全文获取类型
收费全文 | 22233篇 |
免费 | 1739篇 |
国内免费 | 1059篇 |
专业分类
电工技术 | 1298篇 |
技术理论 | 1篇 |
综合类 | 2344篇 |
化学工业 | 2869篇 |
金属工艺 | 609篇 |
机械仪表 | 1130篇 |
建筑科学 | 1146篇 |
矿业工程 | 429篇 |
能源动力 | 885篇 |
轻工业 | 847篇 |
水利工程 | 853篇 |
石油天然气 | 1189篇 |
武器工业 | 229篇 |
无线电 | 969篇 |
一般工业技术 | 2190篇 |
冶金工业 | 2761篇 |
原子能技术 | 124篇 |
自动化技术 | 5158篇 |
出版年
2024年 | 52篇 |
2023年 | 223篇 |
2022年 | 359篇 |
2021年 | 434篇 |
2020年 | 438篇 |
2019年 | 438篇 |
2018年 | 418篇 |
2017年 | 579篇 |
2016年 | 632篇 |
2015年 | 682篇 |
2014年 | 975篇 |
2013年 | 1540篇 |
2012年 | 1151篇 |
2011年 | 1486篇 |
2010年 | 1115篇 |
2009年 | 1280篇 |
2008年 | 1250篇 |
2007年 | 1429篇 |
2006年 | 1365篇 |
2005年 | 1179篇 |
2004年 | 1021篇 |
2003年 | 937篇 |
2002年 | 811篇 |
2001年 | 693篇 |
2000年 | 588篇 |
1999年 | 592篇 |
1998年 | 613篇 |
1997年 | 415篇 |
1996年 | 375篇 |
1995年 | 303篇 |
1994年 | 257篇 |
1993年 | 188篇 |
1992年 | 199篇 |
1991年 | 163篇 |
1990年 | 159篇 |
1989年 | 93篇 |
1988年 | 82篇 |
1987年 | 62篇 |
1986年 | 66篇 |
1985年 | 90篇 |
1984年 | 71篇 |
1983年 | 67篇 |
1982年 | 48篇 |
1981年 | 18篇 |
1980年 | 20篇 |
1979年 | 15篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1975年 | 5篇 |
1959年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
This paper compares state-space and input–output realizations for nonlinear discrete-time dynamic models. For linear models, these two realizations are essentially equivalent and their structures are closely related, but these statements do not hold for nonlinear models. We illustrate this point with simple, realistic examples for which only one of the two realizations exists or for which both exist but their structures are profoundly different. Overall, the main point of this paper is the importance of the choice of realization in the development of nonlinear dynamic models. 相似文献
82.
道路与匝道中线自动绘制的算法与实现 总被引:1,自引:0,他引:1
道路与立交匝道平面中线的计算机自动绘制是道路路线CAD软件的核心功能之一,在道路工程计算机动态交互式设计、计算机辅助成图方面具有基础性作用.依据道路中线线形的曲率变化特点,推导了道路中线坐标计算的通用数学模型,并根据一个工程实例在通用图形系统AutoCAD环境下实现了道路与匝道中线的自动绘制. 相似文献
83.
Withdrawal from an escalating-dose, bingelike regimen of cocaine administration in rats produced significantly depressed levels of locomotor activity during the nocturnal portion of the day-night cycle. This effect was observed during the first 48 hrs of testing. Extracellular single-unit recordings of ventral tegmental area (VTA) dopamine (DA) neurons revealed no differences between saline- and cocaine-treated rats with respect to basal firing rates. However, significantly fewer spontaneously active VTA DA neurons were encountered in rats withdrawn from binge cocaine. As with the nocturnal hypoactivity, this effect was observed only during the first 48 hrs of withdrawal. These findings suggest that short-term DA neuron dysfunction during cocaine withdrawal temporally corresponds to behavioral disruptions that are similar to those described in human addicts. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
84.
