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   580551篇
  免费   7635篇
  国内免费   1034篇
电工技术   10698篇
综合类   488篇
化学工业   92180篇
金属工艺   23722篇
机械仪表   18813篇
建筑科学   13368篇
矿业工程   4417篇
能源动力   14926篇
轻工业   47030篇
水利工程   7076篇
石油天然气   15005篇
武器工业   39篇
无线电   61452篇
一般工业技术   118839篇
冶金工业   98350篇
原子能技术   14778篇
自动化技术   48039篇
  2021年   5706篇
  2020年   4201篇
  2019年   5485篇
  2018年   9518篇
  2017年   9729篇
  2016年   10161篇
  2015年   6293篇
  2014年   10665篇
  2013年   27133篇
  2012年   16428篇
  2011年   22015篇
  2010年   17629篇
  2009年   19497篇
  2008年   19806篇
  2007年   19467篇
  2006年   16882篇
  2005年   15340篇
  2004年   14491篇
  2003年   14140篇
  2002年   13676篇
  2001年   13128篇
  2000年   12581篇
  1999年   12271篇
  1998年   27924篇
  1997年   20280篇
  1996年   15904篇
  1995年   12249篇
  1994年   11085篇
  1993年   10815篇
  1992年   8544篇
  1991年   8240篇
  1990年   8191篇
  1989年   7930篇
  1988年   7615篇
  1987年   6887篇
  1986年   6671篇
  1985年   7548篇
  1984年   6865篇
  1983年   6569篇
  1982年   5927篇
  1981年   6039篇
  1980年   5752篇
  1979年   5872篇
  1978年   5770篇
  1977年   6275篇
  1976年   7822篇
  1975年   5207篇
  1974年   4994篇
  1973年   5075篇
  1972年   4349篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Journal of Communications Technology and Electronics - Abstract—The two-dimensional diffraction problem of a plane polarized TM-wave on two identical solid silver nanocylinders is considered....  相似文献   
82.
Hassan  Lovelu  Khan  K. A. 《Microsystem Technologies》2020,26(3):1031-1041

The efficiency of any electric cell or battery is very important. To keep it in mind it has been studied the columbic efficiency, voltaic efficiency and energy efficiency of a PKL (Pathor Kuchi Leaf) Quasi Voltaic Cell or Modified Voltaic Cell. It was found that the columbic efficiency data illustrated that this efficiency was lower comparing to other efficiencies may be the absence of salt bridge or separator between the electrodes. Because, our designed and fabricated PKL cell does not have any salt bridge. So that the internal resistance is lower than the traditional voltaic cell and as a result more current was found. The voltage and current changes with time and I–V characteristics for PKL unit cell, module, panel and array have also been studied. It is shown that the voltaic and energy efficiency have been studied. However, the highest efficiency was obtained for 40% PKL sap with 5% secondary salt in 55% aqueous solution, which implies that the concentration of PKL juice can play an important role regarding efficiency. It was also found that the average energy efficiency was 97.43% and it was also found that the average voltaic efficiency was 57.29%. Finally, morphological study FESEM (Field Emission Scanning Electron Microscopy) has also been performed. It is seen that the results confirmed that Zn was deposited on the Cu surface during the electro deposition process in PKL solution. Using AAS, it has been measured the concentration of [Cu2+] as a reactant ion and the concentration of [Zn2+] as a product ion those have been tabulated and graphically discussed. The variation of pH has also been studied with time and which was also tabulated and graphically discussed.

  相似文献   
83.
84.
RCAS1 is a protein that participates in regulation of the tumor microenvironment and its immune responses, all in order to evade the immune system. The aim of this study was to analyze RCAS1 expression in urothelial bladder cancer cells (and in fibroblasts and macrophages of the tumor stroma) and its relationship with the histological pattern of malignancy. Eighty-three postcystectomy patients were enrolled. We analyzed the histological maturity (grade), progress (pT stage), tissue invasion type (TIT), nonclassic differentiation number (NDN), and the ability to metastasize (pN). The expression of RCAS1 protein was analyzed by immunohistochemistry. Indicators of histological malignancy were observed solely in association with the RCAS1 expression in cells in the border parts (BPs) of the tumor. Histological malignancy of the tumor, indicated by the pT and pN, and metastasis-free survival time, correlated significantly with RCAS1 expression in tumor neoplastic cells, whereas malignancy determined by grade, TIT, and NDN correlated with RCAS1 expression in fibroblasts and macrophages in the tumor microenvironment. These findings suggest that the increased RCAS1 expression depends on its cellular source and that RCAS1 expression itself is a component of various signaling pathways. The immune escape occurs within the tumor BPs, where the increase in the RCAS1 expression occurs within tumor cells and stromal cells in its microenvironment. We conclude that the histological pattern of tumor malignancy, indicated by grade, TIT, NDN, pT, and pN is a morphological indicator of immune escape.  相似文献   
85.
Number entry is a ubiquitous activity and is often performed in safety- and mission-critical procedures, such as healthcare, science, finance, aviation and in many other areas. We show that Monte Carlo methods can quickly and easily compare the reliability of different number entry systems. A surprising finding is that many common, widely used systems are defective, and induce unnecessary human error. We show that Monte Carlo methods enable designers to explore the implications of normal and unexpected operator behaviour, and to design systems to be more resilient to use error. We demonstrate novel designs with improved resilience, implying that the common problems identified and the errors they induce are avoidable.  相似文献   
86.
87.

Stability constants and formation enthalpies of supramolecular complexes of crown ethers and their cyclic and acyclic analogues are determined on the basis of experimental data obtained by different physicochemical methods in the terms of a general approach developed and implemented in the ChemEqui software package. The established regularities of variation of stability of complexes are discussed as dependent on the ligand structure, nature of the cation, solvent, and anion. The applicability of the suggested method of determining complexation selectivity is shown for multicomponent equilibria in solutions.

  相似文献   
88.
A layer-by-layer analysis of the structures, the phase compositions, and the defect substructures of differentially hardened rails has been carried by optical and transmission electron microscopy. It is found that the material volume of the rail head fillet is cooled faster than the volume located along the central axis.  相似文献   
89.
90.
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