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   818篇
  免费   46篇
  国内免费   2篇
电工技术   18篇
化学工业   245篇
金属工艺   2篇
机械仪表   23篇
建筑科学   36篇
矿业工程   2篇
能源动力   16篇
轻工业   153篇
水利工程   2篇
石油天然气   4篇
无线电   85篇
一般工业技术   103篇
冶金工业   99篇
自动化技术   78篇
  2024年   1篇
  2023年   9篇
  2022年   54篇
  2021年   54篇
  2020年   22篇
  2019年   12篇
  2018年   19篇
  2017年   21篇
  2016年   27篇
  2015年   16篇
  2014年   27篇
  2013年   43篇
  2012年   50篇
  2011年   51篇
  2010年   24篇
  2009年   34篇
  2008年   46篇
  2007年   33篇
  2006年   23篇
  2005年   17篇
  2004年   17篇
  2003年   22篇
  2002年   20篇
  2001年   11篇
  2000年   17篇
  1999年   19篇
  1998年   46篇
  1997年   28篇
  1996年   23篇
  1995年   16篇
  1994年   10篇
  1993年   8篇
  1992年   5篇
  1991年   4篇
  1990年   4篇
  1989年   4篇
  1988年   3篇
  1987年   2篇
  1986年   2篇
  1984年   1篇
  1983年   5篇
  1982年   2篇
  1981年   2篇
  1980年   1篇
  1979年   2篇
  1977年   2篇
  1976年   5篇
  1973年   1篇
  1972年   1篇
排序方式: 共有866条查询结果,搜索用时 15 毫秒
61.
Several investigators have reported the achievement of Stage 6 object concept in a number of species of nonhuman primates. Because Stage 6 object concept implies a capacity for mental representation, such an achievement would demonstrate the presence of a crucial capacity in nonhuman primate cognition. There are, it is suggested, problems in the way nonhuman primates have been tested for Stage 6 object concept (i.e., that the tasks employed could be solved in nonrepresentational ways). The present study attempted to differentiate between representational and nonrepresentational responses in the typical task used for testing Stage 6 object concept (following the invisible displacements of an object). The performance of 2 22-mo-old Ss, a Japanese macaque and a gorilla, was compared. It was found that only the gorilla solved the task with the use of mental representation. The macaque consistently tried to solve the task by employing practical, nonrepresentational strategies. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
62.
63.
64.
The European Space Agency's Soil Moisture and Ocean Salinity satellite comprises a single payload instrument known as the Microwave Interferometric Radiometer with Aperture Synthesis (MIRAS) coupled to a PROTEUS platform. MIRAS synthesizes a large aperture from a reasonably sized 2-D array of passive microwave radiometers. By using interferometric techniques, the required coverage and spatial resolution can be achieved without the need for a large antenna. This paper describes the MIRAS instrument, its observation modes, the imaging geometry, and data products.  相似文献   
65.
A mesiodens is the most common type of supernumerary tooth present in conjunction to normal dentition. A mesiodens may commonly occur in the central region of the upper or lower jaw. A mesiodens is different from normal teeth in terms of structure and shape. The aim of this study is to evaluate the micro‐ and nanoscale structural properties of mesiodens dentin by combined small‐ and wide‐angle X‐ray scattering (SAXS/WAXS) and Fourier transform infrared (FTIR) spectroscopy. Five freshly extracted, noncarious mesiodens and five normal dentin disks prepared from human incisor teeth were compared. Using FTIR, the phosphate‐to‐amide I, carbonate‐to‐phosphate, and carbonate‐to‐amide I band area ratios and the crystallinity index were quantified. SAXS/WAXS were used to study the nanostructure of mesiodens. An increase in the mineral content in the mesiodens dentin with respect to the normal group was found. Crystallinity was also significantly increased and the protein content decreased in the mesiodens dentin compared with that of normal dentin. SAXS/WAXS results revealed that mesiodens dentin has a more calcified tissue. Further, SAXS analysis revealed a nonuniform distribution of dentin fibrils in mesiodens. Microsc. Res. Tech., 78:52–58, 2015. © 2014 Wiley Periodicals, Inc.  相似文献   
66.
Novel thiophene-based oligomer, 2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bithianaphthene (TX), was designed and synthesized, and its electrochemical and spectral properties characterised. TX was readily polymerised electrochemically to form well organized conducting homopolymer films on various solid electrode substrates. Moreover, it was successfully used for deposition by electropolymerisation of electrochemically active thin films of co-polymers with three different monomers of functionalised bis(2,2′-bithienyl)methane derivatives. It appeared that TX was an effective crosslinker and 3D promoter in these electropolymerisations involving co-monomers intrinsically showing limited aptitude for the electropolymerisation or forming polymer films of low conductivity. This attractive TX ability stems from combination of its (i) high conjugation efficiency in each of the two planar moieties, (ii) intrinsic 3D structure on account of the presence of the central node, and (iii) intrinsic regioselectivity in electropolymerisation on account of the positions of the two available free α-thiophene sites.  相似文献   
67.
68.
69.
We demonstrate for the first time herein that electrospinning of soluble crosslinked polymer particles (microgels) is feasible and that it can be used to obtain micron-sized fibers from these macromolecules. Most notably, the electrospinning approach is found to be successful also in the case of microgels bearing metal nanoclusters, and allows to prepare composite fibers containing a homogeneous dispersion of metal nanoparticles without alterations in the nanoparticle size and size distribution. Given the broad applicability of microgels as exotemplates and stabilisers for inorganic nanoparticles, the proposed preparation method stands out as a novel, general approach for the synthesis of potentially useful composite fibers containing inorganic nanoparticles.  相似文献   
70.
An online signal injection approach based on a special current transformer is proposed as part of a solution for improving the test setup of transfer function diagnostics of transformers. However, the method is general and applicable to many types of substation equipment, such as circuit breakers and transmission lines. The system allows a high-power, high-frequency test signal to be injected directly on a high-voltage bus of an energized system. Due to the self-contained nature of the injector, no external power supplies or signal generators are needed and the design does not need to be ground-referenced. The system can thus be at the bus potential. In conjunction with wireless communication for control, no isolator bushings are required and the device can be constructed as a sleeve to be mounted around the busbar. This allows for economical retrofitting to existing installations. In this paper, the operational need for such an injection device is discussed, followed by the theory behind the proposed concept. Finally, a low-voltage, optically controlled, self-powered prototype is designed and demonstrated online to show the practical validity of the concept.  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