全文获取类型
收费全文 | 2557篇 |
免费 | 67篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 31篇 |
综合类 | 3篇 |
化学工业 | 438篇 |
金属工艺 | 90篇 |
机械仪表 | 35篇 |
建筑科学 | 123篇 |
矿业工程 | 4篇 |
能源动力 | 41篇 |
轻工业 | 699篇 |
水利工程 | 8篇 |
石油天然气 | 7篇 |
无线电 | 117篇 |
一般工业技术 | 311篇 |
冶金工业 | 334篇 |
原子能技术 | 30篇 |
自动化技术 | 355篇 |
出版年
2023年 | 20篇 |
2022年 | 33篇 |
2021年 | 46篇 |
2020年 | 23篇 |
2019年 | 29篇 |
2018年 | 31篇 |
2017年 | 23篇 |
2016年 | 51篇 |
2015年 | 33篇 |
2014年 | 42篇 |
2013年 | 103篇 |
2012年 | 59篇 |
2011年 | 115篇 |
2010年 | 79篇 |
2009年 | 90篇 |
2008年 | 91篇 |
2007年 | 73篇 |
2006年 | 66篇 |
2005年 | 68篇 |
2004年 | 61篇 |
2003年 | 57篇 |
2002年 | 52篇 |
2001年 | 32篇 |
2000年 | 30篇 |
1999年 | 44篇 |
1998年 | 107篇 |
1997年 | 79篇 |
1996年 | 50篇 |
1995年 | 43篇 |
1994年 | 20篇 |
1993年 | 26篇 |
1992年 | 18篇 |
1990年 | 23篇 |
1989年 | 22篇 |
1987年 | 20篇 |
1985年 | 28篇 |
1977年 | 17篇 |
1976年 | 23篇 |
1921年 | 21篇 |
1920年 | 30篇 |
1919年 | 22篇 |
1918年 | 27篇 |
1917年 | 84篇 |
1916年 | 45篇 |
1915年 | 43篇 |
1914年 | 39篇 |
1913年 | 68篇 |
1912年 | 115篇 |
1911年 | 31篇 |
1910年 | 31篇 |
排序方式: 共有2626条查询结果,搜索用时 15 毫秒
41.
42.
Cleland LG Proudman SM Hall C Stamp LK McWilliams L Wylie N Neumann M Gibson RA James MJ 《Lipids》2003,38(4):419-424
Dietary fish oil supplements have been shown to have benefits in rheumatoid arthritis (RA), other inflammatory diseases, and
in cardiovascular disease. As with any medical advice, variability will exist with regard to adherence and consequent biochemical
or pharmacophysiologic effects. The aim was to explore the utility of plasma phospholipid EPA as a measure of n−3 PUFA intake
and response to standardized therapeutic advice given in an outpatient or office practice setting, to increase dietary n−3
PUFA, including a fish oil supplement. Patients with early RA were given verbal and written advice to alter their dietary
n−3 PUFA intake, including ingestion of 20 mL of bottled fish oil on juice daily. The advice included instructions to increase
n−3 PUFA and to avoid foods rich in n−6 PUFA. Every 3 mon, blood samples were obtained for analysis of plasma phospholipid
FA. Plasma phospholipid EPA was used as the primary index of n−3 PUFA intake. A diverse response was seen, with about one-third
of patients achieving a substantial elevation of plasma phospholipid EPA over the 12-mon study period. A third had little
change, with the remainder achieving intermediate levels. Data obtained longitudinally from individual patients indicated
that substantial elevations of EPA (>5% total plasma phospholipid FA) could be maintained for more than 3 yr. Plasma phospholipid
EPA is a convenient measure of adherence to advice to take a dietary n−3 PUFA-rich fish oil supplement. This measure may prove
a useful adjunct to intention to treat analyses in determining the effect of dietary fish oil supplements on long-term outcomes
in arthritis and other chronic inflammatory diseases. It may also provide a guide to the effectiveness of therapeutic and
preventive messages designed to increase n−3 PUFA intake. 相似文献
43.
44.
45.
Luis G. Nardin Giulia Andrighetto Rosaria Conte Áron Székely David Anzola Corinna Elsenbroich Ulf Lotzmann Martin Neumann Valentina Punzo Klaus G. Troitzsch 《Autonomous Agents and Multi-Agent Systems》2016,30(6):1117-1147
Protection racketeering groups are powerful, deeply entrenched in multiple societies across the globe, and they harm the societies and economies in which they operate in multiple ways. These reasons make their dynamics important to understand and an objective of both scientific and application-oriented interest. Legal and social norm-based approaches arguably play significant roles in influencing protection racket dynamics. We propose an agent-based simulation model, the Palermo Scenario, to enrich our understanding of these influences and to test the effect of different policies on protection racket dynamics. Our model integrates the legal and the social norm-based approaches and uses a complex normative agent architecture that enables the analysis of both agents’ behaviours and mental normative representations driving behaviour. We demonstrate the usefulness of the model and the benefits of using this complex normative architecture through a case study of the Sicilian Mafia. 相似文献
46.
