全文获取类型
收费全文 | 1555篇 |
免费 | 39篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 22篇 |
化学工业 | 254篇 |
金属工艺 | 42篇 |
机械仪表 | 46篇 |
建筑科学 | 98篇 |
矿业工程 | 3篇 |
能源动力 | 59篇 |
轻工业 | 138篇 |
水利工程 | 12篇 |
石油天然气 | 1篇 |
无线电 | 118篇 |
一般工业技术 | 281篇 |
冶金工业 | 371篇 |
原子能技术 | 10篇 |
自动化技术 | 142篇 |
出版年
2023年 | 6篇 |
2021年 | 17篇 |
2020年 | 11篇 |
2019年 | 14篇 |
2018年 | 17篇 |
2017年 | 25篇 |
2016年 | 24篇 |
2015年 | 23篇 |
2014年 | 33篇 |
2013年 | 69篇 |
2012年 | 54篇 |
2011年 | 61篇 |
2010年 | 48篇 |
2009年 | 70篇 |
2008年 | 59篇 |
2007年 | 72篇 |
2006年 | 58篇 |
2005年 | 57篇 |
2004年 | 53篇 |
2003年 | 37篇 |
2002年 | 41篇 |
2001年 | 30篇 |
2000年 | 36篇 |
1999年 | 36篇 |
1998年 | 128篇 |
1997年 | 82篇 |
1996年 | 59篇 |
1995年 | 44篇 |
1994年 | 34篇 |
1993年 | 29篇 |
1992年 | 21篇 |
1991年 | 15篇 |
1990年 | 17篇 |
1989年 | 12篇 |
1988年 | 13篇 |
1987年 | 16篇 |
1986年 | 10篇 |
1985年 | 21篇 |
1984年 | 6篇 |
1983年 | 10篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 9篇 |
1979年 | 12篇 |
1978年 | 5篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 8篇 |
1974年 | 5篇 |
1971年 | 4篇 |
排序方式: 共有1597条查询结果,搜索用时 812 毫秒
111.
Optimal Power Flow of Multiple Energy Carriers 总被引:1,自引:0,他引:1
This paper presents an approach for combined optimization of coupled power flows of different energy infrastructures such as electricity, gas, and district heating systems. A steady state power flow model is presented that includes conversion and transmission of an arbitrary number of energy carriers. The couplings between the different infrastructures are explicitly taken into account based on the new concept of energy hubs. With this model, combined economic dispatch and optimal power flow problems are stated covering transmission and conversion of energy. A general optimality condition for optimal dispatch of multiple energy carriers is derived, and the approach is compared with the standard method used for electrical power systems. Finally, the developed tools are demonstrated in examples 相似文献
112.
Assigning real-time tasks on heterogeneous multiprocessors with two unrelated types of processors 总被引:2,自引:1,他引:1
Consider the problem of partitioned scheduling of an implicit-deadline sporadic task set on heterogeneous multiprocessors to meet all deadlines. Each processor is either of type-1 or type-2. We present a new algorithm, FF-3C, for this problem. FF-3C offers low time-complexity and provably good performance. Specifically, FF-3C offers (i) a time-complexity of O(n?max(m,logn)+m?logm), where n is the number of tasks and m is the number of processors and (ii) the guarantee that if a task set can be scheduled by an optimal partitioned-scheduling algorithm to meet all deadlines then FF-3C meets all deadlines as well if given processors at most $\frac{1}{1-\alpha}$ times as fast (referred to as speed competitive ratio) and tasks are scheduled using EDF; where α is a property of the task set. The parameter α is in the range (0,0.5] and for each task, it holds that its utilization is no greater than α or greater than 1?α on each processor type. Thus, the speed competitive ratio of FF-3C can never exceed 2. We also present several extensions to FF-3C; these offer the same performance guarantee and time-complexity but with improved average-case performance. Via simulations, we compare the performance of our new algorithms and two state-of-the-art algorithms (and variations of the latter). We evaluate algorithms based on (i) running time and (ii) the necessary multiplication factor, i.e., the amount of extra speed of processors that the algorithm needs, for a given task set, so as to succeed, compared to an optimal task assignment algorithm. Overall, we observed that our new algorithms perform significantly better than the state-of-the-art. We also observed that our algorithms perform much better in practice, i.e., the necessary multiplication factor of the algorithms is much smaller than their speed competitive ratio. Finally, we also present a clustered version of the new algorithm. 相似文献
113.
