全文获取类型
收费全文 | 1116篇 |
免费 | 32篇 |
国内免费 | 8篇 |
专业分类
电工技术 | 13篇 |
综合类 | 2篇 |
化学工业 | 182篇 |
金属工艺 | 45篇 |
机械仪表 | 65篇 |
建筑科学 | 21篇 |
能源动力 | 64篇 |
轻工业 | 28篇 |
水利工程 | 2篇 |
石油天然气 | 3篇 |
无线电 | 148篇 |
一般工业技术 | 267篇 |
冶金工业 | 103篇 |
原子能技术 | 13篇 |
自动化技术 | 200篇 |
出版年
2024年 | 7篇 |
2023年 | 14篇 |
2022年 | 43篇 |
2021年 | 63篇 |
2020年 | 46篇 |
2019年 | 36篇 |
2018年 | 48篇 |
2017年 | 29篇 |
2016年 | 49篇 |
2015年 | 27篇 |
2014年 | 41篇 |
2013年 | 64篇 |
2012年 | 44篇 |
2011年 | 61篇 |
2010年 | 42篇 |
2009年 | 49篇 |
2008年 | 52篇 |
2007年 | 33篇 |
2006年 | 44篇 |
2005年 | 31篇 |
2004年 | 32篇 |
2003年 | 19篇 |
2002年 | 24篇 |
2001年 | 12篇 |
2000年 | 16篇 |
1999年 | 13篇 |
1998年 | 15篇 |
1997年 | 14篇 |
1996年 | 22篇 |
1995年 | 16篇 |
1994年 | 17篇 |
1993年 | 9篇 |
1992年 | 8篇 |
1991年 | 15篇 |
1990年 | 6篇 |
1989年 | 11篇 |
1988年 | 14篇 |
1987年 | 8篇 |
1986年 | 5篇 |
1985年 | 11篇 |
1984年 | 7篇 |
1983年 | 2篇 |
1982年 | 3篇 |
1981年 | 8篇 |
1979年 | 7篇 |
1978年 | 2篇 |
1977年 | 3篇 |
1976年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
排序方式: 共有1156条查询结果,搜索用时 15 毫秒
991.
992.
993.
994.
Pål J. From Vincent Duindam Kristin Y. Pettersen Jan T. Gravdahl Shankar Sastry 《Simulation Modelling Practice and Theory》2010,18(6):712-731
In this paper we derive the singularity-free dynamic equations of vehicle–manipulator systems using a minimal representation. These systems are normally modeled using Euler angles, which leads to singularities, or Euler parameters, which is not a minimal representation and thus not suited for Lagrange’s equations. We circumvent these issues by introducing quasi-coordinates which allows us to derive the dynamics using minimal and globally valid non-Euclidean configuration coordinates. This is a great advantage as the configuration space of the vehicle in general is non-Euclidean. We thus obtain a computationally efficient and singularity-free formulation of the dynamic equations with the same complexity as the conventional Lagrangian approach. The closed form formulation makes the proposed approach well suited for system analysis and model-based control. This paper focuses on the dynamic properties of vehicle–manipulator systems and we present the explicit matrices needed for implementation together with several mathematical relations that can be used to speed up the algorithms. We also show how to calculate the inertia and Coriolis matrices and present these for several different vehicle–manipulator systems in such a way that this can be implemented for simulation and control purposes without extensive knowledge of the mathematical background. By presenting the explicit equations needed for implementation, the approach presented becomes more accessible and should reach a wider audience, including engineers and programmers. 相似文献
995.
996.
997.
S. K. Chaudhury V. Warke S. Shankar D. Apelian 《Metallurgical and Materials Transactions A》2011,42(10):3160-3169
During heat treatment, the work piece experiences a range of heating rates depending upon the sizes and types of furnace.
