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   264255篇
  免费   3507篇
  国内免费   839篇
电工技术   5181篇
综合类   337篇
化学工业   37928篇
金属工艺   10312篇
机械仪表   8582篇
建筑科学   6320篇
矿业工程   1090篇
能源动力   6529篇
轻工业   23186篇
水利工程   2593篇
石油天然气   3930篇
武器工业   68篇
无线电   35235篇
一般工业技术   50668篇
冶金工业   47775篇
原子能技术   5459篇
自动化技术   23408篇
  2021年   2082篇
  2019年   2072篇
  2018年   3519篇
  2017年   3585篇
  2016年   3791篇
  2015年   2360篇
  2014年   4116篇
  2013年   11526篇
  2012年   6703篇
  2011年   9072篇
  2010年   7130篇
  2009年   7971篇
  2008年   8848篇
  2007年   8775篇
  2006年   7937篇
  2005年   7263篇
  2004年   7011篇
  2003年   6843篇
  2002年   6472篇
  2001年   6564篇
  2000年   6254篇
  1999年   6351篇
  1998年   14543篇
  1997年   10447篇
  1996年   8266篇
  1995年   6509篇
  1994年   5802篇
  1993年   5674篇
  1992年   4598篇
  1991年   4258篇
  1990年   4094篇
  1989年   3833篇
  1988年   3666篇
  1987年   3221篇
  1986年   3130篇
  1985年   3677篇
  1984年   3455篇
  1983年   3078篇
  1982年   2904篇
  1981年   3007篇
  1980年   2802篇
  1979年   2677篇
  1978年   2533篇
  1977年   2994篇
  1976年   3632篇
  1975年   2352篇
  1974年   2335篇
  1973年   2347篇
  1972年   1868篇
  1971年   1762篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
942.
The authors describe a 9.02×9.02-mm chip built in 1-μm CMOS with two levels of metal and an additional mask level for fabricating capacitors. It contains both analog and digital circuits and has provisions for self-test. The function includes the transmitter, receiver, protocol handler, an microprocessor, as well as interfaces for RAM/ROM storage, IBM PC bus, IBM PS/2 bus, IBM 3174 bus, and Motorola 68000 bus. The physical design terrains are formed by 24K circuits of standard cell gates, a 10K-circuit equivalent hand-honed custom microprocessor, and an analog macro. The chip operates from a single 5-V supply, and the power consumption is 0.8 W nominal at 16 Mb/s. The chip can also be operated at 4 Mb/s  相似文献   
943.
The effects of adding sodium hydroxide (NaOH), separately or in combinastion with various inorganic phosphates, on meat emulsion characteristics were studied. In comparing the addition of either NaPP or NaOH, 0.075% NaOH resulted in a higher raw emulsion pH and greater solubilized protein than 0.30% NaPP, but NaPP resulted in a more stable emulsion. The combination of 0.075% NaOH and 0.30% NaPP resulted in a soluble protein level less than when the ingredients were added individually and only slightly higher than if neither were present. The addition of NaOH (at 1 part NaOH to 4 parts phosphate) decreased cooked yields. With NaAPP and NaPP, NaOH reduced yields below that of the control.  相似文献   
944.
The mathematical methods for optimising the effects of heat processing food products are reviewed in relation to microbial destruction, nutrient destruction, cooking value and loss of quality. Some data are presented for the kinetics of the various thermal effects. The results obtained by various workers are presented with particular reference to nutrient retention.  相似文献   
945.
During surveillance of hog carcasses from Manitoba for antibiotic residues by the Health of Animals Laboratory, Agriculture Canada, Saskatoon, an unknown substance was found which produced tetracycline-like results with the methods used. This same substance was found in an implicated swine feed premix. Using various HPLC systems and columns, UV spectroscopy, reverse-phase TLC, and mass spectrometry, the substance was isolated from the feed premix, and identified as lumichrome, a photodegradation product of riboflavin. Traces of the same substance were found in riboflavin standard. Analysis of swine kidney, previously found to contain the unknown, showed the same substance was present at a level of about 1 ppm.  相似文献   
946.
A Statistical Method for Reconfiguration of Cognitive Radios   总被引:2,自引:0,他引:2  
Recent developments in computer technology have enabled radio developers to accomplish in software what traditionally was performed with application-specific integrated circuits. A radio that has the core of its functionality implemented in software is called a software-defined radio. When an SDR has the capability to sense, reason, and dynamically adapt to requirements and environmental change, we call this more capable device a cognitive radio. Many private and public agencies are investing in the promise of CR to improve the utilization of radio frequency spectrum. They envision devices that can sense frequency vacancies and dynamically reconfigure to utilize idle channels. The promise of CR depends on the capability of a radio to change operating frequencies, power, and/or modulation schemes (physical layer flexibility). In addition to this physical layer flexibility, there are a large number of opportunities to capitalize on the interplay of the CR physical layer configuration and other parameters in the radio network protocol stack. At the core of CR functionality is the ability to select from thousands of potential configurations to maximize performance-be it in terms of spectrum use, throughput, or reliability. In this article, we describe a method for selecting from a number of potential configurations to fulfill the communication requirements of a CR network. By using accepted statistical methods, we show how parameters at the physical, data link, network, and application layers interact to affect performance. We build upon this parametric insight with our presentation of a technique for predicting radio performance.  相似文献   
947.
The use of prognostic control methods in the digital systems controlling asynchronous electric drives are considered. The methodology for synthesizing predictors on the basis of neural networks is explained. An example of the synthesis of a numeral predictor for a closed control loop is considered.  相似文献   
948.
The objective, strategy, and implementation details of a new undergraduate course, Internet-based Instrumentation and Control, are presented. The course has a companion laboratory that is supported by the National Science Foundation and industry. The combination is offered to senior-level undergraduate engineering students interested in sensing, instrumentation, control, and web programming that want to learn more about the integration of these technologies for solving real-world engineering problems. The course will also be offered to gifted high school seniors with similar interests and can serve as a vehicle to attract them to engineering disciplines. Preliminary assessment of the first offering of the course is encouraging and has shown that the course has achieved success in helping students understand concepts and master basic technologies for developing Internet-based automatic systems.  相似文献   
949.
The viscometric, turbidimetric and potentiometric properties of copolymers of acrylamide (AM) with 2-acrylamido-2-methylpropanedimethylammonium chloride (AMPDAC) were studied in aqueous solutions. The AMPDAC polymers exhibit poor salt tolerance and large, negative viscosity/temperature coefficients. Furthermore, the polymers were found to be sensitive to changes in pH. The AMPDAC polymers undergo phase separation in the presence of dianions as a function of temperature and AMPDAC composition.  相似文献   
950.
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