全文获取类型
收费全文 | 2993篇 |
免费 | 238篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 42篇 |
综合类 | 8篇 |
化学工业 | 621篇 |
金属工艺 | 46篇 |
机械仪表 | 96篇 |
建筑科学 | 102篇 |
能源动力 | 139篇 |
轻工业 | 213篇 |
水利工程 | 15篇 |
石油天然气 | 7篇 |
无线电 | 574篇 |
一般工业技术 | 595篇 |
冶金工业 | 190篇 |
原子能技术 | 10篇 |
自动化技术 | 591篇 |
出版年
2023年 | 21篇 |
2022年 | 56篇 |
2021年 | 90篇 |
2020年 | 58篇 |
2019年 | 72篇 |
2018年 | 91篇 |
2017年 | 87篇 |
2016年 | 100篇 |
2015年 | 93篇 |
2014年 | 143篇 |
2013年 | 284篇 |
2012年 | 199篇 |
2011年 | 187篇 |
2010年 | 176篇 |
2009年 | 179篇 |
2008年 | 169篇 |
2007年 | 151篇 |
2006年 | 120篇 |
2005年 | 94篇 |
2004年 | 77篇 |
2003年 | 81篇 |
2002年 | 78篇 |
2001年 | 59篇 |
2000年 | 56篇 |
1999年 | 63篇 |
1998年 | 92篇 |
1997年 | 59篇 |
1996年 | 42篇 |
1995年 | 40篇 |
1994年 | 34篇 |
1993年 | 30篇 |
1992年 | 23篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 17篇 |
1988年 | 8篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 6篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 5篇 |
1981年 | 6篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 3篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1970年 | 4篇 |
排序方式: 共有3249条查询结果,搜索用时 15 毫秒
61.
In this paper, we present an analytical model to evaluate the hidden station effect on the performance of the IEEE 802.11 Distributed Coordination Function (DCF) in both non-saturation and saturation condition. DCF is a random channel-access scheme based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) method and the exponential backoff procedure. DCF is widely used and can support both wireless network with an access point and ad hoc wireless network because of its random channel-access method. On the other hand, this method unavoidably suffers the hidden station effect that causes significant performance degradation. As shown in this paper, hidden stations occur frequently in real-world settings, and the performance impact on the 802.11 DCF is a significant concern, but it has not been adequately studied. We study this problem through a spatial–temporal analysis and a Markov chain model. Our model generalizes the existing work on the performance modeling of 802.11 DCF for both non-saturation and saturation conditions. The scenario of no hidden station can be considered as a special case in our model. The performance of our model is evaluated by comparison with ns-2 simulations. 相似文献
62.
Enmin Song Dongshan Huang Guangzhi Ma Chih-Cheng Hung 《Expert systems with applications》2011,38(6):6720-6726
Semi-supervised learning has attracted much attention in pattern recognition and machine learning. Most semi-supervised learning algorithms are proposed for binary classification, and then extended to multi-class cases by using approaches such as one-against-the-rest. In this work, we propose a semi-supervised learning method by using the multi-class boosting, which can directly classify the multi-class data and achieve high classification accuracy by exploiting the unlabeled data. There are two distinct features in our proposed semi-supervised learning approach: (1) handling multi-class cases directly without reducing them to multiple two-class problems, and (2) the classification accuracy of each base classifier requiring only at least 1/K or better than 1/K (K is the number of classes). Experimental results show that the proposed method is effective based on the testing of 21 UCI benchmark data sets. 相似文献
63.
Hung Son Nguyen 《Theoretical computer science》2011,412(42):5816-5819
64.
Most of the literatures on machining economics problems tend to focus on single cutting operations. However, in reality most parts that need to be machined require more than one operation. In addition, machining technology has been developed to the point that a single computer numerical control (CNC) machine is capable of performing multiple operations, even simultaneously, employing multiple spindles and cutting tools. When several operations are performed on a CNC turning machine, various tools are required for the cutting operations. Determining the life of these cutting tools under different machining conditions is an arduous task for the operators. They usually replace the tools based on their experience or according to the specific cutting tool handbook. Frequent tool replacements may result in wasted tools and tool utilization, while infrequent tool replacements may result in poorly machined parts. In this study we propose a mathematical model in which several different turning operations (turning, drilling, and parting) with proper constraints are performed. The issue of tool replacement is taken into account in the proposed cutting model. In addition, an evolutionary strategy (ES)-based optimization approach is developed to optimize the cutting conditions of the multiple turning-related operations while taking into account the minimizing unit cost criteria under the economical tool replacement strategy. 相似文献
65.
Shih-Jieh Hung 《Expert systems with applications》2011,38(8):9053-9062
Supply chain management allows modern enterprises to relax their own capacities and produce in a more flexible manner for diversified consumer demands. However, for an enterprise with divergent supply chain (DSC) and multiple product lines, to plan the production allocation for higher competitive advantage in the risky global market is a challenging problem. The existing literature still has not address this problem very well. This paper is aimed to treat this problem by using an integrated approach of activity based costing (ABC) and management, five forces analysis, risk and value-at-risk analysis, decision making trial and evaluation laboratory (DEMATEL), analytic network process (ANP), and fuzzy goal programming (FGP). The proposed model can effectively incorporate the key factors of precise costing, managerial constraints, competitive advantage analysis, and risk management into DSC forecasting and multi-objective production planning. A case study of a consumer-oriented cell phone DSC is also presented. The sensitivity analysis shows that identifying and relaxing crucial constraints can play an important role in DSC planning for higher competitive advantage and lower risk. 相似文献
66.
