全文获取类型
收费全文 | 3910篇 |
免费 | 592篇 |
国内免费 | 403篇 |
专业分类
电工技术 | 327篇 |
综合类 | 325篇 |
化学工业 | 305篇 |
金属工艺 | 102篇 |
机械仪表 | 256篇 |
建筑科学 | 325篇 |
矿业工程 | 98篇 |
能源动力 | 68篇 |
轻工业 | 133篇 |
水利工程 | 91篇 |
石油天然气 | 61篇 |
武器工业 | 22篇 |
无线电 | 418篇 |
一般工业技术 | 328篇 |
冶金工业 | 94篇 |
原子能技术 | 114篇 |
自动化技术 | 1838篇 |
出版年
2024年 | 8篇 |
2023年 | 50篇 |
2022年 | 78篇 |
2021年 | 95篇 |
2020年 | 87篇 |
2019年 | 114篇 |
2018年 | 101篇 |
2017年 | 110篇 |
2016年 | 162篇 |
2015年 | 165篇 |
2014年 | 255篇 |
2013年 | 283篇 |
2012年 | 321篇 |
2011年 | 344篇 |
2010年 | 265篇 |
2009年 | 267篇 |
2008年 | 315篇 |
2007年 | 300篇 |
2006年 | 240篇 |
2005年 | 248篇 |
2004年 | 191篇 |
2003年 | 162篇 |
2002年 | 132篇 |
2001年 | 103篇 |
2000年 | 87篇 |
1999年 | 95篇 |
1998年 | 68篇 |
1997年 | 34篇 |
1996年 | 42篇 |
1995年 | 32篇 |
1994年 | 27篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 12篇 |
1989年 | 13篇 |
1988年 | 8篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1985年 | 6篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 1篇 |
1980年 | 1篇 |
1979年 | 1篇 |
1978年 | 1篇 |
1976年 | 1篇 |
1975年 | 5篇 |
1971年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有4905条查询结果,搜索用时 15 毫秒
1.
Indoor surfaces may be adsorptive sinks with the potential to change Indoor Air Quality. To estimate this effect, the sorption parameters of formaldehyde and toluene were assessed on five floorings by an experimental method using solid-phase microextraction in an airtight emission cell. Adsorption rate constants ranged from 0.003 to 0.075 m·h−1, desorption rate constants from 0.019 to 0.51 h−1, and the partition coefficient from 0.005 to 3.9 m, and these parameters vary greatly from one volatile organic compound/material couple to another indicating contrasted sorption behaviors. A rubber was identified as a sink of formaldehyde characterized by a very low desorption constant close to 0. For these sorbent floorings identified, the adsorption rates of formaldehyde are from 2 to 4 times higher than those of toluene. Two models were used to evaluate the sink effects of floorings on indoor pollutant concentrations in one room from different realistic conditions. The scenarios tested came to the conclusion that the formaldehyde sorption on one rubber (identified as a sink) has a maximum contribution from 15% to 21% for the conditions of low air exchange rate. For other floorings, the sorption has a minor contribution less than or equal to 5%, regardless of the air exchange rate. 相似文献
2.
现有的时态网络可视化方法大多采用等量时间片来可视化网络的演变,不利于时态模式的快速挖掘和发现。为此,根据时态网络固有的特征提出自适应时间片划分方法(Adaptive Time Slice Partition method,ATSP)。在时态网络的两种表示方式(基于事件的表示方式和基于快照的表示方式)的基础上,构建了ATSP的基础模型,同时提出了一种改进模型用来描述事件间隔时间服从长尾分布的时态网络。为了实现时间片的不等量划分,针对探索任务的不同提出了基于时态模式的ATSP规则和基于中心节点的ATSP规则,并提出了实现算法--层次划分算法(Hierarchical Partition algorithm,HP)和增量划分算法(Incremental Partition algorithm,IP)。实验结果表明,ATSP方法比传统的时间片划分方法更能准确地表示网络的时态特征,且该方法应用于可视化时,能有效归纳并展示网络的特征,明显提高了视觉分析的效率。 相似文献
3.
Fatigue crack propagation of multiple coplanar cracks with the coupled extended finite element/fast marching method 总被引:1,自引:0,他引:1
A numerical technique for modeling fatigue crack propagation of multiple coplanar cracks is presented. The proposed method couples the extended finite element method (X-FEM) [Int. J. Numer. Meth. Engng. 48 (11) (2000) 1549] to the fast marching method (FMM) [Level Set Methods & Fast Marching Methods: Evolving Interfaces in Computational Geometry, Fluid Mechanics, Computer Vision, and Materials Science, Cambridge University Press, Cambridge, UK, 1999]. The entire crack geometry, including one or more cracks, is represented by a single signed distance (level set) function. Merging of distinct cracks is handled naturally by the FMM with no collision detection or mesh reconstruction required. The FMM in conjunction with the Paris crack growth law is used to advance the crack front. In the X-FEM, a discontinuous function and the two-dimensional asymptotic crack-tip displacement fields are added to the finite element approximation to account for the crack using the notion of partition of unity [Comput. Meth. Appl. Mech. Engng. 139 (1996) 289]. This enables the domain to be modeled by a single fixed finite element mesh with no explicit meshing of the crack surfaces. In an earlier study [Engng. Fract. Mech. 70 (1) (2003) 29], the methodology, algorithm, and implementation for three-dimensional crack propagation of single cracks was introduced. In this paper, simulations for multiple planar cracks are presented, with crack merging and fatigue growth carried out without any user-intervention or remeshing. 相似文献
4.
5.
Anna Hać 《Journal of Network and Systems Management》1994,2(1):49-62
This paper analyzes the performance of a switching architecture. The performance measures include the elapsed time of packet transfer and the waiting time to begin transfer. The architecture is partitioned depending on the type of network used and the expected traffic in the network. Every partition has a switch with a buffer that can absorb surges of bursty traffic within the network partition. The buffer size depends on the type of the network and incoming traffic. The partition size depends on the network bandwidth, network traffic, packet size and buffer size. Examples of different networks are used to show the applications of the model. The results show that the elapsed time of packet switch transfer depends exponentially on the number of partitions in the network. 相似文献
6.
7.
8.
Level set and geodesic active contours based measurement of material removal between serial sections
Xiuyang Zhao Yansheng Yin Bo Yang Baohong Zhu Xiaofeng Tian 《Computational Materials Science》2007,39(4):857-861
The measurement of the thickness of material removed between serial sections is a crucial step of three-dimension reconstruction. Geodesic active contours is an efficient method for contour detection of objects on an image. The indents on the SiC/Al composite micrographs are segmented by using level set and geodesic active contours. After getting the contours of the indents, we calculate the distance from the uppermost pixel to the lowermost pixel to get the vertical diagonal length, and calculate the distance from the leftmost pixel to the rightmost pixel to get the horizontal diagonal length of each contour. Then the final length of each diagonal is acquired by averaging the vertical diagonal length and the horizontal diagonal length, respectively. The Vickers’ indenter is made by a square pyramidal-shaped diamond with opposite faces at an angle of 136°, so the thickness of material removed between two serial sections and the length difference of the diagonals on the two serial sections has a definite geometrical relation. Thus the thickness of material removed between two serial sections is acquired using the geometrical relation. 相似文献
9.
10.