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   3368篇
  免费   338篇
  国内免费   16篇
电工技术   42篇
综合类   35篇
化学工业   770篇
金属工艺   109篇
机械仪表   249篇
建筑科学   75篇
矿业工程   7篇
能源动力   160篇
轻工业   312篇
水利工程   15篇
石油天然气   20篇
无线电   576篇
一般工业技术   777篇
冶金工业   219篇
原子能技术   45篇
自动化技术   311篇
  2024年   4篇
  2023年   39篇
  2022年   57篇
  2021年   95篇
  2020年   82篇
  2019年   106篇
  2018年   112篇
  2017年   139篇
  2016年   121篇
  2015年   119篇
  2014年   190篇
  2013年   221篇
  2012年   217篇
  2011年   263篇
  2010年   191篇
  2009年   197篇
  2008年   191篇
  2007年   147篇
  2006年   125篇
  2005年   104篇
  2004年   82篇
  2003年   108篇
  2002年   101篇
  2001年   80篇
  2000年   67篇
  1999年   63篇
  1998年   88篇
  1997年   69篇
  1996年   57篇
  1995年   41篇
  1994年   37篇
  1993年   24篇
  1992年   28篇
  1991年   24篇
  1990年   21篇
  1989年   20篇
  1988年   11篇
  1987年   20篇
  1986年   6篇
  1985年   9篇
  1984年   9篇
  1983年   5篇
  1982年   2篇
  1980年   2篇
  1978年   3篇
  1977年   4篇
  1976年   7篇
  1974年   5篇
  1971年   2篇
  1944年   1篇
排序方式: 共有3722条查询结果,搜索用时 0 毫秒
11.
面向企业信息化实现管理现代化   总被引:1,自引:0,他引:1  
为适应社会信息化技术的发展,必须积极推行企业信息化,企业信息化引发管理革命,从而丰富了企业管理现代化的内容。本文论述了上述三方面的内部及演化关系,指出只有面向企业信息化,才能充分实现企业管理现代化。  相似文献   
12.
The effect exerted by transplantation of the 5 day culture of testicles from newly born piglets on the hypogonadal state of mature X-ray irradiated (3 Gy) rats was studied. It has been found that a month after transplantation (two months after irradiation) the hypogonadal state disappeared for a while, which is confirmed by normalization of the weight of seminal vesicles, content of testosterone and biologically active lutropine, restoration of the reproductive function of rats. No significant changes in steroidogenesis activity have been found, which proves a substituent character of transplantation. The effect disappears three months later but certain restoration of the content of nucleic acids in the testicles is observed.  相似文献   
13.
14.
A novel ultracompact 2/spl times/2 wavelength division multiplexer (WDM) for 1.55-/spl mu/m operation based on highly dispersive two-mode interference (TMI) was designed, theoretically modeled, and verified using a finite-difference-time-domain (FDTD) method. A two-moded waveguide assisted with a dispersive tooth-shaped grating provided a mode-dependent reflection band of central wavelength at 1.55 /spl mu/m. The wavelengths of 1538 and 1572 nm that were at the band edges and had the lowest reflection losses and relatively high dispersion were selected for wavelength multiplexing. The result showed that the wavelengths were separated by grating dispersion in a coupler length of 75 /spl mu/m which was much shorter than the required length of 1.1 mm in a regular TMI multiplexer of no grating. Insertion loss of about 1.7 dB and channel contrast of about 12 dB were achieved.  相似文献   
15.
16.
For multi-step heterogeneous consecutive reactions affected entirely by interphase diffusion under isothermal condition, the equations for the effectiveness factors, the surface concentrations and the point yields were derived in terms of the Damkoehler numbers or the measurables from the mass balances set up on the assumption that the mass-transfer rate balances the surface-reaction rate at steady state. From the analyses of the equations derived, the effectiveness factors for the intermediate steps and the surface concentrations of intermediates were understood to be enhanced by the measurables inclusive of the concentrations and the mass-transfer coefficients. Then the effect of the concentrations was concluded to be most significant. The effects of these measurables to the effectiveness factors and the surface concentrations were qualitatively discussed for simple consecutive reactions and also for additive consecutive reactions. Especially, as for two-step additive consecutive reactions, the effects of measurables η Da and the concentrations to the effectiveness factors were examined with graphical presentations. Finally, the brief discussion of the dependency of the Damkoehler number upon reaction time and the effect of the Renolds number and diffusivity to the extent of the mass-transfer resistance were presented.  相似文献   
17.
18.
This paper presents an application of digital signal processing to data acquired by the radio imaging method (RIM) that was adopted to measure moisture distribution inside the human body. RIM was originally developed for the mining industry; we are applying the method to a biomedical measurement because of its simplicity, economy, and safety. When a two‐dimensional image was constructed from the measured data, the method provided insufficient resolution because the wavelength of the measurement medium, a weak electromagnetic wave in a VHF band, was longer than human tissues. We built and measured a phantom, a model simulating the human body, consisting of two water tanks representing large internal organs. A digital equalizer was applied to the measured values as a weight function, and images were reconstructed that corresponded to the original shape of the two water tanks. As a result, a two‐dimensional image containing two individual peaks corresponding to the original two small water tanks was constructed. The result suggests the method was applicable to biomedical measurement by the assistance of digital signal processing. This technique may be applicable to home‐based medical care and other situations in which safety, simplicity, and economy are important.  相似文献   
19.
The observation of murine retrovirus infection of microglial cells in brain regions expressing spongiform neurodegenerative changes suggests that these cells may play an important role in pathogenesis. To evaluate this potential in vitro, murine microglial cells were infected in mixed glial cultures with the highly neurovirulent murine retrovirus, FrCasE. The microglia were then isolated from the mixed cultures on the basis of their differential adherence and shown to be approximately 98% pure. The infected microglia expressed viral envelope protein at the plasma membrane, while viral budding was primarily intracellular. Evaluation of the viral envelope protein by immunoblotting indicated that the immunoreactive species produced was exclusively a 90-kDa precursor protein. Very little of the envelope protein was associated with particles released from these cells, and viral titers in the culture supernatant were low. Interestingly, these cells were still capable of infecting permissive target cells when seeded as infectious centers. This partially defective infection of microglial cells suggests a potential cellular means by which a neurovirulent retrovirus could disrupt normal microglia and in turn central nervous system motor system functioning.  相似文献   
20.
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