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   266340篇
  免费   2521篇
  国内免费   286篇
电工技术   4245篇
综合类   109篇
化学工业   43971篇
金属工艺   15454篇
机械仪表   10443篇
建筑科学   5169篇
矿业工程   3808篇
能源动力   4355篇
轻工业   11313篇
水利工程   4201篇
石油天然气   13062篇
武器工业   29篇
无线电   21731篇
一般工业技术   65678篇
冶金工业   35056篇
原子能技术   11317篇
自动化技术   19206篇
  2021年   3190篇
  2019年   3088篇
  2018年   5834篇
  2017年   6083篇
  2016年   6517篇
  2015年   3463篇
  2014年   5827篇
  2013年   11126篇
  2012年   8138篇
  2011年   10002篇
  2010年   8038篇
  2009年   8896篇
  2008年   9013篇
  2007年   8594篇
  2006年   7036篇
  2005年   6136篇
  2004年   5949篇
  2003年   5723篇
  2002年   5540篇
  2001年   5235篇
  2000年   5248篇
  1999年   4588篇
  1998年   7878篇
  1997年   6292篇
  1996年   4795篇
  1995年   3926篇
  1994年   3679篇
  1993年   3879篇
  1992年   3392篇
  1991年   3510篇
  1990年   3612篇
  1989年   3499篇
  1988年   3389篇
  1987年   3369篇
  1986年   3269篇
  1985年   3446篇
  1984年   3378篇
  1983年   3257篇
  1982年   3081篇
  1981年   3142篇
  1980年   3154篇
  1979年   3348篇
  1978年   3577篇
  1977年   3570篇
  1976年   4045篇
  1975年   3287篇
  1974年   3364篇
  1973年   3402篇
  1972年   3037篇
  1971年   2804篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Reducible rank codes and their applications to cryptography   总被引:2,自引:0,他引:2  
We present a new family of so-called reducible rank codes which are a generalization of rank product codes . This family includes maximal rank distance (MRD) codes for lengths n>N in the field F/sub N/. We give methods for encoding and decoding reducible rank codes. A public key cryptosystem based on these codes and on the idea of a column scrambler is proposed. The column scrambler "mixes" columns of a generator (parity-check) matrix of a code. It makes the system more resistant to structural attacks such as Gibson's attacks. Possible attacks on the system are thoroughly studied. The system is found to be secure against known attacks for public keys of about 16 kbits and greater.  相似文献   
132.
A new and original method of calibrating helium leaks that makes it possible to take into account the existence of a number of auxiliary phenomena is described. For this purpose, a hollow leak the purpose of which is to reproduce only desorbed gas flows, is introduced into the vacuum system of the calibration bench. Analysis of the results of corresponding cumulation measurements makes it possible to introduce corrections for these phenomena.  相似文献   
133.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form.  相似文献   
134.
A model is formulated that describes how radiation-induced charge accumulates in the gate oxide of a MOS structure and how it decays through tunneling and thermal emission. The model is used in a numerical analysis of the x-ray or UV adjustment of threshold voltage in MOS-circuit manufacture. The limits of this process technique are evaluated.  相似文献   
135.
The magneto-optical Kerr effect for red (628 nm) and green (532 nm) light is used to study magnetization processes in 2D magnonic crystals obtained by etching pits with the diameter D ≈ 32 μm to a depth of t ≤ 2 μm in a 16.1-μm-thick film of yttrium iron garnet (YIG). Hysteresis loops obtained in the case of the inplane crystal magnetization at 628 nm are characterized by lower saturation fields H s and higher remanent magnetizations than those obtained at 532 nm, a result that is attributed to different absorption coefficients of the YIG film at these wavelengths. This difference between the magnetization curves reflects the fact that the magnonic-crystal surface probed with the green light makes a greater contribution to the magneto-optical Kerr effect. Therefore, the green light is more sensitive to the demagnetizing fields, which govern magnetization processes in the magnonic crystals.  相似文献   
136.
The electrical properties and microstructure of (Ba,Y)TiO3 PTCR ceramics were studied. The results indicate that the Mn ions increase the intergranular barrier height and produce a high-resistance layer on the grain surface. The temperature-dependent resistances of the grain bulk, surface layer, and grain boundaries, the temperature coefficient of resistance, and the magnitude of the varistor effect were assessed as a function of Mn content.  相似文献   
137.
This work presents a systematic comparative study of the influence of various process options on the analog and RF properties of fully depleted (FD) silicon-on-insulator (SOI), partially depleted (PD) SOI, and bulk MOSFET's with gate lengths down to 0.08 /spl mu/m. We introduce the transconductance-over-drain current ratio and Early voltage as key figures of merits for the analog MOS performance and the gain and the transition and maximum frequencies for RF performances and link them to device engineering. Specifically, we investigate the effects of HALO implantation in FD, PD, and bulk devices, of film thickness in FD, of substrate doping in SOI, and of nonstandard channel engineering (i.e., asymmetric Graded-channel MOSFETs and gate-body contacted DTMOS).  相似文献   
138.
Static energy reduction techniques for microprocessor caches   总被引:1,自引:0,他引:1  
Microprocessor performance has been improved by increasing the capacity of on-chip caches. However, the performance gain comes at the price of static energy consumption due to subthreshold leakage current in cache memory arrays. This paper compares three techniques for reducing static energy consumption in on-chip level-1 and level-2 caches. One technique employs low-leakage transistors in the memory cell. Another technique, power supply switching, can be used to turn off memory cells and discard their contents. A third alternative is dynamic threshold modulation, which places memory cells in a standby state that preserves cell contents. In our experiments, we explore the energy and performance tradeoffs of these techniques. We also investigate the sensitivity of microprocessor performance and energy consumption to additional cache latency caused by leakage-reduction techniques.  相似文献   
139.
The probing of the micromechanical properties within a two‐dimensional polymer structure with sixfold symmetry fabricated via interference lithography reveals a nonuniform spatial distribution in the elastic modulus “imprinted” with an interference pattern in work reported by Tsukruk, Thomas, and co‐workers on p. 1324. The image prepared by M. Lemieux and T. Gorishnyy shows how the interference pattern is formed by three laser beams and is transferred to the solid polymer structure. The elastic and plastic properties within a two‐dimensional polymer (SU8) structure with sixfold symmetry fabricated via interference lithography are presented. There is a nonuniform spatial distribution in the elastic modulus, with a higher elastic modulus obtained for nodes (brightest regions in the laser interference pattern) and a lower elastic modulus for beams (darkest regions in the laser interference pattern) of the photopatterned films. We suggest that such a nonuniformity and unusual plastic behavior are related to the variable material properties “imprinted” by the interference pattern.  相似文献   
140.
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working defects on the behavior of structures under standard and emergency conditions. __________ Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006.  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