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   253297篇
  免费   2796篇
  国内免费   870篇
电工技术   4827篇
综合类   193篇
化学工业   36230篇
金属工艺   9514篇
机械仪表   7553篇
建筑科学   6085篇
矿业工程   880篇
能源动力   7241篇
轻工业   21114篇
水利工程   2202篇
石油天然气   3230篇
武器工业   15篇
无线电   34316篇
一般工业技术   50045篇
冶金工业   48639篇
原子能技术   5095篇
自动化技术   19784篇
  2021年   2185篇
  2020年   1565篇
  2019年   1919篇
  2018年   3277篇
  2017年   3308篇
  2016年   3401篇
  2015年   2227篇
  2014年   3964篇
  2013年   11497篇
  2012年   6243篇
  2011年   8584篇
  2010年   6918篇
  2009年   7893篇
  2008年   8411篇
  2007年   8316篇
  2006年   7371篇
  2005年   6510篇
  2004年   6295篇
  2003年   6572篇
  2002年   6055篇
  2001年   6524篇
  2000年   5985篇
  1999年   6401篇
  1998年   16530篇
  1997年   11430篇
  1996年   8812篇
  1995年   6619篇
  1994年   5918篇
  1993年   5858篇
  1992年   4136篇
  1991年   4026篇
  1990年   3863篇
  1989年   3653篇
  1988年   3562篇
  1987年   3018篇
  1986年   2941篇
  1985年   3212篇
  1984年   2927篇
  1983年   2830篇
  1982年   2641篇
  1981年   2546篇
  1980年   2465篇
  1979年   2305篇
  1978年   2108篇
  1977年   2607篇
  1976年   3567篇
  1975年   1765篇
  1974年   1729篇
  1973年   1666篇
  1972年   1465篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
A 0.9 V 92 dB Double-Sampled Switched-RC Delta-Sigma Audio ADC   总被引:1,自引:0,他引:1  
A 0.9 V third-order double-sampled delta-sigma audio ADC is presented. A new method using a combination of a switched-RC technique and a floating switched-capacitor double-sampling configuration enabled low-voltage operation without clock boosting or bootstrapping. A three-level quantizer with simple dynamic element matching was used to improve linearity. The prototype IC implemented in a 0.13 CMOS process achieves 92 dB DR, 91 dB SNR and 89 dB SNDR in a 24 kHz audio signal bandwidth, while consuming 1.5 mW from a 0.9 V supply. The prototype operates from 0.65 V to 1.5 V supply with minimal performance degradation.  相似文献   
62.
Sol–gel films are actively investigated during the last decade as possible candidates for environmentally friendly pre-treatments. However, the important drawback in this case is the lack of active corrosion protection and self-healing ability.  相似文献   
63.
This paper deals with accurate recipe implementation for abnormal condition management in a batch process using a case‐based reasoning (CBR) approach. A set of new problems can be solved by reusing proven process solutions. The proposed system integrates quantitative and qualitative parameters for adaptation of cases. A novel methodology to generate accurate recipes and to adapt to the processes is introduced during normal and abnormal conditions. In particular, the differences between current conditions and the references (recipes) should be managed to prevent any hazardous conditions arising. The processes are evaluated using their similarity to the past cases. This intelligent approach distinguishes plausible cases, generates accurate recipes, and adapts to new situations. The aim is to use the offline historical process data and safety related information in order to propose changes and adjustments in the processes.  相似文献   
64.
A new supported liquid membrane (SLM) system was prepared for the selective transport of bismuth ions from the aqueous feed into the aqueous permeate phase. The support of the SLM was a thin porous polypropylene or polyvinylidene fluoride membrane impregnated with diisooctyldithiophosphinic acid (Cyanex 301) as mobile carrier in 4‐chloroacetophenon as organic solvent. Cyanex 301 acts as a highly selective carrier for the uphill transport of bismuth ions through the SLM. In the presence of HNO3 as a metal ion acceptor in the strip solution, the transport of bismuth ions into the strip side reached 70 % of the initial feed concentration after 3.5 hours. The selectivity and efficiency of bismuth transport from aqueous solutions containing different mixtures of cations were investigated. In the presence of P2O72– ions as suitable masking agent in the feed solution, the interfering effects of other cations were completely eliminated. The selective transport of bismuth through SLM is superior to liquid‐liquid extraction or through bulk liquid membranes. This is due to the high efficiency. The SLM reduces the solvent requirements, combines extraction and stripping operations in a single process and allows the use of highly selective extractants. The system may be applied to samples containing very low bismuth concentrations.  相似文献   
65.
66.
67.
The latest developments and in particular important synthetic aspects for the preparation of modern poly(styrene‐divinylbenzene) (PS‐DVB) based liquid chromatography (LC) supports are reviewed. In this context, the chemistry of particular porous and nonporous, functionalized, monolithic, coated silica and more specialized mixed organic PS‐DVB media is covered. Special consideration is given to modern approaches such as micro‐(μ)‐HPLC and coating techniques and their most important applications. Synthetic particularities relevant to the corresponding applications are outlined.  相似文献   
68.
This paper examines Total Quality Management (TQM) as defined by Dr. W. Edwards Deming including Deming's fourteen points and explains how the United States' Department of Defense (DOD) defines TQM and why TQM is necessary. It also covers how the DOD is planning on implementing TQM and the policy that has been established as guidance in the implementation process.  相似文献   
69.
Abdelguerfi  M. Sood  A.K. 《Micro, IEEE》1991,11(6):35-43
The design and simulation of a bit-sliced processor for relational database aggregation functions, are discussed. The processor, which addresses an important, computationally expensive problem in database computers, takes two tuples as input (one bit at a time) and returns two bits as output every clock cycle. A larger aggregation unit uses a number of identical slice processors, connected according to odd-even network topology, to achieve improved performance on a parallel pipelined processor. The data processing time is completely overlapped with the input and output of data to and from the unit. The design is independent of the tuple size, and since a bit-serial computation is used, the system requires limited interconnection  相似文献   
70.
The state of the art of debugging is examined. A debugged process model that serves as the basis of a general debugging framework is described. The relationship of the model to traditional debugging processes and support tools is discussed. A minimal set of requirements for a general debugging framework is described in terms of both the theory behind debugging methodologies and the support tools. An execution monitor, Eden, that serves as a debugging tool within this general framework is described  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