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   254978篇
  免费   4007篇
  国内免费   1031篇
电工技术   4348篇
综合类   204篇
化学工业   37717篇
金属工艺   8272篇
机械仪表   7322篇
建筑科学   6876篇
矿业工程   544篇
能源动力   7296篇
轻工业   29238篇
水利工程   2154篇
石油天然气   1867篇
武器工业   6篇
无线电   33488篇
一般工业技术   46669篇
冶金工业   47114篇
原子能技术   3375篇
自动化技术   23526篇
  2021年   1880篇
  2020年   1415篇
  2019年   1733篇
  2018年   2701篇
  2017年   2720篇
  2016年   3013篇
  2015年   2275篇
  2014年   3775篇
  2013年   12173篇
  2012年   6908篇
  2011年   9863篇
  2010年   7585篇
  2009年   8516篇
  2008年   9050篇
  2007年   9063篇
  2006年   8346篇
  2005年   7544篇
  2004年   7275篇
  2003年   7135篇
  2002年   6652篇
  2001年   7058篇
  2000年   6359篇
  1999年   6860篇
  1998年   16583篇
  1997年   11514篇
  1996年   8678篇
  1995年   6597篇
  1994年   5739篇
  1993年   5606篇
  1992年   4003篇
  1991年   3785篇
  1990年   3555篇
  1989年   3376篇
  1988年   3288篇
  1987年   2604篇
  1986年   2497篇
  1985年   3162篇
  1984年   2804篇
  1983年   2563篇
  1982年   2349篇
  1981年   2395篇
  1980年   2212篇
  1979年   2048篇
  1978年   1880篇
  1977年   2185篇
  1976年   2747篇
  1975年   1585篇
  1974年   1489篇
  1973年   1560篇
  1972年   1144篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
G. C. Bakos   《Applied Energy》2002,72(3-4):609-619
This paper deals with the technical feasibility and economic viability of a grid connected wind-energy conversion system (WECS) used to cover the energy demand of an average habitable dwelling. The various parts of the wind-energy system are described and the useful electrical energy production is determined using a simulation program based on the Monte Carlo method. An economic analysis of the WEC system is performed using a computerized assessment tool. Important financial indices are calculated and financial scenarios investigated.  相似文献   
52.
In this letter, a concise process technology is proposed for the first time to enable the fabrication of good quality three-dimensional (3-D) suspended radio frequency (RF) micro-inductors on bulk silicon, without utilizing the lithography process on sidewall and trench-bottom patterning. Samples were fabricated to demonstrate the applicability of the proposed process technology.  相似文献   
53.
'Software defined radio' (SDR) is a technology that will appear in future generations of mobile phones, i.e. following the third-generation mobile phone technology that is currently being defined and developed. Early versions of 'pragmatic' SDR will allow the terminal to be reconfigured at any level of its protocol stack. Ultimately, the 'pure' SDR technology will allow a mobile phone or terminal to have its air interface software configured or reconfigured by other software (or software parameters) that have been downloaded to the terminal, e.g. over the air, or from a remote server via the Internet and one's personal computer (PC). A number of security issues arise with downloaded code that implements the air interface functions, and these may not be obvious simply from looking at the way PC software is updated on-line today. This paper starts with an outline of the code that allows a mobile phone to operate over a particular air interface. This sets the baseline for a discussion of the security issues surrounding the change of this code from one that is fixed and downloaded once only, to code that is reconfigurable during the life of a product.  相似文献   
54.
55.
56.
This paper describes a sequential tripping strategy used in a wide area back-up protection expert system (BPES) to combat situations in which protection relays have maloperated or information is missing. The BPES is an innovative back-up protection scheme designed to prevent the occurrence of widespread blackouts. The BPES evaluates the certainty that transmission lines are likely to be affected by the fault and uses a sequential tripping strategy to isolate the fault if a firm decision is not available due to maloperated relays and/or missing information. The mode of analysis and the sequential tripping strategy ensures that the BPES will clear a fault at minimum risk to the network. An example is included to demonstrate how the certainty factor based sequential tripping strategy is employed by the BPES to clear a fault which occurred on the South Western part of the UK National Grid System  相似文献   
57.
Eliminating the adoption barrier   总被引:1,自引:0,他引:1  
Krueger  C. 《Software, IEEE》2002,19(4):29-31
  相似文献   
58.
The usefulness of selected PCR-protocols for the detection of Salmonella in 117 samples of animal origin (17 raw minced meat, 27 raw chicken meat, 8 raw sausages, and 25 egg samples, as well as 18 poultry faecal, and caecal swabs samples) and DNA-fingerprinting typing is shown. To establish an accurate PCR-procedure for Salmonella detection the following parameters were evaluated: two pre-PCR concentration procedures, centrifugation and immunomagnetic separation (IMS) using Dynabeads anti- Salmonella; the specificity and sensitivity of 10 sets of primers; and different conditions of the amplification reaction. In light of the results obtained from the use of PCR-based procedures alone or in combination with conventional methods, the following findings can be underlined: First, IMS is more efficient than centrifugation in the recovery of Salmonella. Second, the selected IMS/PCR-detection protocol is less time-consuming (45 h) than the IMS/culture procedure (90 h), and a good concordance between them was found when the Kappa coefficient was calculated (0·87). Third, PCR-ribotyping technique showed a very low discrimination power, being able to differentiate only three profiles. Fourth, RAPD technique using specific primers supports previous works in which it was proposed as a simple and useful tool for discriminating isolates between and within serotypes. Fifth, The efficiency, rapidity, and flexibility of the PCR-protocols applied were high, and they can be performed using two PCR-programs and the same basic equipment.  相似文献   
59.
60.
We examine the symmetry-breaking transitions in equilibrium shapes of coherent precipitates in two-dimensional (2-D) systems under a plane-strain condition with the principal misfit strain components ε* xx and ε* yy . For systems with cubic elastic moduli, we first show all the shape transitions associated with different values of t=ε* yy /ε* xx . We also characterize each of these transitions, by studying its dependence on elastic anisotropy and inhomogeneity. For systems with dilatational misfit (t=1) and those with pure shear misfit (t=−1), the transition is from an equiaxed shape to an elongated shape, resulting in a break in rotational symmetry. For systems with nondilatational misfit (−1<t<1; t ≠ 0), the transition involves a break in mirror symmetries normal to the x- and y-axes. The transition is continuous in all cases, except when 0<t<1. For systems which allow an invariant line (−1≤t<0), the critical size increases with an increase in the particle stiffness. However, for systems which do not allow an invariant line (0<t≤1), the critical size first decreases, reaches a minimum, and then starts increasing with increasing particle stiffness; moreover, the transition is also forbidden when the particle stiffness is greater than a critical value.  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