When the Al-Si-Mg cast alloy is heated to the solutionizing temperature, recrystallization takes place during the ramp-up
stage. The effect of heating rate on recrystallization in the A356 (Al-Si-Mg) alloy was studied using dilatometric and calorimetric
methods. Recrystallization in as-cast Al-Si alloys is a localized event and is confined to the elasto-plastic zone surrounding
the eutectic Si phase; there is no evidence of recrystallization in the center of the primary Al dendritic region. The size
of the elasto-plastic zone is of the same order of magnitude as the Si particles, and recrystallized grains are observed in
the elasto-plastic region near the Si particles. The coefficient of thermal expansion of Al is an order of magnitude greater
than Si, and thermal stresses are generated due to the thermal mismatch between the Al phase and Si particles providing the
driving force for recrystallization. In contrast, recrystallization in Al wrought alloy (7075) occurs uniformly throughout
the matrix, stored energy due to cold work being the driving force for recrystallization in wrought alloys. The activation
energy for recrystallization in as-cast A356 alloy is 127 KJ/mole. At a slow heating rate of 4.3 K/min, creep occurs during
the heating stage of solution heat treatment. However, creep does not occur in samples heated at higher heating rates, namely,
520, 130, and 17.3 K/min. 相似文献
998.
Philip A. Bernstein Shankar Pal David Shutt 《The VLDB Journal The International Journal on Very Large Data Bases》2000,9(3):177-189
When implementing persistent objects on a relational database, a major performance issue is prefetching data to minimize
the number of round-trips to the database. This is especially hard with navigational applications, since future accesses are
unpredictable. We propose the use of the context in which an object is loaded as a predictor of future accesses, where a context
can be a stored collection of relationships, a query result, or a complex object. When an object O's state is loaded, similar
state for other objects in O's context is prefetched. We present a design for maintaining context and for using it to guide
prefetch. We give performance measurements of its implementation in Microsoft Repository, showing up to a 70% reduction in
running time. We describe several variations of the optimization: selectively applying the technique based on application
and database characteristics, using application-supplied performance hints, using concurrent database queries to support asynchronous
prefetch, prefetching across relationship paths, and delayed prefetch to save database round-trips.
Received May 3, 2000 / Accepted October 26, 2000 相似文献
999.
A. Ravi Shankar G. Gopalakrishnan V. Balusamy U. Kamachi Mudali 《Journal of Materials Engineering and Performance》2009,18(8):1116-1123
Commercially pure titanium (Ti) has been selected for the fabrication of dissolver for the proposed fast reactor fuel reprocessing
plant at Kalpakkam, India. In the present investigation, microstructural changes and corrosion behavior of tungsten inert
gas (TIG) welds of Ti grade-1 and grade-2 with different heat inputs were carried out. A wider heat affected zone was observed
with higher heat inputs and coarse grains were observed from base metal toward the weld zone with increasing heat input. Fine
and more equiaxed prior β grains were observed at lower heat input and the grain size increased toward fusion zone. The results
indicated that Ti grade-1 and grade-2 with different heat inputs and different microstructures were insensitive to corrosion
in liquid, vapor, and condensate phases of 11.5 M nitric acid tested up to 240 h. The corrosion rate in boiling liquid phase
(0.60-0.76 mm/year) was higher than that in vapor (0.012-0.039 mm/year) and condensate phases (0.04-0.12 mm/year) of nitric
acid for Ti grade-1 and grade-2, as well as for base metal for all heat inputs. Potentiodynamic polarization experiment carried
out at room temperature indicated higher current densities and better passivation in 11.5 M nitric acid. SEM examination of
Ti grade-1 welds for all heat inputs exposed to liquid phase after 240 h showed corrosion attack on the surface, exposing
Widmanstatten microstructure containing acicular alpha. The continuous dissolution of the liquid-exposed samples was attributed
to the heterogeneous microstructure and non-protective passive film formation. 相似文献
1000.
The optimal synthesis of the refrigeration configuration and the selection of the best refrigerants that satisfy a set of process cooling duties at different temperatures is addressed. This approach simultaneously selects refrigerants and synthesizes refrigeration structures by minimizing a weighted sum of investment and operating costs. A superstructure representation considers the majority of refrigeration cycle features encountered in real complex multistage refrigeration cycles such as economizers, multiple refrigerants, and heat integration. A novel theoretical treatment of modeling representations and algorithmic improvements is introduced. Results, for example, involving multiple refrigerants, cooling loads, and heat sinks are obtained. Complex, nonintuitive topologies typically emerge as the optimal refrigeration configurations that are better than those obtained when refrigeration synthesis is performed after refrigerant selection. 相似文献