全文获取类型
收费全文 | 66360篇 |
免费 | 12773篇 |
国内免费 | 9058篇 |
专业分类
电工技术 | 8256篇 |
技术理论 | 1篇 |
综合类 | 8604篇 |
化学工业 | 1312篇 |
金属工艺 | 1267篇 |
机械仪表 | 5278篇 |
建筑科学 | 1195篇 |
矿业工程 | 938篇 |
能源动力 | 1378篇 |
轻工业 | 667篇 |
水利工程 | 1090篇 |
石油天然气 | 809篇 |
武器工业 | 1181篇 |
无线电 | 12179篇 |
一般工业技术 | 4183篇 |
冶金工业 | 490篇 |
原子能技术 | 260篇 |
自动化技术 | 39103篇 |
出版年
2024年 | 536篇 |
2023年 | 1257篇 |
2022年 | 2363篇 |
2021年 | 2517篇 |
2020年 | 2811篇 |
2019年 | 2339篇 |
2018年 | 2343篇 |
2017年 | 2720篇 |
2016年 | 3130篇 |
2015年 | 3748篇 |
2014年 | 4841篇 |
2013年 | 4584篇 |
2012年 | 5808篇 |
2011年 | 6046篇 |
2010年 | 4928篇 |
2009年 | 5063篇 |
2008年 | 5319篇 |
2007年 | 5767篇 |
2006年 | 4525篇 |
2005年 | 3709篇 |
2004年 | 2980篇 |
2003年 | 2357篇 |
2002年 | 1750篇 |
2001年 | 1360篇 |
2000年 | 1158篇 |
1999年 | 904篇 |
1998年 | 725篇 |
1997年 | 578篇 |
1996年 | 443篇 |
1995年 | 304篇 |
1994年 | 269篇 |
1993年 | 200篇 |
1992年 | 193篇 |
1991年 | 94篇 |
1990年 | 126篇 |
1989年 | 82篇 |
1988年 | 59篇 |
1987年 | 23篇 |
1986年 | 32篇 |
1985年 | 30篇 |
1984年 | 26篇 |
1983年 | 24篇 |
1982年 | 25篇 |
1981年 | 13篇 |
1980年 | 20篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1975年 | 9篇 |
1959年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
天然气管网输配气量优化研究 总被引:2,自引:0,他引:2
天然气管网系统管理部门为了明确天然气管网的输气能力和提高天然气管网的利用率,需要对天然气管网系统的输配气量进行优化。为此,以天然气管网系统的最大流量为目标函数,同时考虑了管道强度、节点压力和流量限制等约束条件,建立了天然气管网输配气量优化的数学模型。在研究遗传算法和模拟退火算法的基础上,提出了一种由二者结合构成的具有全域搜索、快速收敛和鲁棒性强等特点的混合遗传算法。结合实例,采用这一新算法求解了天然气管网输配气量优化的数学模型。实例优化结果表明,所建立的数学模型和采用的混合遗传算法是可行和有效的,能够对天然气管网系统输配气量的调度运行起到指导作用。 相似文献
92.
Lie‐Fern Hsu 《Quality and Reliability Engineering International》2007,23(2):269-272
He and Grigoryan (Quality and Reliability Engineering International 2002; 18 :343–355) formulated the design of a double‐sampling (DS) s control chart as an optimization problem and solved it with a genetic algorithm. They concluded that the DS s control charts can be a more economically preferable alternative in detecting small shifts than traditional s control charts. We explain that, since they only considered the average sample size when the process is in control, their conclusion is questionable. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
93.
