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   15720篇
  免费   938篇
  国内免费   28篇
电工技术   192篇
综合类   43篇
化学工业   3354篇
金属工艺   316篇
机械仪表   317篇
建筑科学   709篇
矿业工程   47篇
能源动力   519篇
轻工业   1258篇
水利工程   124篇
石油天然气   52篇
无线电   1170篇
一般工业技术   2987篇
冶金工业   2311篇
原子能技术   121篇
自动化技术   3166篇
  2023年   167篇
  2022年   360篇
  2021年   574篇
  2020年   376篇
  2019年   381篇
  2018年   499篇
  2017年   465篇
  2016年   534篇
  2015年   466篇
  2014年   599篇
  2013年   1068篇
  2012年   980篇
  2011年   1169篇
  2010年   813篇
  2009年   755篇
  2008年   793篇
  2007年   785篇
  2006年   590篇
  2005年   516篇
  2004年   385篇
  2003年   391篇
  2002年   348篇
  2001年   222篇
  2000年   191篇
  1999年   216篇
  1998年   239篇
  1997年   203篇
  1996年   195篇
  1995年   189篇
  1994年   157篇
  1993年   157篇
  1992年   125篇
  1991年   80篇
  1990年   127篇
  1989年   121篇
  1988年   84篇
  1987年   98篇
  1986年   102篇
  1985年   105篇
  1984年   92篇
  1983年   80篇
  1982年   100篇
  1981年   93篇
  1980年   75篇
  1979年   71篇
  1978年   62篇
  1977年   80篇
  1976年   64篇
  1975年   46篇
  1974年   42篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Daniel  E.M. Railton  C.J. 《Electronics letters》1989,25(20):1340-1341
Many analyses of boxed microstrip discontinuities require the location of large numbers of high-order modes. Using Sturm-Liouville theory, this letter derives a relationship between microstrip modes and slab-loaded guide modes, leading to an efficient mode location algorithm for microstrip, including microstrip with finite strip thickness.<>  相似文献   
72.
Global competition, commitment to the Kyoto Protocol and a deregulated, integrated European electricity market will in all probability increase the demand for energy efficiency on the part of companies in Sweden. Investment decisions are an important part of meeting the new demands, because they decide the future efficiency of industrial energy systems. The objective of this study is to investigate, from a managerial perspective, the need to improve decision support in some industries, which can help to facilitate and improve investment decisions concerning energy efficiency. This work has been conducted through in-depth interviews with representatives for a number of energy-intensive companies and non-energy-intensive companies from different sectors. One need that was identified was the improvement of working methods in order to support the decision-making process. Here, external players seem to be playing an increasingly important role. Access to correct information, better follow-up activities, and transparent, understandable calculations are also considered to be important. The study will form the foundation for subsequent work on decision support and energy efficiency in industry.  相似文献   
73.
74.
75.
Fitness development and performance assessment of elite athletes requires an understanding of many physiological factors, many of these are direct and indirect measures of athlete energy expenditure. Many methods are physiological factor assessments and require the athlete to be constrained by laboratory equipment or periodic interruption of activity to take measurements such as blood samples are required to be taken. This paper presents a method that is entirely ambulatory and noninvasive, using microelectromechanical systems (MEMS) accelerometers. The commonly used output of commercial accelerometer-based devices (known as "counts") cannot discriminate activity intensity for the activities of interest. This, in conjunction with variability in output from different systems and lack of commonality across manufacturers, limits the usefulness of commercial devices. This paper identifies anthropometric and kinematic sources of inter-athlete variability in accelerometer output, leading to an alternate energy expenditure estimator based mainly on step frequency modified by anthropometric measures. This energy expenditure estimator is more robust and not influenced by many sources of variability that affect the currently used estimator. In this system, low-power signal processing was implemented to extract both the energy estimator and other information of physiological and statistical interest  相似文献   
76.
77.
Forensic psychology has made important gains in professional recognition and stature in the courts, resulting in increasing demands for mobility of expertise. Current regulations regarding the interjurisdictional temporary forensic practice of psychology, however, are characterized by variability of regulations, ambiguity and inaccessibility, and continuing total barriers. A uniform, well-reasoned policy is needed. A conceptual basis for such a policy is provided by a discussion of licensing rationales and the application of these to forensic practice. Uniformity, public and professional protection, and practicability are identified as fundamental regulatory criteria. A Model Rule Regarding the Temporary Forensic Practice of Psychology is proposed for adoption by state licensing boards on a nationwide basis. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
78.
79.
ZnO is a highly efficient photon emitter, and has optical and piezoelectric properties that are attractive for a variety of applications in sensors and potentially optoelectronic devices such as emitters. Due to its identical stacking order and close lattice match to GaN, it is also being developed as a substrate material for GaN epitaxy. However, the surface finish of the ZnO is such that much of the damage induced by sawing and follow up mechanical polishing remains. We developed a thermal treatment method to eliminate surface damage on the 0 face of ZnO (0 0 0 1) to prepare it for epitaxial growth. Atomic force microscopy images of ZnO (0 0 0 1) annealed at 1050 °C for 3 h etc. show that residual scratches from mechanical polishing are removed and atomically flat, terrace-like surfaces are attained. In addition, low-temperature photoluminescence and high-resolution X-ray diffraction measurements have been employed to investigate the effect of annealing on ZnO substrates.  相似文献   
80.
We discuss the construction of optimized electronic filters using inverse scattering methods. We study a wide range of densities and temperatures, room temperature included. Discretization methods of the potential (including the self-consistent potential of the conduction electrons) are worked out that retain all its properties.  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