全文获取类型
收费全文 | 446426篇 |
免费 | 4964篇 |
国内免费 | 1809篇 |
专业分类
电工技术 | 7723篇 |
综合类 | 640篇 |
化学工业 | 65893篇 |
金属工艺 | 19415篇 |
机械仪表 | 13999篇 |
建筑科学 | 9744篇 |
矿业工程 | 3338篇 |
能源动力 | 10841篇 |
轻工业 | 32999篇 |
水利工程 | 5504篇 |
石油天然气 | 11961篇 |
武器工业 | 64篇 |
无线电 | 50650篇 |
一般工业技术 | 92776篇 |
冶金工业 | 80255篇 |
原子能技术 | 12286篇 |
自动化技术 | 35111篇 |
出版年
2021年 | 3862篇 |
2019年 | 3711篇 |
2018年 | 6535篇 |
2017年 | 6692篇 |
2016年 | 7081篇 |
2015年 | 4344篇 |
2014年 | 7341篇 |
2013年 | 19093篇 |
2012年 | 11614篇 |
2011年 | 15563篇 |
2010年 | 12276篇 |
2009年 | 13987篇 |
2008年 | 14350篇 |
2007年 | 14296篇 |
2006年 | 12313篇 |
2005年 | 11368篇 |
2004年 | 10954篇 |
2003年 | 10625篇 |
2002年 | 10286篇 |
2001年 | 10452篇 |
2000年 | 9843篇 |
1999年 | 10187篇 |
1998年 | 25084篇 |
1997年 | 17699篇 |
1996年 | 13573篇 |
1995年 | 10343篇 |
1994年 | 9076篇 |
1993年 | 9309篇 |
1992年 | 6861篇 |
1991年 | 6653篇 |
1990年 | 6396篇 |
1989年 | 6380篇 |
1988年 | 6094篇 |
1987年 | 5434篇 |
1986年 | 5491篇 |
1985年 | 6063篇 |
1984年 | 5670篇 |
1983年 | 5320篇 |
1982年 | 4839篇 |
1981年 | 4890篇 |
1980年 | 4915篇 |
1979年 | 4736篇 |
1978年 | 4764篇 |
1977年 | 5135篇 |
1976年 | 6479篇 |
1975年 | 4168篇 |
1974年 | 4055篇 |
1973年 | 4123篇 |
1972年 | 3554篇 |
1971年 | 3192篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
82.
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
83.
S N Maitra 《Sadhana》1985,8(4):373-385
The burn time and burnout velocity of a multistage rocket flown vertically in vacuum with constant thrust tangential to the
flight path and a prescribed initial/final thrust-to-weight ratio in an arbitrary stage have been determined.
The present paper also deals with optimal staging under given conditions of flight. 相似文献
84.
85.
86.
87.
Ahn Jaeshin Stromsmoe Keith A. Lawson Ronald P. W. 《Industrial Electronics, IEEE Transactions on》1985,(4):405-409
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films. 相似文献
88.
G.I.N. Rozvany 《International Journal of Mechanical Sciences》1985,27(6):347-360
Existing duality principles in structural optimisation are briefly reviewed and then they are extended to structures with segment-wise constant cross-sections. All theories are discussed in the particular context of optimal plastic beam design with symmetric convex specific cost functions and are confirmed by independent calculations on illustrative examples. It is shown that the optimal solution is always associated with a displacement field in which the mean absolute curvature value for each segment equals the subgradient of the specific cost function, with respect to the maximum absolute moment value for that segment. Moreover, the dual problem consists of the maximisation of the difference of two terms: the first one is the integral of the product of load and deflection (external work), and the second is the sum of products of segment lengths and the mean complementary cost values (taken with respect to the mean absolute curvature for that segment). Finally, some tentative proposals for a class of non-convex optimisation problems are presented. For special cases, the proposed general statements reduce to theorems by Heyman, Foulkes and Hemp. 相似文献
89.
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
90.
A. N. Gudkov V. M. Zhivun A. V. Zvonarev V. V. Kovalenko A. B. Koldobskii Yu. F. Koleganov S. V. Krivasheev V. B. Pavlovich N. S. Piven' E. V. Semenova 《Atomic Energy》1989,66(2):115-118
Translated from Atomnaya Énergiya, Vol. 66, No. 2, pp. 100–103, February, 1989. 相似文献