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   253759篇
  免费   3229篇
  国内免费   863篇
电工技术   4838篇
综合类   198篇
化学工业   36313篇
金属工艺   9555篇
机械仪表   7576篇
建筑科学   6097篇
矿业工程   879篇
能源动力   7286篇
轻工业   21204篇
水利工程   2215篇
石油天然气   3233篇
武器工业   15篇
无线电   34419篇
一般工业技术   50317篇
冶金工业   48632篇
原子能技术   5078篇
自动化技术   19996篇
  2021年   2211篇
  2020年   1617篇
  2019年   1972篇
  2018年   3339篇
  2017年   3370篇
  2016年   3448篇
  2015年   2258篇
  2014年   4014篇
  2013年   11584篇
  2012年   6301篇
  2011年   8666篇
  2010年   6956篇
  2009年   7939篇
  2008年   8485篇
  2007年   8343篇
  2006年   7406篇
  2005年   6541篇
  2004年   6308篇
  2003年   6593篇
  2002年   6068篇
  2001年   6537篇
  2000年   6006篇
  1999年   6415篇
  1998年   16503篇
  1997年   11436篇
  1996年   8818篇
  1995年   6625篇
  1994年   5923篇
  1993年   5853篇
  1992年   4141篇
  1991年   4033篇
  1990年   3868篇
  1989年   3658篇
  1988年   3565篇
  1987年   3027篇
  1986年   2952篇
  1985年   3214篇
  1984年   2930篇
  1983年   2831篇
  1982年   2641篇
  1981年   2548篇
  1980年   2463篇
  1979年   2309篇
  1978年   2109篇
  1977年   2604篇
  1976年   3562篇
  1975年   1766篇
  1974年   1733篇
  1973年   1669篇
  1972年   1465篇
排序方式: 共有10000条查询结果,搜索用时 678 毫秒
1.
2.
Multimedia Tools and Applications - Mammograms are the images used by radiologists to diagnose breast cancer. Breast cancer is one of the most common cancers in women. The early detection of breast...  相似文献   
3.
The effect of microwave roasting parameters (300, 450 and 600 W; 5, 10 and 15 min) on acrylamide content in sorghum grain was determined using High Pressure Liquid Chromatography (HPLC)-photo diode array (PDA) detector coupled with C-18 column. Samples roasted at 300 and 450 W did not possess acrylamide, whereas 600 W (15 min) favoured formation of 2740.19 µg/kg of acrylamide, levels far exceeding the defined European Union (EU) limits. The chronic daily intake (CDI) for acrylamide through consumption of such grain flour was 3.25–9.5-fold higher to Joint FAO/WHO Expert Committee on Food Additives (JECFA) defined high exposure limits. The margin of exposure (MOE) values ranged from 4.3 to 12.76 and from 11.07 to 32.27 for neoplastic and neurological effects, respectively, demonstrating high exposure and serious health concerns associated with dietary intake of this toxicant. This study assesses the risk for the Indian population and highlights the importance of optimising process parameters for food product to minimise such exposure risks.  相似文献   
4.
In this study, dilute chemical bath deposition technique has been used to deposit CdZnS thin films on soda-lime glass substrates. The structural, morphological, optoelectronic properties of as-grown films have been investigated as a function of different Zn2+ precursor concentrations. The X-ray diffractogram of CdS thin-film reveals a peak corresponding to (002) plane with wurtzite structure, and the peak shift has been observed with the increase of the Zn2+ concentration upon formation of CdZnS thin film. From morphological studies, it has been revealed that the diluted chemical bath deposition technique provides homogeneous distribution of film on the substrate even at a lower concentration of Zn2+. Optical characterization has shown that the transparency of the film is influenced by Zn2+ concentration and when the Zn2+ concentration is varied from 0 M to 0.0256 M, bandgap values of resulting films range from 2.42 eV to 3.90 eV while. Furthermore, electrical properties have shown that with increasing zinc concentration the resistivity of the film increases. Finally, numerical simulation validates and suggests that CdZnS buffer layer with composition of 0.0032 M Zn2+ concentration would be a promising candidate in CIGS solar cell.  相似文献   
5.
Wireless Personal Communications - Despite its various benefits, the Mobile Ad-hoc Network (MANET) has a number of obstacles due to its mobility, unstable topology, energy efficiency, and other...  相似文献   
6.
Semiconductors - Abstract—In our work, we carry out a structural-spectroscopic study of AlGaN/GaN epitaxial layers grown by molecular-beam epitaxy with nitrogen-plasma activation on a hybrid...  相似文献   
7.
Journal of Communications Technology and Electronics - In recent years, there has been a rapid improvement in photonics products due to the use of multilayer heterostructures grown on the basis of...  相似文献   
8.

In this paper, we propose to use Artificial Bee Colony (ABC) optimization to solve the joint mode selection, channel assignment, and power allocation (JMSCPA) problem to maximize system throughput and spectral efficiency. JMSCPA is a problem where the allocation of channel and power depends on the mode selection. Such problems require two step solution and are called bi-level optimization problems. As bi-level optimization increases the complexity and computational time, we propose a modified version of single-level ABC algorithm aided with the adaptive transmission mode selection algorithm to allocate the cellular, reuse, and dedicated modes to the DUs along with channel and power allocation based on the network traffic load scenarios. A single variable, represented by the users (CUs and DUs) is used to allocate mode selection, and channel allocation to solve the JMSCPA problem, leading to a simpler solution with faster convergence, and significant reduction in the computational complexity which scales linearly with the number of users. Further, the proposed solution avoids premature stagnation of conventional ABC into local minima by incorporating a modification in its update procedure. The efficacy of the ABC-aided approach, as compared to the results reported in the literature, is validated by extensive numerical investigations under different simulation scenarios.

  相似文献   
9.
Mobile Networks and Applications - Project MindCatcher is an art/research project which has the intention to explore the potential of interactive artistic environments for measuring and a better...  相似文献   
10.
Glass and Ceramics - Ceramic bricks based on low-melting clay and ferro-dust from self-disintegrating, low-carbon, ferrochrome slags, graded from M100 to M175, respectively, were obtained in the...  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