全文获取类型
收费全文 | 54415篇 |
免费 | 2868篇 |
国内免费 | 1246篇 |
专业分类
电工技术 | 1731篇 |
综合类 | 1951篇 |
化学工业 | 10384篇 |
金属工艺 | 2063篇 |
机械仪表 | 2260篇 |
建筑科学 | 3945篇 |
矿业工程 | 705篇 |
能源动力 | 1582篇 |
轻工业 | 3448篇 |
水利工程 | 747篇 |
石油天然气 | 2045篇 |
武器工业 | 211篇 |
无线电 | 5502篇 |
一般工业技术 | 7750篇 |
冶金工业 | 6330篇 |
原子能技术 | 602篇 |
自动化技术 | 7273篇 |
出版年
2023年 | 549篇 |
2022年 | 954篇 |
2021年 | 1365篇 |
2020年 | 1062篇 |
2019年 | 992篇 |
2018年 | 1102篇 |
2017年 | 1255篇 |
2016年 | 1234篇 |
2015年 | 1406篇 |
2014年 | 1905篇 |
2013年 | 3101篇 |
2012年 | 2703篇 |
2011年 | 3067篇 |
2010年 | 2534篇 |
2009年 | 2549篇 |
2008年 | 2624篇 |
2007年 | 2674篇 |
2006年 | 2550篇 |
2005年 | 2333篇 |
2004年 | 1745篇 |
2003年 | 1591篇 |
2002年 | 1559篇 |
2001年 | 1192篇 |
2000年 | 1272篇 |
1999年 | 1340篇 |
1998年 | 1404篇 |
1997年 | 1167篇 |
1996年 | 1156篇 |
1995年 | 1002篇 |
1994年 | 812篇 |
1993年 | 814篇 |
1992年 | 627篇 |
1991年 | 459篇 |
1990年 | 510篇 |
1989年 | 442篇 |
1988年 | 402篇 |
1987年 | 345篇 |
1986年 | 360篇 |
1985年 | 353篇 |
1984年 | 343篇 |
1983年 | 324篇 |
1982年 | 262篇 |
1981年 | 278篇 |
1980年 | 272篇 |
1979年 | 261篇 |
1978年 | 234篇 |
1977年 | 239篇 |
1976年 | 217篇 |
1975年 | 200篇 |
1973年 | 187篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
James W. Conard 《Information Systems Management》1987,4(1):8-17
The concept of the integrated services digital network (ISDN) could revolutionize information management. The purpose of the ISDN is to provide a worldwide network that offers end-to-end digital connectivity supporting a wide variety of communications services. ISDN subscribers will have direct access to a high-speed digital pipeline capable of supporting simultaneous voice, data, facsimile, and various other services and calling features. 相似文献
12.
Buttari D. Chini A. Meneghesso G. Zanoni E. Moran B. Heikman S. Zhang N.Q. Shen L. Coffie R. DenBaars S.P. Mishra U.K. 《Electron Device Letters, IEEE》2002,23(2):76-78
Pre-metal-deposition reactive ion etching (RIE) was performed on an Al0.3Ga0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs 相似文献
13.
Action calculi, which generalise process calculi such as Petri nets, π-calculusand ambient calculus, have been presented
in terms of action graphs. We here offer linear action graphs as a primitive basis for action calculi. This paper presents the category of embeddings of undirected linear
action graphs without nesting, using a novel form of graphical reasoning which simplifies some otherwise complex manipulations
in regular algebra. The results are adapted in a few lines to directed graphs. This work is part of a long-term search for
a uniform behavioural theory for process calculi.
Received October 2000 / Accepted in revised form April 2001 相似文献
14.
Serum total cholesterol, high density lipoprotein (HDL) cholesterol, and triglyceride levels were studied in healthy male
and female subjects consuming for one-week periods a diet of conventional food (CF) providing 42% of energy as fat, principally
butter fat, and then in random order nutritionally complete, defined formula diets of moderate (32%) to very low (1%) fat
content. Compared to CF, the formula with 32% of energy as corn oil lowered serum cholesterol by 25% and the ratio of total
to HDL-cholesterol by 13%. Low (9%) and very low (1–3%) fat formulas reduced HDL-cholesterol by as much as 40%, raised the
total: HDL-cholesterol ratio by about 20% and raised serum triglyceride levels by as much as 100%. When low and very low fat
formulas were ingested for three weeks, these effects persisted although maximal responses occurred during the first week.
These results demonstrated that a moderate fat formula diet with a high P/S ratio had a more favorable effect on serum lipid
levels than various low fat formulas. Low fat conventional food diets should be studied in long-term controlled metabolic
experiments before such diets are recommended to the general population for coronary heart disease or cancer prevention. 相似文献
15.
A novel combline filter is proposed for cellular‐radio base stations. The Q‐factor is significantly improved. The eigenvalue equation is expressed with the single‐team approximation in the gap region of the combline resonator. A two‐pole combline filter is designed. The calculation, simulation, and experiment results are presented and are in good agreement. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. 相似文献
16.
介绍了天线近场测量的基本原理和HD-1型平面近场测试系统,并对近场测量在实际天线测试中的应用情况、发展方向和应用前景等作了简单的描述。 相似文献
17.
Abstract— The paper addresses some aspects of the differences in fatigue crack growth rate behaviour and threshold values obtained for long through-cracks, short through-cracks and surface cracks. Attention is focused on plasticity induced closure in the wake behind the growing crack tip. For long cracks at high K max , closure is found to depend in a linear manner on K max , i.e. K op , increases with the size of the monotonic plastic zone. Closure increases at low δ K and this is primarily a consequence of the load shedding procedure. If short through-cracks are prepared by machining specimens containing long cracks, a substantial part of the plastic wake is removed and this can produce marked effects on the closure contribution during subsequent growth. The length of crack "closed" in a long crack threshold test was found to be of the order of 1 mm. Cracks less than this length exhibited "short crack" behaviour: greater than this length, they behaved as "long cracks", with plastic wake effects apparently fully operative. Small surface cracks exhibit "long crack" behaviour at lengths as short as 0.2 mm and reasons for this are discussed. 相似文献
18.
19.
20.
In this article, we describe a new approach to applying distributed artificial intelligence techniques to manufacturing processes. The construction of intelligent systems is one of the most important techniques among artificial intelligence research. Our goal is to develop an integrated intelligent system for real time manufacturing processes. An integrated intelligent system is a large knowledge integration environment that consists of several symbolic reasoning systems (expert systems) and numerical computation packages. These software programs are controlled by a meta-system which manages the selection, operation and communication of these programs. A meta-system can be implemented in different language environments and applied to many disciplines. This new architecture can serve as a universal configuration to develop high performance intelligent systems for many complicated industrial applications in real world domains.To whom all correspondence should be addressed. 相似文献