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   405305篇
  免费   4814篇
  国内免费   1365篇
电工技术   7573篇
综合类   317篇
化学工业   60127篇
金属工艺   16459篇
机械仪表   13529篇
建筑科学   8392篇
矿业工程   2155篇
能源动力   11562篇
轻工业   28852篇
水利工程   4276篇
石油天然气   7920篇
武器工业   17篇
无线电   49300篇
一般工业技术   83205篇
冶金工业   75320篇
原子能技术   9184篇
自动化技术   33296篇
  2022年   2562篇
  2021年   3919篇
  2020年   2971篇
  2019年   3842篇
  2018年   6577篇
  2017年   6552篇
  2016年   6994篇
  2015年   4377篇
  2014年   7204篇
  2013年   20155篇
  2012年   11497篇
  2011年   15367篇
  2010年   12213篇
  2009年   13767篇
  2008年   14115篇
  2007年   13895篇
  2006年   12454篇
  2005年   11148篇
  2004年   10536篇
  2003年   10456篇
  2002年   9843篇
  2001年   9746篇
  2000年   9150篇
  1999年   9545篇
  1998年   24449篇
  1997年   16788篇
  1996年   12846篇
  1995年   9541篇
  1994年   8392篇
  1993年   8402篇
  1992年   6063篇
  1991年   5704篇
  1990年   5686篇
  1989年   5323篇
  1988年   5052篇
  1987年   4428篇
  1986年   4303篇
  1985年   4815篇
  1984年   4425篇
  1983年   3996篇
  1982年   3655篇
  1981年   3731篇
  1980年   3430篇
  1979年   3326篇
  1978年   3334篇
  1977年   3753篇
  1976年   4863篇
  1975年   2850篇
  1974年   2663篇
  1973年   2730篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Analysis of heart rate variability (HRV) with Holter monitoring is often difficult due to excessive artifacts and arrhythmias. While short sudden surges are treated successfully by most methods, slow heart rate (HR) variations, nocturnal trapezoidally-shaped HR increases and special types of arrhythmias which are similar to normal HRV fluctuations may distort further time domain and spectral analysis. This paper examines the advantages and disadvantages of different methods for preprocessing of HR data. We have developed the following approach to the analysis of HRV. (1) A combination method based on the absolute difference between HR values and both the last normal HR value and an updated mean is used for removal of artifacts and arrhythmias. This method can detect both sudden surges in HR values as well as longer periods of noise combined with slow normal variations. An additional stage of wild point removal is then optionally applied. (2) Certain special problems such as large T-waves, bigeminal rhythm, slow HR variations and nocturnal trapezoidally-shaped HR increases are also identified. Although none of the algorithms can be applied successfully to all cases, the final computer analysis for preprocessing described in the present study has proved to be superior to the simplified methods which are usually used and provides more suitable data for HRV analysis.  相似文献   
992.
A logic language is suitable for specification if it is equipped with features for data abstraction and modularization. In this paper, an effective mechanism to incorporate function and type into logic programming is presented as the means to embed data abstraction mechanism into logic programming. This incorporation is essentially based on Horn clause logic with equality and a polymorphic type system that is an extension of Mycroft and O’Keefe’s system. This paper also presents an implementation based on Warren Abstract Machine (WAM) and shows the performance, along with a comparison with WAM.  相似文献   
993.
The authors propose techniques for adaptive nonlinear cancellation of intersymbol interference (ISI) in the electrical signal at the receiver in Gb/s lightwave systems and describe several demonstrations of these techniques. Techniques for adjustable nonlinear cancellations are discussed and demonstrations of these techniques using commercially available integrated circuits (ICs) at data rates as high as 1.7 Gb/s are described. Techniques for automatic adjustment are discussed, and a demonstration of adaptive nonlinear cancellation at 450 Mb/s is described. The authors discuss how these techniques can be integrated onto the detector IC for operations at 2.5 Gb/s and higher data rates. These techniques allow a single IC detector with adaptive nonlinear cancellation to be used in long-haul and undersea lightwave systems to optimize the detector threshold and compensate for the ISI  相似文献   
994.
Translated from Izmeritel'naya Tekhnika, No. 8, pp. 11–14, August, 1992.  相似文献   
995.
Institute of Geology Siberian Branch, Academy of Sciences of the USSR, Novosibirsk. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 106–109, January-February, 1992.  相似文献   
996.
Describes a low-complexity equalization technique for improving the reliability of portable radio links in the presence of multipath time delay spread. A technique that operates on hard-limited received signals, with only the phase information available, is presented. Suboptimum receivers based on a maximum likelihood estimation criterion are discussed, including a sequence estimator and a decision feedback phase detector. A low-complexity adaptive phase equalizer structure using decision-directed phase tracking is proposed. The equalizer does not require the multiplication operations required in most conventional equalization algorithms. The author also proposes a receiver that includes a time-reversal structure and a joint estimator for optimum timing recovery and equalizer training. The time-reversal structure plays a crucial role in maximizing the compensation capability of the phase equalizer. The combined use of phase equalization and diversity reception is also considered  相似文献   
997.
The present experiments examined several strategies designed to reduce interval overconfidence in group judgments. Results consistently indicated that 3–4 person nominal groups (whose members made independent judgments and later combined the highest and lowest of these estimates into a single confidence interval) were better calibrated than individual judges and interactive groups. This pattern held even when participants were directly instructed to expand their interval estimates, or when interactive groups appointed a devil's advocate or explicitly considered reasons why their interval estimates might be too narrow. Interactive groups did not perform substantially better than individuals, although participants frequently had the impression that group judgments were far superior to individual judgments. This misperception resembles the "illusion of group effectivity" found in brainstorming research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
998.
Gradient interpenetrating polymer networks   总被引:5,自引:0,他引:5  
The methods of synthesis and properties of gradient interpenetrating polymer networks (IPN) are discussed based on literature and authors' own experimental data. Gradient IPN can be treated as a sequence of an infinite number of layers of IPNs, whose composition and properties vary gradually from the surface to the core of specimens. These are analysed the most important properties of gradient IPNs: temperature transitions, thermodynamic and physico-mechanical characteristics and the main direction of practical application of gradient IPN-based materials.  相似文献   
999.
The successful use of palladium ion implantation into polyimide to seed an electroless plated film of copper on the polyimide surface is reported. Polyimide (Hitachi PIX 3400) was implanted with palladium ions to doses of 1.5 × 1015 − 1.2 × 1017 ions cm−2 using a MEVVA ion implanter. The implanted ions acted as sites for nucleation of copper film. A copper film was then deposited on implanted polyimide using a commercial electroless plating solution. The ion energy was kept low enough to facilitate a low critical ‘seed’ threshold dose that was measured to be 3.6× 1016 Pd ions cm−2. Test patterns were made using polyimide to study the adaptability of this technique to form thick structures. Plated films were studied with optical microscopy, Rutherford Backscattering Spectrometry (RBS) and Profilometry. The adhesion of films was qualitatively assessed by a ‘scotch tape test’. The film growth (thickness) was observed to be linear with plating time. A higher implantation dose led to greater plating rates. The adhesion was found to improve with increasing dose.  相似文献   
1000.
The Constant Rate Thermal Analysis method has been used under different experimental conditions to obtain barium titanate powder of very small grain size. Both a crystallographic and a dielectric study ham been carried out on samples sintered at different temperatures. It is deduced that the formation of small coherently diffracting domains is improved by the generation of oxygen vacancies and the cubic phase stabilization depends on the coherently diffracting domain size rather than on the particle size.  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