The fuzzy weighted average (FWA), which is a function of fuzzy numbers and is useful as an aggregation method in engineering or management science based on fuzzy sets theory. It provides a discrete approximate solution by α-cuts level representation of fuzzy sets and interval analysis. Since the FWA method has an exponential complexity, thus several researches have focused on reducing this complexity. This paper also presents an enhanced fuzzy weighted average approach to achieve the objective of reducing the complexity. This proposed approach is through an improved initial solution for original FWA algorithm, and a two-phase concept by extending and applying both the algorithms of Chang et al. [4] and Guu [14]. Although the complexity of the proposed FWA algorithm is O(n) the same as Guu [14] which is the best level achieved to date. But from the experimental results appear that the proposed algorithm is more efficient, which only needs a few evaluated numbers and spend much less overall CPU time than Guu [14] and other FWA algorithms. In order to demonstrate the usefulness of this study, a practical example for unmanned aerial vehicle (UAV) selecting under military requirement has illustrated. Additionally, a computer-based interface, which helps the decision maker make decisions more efficiently, has been developed. 相似文献
67.
Optimal assembly plan generation: a simplifying approach 总被引:3,自引:0,他引:3
The main difficulty in the overall process of optimal assembly plan generation is the great number of different ways to assemble
a product (typically thousands of solutions). This problem confines the application of most existing automated planning methods
to products composed of only a limited number of components. The presented method of assembly plan generation belongs to the
approach called “disassembly” and is founded on a new representation of the assembly process, with introduction of a new concept,
the equivalence of binary trees. This representation allows to generate the minimal list of all non-redundant (really different) assembly plans. Plan generation is directed by assembly operation constraints and plan-level performance
criteria. The method was tested for various assembly applications and compared to other generation approaches. Results show
a great reduction in the combinatorial explosion of the number of plans. Therefore, this simplifying approach of assembly
sequence modeling allows to handle more complex products with a large number of parts. 相似文献
68.
In this paper, we derive a new application of fuzzy systems designed for a generalized autoregression conditional heteroscedasticity (GARCH) model. In general, stock market performance is time-varying and nonlinear, and exhibits properties of clustering. The latter means simply that certain large changes tend to follow other large changes, and in general small changes tend to follow other small changes. This paper shows results from using the method of functional fuzzy systems to analyze the clustering in the case of a GARCH model.The optimal parameters of the fuzzy membership functions and GARCH model are extracted using a genetic algorithm (GA). The GA method aims to achieve a global optimal solution with a fast convergence rate for this fuzzy GARCH model estimation problem. From the simulation results, we have determined that the performance is significantly improved if the leverage effect of clustering is considered in the GARCH model. The simulations use stock market data from the Taiwan weighted index (Taiwan) and the NASDAQ composite index (NASDAQ) to illustrate the performance of the proposed method. 相似文献
69.
The WAT (wafer acceptance test) is the last examination that is performed before a wafer or a chip fab out to ensure the quality and stability of chip performance. In 55 nm CIS (CMOS Image Sensor) technology, a highly smooth wafer surface is critical for the BSI (backside illumination) process. The traditional WAT process cannot be used; rather the in-line WAT must be performed during the process for forming copper interconnect. However, increasing the processing time increases the period of exposure of the copper interconnect to air, which is called the Q-time, affecting the reliability of copper interconnect. Nitrogen-doped silicon carbide (also called NDC or SiCN) has been used to fabricate copper diffusion barrier films. PECVD SiCN dielectric has a promisingly low dielectric constant for use as a copper diffusion barrier. Copper diffusion barrier films comprise one or more layers of silicon carbide. Covering a copper layer with a single thin NDC pre-layer significantly increases the maximum allowable Q-time for wafer probing. However, after the Q-time, a void forms between NDC layer and the NDC pre-layer. This work proposes a new two-step NDC process and the optimization of the thickness of the NDC pre-layer. The process has the advantages of providing a high stability for parametric test and a long allowable Q-time. These advantages are achieved by changing the thickness of the NDC pre-layer. This new approach has been analyzed using TEM and by performing parametric tests, and the feasibility has been confirmed experimentally. No void is formed between the NDC layers and a high test stability is achieved when the thickness of the NDC pre-layer is 120 Å. 相似文献
70.
Starting open source collaborative innovation: the antecedents of network formation in community source
下载免费PDF全文
![点击此处可从《Information Systems Journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Specific needs in the area of enterprise applications have led to a new type of collaborative open source innovation development across institution borders: community source. We use the Kuali community source network, a jointly managed, border‐spanning organization that supplies the institutions that created it, to describe how community source works. This study builds a theoretical basis for understanding the individual and institutional factors affecting community source network formation and the decision by organizations to join a community source network. We identify eight antecedents of decisions about forming or joining community source initiatives: motives, learning, trust, norms and monitoring, institutional similarity, external funding, hostile external environment and information technology. © 2016 John Wiley & Sons Ltd 相似文献