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   63904篇
  免费   8301篇
  国内免费   4231篇
电工技术   5552篇
综合类   7714篇
化学工业   9888篇
金属工艺   2294篇
机械仪表   5522篇
建筑科学   4066篇
矿业工程   510篇
能源动力   3469篇
轻工业   6639篇
水利工程   1430篇
石油天然气   988篇
武器工业   144篇
无线电   6318篇
一般工业技术   8642篇
冶金工业   667篇
原子能技术   241篇
自动化技术   12352篇
  2024年   353篇
  2023年   1755篇
  2022年   2422篇
  2021年   2826篇
  2020年   2923篇
  2019年   2076篇
  2018年   2064篇
  2017年   2234篇
  2016年   2256篇
  2015年   2137篇
  2014年   4336篇
  2013年   5452篇
  2012年   7809篇
  2011年   6967篇
  2010年   5572篇
  2009年   5207篇
  2008年   2942篇
  2007年   4580篇
  2006年   4513篇
  2005年   1975篇
  2004年   985篇
  2003年   635篇
  2002年   547篇
  2001年   451篇
  2000年   500篇
  1999年   420篇
  1998年   356篇
  1997年   283篇
  1996年   231篇
  1995年   163篇
  1994年   121篇
  1993年   152篇
  1992年   123篇
  1991年   96篇
  1990年   91篇
  1989年   69篇
  1988年   117篇
  1987年   222篇
  1986年   214篇
  1985年   56篇
  1984年   35篇
  1983年   25篇
  1982年   24篇
  1981年   28篇
  1980年   24篇
  1979年   33篇
  1978年   16篇
  1977年   3篇
  1976年   5篇
  1951年   12篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
This paper considers the scheduling problem of minimizing earliness–tardiness (E/T) on a single batch processing machine with a common due date. The problem is extended to the environment of non-identical job sizes. First, a mathematical model is formulated, which is tested effectively under IBM ILOG CPLEX using the constraint programming solver. Then several optimal properties are given to schedule batches effectively, and by introducing the concept of ARB (Attribute Ratio of Batch), it is proven that the ARB of each batch should be made as small as possible in order to minimize the objective, designed as the heuristic information for assigning jobs into batches. Based on these properties, a heuristic algorithm MARB (Minimum Attribute Ratio of Batch) for batch forming is proposed, and a hybrid genetic algorithm is developed for the problem under study by combining GA (genetic algorithm) with MARB. Experimental results demonstrate that the proposed algorithm outperforms other algorithms in the literature, both for small and large problem instances.  相似文献   
2.
3.
The top illuminated organic photodetectors (OPDs) with a Dielectric/Metal/Dielectric (DMD) transparent anode are fabricated. The transparent electrode is composed of molybdenum trioxide (MoO3)/silver (Ag)/MoO3 layers and zinc oxide (ZnO)/aluminum (Al) is used for bottom cathode. The optimized DMD electrode has an optical transmittance of 85.7% at the wavelength of 546 nm and sheet resistance of ∼6 Ω/sq. The fabricated OPDs exhibit a high detectivity and wide range linearity.  相似文献   
4.
He-3 is generally recognized for its ability to provide more excellent thermophysical performance than He-4, especially in the 4 K temperature range. However, this was not always the case in our preliminary experiments on a three-stage Stirling-type pulse tube cryocooler (SPTC). Our ongoing studies, as reported in this paper, demonstrate that the different working fluids also affect the performance through their phase shifting capability. This feature has been passed over in large part by researchers considering refrigerant substitution. Unlike previous theoretical analyses that focus primarily on regenerator losses, this report investigates the effects of the working fluid on the phase angle at the cold end in order to quantitatively reveal the relationship between the lowest attainable temperature and the cooling capacity. The analysis agrees well with our experimental results on a three-stage SPTC. While running with the operating parameters optimized for He-3, the lowest temperature of the SPTC decreased from 5.4 K down to 4.03 K. This is the lowest refrigeration temperature ever achieved with a three-stage SPTC.  相似文献   
5.
6.
7.
解释了跨界借鉴的含义,并阐述了其在建筑立面创新设计中运用的可能性和积极意义。通过案例分析,提出建筑立面跨界借鉴的内容和方式。  相似文献   
8.
The electromagnetic shielding effectiveness of kenaf fiber based composites with different iron oxide impregnation levels was investigated. The kenaf fibers were retted for removing the lignin and extractives from the fibers and magnetized. Using the unsaturated polyester and the magnetized fibers, kenaf fiber based composites were manufactured by the compression molding process. The transmission energies of the composites were characterized when the composite samples were exposed under the irradiation of electromagnetic (EM) wave with a variable frequency from 9 GHz to 11 GHz. Using the Scanning Electron Microscope (SEM), the iron oxide nanoparticles were observed on the surfaces and inside the micropore structures of single fibers. As the Fe content increased from 0% to 6.8%, 15.9% and 18.0%, the total surface free energy of kenaf fibers with the magnetizing treatments increased from 44.8 mJ/m2 to 46.1 mJ/m2, 48.8 mJ/m2 and 53.0 mJ/m2, respectively, while the modulus of elasticity reduced from 2875 MPa to 2729 MPa, 2487 MPa and 2007 MPa, respectively. Meanwhile, the shielding effectiveness was increased from 30–50% to 60–70%, 65–75% and 70–80%, respectively.  相似文献   
9.
10.
Ji  Chengang  Yang  Chenying  Shen  Weidong  Lee  Kyu-Tae  Zhang  Yueguang  Liu  Xu  Guo  L. Jay 《Nano Research》2019,12(3):543-548

We present a new scheme for visibly-opaque but near-infrared-transmitting filters involving 7 layers based on one-dimensional ternary photonic crystals, with capabilities in reaching nearly 100% transmission efficiency in the near-infrared region. Different decorative reflection colors can be created by adding additional three layers while maintaining the near-infrared transmission performance. In addition, our proposed structural colors show great angular insensitivity up to ±60° for both transverse electric and transverse magnetic polarizations, which are highly desired in various fields. The facile strategy described here involves a simple deposition method for the fabrication, thereby having great potential in diverse applications such as image sensors, anti-counterfeit tag, and optical measurement systems.

  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