Argyris G. Kagiannas Thanassis Didis Dimitris Th. Askounis John Psarras 《国际能源研究杂志》2003,27(2):173-186
The needs that an energy supply system must meet are constantly changing, due to technological, social and political reasons. Effective energy planning is a dynamic process that is repeated periodically and adjusts to changing conditions. Energy decision makers and planners are no longer able to rely on inductive decision making since they have to investigate the effect of various decision parameters and possible future changes. To help in this process, models have been developed where estimates of future load growth, candidate power plants, fuels and other key factors can be introduced, from which the planners can evaluate decision parameters and the available alternatives. The paper presents the different methodologies and practices that are used by 11 energy models for energy demand forecasting, supply side management and generation expansion planning, demand side management and integrated resource planning. The paper concludes to the presentation of a strategic appraisal of the examined energy models appropriate for energy planning in Mozambique. Three models are proposed for conducting demand forecasting, generation expansion planning and demand side management. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
85.
影响轧辊表面粗糙度的因素很多,为此对影响辊面粗糙度的因素进行了系统分析和实验研究,得出了轧辊和砂轮的速度、砂轮粒度、砂轮直径及磨削液等主要因素对轧辊表面粗糙度影响的一般规律。利用回归分析的方法建立了轧辊表面粗糙度的数学模型,并将计算值与实测值进行了比较,发现两者基本一致。此项研究为适时控制冷轧带钢在线磨辊辊面粗糙度提供了计算模型。 相似文献
86.
Haley William E.; Larson Dale G.; Kasl-Godley Julia; Neimeyer Robert A.; Kwilosz Donna M. 《Canadian Metallurgical Quarterly》2003,34(6):626
Professional psychologists are increasingly likely to encounter opportunities to work with patients and families facing end-of-life issues. Psychologists can provide psychological assessment, intervention for patients and families, consultation with and support of health care team members, grief therapy, and program development and evaluation. Psychological services are useful for healthy individuals who wish to make thoughtful plans about their own future care, patients with life-limiting illnesses, families stressed by providing end-of-life care, bereaved individuals, and health care providers who face issues of burnout and strain. Several challenges for psychologists working in end-of-life care are noted, including training, development of clear roles, and reimbursement. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
87.
Leonhard E. Bernold 《Canadian Metallurgical Quarterly》2003,129(6):645-652
The need for better protecting our vital infrastructure from being damaged or destroyed has received increased attention since the terrorist attacks on September 11, 2001. The tragedy of having thousands of innocent people die before the eyes of an entire nation awakened people to the reality of “managed” attacks of unthinkable magnitudes. However, tragedies of a smaller scale are a daily occurrence but accepted as “collateral damage” of work in an unsafe environment. This paper presents a cost-benefit analysis to address the question of how much money should be spent in protecting underground utilities from damage. During the study of an actual incident it was found that the total costs of such accidents are vastly underreported because only costs for emergency responses and repair are tallied up. This paper makes the case that a comprehensive approach for assessing the total economic impact of such incidents on the public, business, and government is the critical stepping stone to a mathematical optimization of expenditure for damage prevention. In addition, the reader will quickly realize that the use of the presented optimization model provides theoretical underpinning for the engineering profession in its effort to better protect our critical infrastructure from terrorist attacks. 相似文献
88.
This paper reports how the study of formal logical reasoning provides insight into more everyday types of reasoning, such as that involved in language comprehension. Both of these types of cognition are thought to involve the use of mental models, and so it is reasonable to think that the cognitive operations needed for formal logical reasoning would be involved in everyday reasoning as well. We focused on three aspects of formal reasoning: (a) the integration of information into a common mental model, (b) the drawing of inferences, and (c) the coordination of alternative possibilities. We were able to show that the integration and inference components were related to narrative comprehension processes, but the coordination of alternative models was not. Thus, there is evidence for some overlap in the mental processes used in formal and everyday reasoning. This further justifies the study of formal logical reasoning as a window into certain types of everyday reasoning. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
89.
首先以 HERMLE C1200 U 为例分析了五轴铣削加工中心的基本结构,然后据此给出了涉及多轴铣削加工中心后置处理角度分配和坐标变换的数学模型,最后介绍了以此数学模型为核心,为UG 软件开发的后置处理软件 UG-HERP1.0的解决方案。 相似文献
90.