全文获取类型
收费全文 | 151601篇 |
免费 | 2041篇 |
国内免费 | 653篇 |
专业分类
电工技术 | 3112篇 |
综合类 | 187篇 |
化学工业 | 23988篇 |
金属工艺 | 5778篇 |
机械仪表 | 4941篇 |
建筑科学 | 4416篇 |
矿业工程 | 377篇 |
能源动力 | 3926篇 |
轻工业 | 17305篇 |
水利工程 | 1139篇 |
石油天然气 | 618篇 |
武器工业 | 5篇 |
无线电 | 20491篇 |
一般工业技术 | 28841篇 |
冶金工业 | 23749篇 |
原子能技术 | 2341篇 |
自动化技术 | 13081篇 |
出版年
2019年 | 834篇 |
2018年 | 1081篇 |
2017年 | 1131篇 |
2016年 | 1268篇 |
2015年 | 1063篇 |
2014年 | 1795篇 |
2013年 | 6575篇 |
2012年 | 3191篇 |
2011年 | 4608篇 |
2010年 | 3594篇 |
2009年 | 4151篇 |
2008年 | 4647篇 |
2007年 | 4913篇 |
2006年 | 4350篇 |
2005年 | 4108篇 |
2004年 | 4002篇 |
2003年 | 3899篇 |
2002年 | 3928篇 |
2001年 | 3980篇 |
2000年 | 3742篇 |
1999年 | 3691篇 |
1998年 | 6631篇 |
1997年 | 5227篇 |
1996年 | 4460篇 |
1995年 | 3709篇 |
1994年 | 3358篇 |
1993年 | 3184篇 |
1992年 | 2782篇 |
1991年 | 2690篇 |
1990年 | 2628篇 |
1989年 | 2614篇 |
1988年 | 2459篇 |
1987年 | 2166篇 |
1986年 | 2114篇 |
1985年 | 2556篇 |
1984年 | 2316篇 |
1983年 | 2193篇 |
1982年 | 2068篇 |
1981年 | 1991篇 |
1980年 | 1860篇 |
1979年 | 1874篇 |
1978年 | 1770篇 |
1977年 | 2085篇 |
1976年 | 2562篇 |
1975年 | 1583篇 |
1974年 | 1430篇 |
1973年 | 1453篇 |
1972年 | 1196篇 |
1971年 | 1115篇 |
1970年 | 948篇 |
排序方式: 共有10000条查询结果,搜索用时 943 毫秒
151.
Sun J. Gardner M.K. Liu J.W.S. 《IEEE transactions on pattern analysis and machine intelligence》1997,23(10):603-615
The workload of many real time systems can be characterized as a set of preemptable jobs with linear precedence constraints. Typically their execution times are only known to lie within a range of values. In addition, jobs share resources and access to the resources must be synchronized to ensure the integrity of the system. The paper is concerned with the schedulability of such jobs when scheduled on a priority driven basis. It describes three algorithms for computing upper bounds on the completion times of jobs that have arbitrary release times and priorities. The first two are simple but do not yield sufficiently tight bounds, while the last one yields the tightest bounds but has the greatest complexity 相似文献
152.
153.
Recent observations at operating plants and subsequent US NRC requirements have identified flow stratification in surge lines as a phenomenon that must be considered in the design basis of surge lines. To address these concerns, the stratified loading conditions were included in the design of YGN 3 and 4 surge line as a design basis transient and pipe temperature and displacement measurement were taken during YGN 3 pre-core hot functional testing to determine the degree of surge line flow stratification. The measured displacements and temperatures were extensively reviewed and evaluated in detail: (1) to verify the validity of the thermal hydraulic model used to predict the pipe top-to-bottom temperature differentials; (2) to analytically correlate measured surge line temperatures and displacements; and (3) to confirm the validity of the stratified flow analysis procedure. This paper shows that the stratified flow phenomenon is generic and therefore generic loadings can be developed and evaluated for the surge line analyses. 相似文献
154.
A study was undertaken to determine fertility in a group of females who as children had been operated on for appendicitis. The 134 women operated on for appendicitis were reviewed. Their ages ranged from 2-18 years at the time of appendectomy. Our data show that perforated appendicitis before puberty has little if any role in the etiology of tubal infertility. 相似文献
155.
This paper presents the design criteria, procedure, and implementation of a soft-switched power-factor-correction (PFC) circuit based on the extended-period quasi-resonant (EPQR) principles. All power electronic devices including switches and diodes in the circuit are fully soft switched. The design method is demonstrated in a prototype circuit. The operating principles are confirmed with computer simulation and experimental results. A comparison of the EP-QR operation and zero-voltage-transition (ZVT) pulse-width modulation (PWM) method 相似文献
156.
A monitoring of tool wear in different cutting operations has been studied for many years. Special techniques have been used to detect a wear status basing upon cutting forces, acoustic emission, temperature, torque and power, vibration, noise and acceleration sensors. The adapting of a proper prediction method allows to solve problems of an automatic supervision in Computer Integrated Manufacturing systems. A task of the abrasive edge wear index prediction can be formulated as follows: disposing by the data collection of the edge wear status in a time period preceding the concerning the wear status in the successive time period embraced by the prediction method. 相似文献
157.
Douay M. Xie W.X. Taunay T. Bernage P. Niay P. Cordier P. Poumellec B. Dong L. Bayon J.F. Poignant H. Delevaque E. 《Lightwave Technology, Journal of》1997,15(8):1329-1342
A comprehensive survey of photosensitivity in silica glasses and optical fiber is reviewed. Recent work on understanding the mechanisms contributing to germanium or aluminum doped fiber photosensitivity is discussed within the framework of photoelastic densification models 相似文献
158.
159.
For two applications of fuel cells (SOFC and IMFC) system configurations and energy balances are presented. A decentralized combined heat and power plant on SOFC basis can be designed as a flexible system with high efficiency. A drive system with methanol reformer and fuel cell (IMFC) in comparison with a natural gas combustion engine has lower energy comsumption and much lower emissions. 相似文献
160.
Carin L. Felsen L.B. Kralj D.R. Oh H.S. Lee W.C. Unnikrishna Pillai S. 《Antennas and Propagation, IEEE Transactions on》1997,45(4):592-600
Phase-space data processing is receiving increased attention because or its potential for furnishing new discriminants relating to classification and identification of targets and other scattering environments. Primary emphasis has been on time-frequency processing because of its impact on transient, especially wideband, short-pulse excitations. Here, we investigate the windowed Fourier transform, the wavelet transform, and model based superresolution algorithms within the context of a fully quantified and calibrated test problem investigated by us previously: two-dimensional (2-D) short-pulse plane wave scattering by a finite periodic array of perfectly conducting coplanar flat strips. Because the forward problem has been fully calibrated and parametrized, some quantitative measures can be assigned with respect to the tradeoffs of these time-frequency algorithms, yielding tentative performance assessments of the tested processing algorithms 相似文献