全文获取类型
收费全文 | 566534篇 |
免费 | 7386篇 |
国内免费 | 1852篇 |
专业分类
电工技术 | 10723篇 |
综合类 | 454篇 |
化学工业 | 82817篇 |
金属工艺 | 20089篇 |
机械仪表 | 15877篇 |
建筑科学 | 14753篇 |
矿业工程 | 1551篇 |
能源动力 | 14605篇 |
轻工业 | 53335篇 |
水利工程 | 4570篇 |
石油天然气 | 4539篇 |
武器工业 | 20篇 |
无线电 | 75126篇 |
一般工业技术 | 104645篇 |
冶金工业 | 113903篇 |
原子能技术 | 8302篇 |
自动化技术 | 50463篇 |
出版年
2021年 | 3631篇 |
2019年 | 3485篇 |
2018年 | 5518篇 |
2017年 | 5597篇 |
2016年 | 5877篇 |
2015年 | 4611篇 |
2014年 | 7667篇 |
2013年 | 25411篇 |
2012年 | 13432篇 |
2011年 | 19115篇 |
2010年 | 14945篇 |
2009年 | 17268篇 |
2008年 | 18332篇 |
2007年 | 18794篇 |
2006年 | 16937篇 |
2005年 | 15795篇 |
2004年 | 15394篇 |
2003年 | 14965篇 |
2002年 | 14506篇 |
2001年 | 14908篇 |
2000年 | 13907篇 |
1999年 | 14872篇 |
1998年 | 36829篇 |
1997年 | 25954篇 |
1996年 | 20262篇 |
1995年 | 15445篇 |
1994年 | 13731篇 |
1993年 | 13425篇 |
1992年 | 9643篇 |
1991年 | 9278篇 |
1990年 | 8855篇 |
1989年 | 8491篇 |
1988年 | 8049篇 |
1987年 | 6723篇 |
1986年 | 6699篇 |
1985年 | 8058篇 |
1984年 | 7433篇 |
1983年 | 6502篇 |
1982年 | 6028篇 |
1981年 | 6159篇 |
1980年 | 5651篇 |
1979年 | 5436篇 |
1978年 | 5161篇 |
1977年 | 6285篇 |
1976年 | 8498篇 |
1975年 | 4315篇 |
1974年 | 4139篇 |
1973年 | 3969篇 |
1972年 | 3266篇 |
1971年 | 2808篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
'Software defined radio' (SDR) is a technology that will appear in future generations of mobile phones, i.e. following the third-generation mobile phone technology that is currently being defined and developed. Early versions of 'pragmatic' SDR will allow the terminal to be reconfigured at any level of its protocol stack. Ultimately, the 'pure' SDR technology will allow a mobile phone or terminal to have its air interface software configured or reconfigured by other software (or software parameters) that have been downloaded to the terminal, e.g. over the air, or from a remote server via the Internet and one's personal computer (PC). A number of security issues arise with downloaded code that implements the air interface functions, and these may not be obvious simply from looking at the way PC software is updated on-line today. This paper starts with an outline of the code that allows a mobile phone to operate over a particular air interface. This sets the baseline for a discussion of the security issues surrounding the change of this code from one that is fixed and downloaded once only, to code that is reconfigurable during the life of a product. 相似文献
102.
103.
104.
Tan J.C. Crossley P.A. McLaren P.G. Hall I. Farrell J. Gale P. 《Power Delivery, IEEE Transactions on》2002,17(1):68-74
This paper describes a sequential tripping strategy used in a wide area back-up protection expert system (BPES) to combat situations in which protection relays have maloperated or information is missing. The BPES is an innovative back-up protection scheme designed to prevent the occurrence of widespread blackouts. The BPES evaluates the certainty that transmission lines are likely to be affected by the fault and uses a sequential tripping strategy to isolate the fault if a firm decision is not available due to maloperated relays and/or missing information. The mode of analysis and the sequential tripping strategy ensures that the BPES will clear a fault at minimum risk to the network. An example is included to demonstrate how the certainty factor based sequential tripping strategy is employed by the BPES to clear a fault which occurred on the South Western part of the UK National Grid System 相似文献
105.
106.
J. G. Frick 《应用聚合物科学杂志》1985,30(8):3467-3477
Cotton fabric was crosslinked with five agents, three of which were prepared form formaldehyde and two of which were formaldehyde-free. The formaldehyde-free agents produced less bonding between layers in the laminated microstructure of the cotton fiber. One agent, 4,5-dihydroxy-1,3-dimethyl-2-imidazolidinone, gave no evidence of any interlayer bonding. All five agents gave the same relationship between wrinkle recovery angle and molar substitution on the cotton up to moderate recovery angles, but only agents based on formaldehyde gave higher wrinkle recovery angles with additional reaction. Intralayer crosslinking did not reduce absorptivity, as shown by moisture regain and dye receptivity, but did restrict swelling in cupriethylenediamine hydroxide to the same extent as combined interlayer and intralayer crosslinking. The decrease in extensibility of treated fabric with increasing wrinkle recovery angle was the same with all agents. These results indicate the regions of the fiber that are important for each of these properties. 相似文献
107.
The phospholipids of the spongePolymastia gleneni contain saturated long chain (C22–30)-acetoxy fatty acids. Their structures were assigned based on chromatographic and spectrometric data as well as comparison
with a synthetic sample. The use of capillary gas chromatography combined with chemical ionization and electron impact mass
spectrometry was instrumental in the eludication of structures, since only a very small amount of crude lipids was available.
Part 10 of “Phospholipids in Marine Organisms.” For Part 9 in this series, see reference 12. 相似文献
108.
P.J. Campion 《Measurement》1985,3(3):121-124
Two complementary national laboratory accreditation schemes are run by the National Physical Laboratory (NPL) to provide official recognition of competent British laboratories and an assurance of quality to their customers. The first of these, the British Calibration Service (BCS), was set up in 1966 to accredit laboratories to calibrate instruments, gauges and reference materials. In 1981 the National Testing Laboratory Accreditation Scheme (NATLAS) was formed to extend the service to all kinds of testing. Both BCS and NATLAS form an integral part of the UK national measurement system and were combined to form the National Measurement Accreditation Service on 1 October 1985. 相似文献
109.
110.
T Kita 《Canadian Metallurgical Quarterly》1989,40(16):10816-10830