篇
自动化技术   1079篇
  2024年   6篇
  2023年   56篇
  2022年   84篇
  2021年   140篇
  2020年   153篇
  2019年   138篇
  2018年   130篇
  2017年   151篇
  2016年   151篇
  2015年   193篇
  2014年   295篇
  2013年   364篇
  2012年   294篇
  2011年   369篇
  2010年   218篇
  2009年   257篇
  2008年   284篇
  2007年   350篇
  2006年   321篇
  2005年   293篇
  2004年   244篇
  2003年   216篇
  2002年   192篇
  2001年   169篇
  2000年   154篇
  1999年   158篇
  1998年   144篇
  1997年   124篇
  1996年   87篇
  1995年   76篇
  1994年   48篇
  1993年   46篇
  1992年   35篇
  1991年   25篇
  1990年   24篇
  1989年   18篇
  1988年   16篇
  1987年   14篇
  1986年   9篇
  1985年   7篇
  1984年   7篇
  1983年   3篇
  1982年   4篇
  1981年   1篇
  1980年   2篇
  1975年   1篇
  1959年   2篇
排序方式: 共有6073条查询结果,搜索用时 78 毫秒
991.
Obtaining an accurate value of the electric dipole moment μ is essential in the fields of laser application technologies. A direct way of measuring the electric dipole moment μ is to observe the Rabi-oscillation which manifests itself in the coherent photo-excitation behavior of atoms. In the case of the elements which have large angular momenta, identifying the Rabi-oscillation in their excitation behavior becomes rather difficult. We proposed an accurate and straightforward method of determining the electric-dipole moment μ between multifold degenerate levels. The point is to remove the degeneracy by applying an external magnetic field with the aid of the Zeeman effect and, then, to realize a degeneration free coherent excitation. As a result, we can observe the Rabi-oscillations explicitly in the excitation vs. laser-fluence curves. The present method provides a reliable basis of experimental determination of μ. As an example, we applied the present method to a transition to 0–17,362 cm?1 level in uranium and obtained the value μ=0.86±0.06 (Debye).  相似文献   
992.
993.
The cross sections of the 152Sm(γ,n) and 197Au(γ,n) reactions have been measured with the laser-Compton scattering (LCS) γ beam in the 8.3–12.4MeV energy range. The photon difference method has been used for LCS γ rays in the data analysis for the first time. The present data for 197Au measured as the standard are in agreement with the preceding data and the recent recommendation. On the other hand, the preceding data for 152Sm at 8.3 MeV are twice as large as the present data.  相似文献   
994.
A phoswich-type neutron detector was developed in order to measure high-energy cosmic ray neutron spectra in aircraft. The neutron detector consists of an EJ309 organic liquid scintillator that is 121.7mm in diameter and 121.7mm in length and is covered with a 15mm thick EJ299-13 outer plastic scintillator. The neutron response functions of the detector are required for the unfolding method to obtain the energy spectrum. The neutron response functions were created based on MCNPX simulations using an anticoincidence mode with the experimental light-output correlations with particle energies, uniformity of light collection and energy resolutions. The light-output correlation with particle energy, the uniformity of light collection and the energy resolutions were evaluated based on experiments. Measurements of neutron response functions were performed using four quasi-monoenergetic neutron beams from 40 to 80 MeV p-Li reactions to verify the calculated results. The calculated response functions show good agreement with the measurements. The angular response of the phoswich detector was confirmed to be isotropic from the calculation. The photon response functions of the detector were also calculated and agreed well with the measurements for 6.129MeV photons. Neutron and photon response matrices were created up to 300 and 50 MeV, respectively, over a wide energy range for experimental flights.  相似文献   
995.