Christian Müller Ergang Wang L. Mattias Andersson Kristofer Tvingstedt Yi Zhou Mats R. Andersson Olle Inganäs 《Advanced functional materials》2010,20(13):2124-2131
The performance of organic photovoltaic (OPV) bulk‐heterojunction blends comprising a liquid‐crystalline fluorene derivative and a small‐molecular fullerene is found to increase asymptotically with the degree of polymerization of the former. Similar to various thermodynamic transition temperatures as well as the light absorbance of the fluorene moiety, the photocurrent extracted from OPV devices is found to strongly vary with increasing oligomer size up to a number average molecular weight, Mn ≈ 10 kg mol?1, but is rendered less chain‐length dependent for higher Mn as the fluorene derivative gradually adopts polymeric behavior. 相似文献
114.
115.
Arild Hoff Henrik Andersson Marielle Christiansen Geir Hasle Arne Løkketangen 《Computers & Operations Research》2010,37(12):2041-2061
The purpose of this paper is to describe industrial aspects of combined fleet composition and routing in maritime and road-based transportation, and to present the current status of research in the form of a comprehensive literature review. First, presents a classification of problems, and then focuses on a basic definition of combined fleet composition and routing: the fleet size and mix vehicle routing problem. A basic mathematical formulation from the literature is presented. Further, the literature of extended and related problems is described and categorized. Surveys of application oriented research in road-based and maritime transportation conclude the review. Finally, we contrast the literature with aspects of industrial applications from a critical, but constructive stance. Major issues for future work are suggested. 相似文献
116.
Provably good multiprocessor scheduling with resource sharing 总被引:2,自引:1,他引:1
We present a 12(1+3R/(4m)) competitive algorithm for scheduling implicit-deadline sporadic tasks on a platform comprising m processors, where a task may request one of R shared resources. 相似文献
117.
The aim of this study was to reveal how upper level compulsory school students (13 to 16 years old) conceptualize matter. Twenty individually administered interviews were carried out, transcribed word for word and analyzed in accordance with the phenomenographic approach adopted. Six distinctively different conceptions were found. Matter can be understood as (a) homogeneous substance, (b) substance units, (c) substance units with "small atoms," (d) aggregate of particles, (e) particle units, or (f) systems of particles. Differences in focus constitute a variation in the internal structure of each conception. There are also alternative forms of the same conception in some cases. The different conceptions, their varying internal structures, and the alternative forms of conceptions found are logically interrelated in a system, called the "outcome space," which depicts how thinking about matter may vary qualitatively between and within students. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
118.
H. I. Andersson 《Acta Mechanica》2002,158(1-2):121-125
Summary The slip-flow of a Newtonian fluid past a linearly stretching sheet is considered. The partial slip is controlled by a dimensionless slip factor, which varies between zero (total adhesion) and infinity (full slip). An exact analytical solution of the governing Navier-Stokes equation is found, which is formally valid for all Reynolds numbers. 相似文献
119.
Trunk muscle forces during desk work 总被引:1,自引:0,他引:1
120.
The corrosion was investigated on a superheater test coil in a CFB waste boiler. The alloys ranged from ferritic steel T22 to nickel‐based Alloy 65 and the metal temperatures were between 460 and 540°C. The thickness of the deposit was alloy and temperature dependent. The low‐alloyed steels developed thick deposits at all temperatures while the deposit thickness increased with the temperature on the high‐alloyed steels and the nickel‐based alloy. The corrosion attack was alloy dependent and related to the deposit crest. The nickel‐based Alloy 65 was preferentially attacked directly under the crest of the deposit while the other alloys were preferentially attacked at the edge. The corrosion rate increased with temperature for X20, Alloy 304L, Alloy 310 and Alloy 825; decreased on Alloy 65; and was bell shaped on T22 and Alloy 28. Alloy 310 suffered from severe pitting corrosion in a line following the edge of the deposit crest. The best overall corrosion resistant alloy was Alloy 28. 相似文献