Olaf Mersmann Bernd Bischl Heike Trautmann Markus Wagner Jakob Bossek Frank Neumann 《Annals of Mathematics and Artificial Intelligence》2013,69(2):151-182
Meta-heuristics are frequently used to tackle NP-hard combinatorial optimization problems. With this paper we contribute to the understanding of the success of 2-opt based local search algorithms for solving the traveling salesperson problem (TSP). Although 2-opt is widely used in practice, it is hard to understand its success from a theoretical perspective. We take a statistical approach and examine the features of TSP instances that make the problem either hard or easy to solve. As a measure of problem difficulty for 2-opt we use the approximation ratio that it achieves on a given instance. Our investigations point out important features that make TSP instances hard or easy to be approximated by 2-opt. 相似文献
47.
This paper presents a system enabling robotic helicopters to fly safely without user interaction at low altitude over unknown terrain with static obstacles. The system includes a novel reactive behavior‐based method that guides rotorcraft reliably to specified locations in sparsely occupied environments. System dependability is, among other things, achieved by utilizing proven system components in a component‐based design and incorporating safety margins and safety modes. Obstacle and terrain detection is based on a vertically mounted off‐the‐shelf two‐dimensional LIDAR system. We introduce two flight modes, pirouette descent and waggle cruise, which extend the field of view of the sensor by yawing the aircraft. The two flight modes ensure that all obstacles above a minimum size are detected in the direction of travel. The proposed system is designed for robotic helicopters with velocity and yaw control inputs and a navigation system that provides position, velocity, and attitude information. It is cost effective and can be easily implemented on a variety of helicopters of different sizes. We provide sufficient detail to facilitate the implementation on single‐rotor helicopters with a rotor diameter of approximately 1.8 m. The system was extensively flight‐tested in different real‐world scenarios in Queensland, Australia. The tests included flights beyond visual range without a backup pilot. Experimental results show that it is feasible to perform dependable autonomous flight using simple but effective methods. © 2013 Wiley Periodicals, Inc. 相似文献
48.
Uwe Neumann 《Journal of population ageing》2013,6(3):189-209
Among the highly developed countries, demographic ageing is particularly advanced in Germany. Accentuated by migration, there is great regional variation in the progress of demographic change. Within urban areas, residential neighbourhoods differ considerably in their demographic composition and perspectives. Based on municipal data, this paper examines regional variability in the diversity and pace of neighbourhood-level ageing. Focusing on the Rhine-Ruhr conurbation in North Rhine-Westphalia, the analysis outlines at what pace ageing proceeds in a variety of neighbourhoods, which attract no constant influx of working-age migrants. After decades of suburbanisation, in the period from 1998 to 2008 regional migration concentrated on the central districts of large cities. More profoundly in the most prosperous cities growing in population than in other cities, childless working-age adults separate from other age groups and family types in selected central city quarters. The findings suggest that spatial differentials in ageing are likely to affect future location decisions and, thereby, regional and local prosperity. 相似文献
49.
Evolutionary algorithms are randomized search heuristics, which are applied to problems whose structure is not well understood, as well as to problems in combinatorial optimization. They have successfully been applied to different kinds of arc routing problems. To start the analysis of evolutionary algorithms with respect to the expected optimization time on these problems, we consider the Eulerian cycle problem. We show that a variant of the well-known (1+1) EA working on the important encoding of permutations is able to find an Eulerian tour of an Eulerian graph in expected polynomial time. Altering the operator used for mutation in the considered algorithm, the expected optimization time changes from polynomial to exponential. 相似文献
50.
Alim Usman R. Entezari Alireza M ller Torsten 《IEEE transactions on visualization and computer graphics》2009,15(4):630-641
In this paper, we extend the single relaxation time Lattice-Boltzmann Method (LBM) to the 3D body-centered cubic (BCC) lattice. We show that the D3bQ15 lattice defined by a 15 neighborhood connectivity of the BCC lattice is not only capable of more accurately discretizing the velocity space of the continuous Boltzmann equation as compared to the D3Q15 Cartesian lattice, it also achieves a comparable spatial discretization with 30 percent less samples. We validate the accuracy of our proposed lattice by investigating its performance on the 3D lid-driven cavity flow problem and show that the D3bQ15 lattice offers significant cost savings while maintaining a comparable accuracy. We demonstrate the efficiency of our method and the impact on graphics and visualization techniques via the application of line-integral convolution on 2D slices as well as the extraction of streamlines of the 3D flow. We further study the benefits of our proposed lattice by applying it to the problem of simulating smoke and show that the D3bQ15 lattice yields more detail and turbulence at a reduced computational cost. 相似文献