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   86654篇
  免费   6131篇
  国内免费   2931篇
电工技术   4353篇
技术理论   9篇
综合类   4649篇
化学工业   15514篇
金属工艺   4453篇
机械仪表   5232篇
建筑科学   7030篇
矿业工程   1986篇
能源动力   2480篇
轻工业   4902篇
水利工程   1447篇
石油天然气   4540篇
武器工业   488篇
无线电   10443篇
一般工业技术   11305篇
冶金工业   4687篇
原子能技术   831篇
自动化技术   11367篇
  2024年   324篇
  2023年   1316篇
  2022年   2280篇
  2021年   3119篇
  2020年   2337篇
  2019年   2030篇
  2018年   2255篇
  2017年   2518篇
  2016年   2359篇
  2015年   2942篇
  2014年   4018篇
  2013年   5071篇
  2012年   5243篇
  2011年   5519篇
  2010年   4899篇
  2009年   4716篇
  2008年   4467篇
  2007年   4402篇
  2006年   4648篇
  2005年   4133篇
  2004年   2784篇
  2003年   2497篇
  2002年   2192篇
  2001年   2019篇
  2000年   2281篇
  1999年   2560篇
  1998年   2386篇
  1997年   1886篇
  1996年   1743篇
  1995年   1446篇
  1994年   1216篇
  1993年   880篇
  1992年   655篇
  1991年   543篇
  1990年   409篇
  1989年   367篇
  1988年   319篇
  1987年   175篇
  1986年   165篇
  1985年   112篇
  1984年   98篇
  1983年   63篇
  1982年   60篇
  1981年   54篇
  1980年   38篇
  1979年   32篇
  1978年   13篇
  1977年   33篇
  1976年   16篇
  1975年   15篇
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
81.
High density peptide and oligonucleotide chips are fabricated using semiconductor-based technologies. These chips have a variety of biological applications.  相似文献   
82.
用高温X射线衍射方法对磷酸锆钡钾系统陶瓷材料的各向异性热膨胀作了研究.对七个组份试样的77套高温X射线衍射图作了仔细的指标化和精密点阵常数测定.点阵常数随温度作非线性变化·对K_2xBa_1-xZr_4(PO_4)_6的不同组份不同温度(300~1300K)的热膨胀系数。α_a、α_c、 作了测定·该系统零膨胀陶瓷的组份为K_1.16Ba_0.42Zr_4(PO_4)_6(x=0.58)  相似文献   
83.
90°分束偏光镜光强分束比研究   总被引:7,自引:1,他引:6       下载免费PDF全文
吴福全  黄家寅 《激光技术》1994,18(5):310-312
给出了90°分束偏光镜的e,o光光强分束比的计算公式,以及光强分束比随光波长的变化曲线;在6328Å测得的光强分束比与计算值是一致的。  相似文献   
84.
Several fly ash samples from different countries were analyzed for dibromopolychlorodibenzo-p-dioxins and -dibenzofurans (DBPCDD/Fs) using capillary column gas chromatography/high-resolution mass spectrometry. Concentrations of these compounds ranged from low to high parts-per-trillion (pptr) depending on the location where the samples were collected. The mass spectrometer, operated at greater than 10,000 mass resolution in combination with the high resolving power of capillary column GC, permitted characterization of DBPCDD/Fs in municipal waste incinerator fly ash for the first time. The isomer patterns of tetra- through octa-congener groups of DBPCDD/Fs are remarkably similar regardless of where the fly ash originated, indicating common mechanisms of formation of these compounds in the incinerators.  相似文献   
85.
本文讨论了用辉光放电法制备氮化硅薄膜时衬底温度、射频功率和气体流量比对薄膜的电导率、介电常数和击穿强度的影响。通过优化生长条件,制备了优质非晶氮化硅薄膜,其介电常数为7.5、击穿强度为5.5MV/cm、电导率为10-13(Ωcm)-1。  相似文献   
86.
The paper addresses the design of two-level power system stabilizers using an optimal reduced order model whose state variables are torque angles and speeds. The reduced order model retains their physical meaning and is used to design a two-level linear feedback controller that takes into account the realities and constraints of electrical power systems. The two-level control strategy is used, and a global control signal is generated from the output variables to minimize the effect of interactions. The effectiveness of this controller is evaluated and a multimachine system is given as an example to illustrate the advantages of the proposed method. Responses of the system with a two-level scheme and an optimal reduced order scheme are included for comparative analysis.  相似文献   
87.
The buried-type p-channel LDD MOSFETs biased at high positive gate voltage exhibit novel characteristics: (1) the ratio of the drain to gate currents is about 1×10-3 to 5×10-3; and (2) the gate and drain currents both are functions of only the gate voltage minus the n-well bias. Such characteristics are addressed based on the formation of the surface n + inversion layer due to the punchthrough of the buried channel to the underlying shallow p-n junction. The measured gate current is due to the Fowler-Nordheim tunneling of electrons from this inversion layer surface and the holes generated within the high-field oxide constitute the drain current. The n+ inversion layer surface potential is found to be equal to the n-well bias plus 0.55 V. As a result, both the oxide field and the gate and drain currents are independent of drain voltage  相似文献   
88.
Fuzzy reasoning Petri nets   总被引:2,自引:0,他引:2  
This paper presents a fuzzy reasoning Petri net (FRPN) model to represent a fuzzy production rule-based system. The issues of how to represent and reason about rules containing negative literals are addressed in the proposed PN model. The execution rules based on the model are defined formally using the operators in max-algebra. Then, a fuzzy reasoning algorithm is proposed to perform fuzzy reasoning automatically. The algorithm is consistent with the matrix equation expression method in the traditional PNs and allows one to exploit the maximum parallel reasoning potential embedded in the model. The legitimacy and feasibility of the proposed approach are proved and validated through a turbine fault diagnosis expert system.  相似文献   
89.
In recent years, some methods have been proposed to estimate values in relational database systems. However, the estimated accuracy of the existing methods are not good enough. In this paper, we present a new method to generate weighted fuzzy rules from relational database systems for estimating values using genetic algorithms (GAs), where the attributes appearing in the antecedent part of generated fuzzy rules have different weights. After a predefined number of evolutions of the GA, the best chromosome contains the optimal weights of the attributes, and they can be translated into a set of rules to be used for estimating values. The proposed method can get a higher average estimated accuracy rate than the methods we presented in two previous papers.  相似文献   
90.
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