基于光子图的光子映射算法能产生高质量的照片级图像.对于光照复杂的场景,光子图需要存储大量光子以提高生成图像的质量,这不仅占用大量的内存空间,而且光照估计的时间长.论文提出基于栅格的全局光子图重建的算法,即在光子包围盒被栅格化后,其非空栅格中一定比例的光子被用来重建新的光子图,并保证重建前后栅格内光子能量和守恒,这使得重建前后光子图的光照估计的效果相近.通过增加特定栅格中的重建光子数目,能有效减少由几何偏差引起的光照估计误差,增强直接聚焦(焦散)和间接聚焦光照的绘制效果;并使用简单方法检测生成图像中少量噪声,增加少量采样即可有效减少相应的噪声.全局光子图重建算法的计算成本低,并保持生成图像的视觉独立性.  相似文献   
996.
Some dominance properties are proposed for the NP-hard problems of scheduling N jobs on a single machine with due dates, and sequence-dependent setup times. The algorithms based on Ragatz's branch and bound scheme with the dominance properties are developed to minimize the maximum tardiness or the total tardiness. Computational experiments demonstrate the effectiveness of the dominance rules.  相似文献   
997.
Compound orthogonal arrays (COAs) and single arrays are alternatives to the inner–outer arrays advocated by Taguchi for robust parameter design experiments. A criterion based on the word type pattern and strength of COAs is proposed to select optimal COAs. Single arrays are classified into prodigal single arrays (PSAs) and economical single arrays (ESAs) according to their relative estimation capacities, and various optimality criteria, again based on the word type pattern, are proposed for selecting optimal single arrays. Useful optimal COAs, PSAs, and ESAs are constructed and tabulated as convenient references for experimenters in practice.  相似文献   
998.
In this work, we use a two‐photon fluorescence microscope for combined imaging and laser tissue ablation of a living Drosophila Melanogaster embryo. By using tightly focused near‐infrared femtosecond pulses at MHz repetition rate and of sub‐nanojoule energy we are able to produce microsurgery on the epithelial tissue within a Drosophila embryo at the final stages of its embryonic development. Ablation was performed on labelled and unlabelled embryos during and after dorsal closure. We observed that ablation of GFP‐labelled tissue required lower energy deposition than unlabelled tissue ensuring that the tissue ablation is mediated by multiphoton absorption of Green Fluorescent Protein (GFP). In addition, the energy deposition to produce ablation is further decreased during dorsal closure. These results show the presence of additional tensile forces on the tissue during dorsal closure. Furthermore, an increased activity of actin near the laser wounds was observed as the tissue heals.  相似文献   
999.
面心立方晶体单晶材料多轴低周疲劳寿命的估算方法   总被引:1,自引:1,他引:0  
用立方晶体单晶材料的等效应变和等效应力作为参量,考虑正交各向异性材料偏轴受载时存在正应力和切应力的耦合效应,引入k参量描述非对称循环载荷对疲劳寿命的影响,建立工程上实用的幂函数形式的面心立方晶体单晶材料多轴低周疲劳寿命预测模型.将立方晶体单晶材料屈服准则及其弹塑性本构模型集成到ANSYS软件中,对DD3单晶合金在680℃温度下的低周疲劳缺口试样进行非对称载荷循环应力应变分析.对不同的模型参量进行多元回归相关分析,发现用立方晶体单晶材料等效应变和等效应力作为模型参量拟合的回归曲线的相关系数最大,κ参量与循环次数之间呈幂函数关系.利用CMSX-2镍基单晶合金薄壁圆筒试样的拉一扭循环载荷低周疲劳试验数据和DD3镍基单晶合金缺口试样的低周疲劳试验数据对模型进行验证,试验所得数据分别落在2.5倍和2.0倍偏差分布带内.  相似文献   
1000.
基于PIC单片机的无线遥控移动靶控制系统   总被引:1,自引:0,他引:1  
介绍了一种无线遥控移动靶控制系统。系统采用PIC单片机作为控制元件,通过其脉宽调制输出功能来驱动直流电动机,进而实现对靶子速度和转向的控制。系统采用仿人智能控制算法,提高了系统的快速性、准确性和稳定性。叙述了主控制器和遥控器的硬件和软件设计。  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