Education-driven research in CAD 总被引:1,自引:0,他引:1
We argue for a new research category, named education-driven research (EDR), which fills the gap between traditional field-specific research that is not concerned with educational objectives and research in education that focuses on fundamental teaching and learning principles and possibly on their customization to broad areas (such as mathematics or physics), but not to specific disciplines (such as CAD). The objective of EDR is to simplify the formulation of the underlying theoretical foundations and of specific tools and solutions in a specialized domain, so as to make them easy to understand and internalize. As such, EDR is a difficult and genuine research activity, which requires a deep understanding of the specific field and can rarely be carried out by generalists with primary expertise in broad education principles. We illustrate the concept of EDR with three examples in CAD: (1) the Split and Tweak subdivisions of a polygon and its use for generating curves, surfaces, and animations; (2) the construction of a topological partition of a plane induced by an arbitrary arrangement of edges; and (3) a romantic definition of the minimal and Hausdorff distances. These examples demonstrate the value of using analogies, of introducing evocative terminology, and of synthesizing the simplest fundamental building blocks. The intuitive understanding provided by EDR enables the students (and even the instructor) to better appreciate the limitations of a particular solution and to explore alternatives. In particular, in these examples, EDR has allowed the author to: (1) reduce the cost of evaluating a cubic B-spline curve; (2) develop a new subdivision curve that is better approximated by its control polygon than either a cubic B-spline or an interpolating 4-point subdivision curve; (3) discover how a circuit inclusion tree may be used for identifying the faces in an arrangement; and (4) rectify a common misconception about the computation of the Hausdorff error between triangle meshes. We invite the scientific community to encourage the development of EDR by publishing its results as genuine research contributions in peer-reviewed professional journals. 相似文献
94.
Akiyoshi Wakatani 《Parallel Computing》2004,30(12):1345-1359
It is hard to implement the ADI method in an efficient way on distributed-memory parallel computers. We propose “P-scheme” which parallelizes a tridiagonal linear system of equations for the ADI method, but its effectiveness is limited to the cases where the problem size is large enough mainly because of the communication cost of the propagation phase of the scheme.
In order to overcome this difficulty, we propose an improved version of the P-scheme with “message vectorization” which aggregates several communication messages into one and alleviates the communication cost. Also we evaluate the effectiveness of message vectorization for the ADI method and show that the improved version of the P-scheme works well even for smaller problems and linear and super-linear speedups can be achieved for 8194 × 8194 and 16,386 × 16,386 problems, respectively. 相似文献
95.
The main difficulty with EM algorithm for mixture model concerns the number of components, say g. This is the question of model selection, and the EM algorithm itself could not estimate g. On the contrary, the algorithm requires g to be specified before the remaining parameters can be estimated. To solve this problem, a new algorithm, which is called stepwise split-and-merge EM (SSMEM) algorithm, is proposed. The SSMEM algorithm alternately splits and merges components, estimating g and other parameters of components simultaneously. Also, two novel criteria are introduced to efficiently select the components for split or merge. Experimental results on simulated and real data demonstrate the effectivity of the proposed algorithm. 相似文献
96.
Automated currency validation requires a decision to be made regarding the authenticity of a banknote presented to the validation system. This decision often has to be made with little or no information regarding the characteristics of possible counterfeits as is the case for issues of new currency. A method for automated currency validation is presented which segments the whole banknote into different regions, builds individual classifiers on each region and then combines a small subset of the region specific classifiers to provide an overall decision. The segmentation and combination of region specific classifiers to provide optimized false positive and false negative rates is achieved by employing a genetic algorithm. Experiments based on high value notes of Sterling currency were carried out to assess the effectiveness of the proposed solution. 相似文献
97.
Minglun Gong Author Vitae Author Vitae 《Pattern recognition》2004,37(8):1723-1733
Many computer vision problems can be formulated as optimization problems. Presented in this paper is a new framework based on the quadtree-based genetic algorithm that can be applied to solve many of these problems. The proposed algorithm incorporates the quadtree structure into the conventional genetic algorithm. The solutions of image-related problems are encoded through encoding the corresponding quadtrees, and therefore, the 2D locality within a solution can be preserved. Examples addressed using the proposed framework include image segmentation, stereo vision, and motion estimation. In all cases, encouraging results are obtained. 相似文献
98.
99.
100.